PC World Komputer 1998 July & August/Pcwk78a98.iso/Internet/Javadraw/DATA.Z/ObjectInputStream.java

Text File | 1997-08-30 | 53KB | 1,569 lines

/*
 * @(#)ObjectInputStream.java    1.30 97/05/02
 *
 * Copyright (c) 1995, 1996 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 *
 * CopyrightVersion 1.1_beta
 */

package java.io;

import java.util.Vector;
import java.util.Stack;
import java.util.Hashtable;

/**
 * An ObjectInputStream deserializes primitive data and objects previously
 * written using an ObjectOutputStream.
 *
 * ObjectOutputStream and ObjectInputStream can provide an application
 * with persistent storage for graphs of objects when used with a
 * FileOutputStream and FileInputStream respectively.
 * ObjectInputStream is used to recover those objects previously
 * serialized. Other uses include passing objects between hosts using
 * a socket stream or for marshaling and unmarshaling arguments and
 * parameters in a remote communication system.<p>
 *
 * ObjectInputStream ensures that the types of all objects in the
 * graph created from the stream match the classes present in the
 * Java Virtual Machine.  Classes are loaded as required using the
 * standard mechanisms. <p>
 *
 * Only objects that support the java.io.Serializable or
 * java.io.Externalizable interface can be read from streams.
 *
 * The method <STRONG>readObject</STRONG> is used to read an object
 * from the stream.  Java's safe casting should be used to get the
 * desired type.  In Java, strings and arrays are objects and are
 * treated as objects during serialization. When read they need to be
 * cast to the expected type.<p>
 *
 * Primitive data types can be read from the stream using the appropriate
 * method on DataInput. <p>
 *
 * The default deserialization mechanism for objects restores the
 * contents of each field to the value and type it had when it was written.
 * Fields declared as transient or static are ignored by the
 * deserialization process.  References to other objects cause those
 * objects to be read from the stream as necessary.  Graphs of objects
 * are restored correctly using a reference sharing mechanism.  New
 * objects are always allocated when deserializing, which prevents
 * existing objects from being overwritten. <p>
 *
 * Reading an object is analogous to running the constructors of a new
 * object.  Memory is allocated for the object and initialized to zero
 * (NULL).  No-arg constructors are invoked for the non-serializable
 * classes and then the fields of the serializable classes are
 * restored from the stream starting with the serializable class closest to
 * java.lang.object and finishing with the object's most specifiec
 * class. <p>
 *
 * For example to read from a stream as written by the example in
 * ObjectOutputStream: <br>
 *
 * <PRE>
 *    FileInputStream istream = new FileInputStream("t.tmp");
 *    ObjectInputStream p = new ObjectInputStream(istream);
 *
 *    int i = p.readInt();
 *    String today = (String)p.readObject();
 *    Date date = (Date)p.readObject();
 *
 *    istream.close();
 * </PRE>
 *
 * Classes control how they are serialized by implementing either the
 * java.io.Serializable or java.io.Externalizable interfaces.<P>
 *
 * Implementing the Serializable interface allows object serialization
 * to save and restore the entire state of the object and it allows
 * classes to evolve between the time the stream is written and the time it is
 * read.  It automatically traverses references between objects,
 * saving and restoring entire graphs.
 *
 * Serializable classes that require special handling during the
 * serialization and deserialization process should implement both
 * of these methods:<p>
 *
 * <PRE>
 * private void writeObject(java.io.ObjectOutputStream stream)
 *     throws IOException;
 * private void readObject(java.io.ObjectInputStream stream)
 *     throws IOException, ClassNotFoundException;
 * </PRE><p>
 *
 * The readObject method is responsible for reading and restoring the
 * state of the object for its particular class using data written to
 * the stream by the corresponding writeObject method.  The method
 * does not need to concern itself with the state belonging to its
 * superclasses or subclasses.  State is restored by reading data from
 * the ObjectInputStream for the individual fields and making
 * assignments to the appropriate fields of the object.  Reading
 * primitive data types is supported by DataInput. <p>
 *
 * Serialization does not read or assign values to the fields of any
 * object that does not implement the java.io.Serializable interface.
 * Subclasses of Objects that are not serializable can be
 * serializable. In this case the non-serializable class must have a
 * no-arg constructor to allow its fields to be initialized.  In this
 * case it is the responsibility of the subclass to save and restore
 * the state of the non-serializable class. It is frequently the case that
 * the fields of that class are accessible (public, package, or
 * protected) or that there are get and set methods that can be used
 * to restore the state. <p>
 *
 * Any exception that occurs while deserializing an object will be
 * caught by the ObjectInputStream and abort the reading process. <p>
 *
 * Implementing the Externalizable interface allows the object to
 * assume complete control over the contents and format of the object's
 * serialized form.  The methods of the Externalizable interface,
 * writeExternal and readExternal, are called to save and restore the
 * objects state.  When implemented by a class they can write and read
 * their own state using all of the methods of ObjectOutput and
 * ObjectInput.  It is the responsibility of the objects to handle any
 * versioning that occurs.
 *
 * @author  Roger Riggs
 * @version 1.30, 05/02/97
 * @see java.io.DataInput
 * @see java.io.ObjectOutputStream
 * @see java.io.Serializable
 * @since   JDK1.1
 */
public class ObjectInputStream extends InputStream
    implements ObjectInput, ObjectStreamConstants
{
    /**
     * Create an ObjectInputStream that reads from the specified InputStream.
     * The stream header containing the magic number and version number
     * are read from the stream and verified. This method will block
     * until the corresponding ObjectOutputStream has written and flushed the header.
     * @exception StreamCorruptedException The version or magic number are incorrect.
     * @exception IOException An exception occurred in the underlying stream.
     * @since     JDK1.1
     */
    public ObjectInputStream(InputStream in)
    throws IOException, StreamCorruptedException
  {
      /*
       * Save the input stream to read bytes from
       * Create a DataInputStream used to read primitive types.
       * Setup the DataInputStream to read from this ObjectInputStream
       */
    this.in = in;
    dis  = new DataInputStream(this);
    readStreamHeader();
    resetStream();
    }

