objectoutputstream.java

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/* ObjectOutputStream.java -- Class used to write serialized objects
   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */


package java.io;

import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;
import java.util.Hashtable;

import gnu.java.io.ObjectIdentityWrapper;
import gnu.java.lang.reflect.TypeSignature;
import gnu.classpath.Configuration;

/**
   An <code>ObjectOutputStream</code> can be used to write objects
   as well as primitive data in a platform-independent manner to an
   <code>OutputStream</code>.

   The data produced by an <code>ObjectOutputStream</code> can be read
   and reconstituted by an <code>ObjectInputStream</code>.

   <code>writeObject (Object)</code> is used to write Objects, the
   <code>write&lt;type&gt;</code> methods are used to write primitive
   data (as in <code>DataOutputStream</code>). Strings can be written
   as objects or as primitive data.

   Not all objects can be written out using an
   <code>ObjectOutputStream</code>.  Only those objects that are an
   instance of <code>java.io.Serializable</code> can be written.

   Using default serialization, information about the class of an
   object is written, all of the non-transient, non-static fields of
   the object are written, if any of these fields are objects, they are
   written out in the same manner.

   An object is only written out the first time it is encountered.  If
   the object is encountered later, a reference to it is written to
   the underlying stream.  Thus writing circular object graphs
   does not present a problem, nor are relationships between objects
   in a graph lost.

   Example usage:
   <pre>
   Hashtable map = new Hashtable ();
   map.put ("one", new Integer (1));
   map.put ("two", new Integer (2));

   ObjectOutputStream oos =
   new ObjectOutputStream (new FileOutputStream ("numbers"));
   oos.writeObject (map);
   oos.close ();

   ObjectInputStream ois =
   new ObjectInputStream (new FileInputStream ("numbers"));
   Hashtable newmap = (Hashtable)ois.readObject ();

   System.out.println (newmap);
   </pre>

   The default serialization can be overriden in two ways.

   By defining a method <code>private void
   writeObject (ObjectOutputStream)</code>, a class can dictate exactly
   how information about itself is written.
   <code>defaultWriteObject ()</code> may be called from this method to
   carry out default serialization.  This method is not
   responsible for dealing with fields of super-classes or subclasses.

   By implementing <code>java.io.Externalizable</code>.  This gives
   the class complete control over the way it is written to the
   stream.  If this approach is used the burden of writing superclass
   and subclass data is transfered to the class implementing
   <code>java.io.Externalizable</code>.

   @see java.io.DataOutputStream
   @see java.io.Externalizable
   @see java.io.ObjectInputStream
   @see java.io.Serializable
   @see XXX: java serialization spec
*/
public class ObjectOutputStream extends OutputStream
  implements ObjectOutput, ObjectStreamConstants
{
  /**
     Creates a new <code>ObjectOutputStream</code> that will do all of
     its writing onto <code>out</code>.  This method also initializes
     the stream by writing the header information (stream magic number
     and stream version).

     @exception IOException Writing stream header to underlying
     stream cannot be completed.

     @see writeStreamHeader ()
  */
  public ObjectOutputStream (OutputStream out) throws IOException
  {
    realOutput = new DataOutputStream (out);
    blockData = new byte[ BUFFER_SIZE ];
    blockDataCount = 0;
    blockDataOutput = new DataOutputStream (this);
    setBlockDataMode (true);
    replacementEnabled = false;
    isSerializing = false;
    nextOID = baseWireHandle;
    OIDLookupTable = new Hashtable ();
    protocolVersion = defaultProtocolVersion;
    useSubclassMethod = false;
    writeStreamHeader ();
  }


  /**
     Writes a representation of <code>obj</code> to the underlying
     output stream by writing out information about its class, then
     writing out each of the objects non-transient, non-static
     fields.  If any of these fields are other objects,
     they are written out in the same manner.

     This method can be overriden by a class by implementing
     <code>private void writeObject (ObjectOutputStream)</code>.

     If an exception is thrown from this method, the stream is left in
     an undefined state.

     @exception NotSerializableException An attempt was made to
     serialize an <code>Object</code> that is not serializable.

