Package java.io

Source Code of java.io.ObjectInputStream$CallbackContext

/*
* @(#)ObjectInputStream.java  1.176 07/07/14
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/

package java.io;

import java.io.ObjectStreamClass.WeakClassKey;
import java.lang.ref.ReferenceQueue;
import java.lang.reflect.Array;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.Arrays;
import java.util.HashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicBoolean;
import static java.io.ObjectStreamClass.processQueue;

/**
* An ObjectInputStream deserializes primitive data and objects previously
* written using an ObjectOutputStream.
*
* <p>ObjectOutputStream and ObjectInputStream can provide an application with
* persistent storage for graphs of objects when used with a FileOutputStream
* and FileInputStream respectively.  ObjectInputStream is used to recover
* those objects previously serialized. Other uses include passing objects
* between hosts using a socket stream or for marshaling and unmarshaling
* arguments and parameters in a remote communication system.
*
* <p>ObjectInputStream ensures that the types of all objects in the graph
* created from the stream match the classes present in the Java Virtual
* Machine.  Classes are loaded as required using the standard mechanisms.
*
* <p>Only objects that support the java.io.Serializable or
* java.io.Externalizable interface can be read from streams.
*
* <p>The method <code>readObject</code> is used to read an object from the
* stream.  Java's safe casting should be used to get the desired type.  In
* Java, strings and arrays are objects and are treated as objects during
* serialization. When read they need to be cast to the expected type.
*
* <p>Primitive data types can be read from the stream using the appropriate
* method on DataInput.
*
* <p>The default deserialization mechanism for objects restores the contents
* of each field to the value and type it had when it was written.  Fields
* declared as transient or static are ignored by the deserialization process.
* References to other objects cause those objects to be read from the stream
* as necessary.  Graphs of objects are restored correctly using a reference
* sharing mechanism.  New objects are always allocated when deserializing,
* which prevents existing objects from being overwritten.
*
* <p>Reading an object is analogous to running the constructors of a new
* object.  Memory is allocated for the object and initialized to zero (NULL).
* No-arg constructors are invoked for the non-serializable classes and then
* the fields of the serializable classes are restored from the stream starting
* with the serializable class closest to java.lang.object and finishing with
* the object's most specific class.
*
* <p>For example to read from a stream as written by the example in
* ObjectOutputStream:
* <br>
* <pre>
*  FileInputStream fis = new FileInputStream("t.tmp");
*  ObjectInputStream ois = new ObjectInputStream(fis);
*
*  int i = ois.readInt();
*  String today = (String) ois.readObject();
*  Date date = (Date) ois.readObject();
*
*  ois.close();
* </pre>
*
* <p>Classes control how they are serialized by implementing either the
* java.io.Serializable or java.io.Externalizable interfaces.
*
* <p>Implementing the Serializable interface allows object serialization to
* save and restore the entire state of the object and it allows classes to
* evolve between the time the stream is written and the time it is read.  It
* automatically traverses references between objects, saving and restoring
* entire graphs.
*
* <p>Serializable classes that require special handling during the
* serialization and deserialization process should implement the following
* methods:<p>
*
* <pre>
* private void writeObject(java.io.ObjectOutputStream stream)
*     throws IOException;
* private void readObject(java.io.ObjectInputStream stream)
*     throws IOException, ClassNotFoundException;
* private void readObjectNoData()
*     throws ObjectStreamException;
* </pre>
*
* <p>The readObject method is responsible for reading and restoring the state
* of the object for its particular class using data written to the stream by
* the corresponding writeObject method.  The method does not need to concern
* itself with the state belonging to its superclasses or subclasses.  State is
* restored by reading data from the ObjectInputStream for the individual
* fields and making assignments to the appropriate fields of the object.
* Reading primitive data types is supported by DataInput.
*
* <p>Any attempt to read object data which exceeds the boundaries of the
* custom data written by the corresponding writeObject method will cause an
* OptionalDataException to be thrown with an eof field value of true.
* Non-object reads which exceed the end of the allotted data will reflect the
* end of data in the same way that they would indicate the end of the stream:
* bytewise reads will return -1 as the byte read or number of bytes read, and
* primitive reads will throw EOFExceptions.  If there is no corresponding
* writeObject method, then the end of default serialized data marks the end of
* the allotted data.
*
* <p>Primitive and object read calls issued from within a readExternal method
* behave in the same manner--if the stream is already positioned at the end of
* data written by the corresponding writeExternal method, object reads will
* throw OptionalDataExceptions with eof set to true, bytewise reads will
* return -1, and primitive reads will throw EOFExceptions.  Note that this
* behavior does not hold for streams written with the old
* <code>ObjectStreamConstants.PROTOCOL_VERSION_1</code> protocol, in which the
* end of data written by writeExternal methods is not demarcated, and hence
* cannot be detected.
*
* <p>The readObjectNoData method is responsible for initializing the state of
* the object for its particular class in the event that the serialization
* stream does not list the given class as a superclass of the object being
* deserialized.  This may occur in cases where the receiving party uses a
* different version of the deserialized instance's class than the sending
* party, and the receiver's version extends classes that are not extended by
* the sender's version.  This may also occur if the serialization stream has
* been tampered; hence, readObjectNoData is useful for initializing
* deserialized objects properly despite a "hostile" or incomplete source
* stream.
*
* <p>Serialization does not read or assign values to the fields of any object
* that does not implement the java.io.Serializable interface.  Subclasses of
* Objects that are not serializable can be serializable. In this case the
* non-serializable class must have a no-arg constructor to allow its fields to
* be initialized.  In this case it is the responsibility of the subclass to
* save and restore the state of the non-serializable class. It is frequently
* the case that the fields of that class are accessible (public, package, or
* protected) or that there are get and set methods that can be used to restore
* the state.
*
* <p>Any exception that occurs while deserializing an object will be caught by
* the ObjectInputStream and abort the reading process.
*
* <p>Implementing the Externalizable interface allows the object to assume
* complete control over the contents and format of the object's serialized
* form.  The methods of the Externalizable interface, writeExternal and
* readExternal, are called to save and restore the objects state.  When
* implemented by a class they can write and read their own state using all of
* the methods of ObjectOutput and ObjectInput.  It is the responsibility of
* the objects to handle any versioning that occurs.
*
* <p>Enum constants are deserialized differently than ordinary serializable or
* externalizable objects.  The serialized form of an enum constant consists
* solely of its name; field values of the constant are not transmitted.  To
* deserialize an enum constant, ObjectInputStream reads the constant name from
* the stream; the deserialized constant is then obtained by calling the static
* method <code>Enum.valueOf(Class, String)</code> with the enum constant's
* base type and the received constant name as arguments.  Like other
* serializable or externalizable objects, enum constants can function as the
* targets of back references appearing subsequently in the serialization
* stream.  The process by which enum constants are deserialized cannot be
* customized: any class-specific readObject, readObjectNoData, and readResolve
* methods defined by enum types are ignored during deserialization.
* Similarly, any serialPersistentFields or serialVersionUID field declarations
* are also ignored--all enum types have a fixed serialVersionUID of 0L.
*
* @author  Mike Warres
* @author  Roger Riggs
* @version 1.176, 07/07/14
* @see java.io.DataInput
* @see java.io.ObjectOutputStream
* @see java.io.Serializable
* @see <a href="../../../platform/serialization/spec/input.html"> Object Serialization Specification, Section 3, Object Input Classes</a>
* @since   JDK1.1
*/
public class ObjectInputStream
    extends InputStream implements ObjectInput, ObjectStreamConstants
{
    /** handle value representing null */
    private static final int NULL_HANDLE = -1;
   
    /** marker for unshared objects in internal handle table */
    private static final Object unsharedMarker = new Object();
   
    /** table mapping primitive type names to corresponding class objects */
    private static final HashMap primClasses = new HashMap(8, 1.0F);
    static {
  primClasses.put("boolean", boolean.class);
  primClasses.put("byte", byte.class);
  primClasses.put("char", char.class);
  primClasses.put("short", short.class);
  primClasses.put("int", int.class);
  primClasses.put("long", long.class);
  primClasses.put("float", float.class);
  primClasses.put("double", double.class);
  primClasses.put("void", void.class);
    }

    private static class Caches {
  /** cache of subclass security audit results */
  static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
      new ConcurrentHashMap<WeakClassKey,Boolean>();

  /** queue for WeakReferences to audited subclasses */
  static final ReferenceQueue<Class<?>> subclassAuditsQueue =
      new ReferenceQueue<Class<?>>();
    }

    /** filter stream for handling block data conversion */
    private final BlockDataInputStream bin;
    /** validation callback list */
    private final ValidationList vlist;
    /** recursion depth */
    private int depth;
    /** whether stream is closed */
    private boolean closed;
   
    /** wire handle -> obj/exception map */
    private final HandleTable handles;
    /** scratch field for passing handle values up/down call stack */
    private int passHandle = NULL_HANDLE;
    /** flag set when at end of field value block with no TC_ENDBLOCKDATA */
    private boolean defaultDataEnd = false;

    /** buffer for reading primitive field values */
    private byte[] primVals;
   
    /** if true, invoke readObjectOverride() instead of readObject() */
    private final boolean enableOverride;
    /** if true, invoke resolveObject() */
    private boolean enableResolve;

    /**
     * Context during upcalls to class-defined readObject methods; holds
     * object currently being deserialized and descriptor for current class.
     * Null when not during readObject upcall.
     */
    private CallbackContext curContext;

    /**
     * Creates an ObjectInputStream that reads from the specified InputStream.
     * A serialization stream header is read from the stream and verified.
     * This constructor will block until the corresponding ObjectOutputStream
     * has written and flushed the header.
     *
     * <p>If a security manager is installed, this constructor will check for
     * the "enableSubclassImplementation" SerializablePermission when invoked
     * directly or indirectly by the constructor of a subclass which overrides
     * the ObjectInputStream.readFields or ObjectInputStream.readUnshared
     * methods.
     *
     * @param  in input stream to read from
     * @throws  StreamCorruptedException if the stream header is incorrect
     * @throws  IOException if an I/O error occurs while reading stream header
     * @throws  SecurityException if untrusted subclass illegally overrides
     *     security-sensitive methods
     * @throws  NullPointerException if <code>in</code> is <code>null</code>
     * @see  ObjectInputStream#ObjectInputStream()
     * @see  ObjectInputStream#readFields()
     * @see  ObjectOutputStream#ObjectOutputStream(OutputStream)
     */
    public ObjectInputStream(InputStream in) throws IOException {
  verifySubclass();
  bin = new BlockDataInputStream(in);
  handles = new HandleTable(10);
  vlist = new ValidationList();
  enableOverride = false;
  readStreamHeader();
  bin.setBlockDataMode(true);
    }

    /**
     * Provide a way for subclasses that are completely reimplementing
     * ObjectInputStream to not have to allocate private data just used by this
     * implementation of ObjectInputStream.
     *
     * <p>If there is a security manager installed, this method first calls the
     * security manager's <code>checkPermission</code> method with the
     * <code>SerializablePermission("enableSubclassImplementation")</code>
     * permission to ensure it's ok to enable subclassing.
     *
     * @throws  SecurityException if a security manager exists and its
     *     <code>checkPermission</code> method denies enabling
     *     subclassing.
     * @see SecurityManager#checkPermission
     * @see java.io.SerializablePermission
     */
    protected ObjectInputStream() throws IOException, SecurityException {
  SecurityManager sm = System.getSecurityManager();
  if (sm != null) {
      sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
  }
  bin = null;
  handles = null;
  vlist = null;
  enableOverride = true;
    }

    /**
     * Read an object from the ObjectInputStream.  The class of the object, the
     * signature of the class, and the values of the non-transient and
     * non-static fields of the class and all of its supertypes are read.
     * Default deserializing for a class can be overriden using the writeObject
     * and readObject methods.  Objects referenced by this object are read
     * transitively so that a complete equivalent graph of objects is
     * reconstructed by readObject.
     *
     * <p>The root object is completely restored when all of its fields and the
     * objects it references are completely restored.  At this point the object
     * validation callbacks are executed in order based on their registered
     * priorities. The callbacks are registered by objects (in the readObject
     * special methods) as they are individually restored.
     *
     * <p>Exceptions are thrown for problems with the InputStream and for
     * classes that should not be deserialized.  All exceptions are fatal to
     * the InputStream and leave it in an indeterminate state; it is up to the
     * caller to ignore or recover the stream state.
     *
     * @throws  ClassNotFoundException Class of a serialized object cannot be
     *     found.
     * @throws  InvalidClassException Something is wrong with a class used by
     *     serialization.
     * @throws  StreamCorruptedException Control information in the
     *     stream is inconsistent.
     * @throws  OptionalDataException Primitive data was found in the
     *     stream instead of objects.
     * @throws  IOException Any of the usual Input/Output related exceptions.
     */
    public final Object readObject()
  throws IOException, ClassNotFoundException
    {
  if (enableOverride) {
      return readObjectOverride();
  }