    /**
     * Read an object from the ObjectInputStream.
     * The class of the object, the signature of the class, and the values
     * of the non-transient and non-static fields of the class and all
     * of its supertypes are read.  Default deserializing for a class can be
     * overriden using the writeObject and readObject methods.
     * Objects referenced by this object are read transitively so
     * that a complete equivalent graph of objects is reconstructed by readObject. <p>
     *
     * The root object is completly restored when all of its fields
     * and the objects it references are completely restored.  At this
     * point the object validation callbacks are executed in order
     * based on their registered priorities. The callbacks are
     * registered by objects (in the readObject special methods)
     * as they are individually restored.
     *
     * Exceptions are thrown for problems with the InputStream and for classes
     * that should not be deserialized.  All exceptions are fatal to the
     * InputStream and leave it in an indeterminate state; it is up to the caller
     * to ignore or recover the stream state.
     * @exception java.lang.ClassNotFoundException Class of a serialized object
     *      cannot be found.
     * @exception InvalidClassException Something is wrong with a class used by
     *     serialization.
     * @exception StreamCorruptedException Control information in the
     *     stream is inconsistent.
     * @exception OptionalDataException Primitive data was found in the
     * stream instead of objects.
     * @exception IOException Any of the usual Input/Output related exceptions.
     * @since     JDK1.1
     */
    public final Object readObject()
    throws OptionalDataException, ClassNotFoundException, IOException
    {
    /* If the stream is in blockData mode and there's any data
     * left throw an exception to report how much there is.
     */
    int n;
    if (blockDataMode && (n = available()) > 0) {
        throw new OptionalDataException(n);
    }

    /*
     * Look ahead now to absorb any pending reset's.
     * Before changing the state.
     */
    peekCode();

    /* Save the current state and get ready to read an object. */
    Object prevObject = currentObject;
    ObjectStreamClass prevClass = currentClassDesc;
    boolean prevBlockDataMode = setBlockData(false);

    recursionDepth++;    // Entering
    Object obj = null;