     @exception IOException Exception from underlying
     <code>OutputStream</code>.
  */
  public final void writeObject (Object obj) throws IOException
  {
    if (useSubclassMethod)
      {
	writeObjectOverride (obj);
	return;
      }

    boolean was_serializing = isSerializing;
    boolean old_mode = setBlockDataMode (false);
    try
      {
	isSerializing = true;
	boolean replaceDone = false;
	Object replacedObject = null;
	
	while (true)
	  {
	    if (obj == null)
	      {
		realOutput.writeByte (TC_NULL);
		break;
	      }

	    Integer handle = findHandle (obj);
	    if (handle != null)
	      {
		realOutput.writeByte (TC_REFERENCE);
		realOutput.writeInt (handle.intValue ());
		break;
	      }

	    if (obj instanceof Class)
	      {
		Class cl = (Class)obj;
		ObjectStreamClass osc = ObjectStreamClass.lookupForClassObject (cl);
		assignNewHandle (obj);
		realOutput.writeByte (TC_CLASS);
		if (!osc.isProxyClass)
		  {
		    writeObject (osc);
		  }
		else
		  {
		    realOutput.writeByte (TC_PROXYCLASSDESC);
		    Class[] intfs = cl.getInterfaces();
		    realOutput.writeInt(intfs.length);
		    for (int i = 0; i < intfs.length; i++)
		      realOutput.writeUTF(intfs[i].getName());
		    
		    boolean oldmode = setBlockDataMode (true);
		    annotateProxyClass(cl);
		    setBlockDataMode (oldmode);
		    realOutput.writeByte(TC_ENDBLOCKDATA);
		    
		    writeObject (osc.getSuper());
		  }
		break;
	      }

	    if (obj instanceof ObjectStreamClass)
	      {
		ObjectStreamClass osc = (ObjectStreamClass)obj;
		realOutput.writeByte (TC_CLASSDESC);
		realOutput.writeUTF (osc.getName ());
		realOutput.writeLong (osc.getSerialVersionUID ());
		assignNewHandle (obj);

		int flags = osc.getFlags ();

		if (protocolVersion == PROTOCOL_VERSION_2
		    && osc.isExternalizable ())
		  flags |= SC_BLOCK_DATA;

		realOutput.writeByte (flags);

		ObjectStreamField[] fields = osc.fields;
		realOutput.writeShort (fields.length);

		ObjectStreamField field;
		for (int i=0; i < fields.length; i++)
		  {
		    field = fields[i];
		    realOutput.writeByte (field.getTypeCode ());
		    realOutput.writeUTF (field.getName ());

		    if (! field.isPrimitive ())
		      writeObject (field.getTypeString ());
		  }

		boolean oldmode = setBlockDataMode (true);
		annotateClass (osc.forClass ());
		setBlockDataMode (oldmode);
		realOutput.writeByte (TC_ENDBLOCKDATA);

		if (osc.isSerializable ())
		  writeObject (osc.getSuper ());
		else
		  writeObject (null);
		break;
	      }

	    if ((replacementEnabled || obj instanceof Serializable)
		&& ! replaceDone)
	      {
		replacedObject = obj;

		if (obj instanceof Serializable)
		  {
		    Method m = null;
		    try
		      {
			Class classArgs[] = {};
			m = obj.getClass ().getDeclaredMethod ("writeReplace",
							       classArgs);
			// m can't be null by definition since an exception would
			// have been thrown so a check for null is not needed.
			obj = m.invoke (obj, new Object[] {});
		      }
		    catch (NoSuchMethodException ignore)
		      {
		      }
		    catch (IllegalAccessException ignore)
		      {
		      }
		    catch (InvocationTargetException ignore)
		      {
		      }
		  }

		if (replacementEnabled)
		  obj = replaceObject (obj);

		replaceDone = true;
		continue;
	      }

	    if (obj instanceof String)
	      {
		realOutput.writeByte (TC_STRING);
		assignNewHandle (obj);
		realOutput.writeUTF ((String)obj);
		break;
	      }