  // if nested read, passHandle contains handle of enclosing object
  int outerHandle = passHandle;
  try {
      Object obj = readObject0(false);
      handles.markDependency(outerHandle, passHandle);
      ClassNotFoundException ex = handles.lookupException(passHandle);
      if (ex != null) {
    throw ex;
      }
      if (depth == 0) {
    vlist.doCallbacks();
      }
      return obj;
  } finally {
      passHandle = outerHandle;
      if (closed && depth == 0) {
    clear();
      }
  }
    }

    /**
     * This method is called by trusted subclasses of ObjectOutputStream that
     * constructed ObjectOutputStream using the protected no-arg constructor.
     * The subclass is expected to provide an override method with the modifier
     * "final".
     *
     * @return  the Object read from the stream.
     * @throws  ClassNotFoundException Class definition of a serialized object
     *     cannot be found.
     * @throws  OptionalDataException Primitive data was found in the stream
     *     instead of objects.
     * @throws  IOException if I/O errors occurred while reading from the
     *     underlying stream
     * @see #ObjectInputStream()
     * @see #readObject()
     * @since 1.2
     */
    protected Object readObjectOverride()
   throws IOException, ClassNotFoundException
    {
  return null;
    }
    /**
     * Reads an "unshared" object from the ObjectInputStream.  This method is
     * identical to readObject, except that it prevents subsequent calls to
     * readObject and readUnshared from returning additional references to the
     * deserialized instance obtained via this call.  Specifically:
     * <ul>
     *   <li>If readUnshared is called to deserialize a back-reference (the
     *       stream representation of an object which has been written
     *       previously to the stream), an ObjectStreamException will be
     *       thrown.
     *
     *   <li>If readUnshared returns successfully, then any subsequent attempts
     *       to deserialize back-references to the stream handle deserialized
     *       by readUnshared will cause an ObjectStreamException to be thrown.
     * </ul>
     * Deserializing an object via readUnshared invalidates the stream handle
     * associated with the returned object.  Note that this in itself does not
     * always guarantee that the reference returned by readUnshared is unique;
     * the deserialized object may define a readResolve method which returns an
     * object visible to other parties, or readUnshared may return a Class
     * object or enum constant obtainable elsewhere in the stream or through
     * external means. If the deserialized object defines a readResolve method
     * and the invocation of that method returns an array, then readUnshared
     * returns a shallow clone of that array; this guarantees that the returned
     * array object is unique and cannot be obtained a second time from an
     * invocation of readObject or readUnshared on the ObjectInputStream,
     * even if the underlying data stream has been manipulated.
     *
     * <p>ObjectInputStream subclasses which override this method can only be
     * constructed in security contexts possessing the
     * "enableSubclassImplementation" SerializablePermission; any attempt to
     * instantiate such a subclass without this permission will cause a
     * SecurityException to be thrown.
     *
     * @return  reference to deserialized object
     * @throws  ClassNotFoundException if class of an object to deserialize
     *          cannot be found
     * @throws  StreamCorruptedException if control information in the stream
     *          is inconsistent
     * @throws  ObjectStreamException if object to deserialize has already
     *          appeared in stream
     * @throws  OptionalDataException if primitive data is next in stream
     * @throws  IOException if an I/O error occurs during deserialization
     * @since   1.4
     */
    public Object readUnshared() throws IOException, ClassNotFoundException {
  // if nested read, passHandle contains handle of enclosing object
  int outerHandle = passHandle;
  try {
      Object obj = readObject0(true);
      handles.markDependency(outerHandle, passHandle);
      ClassNotFoundException ex = handles.lookupException(passHandle);
      if (ex != null) {
    throw ex;
      }
      if (depth == 0) {
    vlist.doCallbacks();
      }
      return obj;
  } finally {
      passHandle = outerHandle;
      if (closed && depth == 0) {
    clear();
      }
  }
    }

    /**
     * Read the non-static and non-transient fields of the current class from
     * this stream.  This may only be called from the readObject method of the
     * class being deserialized. It will throw the NotActiveException if it is
     * called otherwise.
     *
     * @throws  ClassNotFoundException if the class of a serialized object
     *     could not be found.
     * @throws  IOException if an I/O error occurs.
     * @throws  NotActiveException if the stream is not currently reading
     *     objects.
     */
    public void defaultReadObject()
  throws IOException, ClassNotFoundException
    {
  if (curContext == null) {
      throw new NotActiveException("not in call to readObject");
  }
  Object curObj = curContext.getObj();
  ObjectStreamClass curDesc = curContext.getDesc();
  bin.setBlockDataMode(false);
  defaultReadFields(curObj, curDesc);
  bin.setBlockDataMode(true);
  if (!curDesc.hasWriteObjectData()) {
      /*
       * Fix for 4360508: since stream does not contain terminating
       * TC_ENDBLOCKDATA tag, set flag so that reading code elsewhere
       * knows to simulate end-of-custom-data behavior.
       */
      defaultDataEnd = true;
  }
  ClassNotFoundException ex = handles.lookupException(passHandle);
  if (ex != null) {
      throw ex;
  }
    }
   
    /**
     * Reads the persistent fields from the stream and makes them available by
     * name.
     *
     * @return  the <code>GetField</code> object representing the persistent
     *     fields of the object being deserialized
     * @throws  ClassNotFoundException if the class of a serialized object
     *     could not be found.
     * @throws  IOException if an I/O error occurs.
     * @throws  NotActiveException if the stream is not currently reading
     *     objects.
     * @since 1.2
     */
    public ObjectInputStream.GetField readFields()
      throws IOException, ClassNotFoundException
    {
  if (curContext == null) {
      throw new NotActiveException("not in call to readObject");
  }
  Object curObj = curContext.getObj();
  ObjectStreamClass curDesc = curContext.getDesc();
  bin.setBlockDataMode(false);
  GetFieldImpl getField = new GetFieldImpl(curDesc);
  getField.readFields();
  bin.setBlockDataMode(true);
  if (!curDesc.hasWriteObjectData()) {
      /*
       * Fix for 4360508: since stream does not contain terminating
       * TC_ENDBLOCKDATA tag, set flag so that reading code elsewhere
       * knows to simulate end-of-custom-data behavior.
       */
      defaultDataEnd = true;
  }

  return getField;
    }

    /**
     * Register an object to be validated before the graph is returned.  While
     * similar to resolveObject these validations are called after the entire
     * graph has been reconstituted.  Typically, a readObject method will
     * register the object with the stream so that when all of the objects are
     * restored a final set of validations can be performed.
     *
     * @param  obj the object to receive the validation callback.
     * @param  prio controls the order of callbacks;zero is a good default.
     *     Use higher numbers to be called back earlier, lower numbers for
     *     later callbacks. Within a priority, callbacks are processed in
     *     no particular order.
     * @throws  NotActiveException The stream is not currently reading objects
     *     so it is invalid to register a callback.
     * @throws  InvalidObjectException The validation object is null.
     */
    public void registerValidation(ObjectInputValidation obj, int prio)
  throws NotActiveException, InvalidObjectException
    {
  if (depth == 0) {
      throw new NotActiveException("stream inactive");
  }
  vlist.register(obj, prio);
    }

    /**
     * Load the local class equivalent of the specified stream class
     * description.  Subclasses may implement this method to allow classes to
     * be fetched from an alternate source.
     *
     * <p>The corresponding method in <code>ObjectOutputStream</code> is
     * <code>annotateClass</code>.  This method will be invoked only once for
     * each unique class in the stream.  This method can be implemented by
     * subclasses to use an alternate loading mechanism but must return a
     * <code>Class</code> object. Once returned, if the class is not an array
     * class, its serialVersionUID is compared to the serialVersionUID of the
     * serialized class, and if there is a mismatch, the deserialization fails
     * and an {@link InvalidClassException} is thrown.
     *
     * <p>The default implementation of this method in
     * <code>ObjectInputStream</code> returns the result of calling
     * <pre>
     *     Class.forName(desc.getName(), false, loader)
     * </pre>
     * where <code>loader</code> is determined as follows: if there is a
     * method on the current thread's stack whose declaring class was
     * defined by a user-defined class loader (and was not a generated to
     * implement reflective invocations), then <code>loader</code> is class
     * loader corresponding to the closest such method to the currently
     * executing frame; otherwise, <code>loader</code> is
     * <code>null</code>. If this call results in a
     * <code>ClassNotFoundException</code> and the name of the passed
     * <code>ObjectStreamClass</code> instance is the Java language keyword
     * for a primitive type or void, then the <code>Class</code> object
     * representing that primitive type or void will be returned
     * (e.g., an <code>ObjectStreamClass</code> with the name
     * <code>"int"</code> will be resolved to <code>Integer.TYPE</code>).
     * Otherwise, the <code>ClassNotFoundException</code> will be thrown to
     * the caller of this method.
     *
     * @param   desc an instance of class <code>ObjectStreamClass</code>
     * @return  a <code>Class</code> object corresponding to <code>desc</code>
     * @throws  IOException any of the usual Input/Output exceptions.
     * @throws  ClassNotFoundException if class of a serialized object cannot
     *          be found.
     */    
    protected Class<?> resolveClass(ObjectStreamClass desc)
  throws IOException, ClassNotFoundException
    {
  String name = desc.getName();
  try {
      return Class.forName(name, false, latestUserDefinedLoader());
  } catch (ClassNotFoundException ex) {
      Class cl = (Class) primClasses.get(name);
      if (cl != null) {
    return cl;
      } else {
    throw ex;
      }
  }
    }

    /**
     * Returns a proxy class that implements the interfaces named in a proxy
     * class descriptor; subclasses may implement this method to read custom
     * data from the stream along with the descriptors for dynamic proxy
     * classes, allowing them to use an alternate loading mechanism for the
     * interfaces and the proxy class.
     *
     * <p>This method is called exactly once for each unique proxy class
     * descriptor in the stream.
     *
     * <p>The corresponding method in <code>ObjectOutputStream</code> is
     * <code>annotateProxyClass</code>.  For a given subclass of
     * <code>ObjectInputStream</code> that overrides this method, the
     * <code>annotateProxyClass</code> method in the corresponding subclass of
     * <code>ObjectOutputStream</code> must write any data or objects read by
     * this method.
     *
     * <p>The default implementation of this method in
     * <code>ObjectInputStream</code> returns the result of calling
     * <code>Proxy.getProxyClass</code> with the list of <code>Class</code>
     * objects for the interfaces that are named in the <code>interfaces</code>
     * parameter.  The <code>Class</code> object for each interface name
     * <code>i</code> is the value returned by calling
     * <pre>
     *     Class.forName(i, false, loader)
     * </pre>
     * where <code>loader</code> is that of the first non-<code>null</code>
     * class loader up the execution stack, or <code>null</code> if no
     * non-<code>null</code> class loaders are on the stack (the same class
     * loader choice used by the <code>resolveClass</code> method).  Unless any
     * of the resolved interfaces are non-public, this same value of
     * <code>loader</code> is also the class loader passed to
     * <code>Proxy.getProxyClass</code>; if non-public interfaces are present,
     * their class loader is passed instead (if more than one non-public
     * interface class loader is encountered, an
     * <code>IllegalAccessError</code> is thrown).
     * If <code>Proxy.getProxyClass</code> throws an
     * <code>IllegalArgumentException</code>, <code>resolveProxyClass</code>
     * will throw a <code>ClassNotFoundException</code> containing the
     * <code>IllegalArgumentException</code>.
     *
     * @param interfaces the list of interface names that were
     *                deserialized in the proxy class descriptor
     * @return  a proxy class for the specified interfaces
     * @throws        IOException any exception thrown by the underlying
     *                <code>InputStream</code>
     * @throws        ClassNotFoundException if the proxy class or any of the
     *                named interfaces could not be found
     * @see ObjectOutputStream#annotateProxyClass(Class)
     * @since 1.3
     */
    protected Class<?> resolveProxyClass(String[] interfaces)
  throws IOException, ClassNotFoundException
    {
  ClassLoader latestLoader = latestUserDefinedLoader();
  ClassLoader nonPublicLoader = null;
  boolean hasNonPublicInterface = false;