    /*
     * Check for reset, handle it before reading an object.
     */

    byte rcode;
    rcode = readCode();
    try {
        /*
         * Dispatch on the next code in the stream.
         */
        int wireoffset = -1;

        switch (rcode) {

        case TC_NULL:
        obj = null;
        break;

        case TC_REFERENCE:
        /* This is a reference to a pre-existing object */
        wireoffset = readInt() - baseWireHandle;

        try {
            obj = wireHandle2Object.elementAt(wireoffset);
        } catch (ArrayIndexOutOfBoundsException e) {
            throw new StreamCorruptedException("Reference to object never serialized.");
        }
        break;

        case TC_STRING:
        obj = readUTF();
        assignWireOffset(obj);
        break;

        case TC_CLASS:
        ObjectStreamClass v = (ObjectStreamClass)readObject();
        if (v == null) {
            /*
             * No class descriptor in stream or class not serializable
             */
            throw new StreamCorruptedException("Class not in stream");
        }
        obj = v.forClass();
        assignWireOffset(obj);
        break;

        case TC_CLASSDESC:
        obj = inputClassDescriptor();
        break;

        case TC_ARRAY:
        obj = inputArray();
        break;

        case TC_OBJECT:
        wireoffset = inputObject();
        obj = currentObject;
        if (enableResolve) {
            /* Hook for alternate object */
            obj = resolveObject(obj);
            wireHandle2Object.setElementAt(obj, wireoffset);
        }
        break;

        case TC_ENDBLOCKDATA:
        if (!prevBlockDataMode)
            throw new StreamCorruptedException("Unexpected end of block data");
        pushbackCode(TC_ENDBLOCKDATA);
        count = -1;    /* Flag EOF */
        throw new OptionalDataException(true);

        case TC_BLOCKDATA:
        case TC_BLOCKDATALONG:
        if (rcode == TC_BLOCKDATALONG) { /* long block: 32 bit size */
            int b3 = in.read();
            int b2 = in.read();
            int b1 = in.read();
            int b0 = in.read();
            if ((b3 | b2 | b1 | b0) < 0)
            throw new StreamCorruptedException("EOF expecting count");
            count = (b3 << 24) | (b2 << 16) | (b1 << 8) | b0;
            if (count < 0)
            throw new StreamCorruptedException("Negative block data size");
        } else {            /* normal block: 8 bit size */
            count = in.read();
            if (count < 0)
            throw new StreamCorruptedException("EOF expecting count");
        }

            if (!prevBlockDataMode)
            throw new StreamCorruptedException("Unexpected blockdata");

        throw new OptionalDataException(count);

        case TC_EXCEPTION:
        /* An exception happened during writing, reset the
         * stream, read the exception, reset the stream and
         * throw a writeAbortedException with the exception
         * that was read.
         */
        resetStream();
        IOException ee = (IOException)readObject();
        resetStream();
        throw new WriteAbortedException("Writing aborted by exception", ee);

        default:
        throw new StreamCorruptedException("Unknown code in readObject " + rcode);
        }
    } catch (OptionalDataException optdata) {
        /* OptionalDataExceptions won't terminate everything.
         * so just rethrow it.
         */
        throw optdata;
    } catch(IOException ee) {
        if (abortIOException == null && abortClassNotFoundException == null)
        abortIOException = ee;
    } catch(ClassNotFoundException ee) {
        if (abortIOException == null && abortClassNotFoundException == null)
        abortClassNotFoundException = ee;
    } finally {
        recursionDepth --;
        currentObject = prevObject;
        currentClassDesc = prevClass;
        setBlockData(prevBlockDataMode);
    }

    /* Check for thrown exceptions and re-throw them, clearing them if
     * this is the last recursive call .
     */
    IOException exIOE = abortIOException;
    if (recursionDepth == 0)
        abortIOException = null;
    if (exIOE != null)
        throw exIOE;


    ClassNotFoundException exCNF = abortClassNotFoundException;
    if (recursionDepth == 0)
        abortClassNotFoundException = null;
    if (exCNF != null) {
        throw exCNF;
    }

