marshalledobject.java

来自「Actual Java RMI implementation」· Java 代码 · 共 294 行

/*
 * @(#)MarshalledObject.java	1.30 01/12/03
 *
 * Copyright 2002 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.rmi;

import java.io.*;
import sun.rmi.server.MarshalInputStream;
import sun.rmi.server.MarshalOutputStream;

/**
 * A <code>MarshalledObject</code> contains a byte stream with the serialized
 * representation of an object given to its constructor.  The <code>get</code>
 * method returns a new copy of the original object, as deserialized from
 * the contained byte stream.  The contained object is serialized and
 * deserialized with the same serialization semantics used for marshaling
 * and unmarshaling parameters and return values of RMI calls:  When the
 * serialized form is created:
 *
 * <ul>
 * <li> classes are annotated with a codebase URL from where the class
 *      can be loaded (if available), and
 * <li> any remote object in the <code>MarshalledObject</code> is
 *      represented by a serialized instance of its stub.
 * </ul>
 *
 * <p>When copy of the object is retrieved (via the <code>get</code> method),
 * if the class is not available locally, it will be loaded from the
 * appropriate location (specified the URL annotated with the class descriptor
 * when the class was serialized.
 *
 * <p><code>MarshalledObject</code> facilitates passing objects in RMI calls
 * that are not automatically deserialized immediately by the remote peer.
 *
 * @version 1.30, 12/03/01
 * @author  Ann Wollrath
 * @author  Peter Jones
 * @since   1.2
 */
public final class MarshalledObject implements Serializable {
    /**
     * @serial Bytes of serialized representation.  If <code>objBytes</code> is
     * <code>null</code> then the object marshalled was a <code>null</code>
     * reference.
     */
    private byte[] objBytes = null;

    /**
     * @serial Bytes of location annotations, which are ignored by
     * <code>equals</code>.  If <code>locBytes</code> is null, there were no
     * non-<code>null</code> annotations during marshalling.
     */
    private byte[] locBytes = null;

    /** 
     * @serial Stored hash code of contained object. 
     *
     * @see #hashCode
     */
    private int hash;

    /** Indicate compatibility with 1.2 version of class. */
    private static final long serialVersionUID = 8988374069173025854L;

    /**
     * Creates a new <code>MarshalledObject</code> that contains the
     * serialized representation of the current state of the supplied object.
     * The object is serialized with the semantics used for marshaling
     * parameters for RMI calls.
     *
     * @param obj the object to be serialized (must be serializable)
     * @exception IOException if an <code>IOException</code> occurs; an
     * <code>IOException</code> may occur if <code>obj</code> is not
     * serializable.
     * @since 1.2
     */
    public MarshalledObject(Object obj)
	throws java.io.IOException
    {
	if (obj == null) {
	    hash = 13;
	    return;
	}

	ByteArrayOutputStream bout = new ByteArrayOutputStream();
	ByteArrayOutputStream lout = new ByteArrayOutputStream();
	MarshalledObjectOutputStream out =
	    new MarshalledObjectOutputStream(bout, lout);
	out.writeObject(obj);
	out.flush();
	objBytes = bout.toByteArray();
	// locBytes is null if no annotations
	locBytes = (out.hadAnnotations() ? lout.toByteArray() : null);

	/*
	 * Calculate hash from the marshalled representation of object
	 * so the hashcode will be comparable when sent between VMs.
	 */
	int h = 0;
	for (int i = 0; i < objBytes.length; i++) {
	    h = 31 * h + objBytes[i];
	}
	hash = h;
    }

    /**
     * Returns a new copy of the contained marshalledobject.  The internal
     * representation is deserialized with the semantics used for
     * unmarshaling paramters for RMI calls.
     *
     * @return a copy of the contained object
     * @exception IOException if an <code>IOException</code> occurs while
     * deserializing the object from its internal representation.
     * @exception ClassNotFoundException if a
     * <code>ClassNotFoundException</code> occurs while deserializing the
     * object from its internal representation.
     * could not be found
     * @since 1.2
     */
    public Object get()
	throws java.io.IOException, java.lang.ClassNotFoundException
    {
	if (objBytes == null)	// must have been a null object
	    return null;

	ByteArrayInputStream bin = new ByteArrayInputStream(objBytes);
	// locBytes is null if no annotations
	ByteArrayInputStream lin =
	    (locBytes == null ? null : new ByteArrayInputStream(locBytes));
	MarshalledObjectInputStream in =
	    new MarshalledObjectInputStream(bin, lin);
	Object obj = in.readObject();
	in.close();
	return obj;
    }