  // define proxy in class loader of non-public interface(s), if any
  Class[] classObjs = new Class[interfaces.length];
  for (int i = 0; i < interfaces.length; i++) {
      Class cl = Class.forName(interfaces[i], false, latestLoader);
      if ((cl.getModifiers() & Modifier.PUBLIC) == 0) {
    if (hasNonPublicInterface) {
        if (nonPublicLoader != cl.getClassLoader()) {
      throw new IllegalAccessError(
          "conflicting non-public interface class loaders");
        }
    } else {
        nonPublicLoader = cl.getClassLoader();
        hasNonPublicInterface = true;
    }
      }
      classObjs[i] = cl;
  }
  try {
      return Proxy.getProxyClass(
    hasNonPublicInterface ? nonPublicLoader : latestLoader,
    classObjs);
  } catch (IllegalArgumentException e) {
      throw new ClassNotFoundException(null, e);
  }
    }

    /**
     * This method will allow trusted subclasses of ObjectInputStream to
     * substitute one object for another during deserialization. Replacing
     * objects is disabled until enableResolveObject is called. The
     * enableResolveObject method checks that the stream requesting to resolve
     * object can be trusted. Every reference to serializable objects is passed
     * to resolveObject.  To insure that the private state of objects is not
     * unintentionally exposed only trusted streams may use resolveObject.
     *
     * <p>This method is called after an object has been read but before it is
     * returned from readObject.  The default resolveObject method just returns
     * the same object.
     *
     * <p>When a subclass is replacing objects it must insure that the
     * substituted object is compatible with every field where the reference
     * will be stored.  Objects whose type is not a subclass of the type of the
     * field or array element abort the serialization by raising an exception
     * and the object is not be stored.
     *
     * <p>This method is called only once when each object is first
     * encountered.  All subsequent references to the object will be redirected
     * to the new object.
     *
     * @param  obj object to be substituted
     * @return  the substituted object
     * @throws  IOException Any of the usual Input/Output exceptions.
     */
    protected Object resolveObject(Object obj) throws IOException {
  return obj;
    }

    /**
     * Enable the stream to allow objects read from the stream to be replaced.
     * When enabled, the resolveObject method is called for every object being
     * deserialized.
     *
     * <p>If <i>enable</i> is true, and there is a security manager installed,
     * this method first calls the security manager's
     * <code>checkPermission</code> method with the
     * <code>SerializablePermission("enableSubstitution")</code> permission to
     * ensure it's ok to enable the stream to allow objects read from the
     * stream to be replaced.
     *
     * @param  enable true for enabling use of <code>resolveObject</code> for
     *     every object being deserialized
     * @return  the previous setting before this method was invoked
     * @throws  SecurityException if a security manager exists and its
     *     <code>checkPermission</code> method denies enabling the stream
     *     to allow objects read from the stream to be replaced.
     * @see SecurityManager#checkPermission
     * @see java.io.SerializablePermission
     */
    protected boolean enableResolveObject(boolean enable)
  throws SecurityException
    {
  if (enable == enableResolve) {
      return enable;
  }
  if (enable) {
      SecurityManager sm = System.getSecurityManager();
      if (sm != null) {
    sm.checkPermission(SUBSTITUTION_PERMISSION);
      }
  }
  enableResolve = enable;
  return !enableResolve;
    }

    /**
     * The readStreamHeader method is provided to allow subclasses to read and
     * verify their own stream headers. It reads and verifies the magic number
     * and version number.
     *
     * @throws  IOException if there are I/O errors while reading from the
     *     underlying <code>InputStream</code>
     * @throws  StreamCorruptedException if control information in the stream
     *     is inconsistent
     */
    protected void readStreamHeader()
  throws IOException, StreamCorruptedException
    {
  short s0 = bin.readShort();
  short s1 = bin.readShort();
  if (s0 != STREAM_MAGIC || s1 != STREAM_VERSION) {
      throw new StreamCorruptedException(
    String.format("invalid stream header: %04X%04X", s0, s1));
  }
    }

    /**
     * Read a class descriptor from the serialization stream.  This method is
     * called when the ObjectInputStream expects a class descriptor as the next
     * item in the serialization stream.  Subclasses of ObjectInputStream may
     * override this method to read in class descriptors that have been written
     * in non-standard formats (by subclasses of ObjectOutputStream which have
     * overridden the <code>writeClassDescriptor</code> method).  By default,
     * this method reads class descriptors according to the format defined in
     * the Object Serialization specification.
     *
     * @return  the class descriptor read
     * @throws  IOException If an I/O error has occurred.
     * @throws  ClassNotFoundException If the Class of a serialized object used
     *     in the class descriptor representation cannot be found
     * @see java.io.ObjectOutputStream#writeClassDescriptor(java.io.ObjectStreamClass)
     * @since 1.3
     */
    protected ObjectStreamClass readClassDescriptor()
  throws IOException, ClassNotFoundException
    {
  ObjectStreamClass desc = new ObjectStreamClass();
  desc.readNonProxy(this);
  return desc;
    }

    /**
     * Reads a byte of data. This method will block if no input is available.
     *
     * @return  the byte read, or -1 if the end of the stream is reached.
     * @throws  IOException If an I/O error has occurred.
     */
    public int read() throws IOException {
  return bin.read();
    }
   
    /**
     * Reads into an array of bytes.  This method will block until some input
     * is available. Consider using java.io.DataInputStream.readFully to read
     * exactly 'length' bytes.
     *
     * @param  buf the buffer into which the data is read
     * @param  off the start offset of the data
     * @param  len the maximum number of bytes read
     * @return  the actual number of bytes read, -1 is returned when the end of
     *     the stream is reached.
     * @throws  IOException If an I/O error has occurred.
     * @see java.io.DataInputStream#readFully(byte[],int,int)
     */
    public int read(byte[] buf, int off, int len) throws IOException {
  if (buf == null) {
      throw new NullPointerException();
  }
  int endoff = off + len;
  if (off < 0 || len < 0 || endoff > buf.length || endoff < 0) {
      throw new IndexOutOfBoundsException();
  }
  return bin.read(buf, off, len, false);
    }

    /**
     * Returns the number of bytes that can be read without blocking.
     *
     * @return  the number of available bytes.
     * @throws  IOException if there are I/O errors while reading from the
     *     underlying <code>InputStream</code>
     */
    public int available() throws IOException {
  return bin.available();
    }

    /**
     * Closes the input stream. Must be called to release any resources
     * associated with the stream.
     *
     * @throws  IOException If an I/O error has occurred.
     */
    public void close() throws IOException {
  /*
   * Even if stream already closed, propagate redundant close to
   * underlying stream to stay consistent with previous implementations.
   */
  closed = true;
  if (depth == 0) {
      clear();
  }
  bin.close();
    }

    /**
     * Reads in a boolean.
     *
     * @return  the boolean read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public boolean readBoolean() throws IOException {
  return bin.readBoolean();
    }

    /**
     * Reads an 8 bit byte.
     *
     * @return  the 8 bit byte read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public byte readByte() throws IOException  {
  return bin.readByte();
    }

    /**
     * Reads an unsigned 8 bit byte.
     *
     * @return  the 8 bit byte read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public int readUnsignedByte()  throws IOException {
  return bin.readUnsignedByte();
    }

    /**
     * Reads a 16 bit char.
     *
     * @return  the 16 bit char read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public char readChar()  throws IOException {
  return bin.readChar();
    }

    /**
     * Reads a 16 bit short.
     *
     * @return  the 16 bit short read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public short readShort()  throws IOException {
  return bin.readShort();
    }

    /**
     * Reads an unsigned 16 bit short.
     *
     * @return  the 16 bit short read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public int readUnsignedShort() throws IOException {
  return bin.readUnsignedShort();
    }

    /**
     * Reads a 32 bit int.
     *
     * @return  the 32 bit integer read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public int readInt()  throws IOException {
  return bin.readInt();
    }

    /**
     * Reads a 64 bit long.
     *
     * @return  the read 64 bit long.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public long readLong()  throws IOException {
  return bin.readLong();
    }

    /**
     * Reads a 32 bit float.
     *
     * @return  the 32 bit float read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public float readFloat() throws IOException {
  return bin.readFloat();
    }

    /**
     * Reads a 64 bit double.
     *
     * @return  the 64 bit double read.
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public double readDouble() throws IOException {
  return bin.readDouble();
    }

    /**
     * Reads bytes, blocking until all bytes are read.
     *
     * @param  buf the buffer into which the data is read
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public void readFully(byte[] buf) throws IOException {
  bin.readFully(buf, 0, buf.length, false);
    }

    /**
     * Reads bytes, blocking until all bytes are read.
     *
     * @param  buf the buffer into which the data is read
     * @param  off the start offset of the data
     * @param  len the maximum number of bytes to read
     * @throws  EOFException If end of file is reached.
     * @throws  IOException If other I/O error has occurred.
     */
    public void readFully(byte[] buf, int off, int len) throws IOException {
  int endoff = off + len;
  if (off < 0 || len < 0 || endoff > buf.length || endoff < 0) {
      throw new IndexOutOfBoundsException();
  }
  bin.readFully(buf, off, len, false);
    }

    /**
     * Skips bytes.
     *
     * @param  len the number of bytes to be skipped
     * @return  the actual number of bytes skipped.
     * @throws  IOException If an I/O error has occurred.
     */
    public int skipBytes(int len) throws IOException {
  return bin.skipBytes(len);
    }

    /**
     * Reads in a line that has been terminated by a \n, \r, \r\n or EOF.
     *
     * @return  a String copy of the line.
     * @throws  IOException if there are I/O errors while reading from the
     *     underlying <code>InputStream</code>
     * @deprecated This method does not properly convert bytes to characters.
     *     see DataInputStream for the details and alternatives.
     */
    @Deprecated
    public String readLine() throws IOException {
  return bin.readLine();
    }

    /**
     * Reads a String in
     * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
     * format.
     *
     * @return  the String.
     * @throws  IOException if there are I/O errors while reading from the
     *     underlying <code>InputStream</code>
     * @throws  UTFDataFormatException if read bytes do not represent a valid
     *     modified UTF-8 encoding of a string
     */
    public String readUTF() throws IOException {
  return bin.readUTF();
    }

    /**
     * Provide access to the persistent fields read from the input stream.
     */
    public static abstract class GetField {
   /**
    * Get the ObjectStreamClass that describes the fields in the stream.
   *
   * @return  the descriptor class that describes the serializable fields
    */
   public abstract ObjectStreamClass getObjectStreamClass();
   /**
   * Return true if the named field is defaulted and has no value in this
   * stream.
   *
   * @param  name the name of the field
   * @return true, if and only if the named field is defaulted
   * @throws IOException if there are I/O errors while reading from
   *      the underlying <code>InputStream</code>
   * @throws IllegalArgumentException if <code>name</code> does not
   *      correspond to a serializable field
   */
   public abstract boolean defaulted(String name) throws IOException;
  /**
   * Get the value of the named boolean field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>boolean</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract boolean get(String name, boolean val)
      throws IOException;
  /**
   * Get the value of the named byte field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>byte</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract byte get(String name, byte val) throws IOException;
  /**
   * Get the value of the named char field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>char</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract char get(String name, char val) throws IOException;
  /**
   * Get the value of the named short field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>short</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract short get(String name, short val) throws IOException;
  /**
   * Get the value of the named int field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>int</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract int get(String name, int val) throws IOException;
  /**
   * Get the value of the named long field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>long</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract long get(String name, long val) throws IOException;
  /**
   * Get the value of the named float field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>float</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract float get(String name, float val) throws IOException;
  /**
   * Get the value of the named double field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>double</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract double get(String name, double val) throws IOException;
  /**
   * Get the value of the named Object field from the persistent field.
   *
   * @param  name the name of the field
   * @param  val the default value to use if <code>name</code> does not
   *      have a value
   * @return the value of the named <code>Object</code> field
   * @throws IOException if there are I/O errors while reading from the
   *      underlying <code>InputStream</code>
   * @throws IllegalArgumentException if type of <code>name</code> is
   *      not serializable or if the field type is incorrect
   */
  public abstract Object get(String name, Object val) throws IOException;
    }

    /**
     * Verifies that this (possibly subclass) instance can be constructed
     * without violating security constraints: the subclass must not override
     * security-sensitive non-final methods, or else the
     * "enableSubclassImplementation" SerializablePermission is checked.
     */
    private void verifySubclass() {
  Class cl = getClass();
  if (cl == ObjectInputStream.class) {
      return
  }
  SecurityManager sm = System.getSecurityManager();
  if (sm == null) {
      return;
  }
  processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
  WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
  Boolean result = Caches.subclassAudits.get(key);
  if (result == null) {
      result = Boolean.valueOf(auditSubclass(cl));
      Caches.subclassAudits.putIfAbsent(key, result);
  }
  if (result.booleanValue()) {
      return;
  }
  sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
    }