    // Check if this is the last nested read, if so
    // Call the validations
    if (recursionDepth == 0) {
        doValidations();
    }

    return obj;
    }

    /**
     * Read the non-static and non-transient fields of the current class
     * from this stream.  This may only be called from the readObject method
     * of the class being deserialized. It will throw the NotActiveException
     * if it is called otherwise.
     *
     * @exception java.lang.ClassNotFoundException if the class of a serialized
     *              object could not be found.
     * @exception IOException        if an I/O error occurs.
     * @exception NotActiveException if the stream is not currently reading
     *              objects.
     * @since     JDK1.1
     */
    public final void defaultReadObject()
    throws IOException, ClassNotFoundException, NotActiveException
    {
    if (currentObject == null || currentClassDesc == null)
        throw new NotActiveException("defaultReadObject");


    if (currentClassDesc.getFieldSequence() != null) {
        boolean prevmode = setBlockData(false);
        inputClassFields(currentObject, currentClass,
                 currentClassDesc.getFieldSequence());
        setBlockData(prevmode);
    }
    }

    /**
     * Register an object to be validated before the graph is
     * returned.  While similar to resolveObject these validations are
     * called after the entire graph has been reconstituted.
     * Typically, a readObject method will register the object with
     * the stream so that when all of the objects are restored a final
     * set of validations can be performed.
     * @param obj the object to receive the validation callback.
     * @param prio controls the order of callbacks;zero is a good default.
     * Use higher numbers to be called back earlier, lower numbers for later
     * callbacks. Within a priority, callbacks are processed in no
     * particular order.
     *
     * @exception NotActiveException The stream is not currently reading objects
     * so it is invalid to register a callback.
     * @exception InvalidObjectException The validation object is null.
     * @since     JDK1.1
     */
    public synchronized void registerValidation(ObjectInputValidation obj,
                        int prio)
    throws NotActiveException, InvalidObjectException
    {
    if (recursionDepth == 0) {
        throw new NotActiveException("readObject not Active");
    }
    if (obj == null) {
        throw new InvalidObjectException("Null is not a valid callback object");
    }

    ValidationCallback cb = new ValidationCallback(obj, prio);

    if (callbacks == null) {
        callbacks = new Vector(100,100);
    }
    // insert at the end if the priority is less than or equal to
    // the last element.
    if (callbacks.isEmpty() ||
        ((ValidationCallback)(callbacks.lastElement())).priority >= prio) {
        callbacks.addElement(cb);
        return;
    }

    // search for the element with priority that is <= to the new
    // priority, insert before it.
    int size = callbacks.size();
    for (int i = 0; i < size; i++) {
        ValidationCallback curr = (ValidationCallback)callbacks.elementAt(i);
        if (curr.priority <= prio) {
        callbacks.insertElementAt(cb, i);
        break;
        }
    }
    }

    /*
     * If any validations are pending, do them and cleanup the validation vector
     * if an exception is raised, it is passed on to abort the deserialization.
     */
    private void doValidations() throws InvalidObjectException {
    if (callbacks == null)
        return;

    int size = callbacks.size();
    for (int i = 0; i < size; i++) {
        ValidationCallback curr = (ValidationCallback)callbacks.elementAt(i);
        curr.callback.validateObject();
    }
    }

    /**
     * Subclasses may implement this method to allow classes to be
     * fetched from an alternate source.
     *
     * The corresponding method in ObjectOutputStream is
     * annotateClass.  This method will be invoked only once for each
     * unique class in the stream.  This method can be implemented by
     * subclasses to use an alternate loading mechanism but must
     * return a Class object.  Once returned, the serialVersionUID of the
     * class is compared to the serialVersionUID of the serialized class.
     * If there is a mismatch, the deserialization fails and an exception
     * is raised. <p>
     *
     * By default the class name is resolved relative to the class
     * that called readObject. <p>
     *
     * @exception ClassNotFoundException If class of
     * a serialized object cannot be found.
     * @since     JDK1.1
     */
    protected Class resolveClass(ObjectStreamClass v)
    throws IOException, ClassNotFoundException
    {
    /* Resolve by looking up the stack for a non-zero class
     * loader. If not found use the system loader.
     */
    return loadClass0(null, v.getName());
    }