    /**
     * Return a hash code for this <code>MarshalledObject</code>.
     *
     * @return a hash code
     */
    public int hashCode() {
	return hash;
    }

    /**
     * Compares this <code>MarshalledObject</code> to another object.
     * Returns true if and only if the argument refers to a
     * <code>MarshalledObject</code> that contains exactly the same
     * serialized representation of an object as this one does. The
     * comparison ignores any class codebase annotation, meaning that
     * two objects are equivalent if they have the same serialized
     * representation <i>except</i> for the codebase of each class
     * in the serialized representation.
     *
     * @param obj the object to compare with this <code>MarshalledObject</code>
     * @return <code>true</code> if the argument contains an equaivalent
     * serialized object; <code>false</code> otherwise
     * @since 1.2
     */
    public boolean equals(Object obj) {
	if (obj == this)
	    return true;

	if (obj != null && obj instanceof MarshalledObject) {
	    MarshalledObject other = (MarshalledObject) obj;

	    // if either is a ref to null, both must be
	    if (objBytes == null || other.objBytes == null)
		return objBytes == other.objBytes;

	    // quick, easy test
	    if (objBytes.length != other.objBytes.length)
		return false;

	    //!! There is talk about adding an array comparision method
	    //!! at 1.2 -- if so, this should be rewritten.  -arnold
	    for (int i = 0; i < objBytes.length; ++i) {
		if (objBytes[i] != other.objBytes[i])
		    return false;
	    }
	    return true;
	} else {
	    return false;
	}
    }

    /**
     * This class is used to marshal objects for
     * <code>MarshalledObject</code>.  It places the location annotations
     * to one side so that two <code>MarshalledObject</code>s can be
     * compared for equality if they differ only in location
     * annotations.  Objects written using this stream should be read back
     * from a <code>MarshalledObjectInputStream</code>.
     *
     * @see java.rmi.MarshalledObject
     * @see MarshalledObjectInputStream
     */
    private static class MarshalledObjectOutputStream
    	extends MarshalOutputStream
    {
	/** The stream on which location objects are written. */
	private ObjectOutputStream locOut;

	/** <code>true</code> if non-<code>null</code> annotations are
         *  written.
	 */
	private boolean hadAnnotations;

	/**
	 * Creates a new <code>MarshalledObjectOutputStream</code> whose
	 * non-location bytes will be written to <code>objOut</code> and whose
	 * location annotations (if any) will be written to
	 * <code>locOut</code>.
	 */
	public MarshalledObjectOutputStream(OutputStream objOut,
					    OutputStream locOut)
	    throws IOException
	{
	    super(objOut);
	    this.useProtocolVersion(ObjectStreamConstants.PROTOCOL_VERSION_2);
	    this.locOut = new ObjectOutputStream(locOut);
	    hadAnnotations = false;
	}

	/**
	 * Returns <code>true</code> if any non-<code>null</code> location
	 * annotations have been written to this stream.
	 */
	public boolean hadAnnotations() {
	    return hadAnnotations;
	}

	/**
	 * Overrides MarshalOutputStream.writeLocation implementation to write
	 * annotations to the location stream.
	 */
	protected void writeLocation(String loc) throws IOException {
	    hadAnnotations |= (loc != null);
	    locOut.writeObject(loc);
	}
	
	
	public void flush() throws IOException {
	    super.flush();
	    locOut.flush();
	}
    }
    
    /**
     * The counterpart to <code>MarshalledObjectOutputStream</code>.
     *
     * @see MarshalledObjectOutputStream
     */
    private static class MarshalledObjectInputStream
    	extends MarshalInputStream
    {
	/**
	 * The stream from which annotations will be read.  If this is
	 * <code>null</code>, then all annotations were <code>null</code>.
	 */
	private ObjectInputStream locIn;

	/**
	 * Creates a new <code>MarshalledObjectInputStream</code> that
	 * reads its objects from <code>objIn</code> and annotations
	 * from <code>locIn</code>.  If <code>locIn</code> is
	 * <code>null</code>, then all annotations will be
	 * <code>null</code>.
	 */
	MarshalledObjectInputStream(InputStream objIn, InputStream locIn)
	    throws IOException
	{
	    super(objIn);
	    this.locIn = (locIn == null ? null : new ObjectInputStream(locIn));
	}

	/**
	 * Overrides MarshalInputStream.readLocation to return locations from
	 * the stream we were given, or <code>null</code> if we were given a
	 * <code>null</code> location stream.
	 */
	protected Object readLocation()
	    throws IOException, ClassNotFoundException
	{
	    return (locIn == null ? null : locIn.readObject());
	}
    }

}