    /**
     * Performs reflective checks on given subclass to verify that it doesn't
     * override security-sensitive non-final methods.  Returns true if subclass
     * is "safe", false otherwise.
     */
    private static boolean auditSubclass(final Class subcl) {
  Boolean result = (Boolean) AccessController.doPrivileged(
      new PrivilegedAction() {
    public Object run() {
        for (Class cl = subcl;
       cl != ObjectInputStream.class;
       cl = cl.getSuperclass())
        {
      try {
          cl.getDeclaredMethod(
              "readUnshared", (Class[]) null);
          return Boolean.FALSE;
      } catch (NoSuchMethodException ex) {
      }
      try {
          cl.getDeclaredMethod("readFields", (Class[]) null);
          return Boolean.FALSE;
      } catch (NoSuchMethodException ex) {
      }
        }
        return Boolean.TRUE;
    }
      }
  );
  return result.booleanValue();
    }

    /**
     * Clears internal data structures.
     */
    private void clear() {
  handles.clear();
  vlist.clear();
    }

    /**
     * Underlying readObject implementation.
     */
    private Object readObject0(boolean unshared) throws IOException {
  boolean oldMode = bin.getBlockDataMode();
  if (oldMode) {
      int remain = bin.currentBlockRemaining();
      if (remain > 0) {
    throw new OptionalDataException(remain);
      } else if (defaultDataEnd) {
    /*
     * Fix for 4360508: stream is currently at the end of a field
     * value block written via default serialization; since there
     * is no terminating TC_ENDBLOCKDATA tag, simulate
     * end-of-custom-data behavior explicitly.
     */
    throw new OptionalDataException(true);
      }
      bin.setBlockDataMode(false);
  }
 
  byte tc;
  while ((tc = bin.peekByte()) == TC_RESET) {
      bin.readByte();
      handleReset();
  }

  depth++;
  try {
      switch (tc) {
    case TC_NULL:
        return readNull();

    case TC_REFERENCE:
        return readHandle(unshared);

    case TC_CLASS:
        return readClass(unshared);

    case TC_CLASSDESC:
    case TC_PROXYCLASSDESC:
        return readClassDesc(unshared);

    case TC_STRING:
    case TC_LONGSTRING:
        return checkResolve(readString(unshared));

    case TC_ARRAY:
        return checkResolve(readArray(unshared));

    case TC_ENUM:
        return checkResolve(readEnum(unshared));

    case TC_OBJECT:
        return checkResolve(readOrdinaryObject(unshared));

    case TC_EXCEPTION:
        IOException ex = readFatalException();
        throw new WriteAbortedException("writing aborted", ex);

    case TC_BLOCKDATA:
    case TC_BLOCKDATALONG:
        if (oldMode) {
      bin.setBlockDataMode(true);
      bin.peek();    // force header read
      throw new OptionalDataException(
          bin.currentBlockRemaining());
        } else {
      throw new StreamCorruptedException(
          "unexpected block data");
        }
       
    case TC_ENDBLOCKDATA:
        if (oldMode) {
      throw new OptionalDataException(true);
        } else {
      throw new StreamCorruptedException(
          "unexpected end of block data");
        }

    default:
        throw new StreamCorruptedException(
      String.format("invalid type code: %02X", tc));
      }
  } finally {
      depth--;
      bin.setBlockDataMode(oldMode);
  }
    }

    /**
     * If resolveObject has been enabled and given object does not have an
     * exception associated with it, calls resolveObject to determine
     * replacement for object, and updates handle table accordingly.  Returns
     * replacement object, or echoes provided object if no replacement
     * occurred.  Expects that passHandle is set to given object's handle prior
     * to calling this method.
     */
    private Object checkResolve(Object obj) throws IOException {
  if (!enableResolve || handles.lookupException(passHandle) != null) {
      return obj;
  }
  Object rep = resolveObject(obj);
  if (rep != obj) {
      handles.setObject(passHandle, rep);
  }
  return rep;
    }

    /**
     * Reads string without allowing it to be replaced in stream.  Called from
     * within ObjectStreamClass.read().
     */
    String readTypeString() throws IOException {
  int oldHandle = passHandle;
  try {
      byte tc = bin.peekByte();
      switch (tc) {
    case TC_NULL:
        return (String) readNull();

    case TC_REFERENCE:
        return (String) readHandle(false);

    case TC_STRING:
    case TC_LONGSTRING:
        return readString(false);

    default:
        throw new StreamCorruptedException(
      String.format("invalid type code: %02X", tc));
      }
  } finally {
      passHandle = oldHandle;
  }
    }

    /**
     * Reads in null code, sets passHandle to NULL_HANDLE and returns null.
     */
    private Object readNull() throws IOException {
  if (bin.readByte() != TC_NULL) {
      throw new InternalError();
  }
  passHandle = NULL_HANDLE;
  return null;
    }

    /**
     * Reads in object handle, sets passHandle to the read handle, and returns
     * object associated with the handle.
     */
    private Object readHandle(boolean unshared) throws IOException {
  if (bin.readByte() != TC_REFERENCE) {
      throw new InternalError();
  }
  passHandle = bin.readInt() - baseWireHandle;
  if (passHandle < 0 || passHandle >= handles.size()) {
      throw new StreamCorruptedException(
    String.format("invalid handle value: %08X", passHandle +
    baseWireHandle));
  }
  if (unshared) {
      // REMIND: what type of exception to throw here?
      throw new InvalidObjectException(
    "cannot read back reference as unshared");
  }
 
  Object obj = handles.lookupObject(passHandle);
  if (obj == unsharedMarker) {
      // REMIND: what type of exception to throw here?
      throw new InvalidObjectException(
    "cannot read back reference to unshared object");
  }
  return obj;
    }
   
    /**
     * Reads in and returns class object.  Sets passHandle to class object's
     * assigned handle.  Returns null if class is unresolvable (in which case a
     * ClassNotFoundException will be associated with the class' handle in the
     * handle table).
     */
    private Class readClass(boolean unshared) throws IOException {
  if (bin.readByte() != TC_CLASS) {
      throw new InternalError();
  }
  ObjectStreamClass desc = readClassDesc(false);
  Class cl = desc.forClass();
  passHandle = handles.assign(unshared ? unsharedMarker : cl);

  ClassNotFoundException resolveEx = desc.getResolveException();
  if (resolveEx != null) {
      handles.markException(passHandle, resolveEx);
  }

  handles.finish(passHandle);
  return cl;
    }
   
    /**
     * Reads in and returns (possibly null) class descriptor.  Sets passHandle
     * to class descriptor's assigned handle.  If class descriptor cannot be
     * resolved to a class in the local VM, a ClassNotFoundException is
     * associated with the class descriptor's handle.
     */
    private ObjectStreamClass readClassDesc(boolean unshared)
  throws IOException
    {
  byte tc = bin.peekByte();
  switch (tc) {
      case TC_NULL:
    return (ObjectStreamClass) readNull();

      case TC_REFERENCE:
    return (ObjectStreamClass) readHandle(unshared);

      case TC_PROXYCLASSDESC:
    return readProxyDesc(unshared);

      case TC_CLASSDESC:
    return readNonProxyDesc(unshared);
   
      default:
    throw new StreamCorruptedException(
        String.format("invalid type code: %02X", tc));
  }
    }
   
    /**
     * Reads in and returns class descriptor for a dynamic proxy class.  Sets
     * passHandle to proxy class descriptor's assigned handle.  If proxy class
     * descriptor cannot be resolved to a class in the local VM, a
     * ClassNotFoundException is associated with the descriptor's handle.
     */
    private ObjectStreamClass readProxyDesc(boolean unshared)
  throws IOException
    {
  if (bin.readByte() != TC_PROXYCLASSDESC) {
      throw new InternalError();
  }
 
  ObjectStreamClass desc = new ObjectStreamClass();
  int descHandle = handles.assign(unshared ? unsharedMarker : desc);
  passHandle = NULL_HANDLE;
 
  int numIfaces = bin.readInt();
  String[] ifaces = new String[numIfaces];
  for (int i = 0; i < numIfaces; i++) {
      ifaces[i] = bin.readUTF();
  }
 
  Class cl = null;
  ClassNotFoundException resolveEx = null;
  bin.setBlockDataMode(true);
  try {
      if ((cl = resolveProxyClass(ifaces)) == null) {
    resolveEx = new ClassNotFoundException("null class");
      }
  } catch (ClassNotFoundException ex) {
      resolveEx = ex;
  }
  skipCustomData();
 
  desc.initProxy(cl, resolveEx, readClassDesc(false));

  handles.finish(descHandle);
  passHandle = descHandle;
  return desc;
    }
   
    /**
     * Reads in and returns class descriptor for a class that is not a dynamic
     * proxy class.  Sets passHandle to class descriptor's assigned handle.  If
     * class descriptor cannot be resolved to a class in the local VM, a
     * ClassNotFoundException is associated with the descriptor's handle.
     */
    private ObjectStreamClass readNonProxyDesc(boolean unshared)
  throws IOException
    {
  if (bin.readByte() != TC_CLASSDESC) {
      throw new InternalError();
  }
 
  ObjectStreamClass desc = new ObjectStreamClass();
  int descHandle = handles.assign(unshared ? unsharedMarker : desc);
  passHandle = NULL_HANDLE;

  ObjectStreamClass readDesc = null;
  try {
      readDesc = readClassDescriptor();
  } catch (ClassNotFoundException ex) {
      throw (IOException) new InvalidClassException(
    "failed to read class descriptor").initCause(ex);
  }
 
  Class cl = null;
  ClassNotFoundException resolveEx = null;
  bin.setBlockDataMode(true);
  try {
      if ((cl = resolveClass(readDesc)) == null) {
    resolveEx = new ClassNotFoundException("null class");
      }
  } catch (ClassNotFoundException ex) {
      resolveEx = ex;
  }
  skipCustomData();
 
  desc.initNonProxy(readDesc, cl, resolveEx, readClassDesc(false));

  handles.finish(descHandle);
  passHandle = descHandle;
  return desc;
    }
   
    /**
     * Reads in and returns new string.  Sets passHandle to new string's
     * assigned handle.
     */
    private String readString(boolean unshared) throws IOException {
  String str;
  byte tc = bin.readByte();
  switch (tc) {
      case TC_STRING:
    str = bin.readUTF();
    break;
   
      case TC_LONGSTRING:
    str = bin.readLongUTF();
    break;
   
      default:
    throw new StreamCorruptedException(
        String.format("invalid type code: %02X", tc));
  }
  passHandle = handles.assign(unshared ? unsharedMarker : str);
  handles.finish(passHandle);
  return str;
    }
   
    /**
     * Reads in and returns array object, or null if array class is
     * unresolvable.  Sets passHandle to array's assigned handle.
     */
    private Object readArray(boolean unshared) throws IOException {
  if (bin.readByte() != TC_ARRAY) {
      throw new InternalError();
  }

  ObjectStreamClass desc = readClassDesc(false);
  int len = bin.readInt();
 
  Object array = null;
  Class cl, ccl = null;
  if ((cl = desc.forClass()) != null) {
      ccl = cl.getComponentType();
      array = Array.newInstance(ccl, len);
  }

  int arrayHandle = handles.assign(unshared ? unsharedMarker : array);
  ClassNotFoundException resolveEx = desc.getResolveException();
  if (resolveEx != null) {
      handles.markException(arrayHandle, resolveEx);
  }
 
  if (ccl == null) {
      for (int i = 0; i < len; i++) {
    readObject0(false);
      }
  } else if (ccl.isPrimitive()) {
      if (ccl == Integer.TYPE) {
    bin.readInts((int[]) array, 0, len);
      } else if (ccl == Byte.TYPE) {
    bin.readFully((byte[]) array, 0, len, true);
      } else if (ccl == Long.TYPE) {
    bin.readLongs((long[]) array, 0, len);
      } else if (ccl == Float.TYPE) {
    bin.readFloats((float[]) array, 0, len);
      } else if (ccl == Double.TYPE) {
    bin.readDoubles((double[]) array, 0, len);
      } else if (ccl == Short.TYPE) {
    bin.readShorts((short[]) array, 0, len);
      } else if (ccl == Character.TYPE) {
    bin.readChars((char[]) array, 0, len);
      } else if (ccl == Boolean.TYPE) {
    bin.readBooleans((boolean[]) array, 0, len);
      } else {
    throw new InternalError();
      }
  } else {
      Object[] oa = (Object[]) array;
      for (int i = 0; i < len; i++) {
    oa[i] = readObject0(false);
    handles.markDependency(arrayHandle, passHandle);
      }
  }
 
  handles.finish(arrayHandle);
  passHandle = arrayHandle;
  return array;
    }

    /**
     * Reads in and returns enum constant, or null if enum type is
     * unresolvable.  Sets passHandle to enum constant's assigned handle.
     */
    private Enum readEnum(boolean unshared) throws IOException {
  if (bin.readByte() != TC_ENUM) {
      throw new InternalError();
  }