    /* Resolve a class name relative to the specified class.  If the
     * class is null find the first available class loader up the
     * stack.  This will resolve classes relative to the caller of
     * ObjectInputStream instead of the itself. Classes must be
     * loaded/resolved relative to the application.
     */
    private native Class loadClass0(Class cl, String classname)
    throws ClassNotFoundException;

    /**
     * This method will allow trusted subclasses of ObjectInputStream
     * to substitute one object for another during
     * deserialization. Replacing objects is disabled until
     * enableResolveObject is called. The enableResolveObject method
     * checks that the stream requesting to resolve object can be
     * trusted. Every reference to serializable objects is passed to
     * resolveObject.  To insure that the private state of objects is
     * not unintentionally exposed only trusted streams may use
     * resolveObject. <p>
     *
     * This method is called after an object has been read but before it is
     * returned from readObject.  The default resolveObject method
     * just returns the new object. <p>
     *
     * When a subclass is replacing objects it must insure that the
     * substituted object is compatible with every field where the
     * reference will be stored.  Objects whose type is not a subclass
     * of the type of the field or array element abort the
     * serialization by raising an exception and the object is not be
     * stored. <p>
     *
     * This method is called only once when each object is first encountered.
     * All subsequent references to the object will be redirected to the
     * new object. <P>
     *
     * @exception IOException Any of the usual Input/Output exceptions.
     * @since     JDK1.1
     */
    protected Object resolveObject(Object obj)
        throws IOException
    {
    return obj;
    }

    /**
     * Enable the stream to allow objects read from the stream to be replaced.
     * If the stream is a trusted class it is allowed to enable replacment.
     * Trusted classes are those classes with a classLoader equals null. <p>
     *
     * When enabled the resolveObject method is called for every object
     * being deserialized.
     *
     * @exception SecurityException The classloader of this stream object is non-null.
     * @since     JDK1.1
     */
    protected final boolean enableResolveObject(boolean enable)
    throws SecurityException
    {
    boolean previous = enableResolve;
    if (enable) {
        ClassLoader loader = this.getClass().getClassLoader();
        if (loader == null) {
        enableResolve = true;
        return previous;
        }
        throw new SecurityException("Not trusted class");
    } else {
        enableResolve = false;
    }
    return previous;
    }


    /**
     * The readStreamHeader method is provided to allow subclasses to
     * read and verify their own stream headers. It reads and
     * verifies the magic number and version number.
     * @since     JDK1.1
     */
    protected void readStreamHeader()
    throws IOException, StreamCorruptedException
    {
    short incoming_magic = readShort();
    short incoming_version = readShort();
    if (incoming_magic != STREAM_MAGIC)
        throw new StreamCorruptedException("InputStream does not contain a serialized object");

    if (incoming_version != STREAM_VERSION)
        throw new StreamCorruptedException("Version Mismatch, Expected " +
                           STREAM_VERSION + " and got " +
                           incoming_version);
    }

    /*
     * Read a ObjectStreamClasss from the stream, it may recursively
     * create other ObjectStreamClasss for the classes it references.
     */
    private ObjectStreamClass inputClassDescriptor()
    throws IOException, InvalidClassException, ClassNotFoundException
    {

    /* Read the class name and hash */
    Class aclass;
    String classname = readUTF();
    long hash = readLong();

    /* Read a new class version descriptor from the stream */
    ObjectStreamClass v = new ObjectStreamClass(classname, hash);

    /* Assign the wire handle for this ObjectStreamClass and read it */
    int wireoffset = assignWireOffset(v);
    v.read(this);

    /* Switch to BlockDataMode and call resolveClass.
     * It may raise ClassNotFoundException.
     * Consume any extra data or objects left by resolve class and
     * read the endOfBlockData. Then switch out of BlockDataMode.
     */
    boolean prevMode = setBlockData(true);
    aclass = resolveClass((ObjectStreamClass)v);
    SkipToEndOfBlockData();
    prevMode = setBlockData(prevMode);


