/*
* @(#)ObjID.java 1.31 06/02/23
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.rmi.server;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.Serializable;
import java.security.AccessController;
import java.security.SecureRandom;
import java.util.concurrent.atomic.AtomicLong;
import sun.security.action.GetPropertyAction;
/**
* An <code>ObjID</code> is used to identify a remote object exported
* to an RMI runtime. When a remote object is exported, it is assigned
* an object identifier either implicitly or explicitly, depending on
* the API used to export.
*
* <p>The {@link #ObjID()} constructor can be used to generate a unique
* object identifier. Such an <code>ObjID</code> is unique over time
* with respect to the host it is generated on.
*
* The {@link #ObjID(int)} constructor can be used to create a
* "well-known" object identifier. The scope of a well-known
* <code>ObjID</code> depends on the RMI runtime it is exported to.
*
* <p>An <code>ObjID</code> instance contains an object number (of type
* <code>long</code>) and an address space identifier (of type
* {@link UID}). In a unique <code>ObjID</code>, the address space
* identifier is unique with respect to a given host over time. In a
* well-known <code>ObjID</code>, the address space identifier is
* equivalent to one returned by invoking the {@link UID#UID(short)}
* constructor with the value zero.
*
* <p>If the system property <code>java.rmi.server.randomIDs</code>
* is defined to equal the string <code>"true"</code> (case insensitive),
* then the {@link #ObjID()} constructor will use a cryptographically
* strong random number generator to choose the object number of the
* returned <code>ObjID</code>.
*
* @author Ann Wollrath
* @author Peter Jones
* @version 1.31, 06/02/23
* @since JDK1.1
*/
public final class ObjID implements Serializable {
/** Object number for well-known <code>ObjID</code> of the registry. */
public static final int REGISTRY_ID = 0;
/** Object number for well-known <code>ObjID</code> of the activator. */
public static final int ACTIVATOR_ID = 1;
/**
* Object number for well-known <code>ObjID</code> of
* the distributed garbage collector.
*/
public static final int DGC_ID = 2;
/** indicate compatibility with JDK 1.1.x version of class */
private static final long serialVersionUID = -6386392263968365220L;
private static final AtomicLong nextObjNum = new AtomicLong(0);
private static final UID mySpace = new UID();
private static final SecureRandom secureRandom = new SecureRandom();
/**
* @serial object number
* @see #hashCode
*/
private final long objNum;
/**
* @serial address space identifier (unique to host over time)
*/
private final UID space;
/**
* Generates a unique object identifier.
*
* <p>If the system property <code>java.rmi.server.randomIDs</code>
* is defined to equal the string <code>"true"</code> (case insensitive),
* then this constructor will use a cryptographically
* strong random number generator to choose the object number of the
* returned <code>ObjID</code>.
*/
public ObjID() {
/*
* If generating random object numbers, create a new UID to
* ensure uniqueness; otherwise, use a shared UID because
* sequential object numbers already ensure uniqueness.
*/
if (useRandomIDs()) {
space = new UID();
objNum = secureRandom.nextLong();
} else {
space = mySpace;
objNum = nextObjNum.getAndIncrement();
}
}
/**
* Creates a "well-known" object identifier.
*
* <p>An <code>ObjID</code> created via this constructor will not
* clash with any <code>ObjID</code>s generated via the no-arg
* constructor.
*
* @param objNum object number for well-known object identifier
*/
public ObjID(int objNum) {
space = new UID((short) 0);
this.objNum = objNum;
}
/**
* Constructs an object identifier given data read from a stream.
*/
private ObjID(long objNum, UID space) {
this.objNum = objNum;
this.space = space;
}
/**
* Marshals a binary representation of this <code>ObjID</code> to
* an <code>ObjectOutput</code> instance.
*
* <p>Specifically, this method first invokes the given stream's
* {@link ObjectOutput#writeLong(long)} method with this object
* identifier's object number, and then it writes its address
* space identifier by invoking its {@link UID#write(DataOutput)}
* method with the stream.
*
* @param out the <code>ObjectOutput</code> instance to write
* this <code>ObjID</code> to
*
* @throws IOException if an I/O error occurs while performing
* this operation
*/
public void write(ObjectOutput out) throws IOException {
out.writeLong(objNum);
space.write(out);
}
/**
* Constructs and returns a new <code>ObjID</code> instance by
* unmarshalling a binary representation from an
* <code>ObjectInput</code> instance.
*
* <p>Specifically, this method first invokes the given stream's
* {@link ObjectInput#readLong()} method to read an object number,
* then it invokes {@link UID#read(DataInput)} with the
* stream to read an address space identifier, and then it
* creates and returns a new <code>ObjID</code> instance that
* contains the object number and address space identifier that
* were read from the stream.
*
* @param in the <code>ObjectInput</code> instance to read
* <code>ObjID</code> from
*
* @return unmarshalled <code>ObjID</code> instance
*
* @throws IOException if an I/O error occurs while performing
* this operation
*/
public static ObjID read(ObjectInput in) throws IOException {
long num = in.readLong();
UID space = UID.read(in);
return new ObjID(num, space);
}
/**
* Returns the hash code value for this object identifier, the
* object number.
*
* @return the hash code value for this object identifier
*/
public int hashCode() {
return (int) objNum;
}
/**
* Compares the specified object with this <code>ObjID</code> for
* equality.
*
* This method returns <code>true</code> if and only if the
* specified object is an <code>ObjID</code> instance with the same
* object number and address space identifier as this one.
*
* @param obj the object to compare this <code>ObjID</code> to
*
* @return <code>true</code> if the given object is equivalent to
* this one, and <code>false</code> otherwise
*/
public boolean equals(Object obj) {
if (obj instanceof ObjID) {
ObjID id = (ObjID) obj;
return objNum == id.objNum && space.equals(id.space);
} else {
return false;
}
}
/**
* Returns a string representation of this object identifier.
*
* @return a string representation of this object identifier
*/
/*
* The address space identifier is only included in the string
* representation if it does not denote the local address space
* (or if the randomIDs property was set).
*/
public String toString() {
return "[" + (space.equals(mySpace) ? "" : space + ", ") +
objNum + "]";
}
private static boolean useRandomIDs() {
String value = AccessController.doPrivileged(
new GetPropertyAction("java.rmi.server.randomIDs"));
return value == null ? true : Boolean.parseBoolean(value);
}
}