  ObjectStreamClass desc = readClassDesc(false);
  if (!desc.isEnum()) {
      throw new InvalidClassException("non-enum class: " + desc);
  }

  int enumHandle = handles.assign(unshared ? unsharedMarker : null);
  ClassNotFoundException resolveEx = desc.getResolveException();
  if (resolveEx != null) {
      handles.markException(enumHandle, resolveEx);
  }

  String name = readString(false);
  Enum en = null;
  Class cl = desc.forClass();
  if (cl != null) {
      try {
    en = Enum.valueOf(cl, name);
      } catch (IllegalArgumentException ex) {
    throw (IOException) new InvalidObjectException(
        "enum constant " + name + " does not exist in " +
        cl).initCause(ex);
      }
      if (!unshared) {
    handles.setObject(enumHandle, en);
      }
  }

  handles.finish(enumHandle);
  passHandle = enumHandle;
  return en;
    }
   
    /**
     * Reads and returns "ordinary" (i.e., not a String, Class,
     * ObjectStreamClass, array, or enum constant) object, or null if object's
     * class is unresolvable (in which case a ClassNotFoundException will be
     * associated with object's handle).  Sets passHandle to object's assigned
     * handle.
     */
    private Object readOrdinaryObject(boolean unshared)
  throws IOException
    {
  if (bin.readByte() != TC_OBJECT) {
      throw new InternalError();
  }

  ObjectStreamClass desc = readClassDesc(false);
  desc.checkDeserialize();

  Object obj;
  try {
      obj = desc.isInstantiable() ? desc.newInstance() : null;
  } catch (Exception ex) {
      throw (IOException) new InvalidClassException(
    desc.forClass().getName(),
    "unable to create instance").initCause(ex);
  }

  passHandle = handles.assign(unshared ? unsharedMarker : obj);
  ClassNotFoundException resolveEx = desc.getResolveException();
  if (resolveEx != null) {
      handles.markException(passHandle, resolveEx);
  }
 
  if (desc.isExternalizable()) {
      readExternalData((Externalizable) obj, desc);
  } else {
      readSerialData(obj, desc);
  }

  handles.finish(passHandle);
 
  if (obj != null &&
      handles.lookupException(passHandle) == null &&
      desc.hasReadResolveMethod())
  {
      Object rep = desc.invokeReadResolve(obj);
      if (unshared && rep.getClass().isArray()) {
    rep = cloneArray(rep);
      }
      if (rep != obj) {
    handles.setObject(passHandle, obj = rep);
      }
  }

  return obj;
    }
   
    /**
     * If obj is non-null, reads externalizable data by invoking readExternal()
     * method of obj; otherwise, attempts to skip over externalizable data.
     * Expects that passHandle is set to obj's handle before this method is
     * called.
     */
    private void readExternalData(Externalizable obj, ObjectStreamClass desc)
  throws IOException
    {
  CallbackContext oldContext = curContext;
        try {
      curContext = null;
             boolean blocked = desc.hasBlockExternalData();
      if (blocked) {
          bin.setBlockDataMode(true);
      }
      if (obj != null) {
          try {
        obj.readExternal(this);
          } catch (ClassNotFoundException ex) {
        /*
         * In most cases, the handle table has already propagated
         * a CNFException to passHandle at this point; this mark
         * call is included to address cases where the readExternal
         * method has cons'ed and thrown a new CNFException of its
         * own.
                     */
        handles.markException(passHandle, ex);
          }
      }
      if (blocked) {
          skipCustomData();
      }
  } finally {
            curContext = oldContext;
        }
  /*
   * At this point, if the externalizable data was not written in
   * block-data form and either the externalizable class doesn't exist
   * locally (i.e., obj == null) or readExternal() just threw a
   * CNFException, then the stream is probably in an inconsistent state,
   * since some (or all) of the externalizable data may not have been
   * consumed.  Since there's no "correct" action to take in this case,
   * we mimic the behavior of past serialization implementations and
   * blindly hope that the stream is in sync; if it isn't and additional
   * externalizable data remains in the stream, a subsequent read will
   * most likely throw a StreamCorruptedException.
   */
    }
   
    /**
     * Reads (or attempts to skip, if obj is null or is tagged with a
     * ClassNotFoundException) instance data for each serializable class of
     * object in stream, from superclass to subclass.  Expects that passHandle
     * is set to obj's handle before this method is called.
     */
    private void readSerialData(Object obj, ObjectStreamClass desc)
  throws IOException
    {
  ObjectStreamClass.ClassDataSlot[] slots = desc.getClassDataLayout();
  for (int i = 0; i < slots.length; i++) {
      ObjectStreamClass slotDesc = slots[i].desc;
     
      if (slots[i].hasData) {
    if (obj != null &&
        slotDesc.hasReadObjectMethod() &&
        handles.lookupException(passHandle) == null)
    {
        CallbackContext oldContext = curContext;

                    try {
            curContext = new CallbackContext(obj, slotDesc);

            bin.setBlockDataMode(true);

      slotDesc.invokeReadObject(obj, this);
        } catch (ClassNotFoundException ex) {
            /*
       * In most cases, the handle table has already
       * propagated a CNFException to passHandle at this
       * point; this mark call is included to address cases
       * where the custom readObject method has cons'ed and
       * thrown a new CNFException of its own.
       */
      handles.markException(passHandle, ex);
        } finally {
            curContext.setUsed();
      curContext = oldContext;
        }
       
        /*
         * defaultDataEnd may have been set indirectly by custom
         * readObject() method when calling defaultReadObject() or
         * readFields(); clear it to restore normal read behavior.
         */
        defaultDataEnd = false;
    } else {
        defaultReadFields(obj, slotDesc);
    }
    if (slotDesc.hasWriteObjectData()) {
        skipCustomData();
    } else {
        bin.setBlockDataMode(false);
    }
      } else {
    if (obj != null &&
        slotDesc.hasReadObjectNoDataMethod() &&
        handles.lookupException(passHandle) == null)
    {
        slotDesc.invokeReadObjectNoData(obj);
    }
      }
  }
    }
   
    /**
     * Skips over all block data and objects until TC_ENDBLOCKDATA is
     * encountered.
     */
    private void skipCustomData() throws IOException {
  int oldHandle = passHandle;
  for (;;) {
      if (bin.getBlockDataMode()) {
    bin.skipBlockData();
    bin.setBlockDataMode(false);
      }
      switch (bin.peekByte()) {
    case TC_BLOCKDATA:
    case TC_BLOCKDATALONG:
        bin.setBlockDataMode(true);
        break;
       
    case TC_ENDBLOCKDATA:
        bin.readByte();
        passHandle = oldHandle;
        return;
       
    default:
        readObject0(false);
        break;
      }
  }
    }

    /**
     * Reads in values of serializable fields declared by given class
     * descriptor.  If obj is non-null, sets field values in obj.  Expects that
     * passHandle is set to obj's handle before this method is called.
     */
    private void defaultReadFields(Object obj, ObjectStreamClass desc)
  throws IOException
    {
  // REMIND: is isInstance check necessary?
  Class cl = desc.forClass();
  if (cl != null && obj != null && !cl.isInstance(obj)) {
      throw new ClassCastException();
  }

  int primDataSize = desc.getPrimDataSize();
  if (primVals == null || primVals.length < primDataSize) {
      primVals = new byte[primDataSize];
  }
  bin.readFully(primVals, 0, primDataSize, false);
  if (obj != null) {
      desc.setPrimFieldValues(obj, primVals);
  }
 
  int objHandle = passHandle;
  ObjectStreamField[] fields = desc.getFields(false);
  Object[] objVals = new Object[desc.getNumObjFields()];
  int numPrimFields = fields.length - objVals.length;
  for (int i = 0; i < objVals.length; i++) {
      ObjectStreamField f = fields[numPrimFields + i];
      objVals[i] = readObject0(f.isUnshared());
      if (f.getField() != null) {
    handles.markDependency(objHandle, passHandle);
      }
  }
  if (obj != null) {
      desc.setObjFieldValues(obj, objVals);
  }
  passHandle = objHandle;
    }

    /**
     * Reads in and returns IOException that caused serialization to abort.
     * All stream state is discarded prior to reading in fatal exception.  Sets
     * passHandle to fatal exception's handle.
     */
    private IOException readFatalException() throws IOException {
  if (bin.readByte() != TC_EXCEPTION) {
      throw new InternalError();
  }
  clear();
  return (IOException) readObject0(false);
    }
   
    /**
     * If recursion depth is 0, clears internal data structures; otherwise,
     * throws a StreamCorruptedException.  This method is called when a
     * TC_RESET typecode is encountered.
     */
    private void handleReset() throws StreamCorruptedException {
  if (depth > 0) {
      throw new StreamCorruptedException(
    "unexpected reset; recursion depth: " + depth);
  }
  clear();
    }

    /**
     * Converts specified span of bytes into float values.
     */
    // REMIND: remove once hotspot inlines Float.intBitsToFloat
    private static native void bytesToFloats(byte[] src, int srcpos,
               float[] dst, int dstpos,
               int nfloats);

    /**
     * Converts specified span of bytes into double values.
     */
    // REMIND: remove once hotspot inlines Double.longBitsToDouble
    private static native void bytesToDoubles(byte[] src, int srcpos,
                double[] dst, int dstpos,
                int ndoubles);
   
    /**
     * Returns the first non-null class loader (not counting class loaders of
     * generated reflection implementation classes) up the execution stack, or
     * null if only code from the null class loader is on the stack.  This
     * method is also called via reflection by the following RMI-IIOP class:
     *
     *     com.sun.corba.se.internal.util.JDKClassLoader
     *    
     * This method should not be removed or its signature changed without
     * corresponding modifications to the above class.
     */
    // REMIND: change name to something more accurate?
    private static native ClassLoader latestUserDefinedLoader();

    /**
     * Default GetField implementation.
     */
    private class GetFieldImpl extends GetField {
  /** class descriptor describing serializable fields */
  private final ObjectStreamClass desc;
  /** primitive field values */
  private final byte[] primVals;
  /** object field values */
  private final Object[] objVals;
  /** object field value handles */
  private final int[] objHandles;

  /**
   * Creates GetFieldImpl object for reading fields defined in given
   * class descriptor.
   */
  GetFieldImpl(ObjectStreamClass desc) {
      this.desc = desc;
      primVals = new byte[desc.getPrimDataSize()];
      objVals = new Object[desc.getNumObjFields()];
      objHandles = new int[objVals.length];
  }

   public ObjectStreamClass getObjectStreamClass() {
      return desc;
  }
   public boolean defaulted(String name) throws IOException {
      return (getFieldOffset(name, null) < 0);
  }
  public boolean get(String name, boolean val) throws IOException {
      int off = getFieldOffset(name, Boolean.TYPE);
      return (off >= 0) ? Bits.getBoolean(primVals, off) : val;
  }
  public byte get(String name, byte val) throws IOException {
      int off = getFieldOffset(name, Byte.TYPE);
      return (off >= 0) ? primVals[off] : val;
  }
  public char get(String name, char val) throws IOException {
      int off = getFieldOffset(name, Character.TYPE);
      return (off >= 0) ? Bits.getChar(primVals, off) : val;
  }
  public short get(String name, short val) throws IOException {
      int off = getFieldOffset(name, Short.TYPE);
      return (off >= 0) ? Bits.getShort(primVals, off) : val;
  }
  public int get(String name, int val) throws IOException {
      int off = getFieldOffset(name, Integer.TYPE);
      return (off >= 0) ? Bits.getInt(primVals, off) : val;
  }
  public float get(String name, float val) throws IOException {
      int off = getFieldOffset(name, Float.TYPE);
      return (off >= 0) ? Bits.getFloat(primVals, off) : val;
  }
  public long get(String name, long val) throws IOException {
      int off = getFieldOffset(name, Long.TYPE);
      return (off >= 0) ? Bits.getLong(primVals, off) : val;
  }
  public double get(String name, double val) throws IOException {
      int off = getFieldOffset(name, Double.TYPE);
      return (off >= 0) ? Bits.getDouble(primVals, off) : val;
  }
  public Object get(String name, Object val) throws IOException {
      int off = getFieldOffset(name, Object.class);
      if (off >= 0) {
    int objHandle = objHandles[off];
    handles.markDependency(passHandle, objHandle);
    return (handles.lookupException(objHandle) == null) ?
        objVals[off] : null;
      } else {
    return val;
      }
  }