    /* Verify that the class returned is "compatible" with
     * the class description.  i.e. the name and hash match.
     * Set the class this ObjectStreamClass will use to create
     * instances.
     */
    if (aclass == null) {
        throw new ClassNotFoundException(v.getName());
    }
    v.setClass(aclass);

    /* Get the superdescriptor of this one and it set it.
     */
    ObjectStreamClass superdesc = (ObjectStreamClass)readObject();
    v.setSuperclass(superdesc);

    return v;
    }

    /* Private routine to read in an array. Called from inputObject
     * after the typecode has been read from the stream.
     */
    private Object inputArray()
    throws IOException, ClassNotFoundException
    {
    /* May raise ClassNotFoundException */
    ObjectStreamClass v = (ObjectStreamClass)readObject();

    Class arrayclass = v.forClass();

    /* This can't be done with new because only the top level array
     * is needed and the type must be set properly.
     * the lower level arrays will be created when they are read.
     */
    int length = readInt();
    currentObject = allocateNewArray(arrayclass, length);
    assignWireOffset(currentObject);

    /* Read in the values from the array,
     * It dispatches using the type and read using the read* methods.
     */
    int i;
    Class type = arrayclass.getComponentType();

    if (type.isPrimitive()) {
        /* Arrays of primitive types read data in blocks and
         * decode the data types from the buffer.
         */
        if (buffer == null)
        buffer = new byte[1024];
        int offset = buffer.length;
        int buflen = buffer.length;

        if (type == Boolean.TYPE) {
        boolean[] array = (boolean[])currentObject;
        for (i = 0; i < length; i++) {
            if (offset >= buflen) {
            int readlen = Math.min(length-i, buflen);
            readFully(buffer, 0, readlen);
            offset = 0;
            }
            array[i] = (buffer[offset] != 0);
            offset += 1;
        }
        } else if (type == Byte.TYPE) {
        byte[] array = (byte[])currentObject;
        readFully(array, 0, length);
        } else if (type == Short.TYPE) {
        short[] array = (short[])currentObject;
        for (i = 0; i < length; i++) {
            if (offset > buflen - 2) {
            int readlen = Math.min((length-i)*2, buflen);
            readFully(buffer, 0, readlen);
            offset = 0;
            }
            array[i] = (short)(((buffer[offset] & 0xff) << 8) +
                       ((buffer[offset+1] & 0xff) << 0));
            offset += 2;
        }
        } else if (type == Integer.TYPE) {
        int[] array = (int[])currentObject;
        for (i = 0; i < length; i++) {
            if (offset > buflen - 4) {
            int readlen = Math.min((length-i)*4, buflen);
            readFully(buffer, 0, readlen);
            offset = 0;
            }
            array[i] = (((buffer[offset] & 0xff) << 24) +
                ((buffer[offset+1] & 0xff) << 16) +
                ((buffer[offset+2] & 0xff) << 8) +
                ((buffer[offset+3] & 0xff) << 0));
            offset += 4;
        }
        } else if (type == Long.TYPE) {
        long[] array = (long[])currentObject;
        for (i = 0; i < length; i++) {
            if (offset > buflen - 8) {
            int readlen = Math.min((length-i)*8, buflen);
            readFully(buffer, 0, readlen);
            offset = 0;
            }
            int upper = (((buffer[offset] & 0xff) << 24) +
                ((buffer[offset+1] & 0xff) << 16) +
                ((buffer[offset+2] & 0xff) << 8) +
                ((buffer[offset+3] & 0xff) << 0));
            int lower = (((buffer[offset+4] & 0xff) << 24) +
                ((buffer[offset+5] & 0xff) << 16) +
                ((buffer[offset+6] & 0xff) << 8) +
                ((buffer[offset+7] & 0xff) << 0));
            array[i] = ((long)upper << 32) + ((long)lower & 0xFFFFFFFFL);
            offset += 8;
        }
        } else if (type == Float.TYPE) {
        float[] array = (float[])currentObject;
        for (i = 0; i < length; i++) {
            if (offset > buflen - 4) {
            int readlen = Math.min((length-i)*4, buflen);
            readFully(buffer, 0, readlen);
            offset = 0;
            }
            int value = (((buffer[offset] & 0xff) << 24) +
                 ((buffer[offset+1] & 0xff) << 16) +
                 ((buffer[offset+2] & 0xff) << 8) +
                 ((buffer[offset+3] & 0xff) << 0));
            offset += 4;
            array[i] = Float.intBitsToFloat(value);
        }
        } else if (type == Double.TYPE) {
        double[] array = (double[])currentObject;
        for (i = 0; i < length; i++) {
            if (offset > buflen - 8) {
            int readlen = Math.min((length-i)*8, buflen);
            readFully(buffer, 0, readlen);
            offset = 0;
            }
            int upper = (((buffer[offset] & 0xff) << 24) +
                 ((buffer[offset+1] & 0xff) << 16) +
                 ((buffer[offset+2] & 0xff) << 8) +
                 ((buffer[offset+3] & 0xff) << 0));
            int lower = (((buffer[offset+4] & 0xff) << 24) +
                 ((buffer[offset+5] & 0xff) << 16) +
                 ((buffer[offset+6] & 0xff) << 8) +
                 ((buffer[offset+7] & 0xff) << 0));
            offset += 8;
            array[i] = Double.longBitsToDouble((((long)upper) << 32) +
                               (lower & 0xFFFFFFFFL));
        }
        } else if (type == Character.TYPE) {
        char[] array = (char[])currentObject;
        for (i = 0; i < length; i++) {
            if (offset > buflen - 2) {
            int readlen = Math.min((length-i)*2, buflen);
            readFully(buffer, 0, readlen);
            offset = 0;
            }
            array[i] = (char)(((buffer[offset] & 0xff) << 8) +
                      ((buffer[offset+1] & 0xff) << 0));
            offset += 2;
        }
        } else {
        throw new InvalidClassException(arrayclass.getName());
        }
    } else {        // Is array of objects
        Object[] array = (Object[])currentObject;
        for (i = 0; i < length; i++) {
        array[i] = readObject();
        }
    }