	    Class clazz = obj.getClass ();
	    ObjectStreamClass osc = ObjectStreamClass.lookupForClassObject (clazz);
	    if (osc == null)
	      throw new NotSerializableException (clazz.getName ());

	    if (clazz.isArray ())
	      {
		realOutput.writeByte (TC_ARRAY);
		writeObject (osc);
		assignNewHandle (obj);
		writeArraySizeAndElements (obj, clazz.getComponentType ());
		break;
	      }

	    realOutput.writeByte (TC_OBJECT);
	    writeObject (osc);

	    if (replaceDone)
	      assignNewHandle (replacedObject);
	    else
	      assignNewHandle (obj);

	    if (obj instanceof Externalizable)
	      {
		if (protocolVersion == PROTOCOL_VERSION_2)
		  setBlockDataMode (true);

		((Externalizable)obj).writeExternal (this);

		if (protocolVersion == PROTOCOL_VERSION_2)
		  {
		    setBlockDataMode (false);
		    realOutput.writeByte (TC_ENDBLOCKDATA);
		  }

		break;
	      }

	    if (obj instanceof Serializable)
	      {
		currentObject = obj;
		ObjectStreamClass[] hierarchy =
		  ObjectStreamClass.getObjectStreamClasses (clazz);

		for (int i=0; i < hierarchy.length; i++)
		  {
		    currentObjectStreamClass = hierarchy[i];

		    fieldsAlreadyWritten = false;
		    if (currentObjectStreamClass.hasWriteMethod ())
		      {
			setBlockDataMode (true);
			callWriteMethod (obj, currentObjectStreamClass);
			setBlockDataMode (false);
			realOutput.writeByte (TC_ENDBLOCKDATA);
		      }
		    else
		      writeFields (obj, currentObjectStreamClass);
		  }

		currentObject = null;
		currentObjectStreamClass = null;
		currentPutField = null;
		break;
	      }

	    throw new NotSerializableException (clazz.getName ());
	  } // end pseudo-loop
      }
    catch (ObjectStreamException ose)
      {
	// Rethrow these are fatal.
	throw ose;
      }
    catch (IOException e)
      {
	realOutput.writeByte (TC_EXCEPTION);
	reset (true);

	setBlockDataMode (false);
	try
	  {
	    writeObject (e);
	  }
	catch (IOException ioe)
	  {
	    throw new StreamCorruptedException ("Exception " + ioe + " thrown while exception was being written to stream.");
	  }

	reset (true);
      }
    finally
      {
	isSerializing = was_serializing;
	setBlockDataMode (old_mode);
      }
  }

  /**
     Writes the current objects non-transient, non-static fields from
     the current class to the underlying output stream.

     This method is intended to be called from within a object's
     <code>private void writeObject (ObjectOutputStream)</code>
     method.

     @exception NotActiveException This method was called from a
     context other than from the current object's and current class's
     <code>private void writeObject (ObjectOutputStream)</code>
     method.

     @exception IOException Exception from underlying
     <code>OutputStream</code>.
  */
  public void defaultWriteObject ()
    throws IOException, NotActiveException
  {
    markFieldsWritten ();
    writeFields (currentObject, currentObjectStreamClass);
  }


  private void markFieldsWritten () throws IOException
  {
    if (currentObject == null || currentObjectStreamClass == null)
      throw new NotActiveException ("defaultWriteObject called by non-active class and/or object");

    if (fieldsAlreadyWritten)
      throw new IOException ("Only one of putFields and defaultWriteObject may be called, and it may only be called once");

    fieldsAlreadyWritten = true;
  }


  /**
     Resets stream to state equivalent to the state just after it was
     constructed.

     Causes all objects previously written to the stream to be
     forgotten.  A notification of this reset is also written to the
     underlying stream.

     @exception IOException Exception from underlying
     <code>OutputStream</code> or reset called while serialization is
     in progress.
  */
  public void reset () throws IOException
  {
    reset (false);
  }


  private void reset (boolean internal) throws IOException
  {
    if (!internal)
      {
	if (isSerializing)
	  throw new IOException ("Reset called while serialization in progress");

	realOutput.writeByte (TC_RESET);