edu.umd.cs.piccolo.util
Class PObjectOutputStream

java.lang.Object
  extended by java.io.OutputStream
      extended by java.io.ObjectOutputStream
          extended by edu.umd.cs.piccolo.util.PObjectOutputStream
All Implemented Interfaces:
java.io.Closeable, java.io.DataOutput, java.io.Flushable, java.io.ObjectOutput, java.io.ObjectStreamConstants

public class PObjectOutputStream
extends java.io.ObjectOutputStream

PObjectOutputStream is an extension of ObjectOutputStream to handle optional elements. This is similar to the concept of Java's "weak references", but applied to object serialization rather than garbage collection. Here, PObjectOutputStream provides a method, writeConditionalObject, which only serializes the specified object to the stream if there is a strong reference (if it has been written somewhere else using writeObject()) to that object elsewhere in the stream.

To discover strong references to objects, PObjectOutputStream uses a two-phase writing process. First, a "discovery" phase is used to find out what objects are about to be serialized. This works by effectively serializing the object graph to /dev/null, recording which objects are unconditionally written using the standard writeObject method. Then, in the second "write" phase, ObjectOutputStream actually serializes the data to the output stream. During this phase, calls to writeConditionalObject() will only write the specified object if the object was found to be serialized during the discovery stage. If the object was not recorded during the discovery stage, a an optional null (the default) is unconditionally written in place of the object. To skip writting out the null use writeConditionalObject(object, false)

By careful implementation of readObject and writeObject methods, streams serialized using PObjectOutputStream can be deserialized using the standard ObjectInputStream.

Version:
1.0
Author:
Jon Meyer, Jesse Grosjean

Nested Class Summary
 
Nested classes/interfaces inherited from class java.io.ObjectOutputStream
java.io.ObjectOutputStream.PutField
 
Field Summary
 
Fields inherited from interface java.io.ObjectStreamConstants
baseWireHandle, PROTOCOL_VERSION_1, PROTOCOL_VERSION_2, SC_BLOCK_DATA, SC_ENUM, SC_EXTERNALIZABLE, SC_SERIALIZABLE, SC_WRITE_METHOD, STREAM_MAGIC, STREAM_VERSION, SUBCLASS_IMPLEMENTATION_PERMISSION, SUBSTITUTION_PERMISSION, TC_ARRAY, TC_BASE, TC_BLOCKDATA, TC_BLOCKDATALONG, TC_CLASS, TC_CLASSDESC, TC_ENDBLOCKDATA, TC_ENUM, TC_EXCEPTION, TC_LONGSTRING, TC_MAX, TC_NULL, TC_OBJECT, TC_PROXYCLASSDESC, TC_REFERENCE, TC_RESET, TC_STRING
 
Constructor Summary
PObjectOutputStream(java.io.OutputStream out)
           
 
Method Summary
protected  void recordUnconditionallyWritten(java.lang.Object aRoot)
           
 void reset()
           
static byte[] toByteArray(java.lang.Object aRoot)
           
 void writeConditionalObject(java.lang.Object object)
           
 void writeObjectTree(java.lang.Object aRoot)
           
 
Methods inherited from class java.io.ObjectOutputStream
annotateClass, annotateProxyClass, close, defaultWriteObject, drain, enableReplaceObject, flush, putFields, replaceObject, useProtocolVersion, write, write, write, writeBoolean, writeByte, writeBytes, writeChar, writeChars, writeClassDescriptor, writeDouble, writeFields, writeFloat, writeInt, writeLong, writeObject, writeObjectOverride, writeShort, writeStreamHeader, writeUnshared, writeUTF
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

PObjectOutputStream

public PObjectOutputStream(java.io.OutputStream out)
                    throws java.io.IOException
Throws:
java.io.IOException
Method Detail

toByteArray

public static byte[] toByteArray(java.lang.Object aRoot)
                          throws java.io.IOException
Throws:
java.io.IOException

writeObjectTree

public void writeObjectTree(java.lang.Object aRoot)
                     throws java.io.IOException
Throws:
java.io.IOException

writeConditionalObject

public void writeConditionalObject(java.lang.Object object)
                            throws java.io.IOException
Throws:
java.io.IOException

reset

public void reset()
           throws java.io.IOException
Overrides:
reset in class java.io.ObjectOutputStream
Throws:
java.io.IOException

recordUnconditionallyWritten

protected void recordUnconditionallyWritten(java.lang.Object aRoot)
                                     throws java.io.IOException
Throws:
java.io.IOException


Copyright 2005 by University of Maryland, College Park, MD 20742, USA All rights reserved.

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