    return currentObject;
    }

    /*
     * Read an instance of a class from the stream
     * The new object typecode has already been read and used to dispatch to here.
     * The ObjectStreamClass for the class is read and the class
     * of the object retrieved from it.
     * A new object is created of the specified class and
     * each serializable class is processed using either
     * the default serialization methods or class defined special methods
     * if they have been defined.
     * The handle for the object is returned, the object itself is in currentObject.
     */
    private int inputObject()
    throws IOException, ClassNotFoundException
    {
    int handle = -1;
    /*
     * Get the descriptor and then class of the incomming object.
     */
    currentClassDesc = (ObjectStreamClass)readObject();
    currentClass = currentClassDesc.forClass();


    /* If Externalizable,
     *  Create an instance and tell it to read its data.
     * else,
     *  Handle it as a serializable class.
     */
    if (currentClassDesc.isExternalizable()) {
        try {
        currentObject = allocateNewObject(currentClass, currentClass);
        handle = assignWireOffset(currentObject);
        Externalizable ext = (Externalizable)currentObject;
        ext.readExternal(this);
        } catch (IllegalAccessException e) {
        throw new InvalidClassException(currentClass.getName(),
                        "IllegalAccessException");
        } catch (InstantiationException e) {
        throw new InvalidClassException(currentClass.getName(),
                        "InstantiationException");
        }
    } else {
        /* Count number of classes and descriptors we might have
         * to work on.
         */
        ObjectStreamClass currdesc = currentClassDesc;
        Class currclass = currentClass;

        int spBase = spClass;    // current top of stack

        /* The object's classes should be processed from supertype to subtype
         * Push all the clases of the current object onto a stack.
         * Note that only the serializable classes are represented
         * in the descriptor list.
         *
         * Handle versioning where one or more supertypes of
         * have been inserted or removed.  The stack will
         * contain pairs of descriptors and the corresponding
         * class.  If the object has a class that did not occur in
         * the original the descriptor will be null.  If the
         * original object had a descriptor for a class not
         * present in the local hierarchy of the object the class will be
         * null.
         *
         */

