Examples of java.beans.PersistenceDelegate

java.beans.PersistenceDelegate
The PersistenceDelegate class takes the responsibility for expressing the state of an instance of a given class in terms of the methods in the class's public API. Instead of associating the responsibility of persistence with the class itself as is done, for example, by the readObject and writeObject methods used by the ObjectOutputStream, streams like the XMLEncoder which use this delegation model can have their behavior controlled independently of the classes themselves. Normally, the class is the best place to put such information and conventions can easily be expressed in this delegation scheme to do just that. Sometimes however, it is the case that a minor problem in a single class prevents an entire object graph from being written and this can leave the application developer with no recourse but to attempt to shadow the problematic classes locally or use alternative persistence techniques. In situations like these, the delegation model gives a relatively clean mechanism for the application developer to intervene in all parts of the serialization process without requiring that modifications be made to the implementation of classes which are not part of the application itself.
In addition to using a delegation model, this persistence scheme differs from traditional serialization schemes in requiring an analog of the writeObject method without a corresponding readObject method. The writeObject analog encodes each instance in terms of its public API and there is no need to define a readObject analog since the procedure for reading the serialized form is defined by the semantics of method invocation as laid out in the Java Language Specification. Breaking the dependency between writeObject and readObject implementations, which may change from version to version, is the key factor in making the archives produced by this technique immune to changes in the private implementations of the classes to which they refer.
A persistence delegate, may take control of all aspects of the persistence of an object including:
- Deciding whether or not an instance can be mutated into another instance of the same class.
- Instantiating the object, either by calling a public constructor or a public factory method.
- Performing the initialization of the object.
@see XMLEncoder @since 1.4 @version 1.12 11/17/05 @author Philip Milne

                .getSystemClassLoader(), new Class[] { List.class }));
    }


    public void testGetPersistenceDelegate_BeanInfo() {
        Encoder enc = new Encoder();
        PersistenceDelegate pd = enc
                .getPersistenceDelegate(MockFooLiYang.class);
        assertTrue(pd instanceof DefaultPersistenceDelegate);
    }

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    public void testGetPersistenceDelegate_Default() {
        Encoder enc = new Encoder();
        Encoder enc2 = new Encoder();


        PersistenceDelegate pd1 = enc.getPersistenceDelegate(SampleBean.class);
        assertTrue(pd1 instanceof DefaultPersistenceDelegate);


        PersistenceDelegate pd2 = enc.getPersistenceDelegate(SampleBean.class);
        assertTrue(pd2 instanceof DefaultPersistenceDelegate);


        PersistenceDelegate pd3 = enc2
                .getPersistenceDelegate(MockBean4Codec.class);
        assertTrue(pd3 instanceof DefaultPersistenceDelegate);


        assertSame(pd1, pd2);
        assertSame(pd1, pd3);

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    }


    public void testSetPersistenceDelegate_Null() {
        // Regression for HARMONY-1304
        Encoder enc = new Encoder();
        PersistenceDelegate pd = enc.getPersistenceDelegate(EncoderTest.class);


        try {
            enc.setPersistenceDelegate(null, pd);
            fail("NPE expected");
        } catch (NullPointerException e) {

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        }
    }


    public void testSetPersistenceDelegate() {
        Encoder enc = new Encoder();
        PersistenceDelegate pd = enc.getPersistenceDelegate(EncoderTest.class);
        assertTrue(pd instanceof DefaultPersistenceDelegate);


        enc.setPersistenceDelegate(EncoderTest.class, new VerbosePD());
        assertTrue(enc.getPersistenceDelegate(EncoderTest.class) instanceof VerbosePD);

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            return result;
        }


        @Override
        public PersistenceDelegate getPersistenceDelegate(Class type) {
            PersistenceDelegate result = super.getPersistenceDelegate(type);
            return result;
        }

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    private static PersistenceDelegate createPersistenceDelegate(Class<?> type) {
        if (type == null) {
            return new NullPersistenceDelegate();
        }


        PersistenceDelegate pd = null;
        try {
            String className = createDefaultNameForPersistenceDelegateClass(type);


            pd = (PersistenceDelegate) Class.forName(className, true,
                    type.getClassLoader()).newInstance();

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        return pd;
    }


    public static PersistenceDelegate getPersistenceDelegate(Class<?> type) {
        String className = (type == null) ? null : type.getName();
        PersistenceDelegate result = persistenceDelegates.get(className);


        if (result == null) {
            if (type != null && type.isArray()) {
                result = org.apache.harmony.beans.ArrayPersistenceDelegate
                        .getInstance();

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        }


        @SuppressWarnings("unchecked")
        @Override
        public PersistenceDelegate getPersistenceDelegate(Class type) {
            PersistenceDelegate result = super.getPersistenceDelegate(type);
            return result;
        }

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        }


        @SuppressWarnings("unchecked")
        @Override
        public PersistenceDelegate getPersistenceDelegate(Class type) {
            PersistenceDelegate result = super.getPersistenceDelegate(type);
            return result;
        }

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            e.setExceptionListener(new ExceptionListener() {
                public void exceptionThrown(Exception e) {
                    throw new EmsException("Could not encode connection settings",e);
                }
            });
            e.setPersistenceDelegate(File.class,new PersistenceDelegate() {
                protected Expression instantiate(Object oldInstance, Encoder out) {
                    File f = (File) oldInstance;
                    return new Expression(oldInstance, oldInstance.getClass(),"new", new Object[]{ f.getAbsolutePath() });
                }

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