  /**
   * Reads primitive and object field values from stream.
   */
  void readFields() throws IOException {
      bin.readFully(primVals, 0, primVals.length, false);
     
      int oldHandle = passHandle;
      ObjectStreamField[] fields = desc.getFields(false);
      int numPrimFields = fields.length - objVals.length;
      for (int i = 0; i < objVals.length; i++) {
    objVals[i] =
        readObject0(fields[numPrimFields + i].isUnshared());
    objHandles[i] = passHandle;
      }
      passHandle = oldHandle;
  }
 
  /**
   * Returns offset of field with given name and type.  A specified type
   * of null matches all types, Object.class matches all non-primitive
   * types, and any other non-null type matches assignable types only.
   * If no matching field is found in the (incoming) class
   * descriptor but a matching field is present in the associated local
   * class descriptor, returns -1.  Throws IllegalArgumentException if
   * neither incoming nor local class descriptor contains a match.
   */
  private int getFieldOffset(String name, Class type) {
      ObjectStreamField field = desc.getField(name, type);
      if (field != null) {
    return field.getOffset();
      } else if (desc.getLocalDesc().getField(name, type) != null) {
    return -1;
      } else {
    throw new IllegalArgumentException("no such field " + name +
               " with type " + type);
      }
  }
    }
    /**
     * Prioritized list of callbacks to be performed once object graph has been
     * completely deserialized.
     */
    private static class ValidationList {

  private static class Callback {
      final ObjectInputValidation obj;
      final int priority;
      Callback next;
      final AccessControlContext acc; 
     
      Callback(ObjectInputValidation obj, int priority, Callback next,
    AccessControlContext acc)
      {
    this.obj = obj;
    this.priority = priority;
    this.next = next;
    this.acc = acc;
      }
  }
 
  /** linked list of callbacks */
  private Callback list;

  /**
   * Creates new (empty) ValidationList.
   */
  ValidationList() {
  }
 
  /**
   * Registers callback.  Throws InvalidObjectException if callback
   * object is null.
   */
  void register(ObjectInputValidation obj, int priority)
      throws InvalidObjectException
  {
      if (obj == null) {
    throw new InvalidObjectException("null callback");
      }
     
      Callback prev = null, cur = list;
      while (cur != null && priority < cur.priority) {
    prev = cur;
    cur = cur.next;
      }
      AccessControlContext acc = AccessController.getContext();
      if (prev != null) {
    prev.next = new Callback(obj, priority, cur, acc);
      } else {
    list = new Callback(obj, priority, list, acc);
      }
  }
 
  /**
   * Invokes all registered callbacks and clears the callback list.
   * Callbacks with higher priorities are called first; those with equal
   * priorities may be called in any order.  If any of the callbacks
   * throws an InvalidObjectException, the callback process is terminated
   * and the exception propagated upwards.
   */
  void doCallbacks() throws InvalidObjectException {
      try {
        while (list != null) {
        AccessController.doPrivileged(
      new PrivilegedExceptionAction()
        {
                public Object run() throws InvalidObjectException {
                      list.obj.validateObject();
          return null;
                }
        }, list.acc);
        list = list.next;
          }
      } catch (PrivilegedActionException ex) {
    list = null;
    throw (InvalidObjectException) ex.getException();
      }
  }
 
  /**
   * Resets the callback list to its initial (empty) state.
   */
  public void clear() {
      list = null;
  }
    }
   
    /**
     * Input stream supporting single-byte peek operations.
     */
    private static class PeekInputStream extends InputStream {

  /** underlying stream */
  private final InputStream in;
  /** peeked byte */
  private int peekb = -1;

  /**
   * Creates new PeekInputStream on top of given underlying stream.
   */
  PeekInputStream(InputStream in) {
      this.in = in;
  }

  /**
   * Peeks at next byte value in stream.  Similar to read(), except
   * that it does not consume the read value.
   */
  int peek() throws IOException {
      return (peekb >= 0) ? peekb : (peekb = in.read());
  }

  public int read() throws IOException {
      if (peekb >= 0) {
    int v = peekb;
    peekb = -1;
    return v;
      } else {
    return in.read();
      }
  }

  public int read(byte[] b, int off, int len) throws IOException {
      if (len == 0) {
    return 0;
      } else if (peekb < 0) {
    return in.read(b, off, len);
      } else {
    b[off++] = (byte) peekb;
    len--;
    peekb = -1;
    int n = in.read(b, off, len);
    return (n >= 0) ? (n + 1) : 1;
      }
  }

  void readFully(byte[] b, int off, int len) throws IOException {
      int n = 0;
      while (n < len) {
    int count = read(b, off + n, len - n);
    if (count < 0) {
        throw new EOFException();
    }
    n += count;
      }
  }

  public long skip(long n) throws IOException {
      if (n <= 0) {
    return 0;
      }
      int skipped = 0;
      if (peekb >= 0) {
    peekb = -1;
    skipped++;
    n--;
      }
      return skipped + skip(n);
  }

  public int available() throws IOException {
      return in.available() + ((peekb >= 0) ? 1 : 0);
  }

  public void close() throws IOException {
      in.close();
  }
    }

    /**
     * Input stream with two modes: in default mode, inputs data written in the
     * same format as DataOutputStream; in "block data" mode, inputs data
     * bracketed by block data markers (see object serialization specification
     * for details).  Buffering depends on block data mode: when in default
     * mode, no data is buffered in advance; when in block data mode, all data
     * for the current data block is read in at once (and buffered).
     */
    private class BlockDataInputStream
  extends InputStream implements DataInput
    {
  /** maximum data block length */
  private static final int MAX_BLOCK_SIZE = 1024;
  /** maximum data block header length */
  private static final int MAX_HEADER_SIZE = 5;
  /** (tunable) length of char buffer (for reading strings) */
  private static final int CHAR_BUF_SIZE = 256;
  /** readBlockHeader() return value indicating header read may block */
  private static final int HEADER_BLOCKED = -2;

  /** buffer for reading general/block data */
  private final byte[] buf = new byte[MAX_BLOCK_SIZE];
  /** buffer for reading block data headers */
  private final byte[] hbuf = new byte[MAX_HEADER_SIZE];
  /** char buffer for fast string reads */
  private final char[] cbuf = new char[CHAR_BUF_SIZE];

  /** block data mode */
  private boolean blkmode = false;

  // block data state fields; values meaningful only when blkmode true
  /** current offset into buf */
  private int pos = 0;
  /** end offset of valid data in buf, or -1 if no more block data */
  private int end = -1;
  /** number of bytes in current block yet to be read from stream */
  private int unread = 0;

  /** underlying stream (wrapped in peekable filter stream) */
  private final PeekInputStream in;
  /** loopback stream (for data reads that span data blocks) */
  private final DataInputStream din;

  /**
   * Creates new BlockDataInputStream on top of given underlying stream.
   * Block data mode is turned off by default.
   */
  BlockDataInputStream(InputStream in) {
      this.in = new PeekInputStream(in);
      din = new DataInputStream(this);
  }

  /**
   * Sets block data mode to the given mode (true == on, false == off)
   * and returns the previous mode value.  If the new mode is the same as
   * the old mode, no action is taken.  Throws IllegalStateException if
   * block data mode is being switched from on to off while unconsumed
   * block data is still present in the stream.
   */
  boolean setBlockDataMode(boolean newmode) throws IOException {
      if (blkmode == newmode) {
    return blkmode;
      }
      if (newmode) {
    pos = 0;
    end = 0;
    unread = 0;
      } else if (pos < end) {
    throw new IllegalStateException("unread block data");
      }
      blkmode = newmode;
      return !blkmode;
  }

  /**
   * Returns true if the stream is currently in block data mode, false
   * otherwise.
   */
  boolean getBlockDataMode() {
      return blkmode;
  }

  /**
   * If in block data mode, skips to the end of the current group of data
   * blocks (but does not unset block data mode).  If not in block data
   * mode, throws an IllegalStateException.
   */
  void skipBlockData() throws IOException {
      if (!blkmode) {
    throw new IllegalStateException("not in block data mode");
      }
      while (end >= 0) {
    refill();
      }
  }

  /**
   * Attempts to read in the next block data header (if any).  If
   * canBlock is false and a full header cannot be read without possibly
   * blocking, returns HEADER_BLOCKED, else if the next element in the
   * stream is a block data header, returns the block data length
   * specified by the header, else returns -1.
   */
  private int readBlockHeader(boolean canBlock) throws IOException {
      if (defaultDataEnd) {
    /*
     * Fix for 4360508: stream is currently at the end of a field
     * value block written via default serialization; since there
     * is no terminating TC_ENDBLOCKDATA tag, simulate
     * end-of-custom-data behavior explicitly.
     */
    return -1;
      }
      try {
    for (;;) {
        int avail = canBlock ? Integer.MAX_VALUE : in.available();
        if (avail == 0) {
      return HEADER_BLOCKED;
        }
       
        int tc = in.peek();
        switch (tc) {
      case TC_BLOCKDATA:
          if (avail < 2) {
        return HEADER_BLOCKED;
          }
          in.readFully(hbuf, 0, 2);
          return hbuf[1] & 0xFF;
         
      case TC_BLOCKDATALONG:
          if (avail < 5) {
        return HEADER_BLOCKED;
          }
          in.readFully(hbuf, 0, 5);
          int len = Bits.getInt(hbuf, 1);
          if (len < 0) {
        throw new StreamCorruptedException(
            "illegal block data header length: " +
            len);
          }
          return len;

      /*
       * TC_RESETs may occur in between data blocks.
       * Unfortunately, this case must be parsed at a lower
       * level than other typecodes, since primitive data
       * reads may span data blocks separated by a TC_RESET.
       */
      case TC_RESET:
          in.read();
          handleReset();
          break;

      default:
          if (tc >= 0 && (tc < TC_BASE || tc > TC_MAX)) {
        throw new StreamCorruptedException(
            String.format("invalid type code: %02X",
            tc));
          }
          return -1;
        }
    }
      } catch (EOFException ex) {
    throw new StreamCorruptedException(
        "unexpected EOF while reading block data header");
      }
  }

  /**
   * Refills internal buffer buf with block data.  Any data in buf at the
   * time of the call is considered consumed.  Sets the pos, end, and
   * unread fields to reflect the new amount of available block data; if
   * the next element in the stream is not a data block, sets pos and
   * unread to 0 and end to -1.
   */
  private void refill() throws IOException {
      try {
    do {
        pos = 0;
        if (unread > 0) {
      int n =
          in.read(buf, 0, Math.min(unread, MAX_BLOCK_SIZE));
      if (n >= 0) {
          end = n;
          unread -= n;
      } else {
          throw new StreamCorruptedException(
        "unexpected EOF in middle of data block");
      }
        } else {
      int n = readBlockHeader(true);
      if (n >= 0) {
          end = 0;
          unread = n;
      } else {
          end = -1;
          unread = 0;
      }
        }
    } while (pos == end);
      } catch (IOException ex) {
    pos = 0;
    end = -1;
    unread = 0;
    throw ex;
      }
  }
 
  /**
   * If in block data mode, returns the number of unconsumed bytes
   * remaining in the current data block.  If not in block data mode,
   * throws an IllegalStateException.
   */
  int currentBlockRemaining() {
      if (blkmode) {
    return (end >= 0) ? (end - pos) + unread : 0;
      } else {
    throw new IllegalStateException();
      }
  }

  /**
   * Peeks at (but does not consume) and returns the next byte value in
   * the stream, or -1 if the end of the stream/block data (if in block
   * data mode) has been reached.
   */
  int peek() throws IOException {
      if (blkmode) {
    if (pos == end) {
        refill();
    }
    return (end >= 0) ? (buf[pos] & 0xFF) : -1;
      } else {
    return in.peek();
      }
  }

  /**
   * Peeks at (but does not consume) and returns the next byte value in
   * the stream, or throws EOFException if end of stream/block data has
   * been reached.
   */
  byte peekByte() throws IOException {
      int val = peek();
      if (val < 0) {
    throw new EOFException();
      }
      return (byte) val;
  }


  /* ----------------- generic input stream methods ------------------ */
  /*
   * The following methods are equivalent to their counterparts in
   * InputStream, except that they interpret data block boundaries and
   * read the requested data from within data blocks when in block data
   * mode.
   */

  public int read() throws IOException {
      if (blkmode) {
    if (pos == end) {
        refill();
    }
    return (end >= 0) ? (buf[pos++] & 0xFF) : -1;
      } else {
    return in.read();
      }
  }

  public int read(byte[] b, int off, int len) throws IOException {
      return read(b, off, len, false);
  }

  public long skip(long len) throws IOException {
      long remain = len;
      while (remain > 0) {
    if (blkmode) {
        if (pos == end) {
      refill();
        }
        if (end < 0) {
      break;
        }
        int nread = (int) Math.min(remain, end - pos);
        remain -= nread;
        pos += nread;
    } else {
        int nread = (int) Math.min(remain, MAX_BLOCK_SIZE);
        if ((nread = in.read(buf, 0, nread)) < 0) {
      break;
        }
        remain -= nread;
    }
      }
      return len - remain;
  }

  public int available() throws IOException {
      if (blkmode) {
    if ((pos == end) && (unread == 0)) {
        int n;
        while ((n = readBlockHeader(false)) == 0) ;
        switch (n) {
      case HEADER_BLOCKED:
          break;
         
      case -1:
          pos = 0;
          end = -1;
          break;
         
      default:
          pos = 0;
          end = 0;
          unread = n;
          break;
        }
    }
    // avoid unnecessary call to in.available() if possible
    int unreadAvail = (unread > 0) ?
        Math.min(in.available(), unread) : 0;
    return (end >= 0) ? (end - pos) + unreadAvail : 0;
      } else {
    return in.available();
      }
  }

  public void close() throws IOException {
      if (blkmode) {
    pos = 0;
    end = -1;
    unread = 0;
      }
      in.close();
  }

  /**
   * Attempts to read len bytes into byte array b at offset off.  Returns
   * the number of bytes read, or -1 if the end of stream/block data has
   * been reached.  If copy is true, reads values into an intermediate
   * buffer before copying them to b (to avoid exposing a reference to
   * b).
   */
  int read(byte[] b, int off, int len, boolean copy) throws IOException {
      if (len == 0) {
    return 0;
      } else if (blkmode) {
    if (pos == end) {
        refill();
    }
    if (end < 0) {
        return -1;
    }
    int nread = Math.min(len, end - pos);
    System.arraycopy(buf, pos, b, off, nread);
    pos += nread;
    return nread;
      } else if (copy) {
    int nread = in.read(buf, 0, Math.min(len, MAX_BLOCK_SIZE));
    if (nread > 0) {
        System.arraycopy(buf, 0, b, off, nread);
    }
    return nread;
      } else {
    return in.read(b, off, len);
      }
  }

  /* ----------------- primitive data input methods ------------------ */
  /*
   * The following methods are equivalent to their counterparts in
   * DataInputStream, except that they interpret data block boundaries
   * and read the requested data from within data blocks when in block
   * data mode.
   */

  public void readFully(byte[] b) throws IOException {
      readFully(b, 0, b.length, false);
  }

  public void readFully(byte[] b, int off, int len) throws IOException {
      readFully(b, off, len, false);
  }

  public void readFully(byte[] b, int off, int len, boolean copy)
      throws IOException
  {
      while (len > 0) {
    int n = read(b, off, len, copy);
    if (n < 0) {
        throw new EOFException();
    }
    off += n;
    len -= n;
      }
  }

  public int skipBytes(int n) throws IOException {
      return din.skipBytes(n);
  }

  public boolean readBoolean() throws IOException {
      int v = read();
      if (v < 0) {
    throw new EOFException();
      }
      return (v != 0);
  }

  public byte readByte() throws IOException {
      int v = read();
      if (v < 0) {
    throw new EOFException();
      }
      return (byte) v;
  }

  public int readUnsignedByte() throws IOException {
      int v = read();
      if (v < 0) {
    throw new EOFException();
      }
      return v;
  }

  public char readChar() throws IOException {
      if (!blkmode) {
    pos = 0;
    in.readFully(buf, 0, 2);
      } else if (end - pos < 2) {
    return din.readChar();
      }
      char v = Bits.getChar(buf, pos);
      pos += 2;
      return v;
  }

  public short readShort() throws IOException {
      if (!blkmode) {
    pos = 0;
    in.readFully(buf, 0, 2);
      } else if (end - pos < 2) {
    return din.readShort();
      }
      short v = Bits.getShort(buf, pos);
      pos += 2;
      return v;
  }

  public int readUnsignedShort() throws IOException {
      if (!blkmode) {
    pos = 0;
    in.readFully(buf, 0, 2);
      } else if (end - pos < 2) {
    return din.readUnsignedShort();
      }
      int v = Bits.getShort(buf, pos) & 0xFFFF;
      pos += 2;
      return v;
  }

  public int readInt() throws IOException {
      if (!blkmode) {
    pos = 0;
    in.readFully(buf, 0, 4);
      } else if (end - pos < 4) {
    return din.readInt();
      }
      int v = Bits.getInt(buf, pos);
      pos += 4;
      return v;
  }

  public float readFloat() throws IOException {
      if (!blkmode) {
    pos = 0;
    in.readFully(buf, 0, 4);
      } else if (end - pos < 4) {
    return din.readFloat();
      }
      float v = Bits.getFloat(buf, pos);
      pos += 4;
      return v;
  }

  public long readLong() throws IOException {
      if (!blkmode) {
    pos = 0;
    in.readFully(buf, 0, 8);
      } else if (end - pos < 8) {
    return din.readLong();
      }
      long v = Bits.getLong(buf, pos);
      pos += 8;
      return v;
  }

  public double readDouble() throws IOException {
      if (!blkmode) {
    pos = 0;
    in.readFully(buf, 0, 8);
      } else if (end - pos < 8) {
    return din.readDouble();
      }
      double v = Bits.getDouble(buf, pos);
      pos += 8;
      return v;
  }

  public String readUTF() throws IOException {
      return readUTFBody(readUnsignedShort());
  }

  public String readLine() throws IOException {
      return din.readLine()// deprecated, not worth optimizing
  }
 
  /* -------------- primitive data array input methods --------------- */
  /*
   * The following methods read in spans of primitive data values.
   * Though equivalent to calling the corresponding primitive read
   * methods repeatedly, these methods are optimized for reading groups
   * of primitive data values more efficiently.
   */

  void readBooleans(boolean[] v, int off, int len) throws IOException {
      int stop, endoff = off + len;
      while (off < endoff) {
    if (!blkmode) {
        int span = Math.min(endoff - off, MAX_BLOCK_SIZE);
        in.readFully(buf, 0, span);
        stop = off + span;
        pos = 0;
    } else if (end - pos < 1) {
        v[off++] = din.readBoolean();
        continue;
    } else {
        stop = Math.min(endoff, off + end - pos);
    }

    while (off < stop) {
        v[off++] = Bits.getBoolean(buf, pos++);
    }
      }
  }

  void readChars(char[] v, int off, int len) throws IOException {
      int stop, endoff = off + len;
      while (off < endoff) {
    if (!blkmode) {
        int span = Math.min(endoff - off, MAX_BLOCK_SIZE >> 1);
        in.readFully(buf, 0, span << 1);
        stop = off + span;
        pos = 0;
    } else if (end - pos < 2) {
        v[off++] = din.readChar();
        continue;
    } else {
        stop = Math.min(endoff, off + ((end - pos) >> 1));
    }
   
    while (off < stop) {
        v[off++] = Bits.getChar(buf, pos);
        pos += 2;
    }
      }
  }

  void readShorts(short[] v, int off, int len) throws IOException {
      int stop, endoff = off + len;
      while (off < endoff) {
    if (!blkmode) {
        int span = Math.min(endoff - off, MAX_BLOCK_SIZE >> 1);
        in.readFully(buf, 0, span << 1);
        stop = off + span;
        pos = 0;
    } else if (end - pos < 2) {
        v[off++] = din.readShort();
        continue;
    } else {
        stop = Math.min(endoff, off + ((end - pos) >> 1));
    }
   
    while (off < stop) {
        v[off++] = Bits.getShort(buf, pos);
        pos += 2;
    }
      }
  }

  void readInts(int[] v, int off, int len) throws IOException {
      int stop, endoff = off + len;
      while (off < endoff) {
    if (!blkmode) {
        int span = Math.min(endoff - off, MAX_BLOCK_SIZE >> 2);
        in.readFully(buf, 0, span << 2);
        stop = off + span;
        pos = 0;
    } else if (end - pos < 4) {
        v[off++] = din.readInt();
        continue;
    } else {
        stop = Math.min(endoff, off + ((end - pos) >> 2));
    }
   
    while (off < stop) {
        v[off++] = Bits.getInt(buf, pos);
        pos += 4;
    }
      }
  }

  void readFloats(float[] v, int off, int len) throws IOException {
      int span, endoff = off + len;
      while (off < endoff) {
    if (!blkmode) {
        span = Math.min(endoff - off, MAX_BLOCK_SIZE >> 2);
        in.readFully(buf, 0, span << 2);
        pos = 0;
    } else if (end - pos < 4) {
        v[off++] = din.readFloat();
        continue;
    } else {
        span = Math.min(endoff - off, ((end - pos) >> 2));
    }
   
    bytesToFloats(buf, pos, v, off, span);
    off += span;
    pos += span << 2;
      }
  }

  void readLongs(long[] v, int off, int len) throws IOException {
      int stop, endoff = off + len;
      while (off < endoff) {
    if (!blkmode) {
        int span = Math.min(endoff - off, MAX_BLOCK_SIZE >> 3);
        in.readFully(buf, 0, span << 3);
        stop = off + span;
        pos = 0;
    } else if (end - pos < 8) {
        v[off++] = din.readLong();
        continue;
    } else {
        stop = Math.min(endoff, off + ((end - pos) >> 3));
    }
   
    while (off < stop) {
        v[off++] = Bits.getLong(buf, pos);
        pos += 8;
    }
      }
  }

  void readDoubles(double[] v, int off, int len) throws IOException {
      int span, endoff = off + len;
      while (off < endoff) {
    if (!blkmode) {
        span = Math.min(endoff - off, MAX_BLOCK_SIZE >> 3);
        in.readFully(buf, 0, span << 3);
        pos = 0;
    } else if (end - pos < 8) {
        v[off++] = din.readDouble();
        continue;
    } else {
        span = Math.min(endoff - off, ((end - pos) >> 3));
    }
   
    bytesToDoubles(buf, pos, v, off, span);
    off += span;
    pos += span << 3;
      }
  }

  /**
   * Reads in string written in "long" UTF format.  "Long" UTF format is
   * identical to standard UTF, except that it uses an 8 byte header
   * (instead of the standard 2 bytes) to convey the UTF encoding length.
   */
  String readLongUTF() throws IOException {
      return readUTFBody(readLong());
  }

  /**
   * Reads in the "body" (i.e., the UTF representation minus the 2-byte
   * or 8-byte length header) of a UTF encoding, which occupies the next
   * utflen bytes.
   */
  private String readUTFBody(long utflen) throws IOException {
      StringBuilder sbuf = new StringBuilder();
      if (!blkmode) {
    end = pos = 0;
      }

      while (utflen > 0) {
    int avail = end - pos;
    if (avail >= 3 || (long) avail == utflen) {
        utflen -= readUTFSpan(sbuf, utflen);
    } else {
        if (blkmode) {
      // near block boundary, read one byte at a time
      utflen -= readUTFChar(sbuf, utflen);
        } else {
      // shift and refill buffer manually
      if (avail > 0) {
          System.arraycopy(buf, pos, buf, 0, avail);
      }
      pos = 0;
      end = (int) Math.min(MAX_BLOCK_SIZE, utflen);
      in.readFully(buf, avail, end - avail);
        }
    }
      }

      return sbuf.toString();
  }

  /**
   * Reads span of UTF-encoded characters out of internal buffer
   * (starting at offset pos and ending at or before offset end),
   * consuming no more than utflen bytes.  Appends read characters to
   * sbuf.  Returns the number of bytes consumed.
   */
  private long readUTFSpan(StringBuilder sbuf, long utflen)
      throws IOException
  {
      int cpos = 0;
      int start = pos;
      int avail = Math.min(end - pos, CHAR_BUF_SIZE);
      // stop short of last char unless all of utf bytes in buffer
      int stop = pos + ((utflen > avail) ? avail - 2 : (int) utflen);
      boolean outOfBounds = false;

      try {
    while (pos < stop) {
        int b1, b2, b3;
        b1 = buf[pos++] & 0xFF;
        switch (b1 >> 4) {
      case 0:
      case 1:
      case 2:
      case 3:
      case 4:
      case 5:
      case 6:
      case 7:    // 1 byte format: 0xxxxxxx
          cbuf[cpos++] = (char) b1;
          break;

      case 12:
      case 13// 2 byte format: 110xxxxx 10xxxxxx
          b2 = buf[pos++];
          if ((b2 & 0xC0) != 0x80) {
        throw new UTFDataFormatException();
          }
          cbuf[cpos++] = (char) (((b1 & 0x1F) << 6) |
               ((b2 & 0x3F) << 0));
          break;

      case 14// 3 byte format: 1110xxxx 10xxxxxx 10xxxxxx
          b3 = buf[pos + 1];
          b2 = buf[pos + 0];
          pos += 2;
          if ((b2 & 0xC0) != 0x80 || (b3 & 0xC0) != 0x80) {
        throw new UTFDataFormatException();
          }
          cbuf[cpos++] = (char) (((b1 & 0x0F) << 12) |
               ((b2 & 0x3F) << 6) |
               ((b3 & 0x3F) << 0));
          break;

      default// 10xx xxxx, 1111 xxxx
          throw new UTFDataFormatException();
        }
    }
      } catch (ArrayIndexOutOfBoundsException ex) {
    outOfBounds = true;
      } finally {
    if (outOfBounds || (pos - start) > utflen) {
        /*
         * Fix for 4450867: if a malformed utf char causes the
         * conversion loop to scan past the expected end of the utf
         * string, only consume the expected number of utf bytes.
         */
        pos = start + (int) utflen;
        throw new UTFDataFormatException();
    }
      }

      sbuf.append(cbuf, 0, cpos);
      return pos - start;
  }

  /**
   * Reads in single UTF-encoded character one byte at a time, appends
   * the character to sbuf, and returns the number of bytes consumed.
   * This method is used when reading in UTF strings written in block
   * data mode to handle UTF-encoded characters which (potentially)
   * straddle block-data boundaries.
   */
  private int readUTFChar(StringBuilder sbuf, long utflen)
      throws IOException
  {
      int b1, b2, b3;
      b1 = readByte() & 0xFF;
      switch (b1 >> 4) {
    case 0:
    case 1:
    case 2:
    case 3:
    case 4:
    case 5:
    case 6:
    case 7:     // 1 byte format: 0xxxxxxx
        sbuf.append((char) b1);
        return 1;

    case 12:
    case 13:    // 2 byte format: 110xxxxx 10xxxxxx
        if (utflen < 2) {
      throw new UTFDataFormatException();
        }
        b2 = readByte();
        if ((b2 & 0xC0) != 0x80) {
      throw new UTFDataFormatException();
        }
        sbuf.append((char) (((b1 & 0x1F) << 6) |
          ((b2 & 0x3F) << 0)));
        return 2;

    case 14:    // 3 byte format: 1110xxxx 10xxxxxx 10xxxxxx
        if (utflen < 3) {
      if (utflen == 2) {
          readByte();    // consume remaining byte
      }
      throw new UTFDataFormatException();
        }
        b2 = readByte();
        b3 = readByte();
        if ((b2 & 0xC0) != 0x80 || (b3 & 0xC0) != 0x80) {
      throw new UTFDataFormatException();
        }
        sbuf.append((char) (((b1 & 0x0F) << 12) |
          ((b2 & 0x3F) << 6) |
          ((b3 & 0x3F) << 0)));
        return 3;

    default:   // 10xx xxxx, 1111 xxxx
        throw new UTFDataFormatException();
      }
  }
    }

    /**
     * Unsynchronized table which tracks wire handle to object mappings, as
     * well as ClassNotFoundExceptions associated with deserialized objects.
     * This class implements an exception-propagation algorithm for
     * determining which objects should have ClassNotFoundExceptions associated
     * with them, taking into account cycles and discontinuities (e.g., skipped
     * fields) in the object graph.
     *
     * <p>General use of the table is as follows: during deserialization, a
     * given object is first assigned a handle by calling the assign method.
     * This method leaves the assigned handle in an "open" state, wherein
     * dependencies on the exception status of other handles can be registered
     * by calling the markDependency method, or an exception can be directly
     * associated with the handle by calling markException.  When a handle is
     * tagged with an exception, the HandleTable assumes responsibility for
     * propagating the exception to any other objects which depend
     * (transitively) on the exception-tagged object.
     *
     * <p>Once all exception information/dependencies for the handle have been
     * registered, the handle should be "closed" by calling the finish method
     * on it.  The act of finishing a handle allows the exception propagation
     * algorithm to aggressively prune dependency links, lessening the
     * performance/memory impact of exception tracking.
     *
     * <p>Note that the exception propagation algorithm used depends on handles
     * being assigned/finished in LIFO order; however, for simplicity as well
     * as memory conservation, it does not enforce this constraint.
     */
    // REMIND: add full description of exception propagation algorithm?
    private static class HandleTable {

  /* status codes indicating whether object has associated exception */
  private static final byte STATUS_OK = 1;
  private static final byte STATUS_UNKNOWN = 2;
  private static final byte STATUS_EXCEPTION = 3;
 
  /** array mapping handle -> object status */
  byte[] status;
  /** array mapping handle -> object/exception (depending on status) */
  Object[] entries;
  /** array mapping handle -> list of dependent handles (if any) */
  HandleList[] deps;
  /** lowest unresolved dependency */
  int lowDep = -1;
  /** number of handles in table */
  int size = 0;

  /**
   * Creates handle table with the given initial capacity.
   */
  HandleTable(int initialCapacity) {
      status = new byte[initialCapacity];
      entries = new Object[initialCapacity];
      deps = new HandleList[initialCapacity];
  }
 
  /**
   * Assigns next available handle to given object, and returns assigned
   * handle.  Once object has been completely deserialized (and all
   * dependencies on other objects identified), the handle should be
   * "closed" by passing it to finish().
   */
  int assign(Object obj) {
      if (size >= entries.length) {
    grow();
      }
      status[size] = STATUS_UNKNOWN;
      entries[size] = obj;
      return size++;
  }

  /**
   * Registers a dependency (in exception status) of one handle on
   * another.  The dependent handle must be "open" (i.e., assigned, but
   * not finished yet).  No action is taken if either dependent or target
   * handle is NULL_HANDLE.
   */
  void markDependency(int dependent, int target) {
      if (dependent == NULL_HANDLE || target == NULL_HANDLE) {
    return;
      }
      switch (status[dependent]) {

    case STATUS_UNKNOWN:
        switch (status[target]) {
      case STATUS_OK:
          // ignore dependencies on objs with no exception
          break;
         
      case STATUS_EXCEPTION:
          // eagerly propagate exception
          markException(dependent,
        (ClassNotFoundException) entries[target]);
          break;
         
      case STATUS_UNKNOWN:
          // add to dependency list of target
          if (deps[target] == null) {
        deps[target] = new HandleList();
          }
          deps[target].add(dependent);
         
          // remember lowest unresolved target seen
          if (lowDep < 0 || lowDep > target) {
        lowDep = target;
          }
          break;
         
      default:
          throw new InternalError();
        }
        break;

    case STATUS_EXCEPTION:
        break;

    default:
        throw new InternalError();
      }
  }
 
  /**
   * Associates a ClassNotFoundException (if one not already associated)
   * with the currently active handle and propagates it to other
   * referencing objects as appropriate.  The specified handle must be
   * "open" (i.e., assigned, but not finished yet).
   */
  void markException(int handle, ClassNotFoundException ex) {
      switch (status[handle]) {
    case STATUS_UNKNOWN:
        status[handle] = STATUS_EXCEPTION;
        entries[handle] = ex;
       
        // propagate exception to dependents
        HandleList dlist = deps[handle];
        if (dlist != null) {
      int ndeps = dlist.size();
      for (int i = 0; i < ndeps; i++) {
          markException(dlist.get(i), ex);
      }
      deps[handle] = null;
        }
        break;
       
    case STATUS_EXCEPTION:
        break;
       
    default:
        throw new InternalError();
      }
  }

  /**
   * Marks given handle as finished, meaning that no new dependencies
   * will be marked for handle.  Calls to the assign and finish methods
   * must occur in LIFO order.
   */
  void finish(int handle) {
      int end;
      if (lowDep < 0) {
    // no pending unknowns, only resolve current handle
    end = handle + 1;
      } else if (lowDep >= handle) {
    // pending unknowns now clearable, resolve all upward handles
    end = size;
    lowDep = -1;
      } else {
    // unresolved backrefs present, can't resolve anything yet
    return;
      }
     
      // change STATUS_UNKNOWN -> STATUS_OK in selected span of handles
      for (int i = handle; i < end; i++) {
    switch (status[i]) {
        case STATUS_UNKNOWN:
      status[i] = STATUS_OK;
      deps[i] = null;
      break;
     
        case STATUS_OK:
        case STATUS_EXCEPTION:
      break;
     
        default:
      throw new InternalError();
    }
      }
  }

  /**
   * Assigns a new object to the given handle.  The object previously
   * associated with the handle is forgotten.  This method has no effect
   * if the given handle already has an exception associated with it.
   * This method may be called at any time after the handle is assigned.
   */
  void setObject(int handle, Object obj) {
      switch (status[handle]) {
    case STATUS_UNKNOWN:
    case STATUS_OK:
        entries[handle] = obj;
        break;
       
    case STATUS_EXCEPTION:
        break;
       
    default:
        throw new InternalError();
      }
  }
 
  /**
   * Looks up and returns object associated with the given handle.
   * Returns null if the given handle is NULL_HANDLE, or if it has an
   * associated ClassNotFoundException.
   */
  Object lookupObject(int handle) {
      return (handle != NULL_HANDLE &&
        status[handle] != STATUS_EXCEPTION) ?
    entries[handle] : null;
  }

  /**
   * Looks up and returns ClassNotFoundException associated with the
   * given handle.  Returns null if the given handle is NULL_HANDLE, or
   * if there is no ClassNotFoundException associated with the handle.
   */
  ClassNotFoundException lookupException(int handle) {
      return (handle != NULL_HANDLE &&
        status[handle] == STATUS_EXCEPTION) ?
    (ClassNotFoundException) entries[handle] : null;
  }
 
  /**
   * Resets table to its initial state.
   */
  void clear() {
      Arrays.fill(status, 0, size, (byte) 0);
      Arrays.fill(entries, 0, size, null);
      Arrays.fill(deps, 0, size, null);
      lowDep = -1;
      size = 0;
  }
 
  /**
   * Returns number of handles registered in table.
   */
  int size() {
      return size;
  }
 
  /**
   * Expands capacity of internal arrays.
   */
  private void grow() {
      int newCapacity = (entries.length << 1) + 1;
     
      byte[] newStatus = new byte[newCapacity];
      Object[] newEntries = new Object[newCapacity];
      HandleList[] newDeps = new HandleList[newCapacity];
     
      System.arraycopy(status, 0, newStatus, 0, size);
      System.arraycopy(entries, 0, newEntries, 0, size);
      System.arraycopy(deps, 0, newDeps, 0, size);
     
      status = newStatus;
      entries = newEntries;
      deps = newDeps;
  }

  /**
   * Simple growable list of (integer) handles.
   */
  private static class HandleList {
      private int[] list = new int[4];
      private int size = 0;
     
      public HandleList() {
      }
     
      public void add(int handle) {
    if (size >= list.length) {
        int[] newList = new int[list.length << 1];
        System.arraycopy(list, 0, newList, 0, list.length);
        list = newList;
    }
    list[size++] = handle;
      }
     
      public int get(int index) {
    if (index >= size) {
        throw new ArrayIndexOutOfBoundsException();
    }
    return list[index];
      }

      public int size() {
    return size;
      }
  }
    }

    /**
     * Method for cloning arrays in case of using unsharing reading
     */
    private static Object cloneArray(Object array) {
  if (array instanceof Object[]) {
      return ((Object[]) array).clone();
  } else if (array instanceof boolean[]) {
      return ((boolean[]) array).clone();
  } else if (array instanceof byte[]) {
      return ((byte[]) array).clone();
  } else if (array instanceof char[]) {
      return ((char[]) array).clone();
  } else if (array instanceof double[]) {
      return ((double[]) array).clone();
  } else if (array instanceof float[]) {
      return ((float[]) array).clone();
  } else if (array instanceof int[]) {
      return ((int[]) array).clone();
  } else if (array instanceof long[]) {
      return ((long[]) array).clone();
  } else if (array instanceof double[]) {
      return ((double[]) array).clone();
  } else {
      throw new AssertionError();
  }
    }

    /**
     * Context that during upcalls to class-defined readObject methods; holds
     * object currently being deserialized and descriptor for current class.
     * This context keeps a boolean state to indicate that defaultReadObject
     * or readFields has already been invoked with this context or the class's
     * readObject method has returned; if true, the getObj method throws
     * NotActiveException.
     */
    private static class CallbackContext {
  private final Object obj;
  private final ObjectStreamClass desc;
  private final AtomicBoolean used = new AtomicBoolean();

  public CallbackContext(Object obj, ObjectStreamClass desc) {
      this.obj = obj;
      this.desc = desc;
  }

  public Object getObj() throws NotActiveException {
      checkAndSetUsed();
      return obj;
  }

  public ObjectStreamClass getDesc() {
      return desc;
  }

  private void checkAndSetUsed() throws NotActiveException {
      if (!used.compareAndSet(false, true)) {
           throw new NotActiveException(
          "not in readObject invocation or fields already read");
      }
  }

  public void setUsed() {
      used.set(true);
  }
    }
}
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