        /*
         * This is your basic diff pattern, made simpler
         * because reordering is not allowed.
         */
        for (currdesc = currentClassDesc, currclass = currentClass;
         currdesc != null;
         currdesc = currdesc.getSuperclass()) {

        /*
         * Search the classes to see if thisthe class of this
         * descriptor appears further up the hierarchy. Until
         * it's found assume its an inserted class.  If it's
         * not found, its the descriptor's class that has been
         * removed.
         */
        Class cc = currdesc.forClass();
        Class cl;
        for (cl = currclass; cl != null; cl = cl.getSuperclass()) {
            if (cc == cl) {
            // found a superclass that matches this descriptor
            break;
            } else {
            /* Ignore a class that doesn't match.  No
             * action is needed since it is already
             * initialized.
             */
            }
        }
        /* Test if there is room for this new entry.
         * If not, double the size of the arrays and copy the contents.
         */
        spClass++;
        if (spClass >= classes.length) {
            int newlen = classes.length * 2;
            Class[] newclasses = new Class[newlen];
            ObjectStreamClass[] newclassdesc = new ObjectStreamClass[newlen];

            System.arraycopy(classes, 0,
                 newclasses, 0,
                 classes.length);
            System.arraycopy(classdesc, 0,
                     newclassdesc, 0,
                     classes.length);

            classes = newclasses;
            classdesc = newclassdesc;
        }

        if (cl == null) {
            /* Class not found corresponding to this descriptor.
             * Pop off all the extra classes pushed.
             * Push the descriptor and a null class.
             */
            classdesc[spClass] = currdesc;
            classes[spClass] = null;
        } else {
                   /* Current class descriptor matches current class.
             * Some classes may have been inserted.
             * Record the match and advance the class, continue
             * with the next descriptor.
             */
            classdesc[spClass] = currdesc;
            classes[spClass] = cl;
            currclass = cl.getSuperclass();
        }
        }

        /* Allocate a new object.  The object is only constructed
         * above the highest serializable class and is set to
         * default values for all more specialized classes.
         * Remember the next wirehandle goes with the new object
         */
        try {
        currentObject = allocateNewObject(currentClass, currclass);
        } catch (NoSuchMethodError e) {
        throw new InvalidClassException(currclass.getName(),
                        "NoSuchMethodError");
        } catch (IllegalAccessException e) {
        throw new InvalidClassException(currclass.getName(),
                        "IllegalAccessException");
        } catch (InstantiationException e) {
        throw new InvalidClassException(currclass.getName(),
                        "InstantiationException");
        }
        handle = assignWireOffset(currentObject);

        /*
         * For all the pushed descriptors and classes.
         * If there is a descriptor but no class, skip the
         * data for that class.
         * If there is a class but no descriptor, just advance,
         * The classes fields have already been initialized to default
         * values.
         * Otherwise, there is both a descriptor and class,
         *     if the class has its own writeObject and readObject methods
         *        set blockData = true; and call the readObject method
         *    else
         *        invoke the defaultReadObject method
         *    if the stream was written by class specific methods
         *        skip any remaining data a objects until TC_ENDBLOCKDATA
         * Avoid setting BlockData=true unless necessary becase it flushes
         * the buffer.
         */
        try {
        for (spClass = spClass; spClass > spBase; spClass--) {
            /*
             * Set current descriptor and corresponding class
             */
            currentClassDesc = classdesc[spClass];
            currentClass = classes[spClass];

            if (classes[spClass] != null) {
            /* Read the data from the stream described by the
             * descriptor and store into the matching class.
             */
            setBlockData(true);    /* any reads are from datablocks */
            ObjectStreamClass localDesc = currentClassDesc.localClassDescriptor();
            if (!invokeObjectReader(currentObject, currentClass)) {
                defaultReadObject();
            }
            } else {
            /* No class for this descriptor,
             * Skip over the data for this class.
             * like defaultReadObject with a null currentObject.
             * The native code will read the values but discard them.
             */
            if (currentClassDesc.getFieldSequence() != null) {
                boolean prevmode = setBlockData(false);
                inputClassFields(null, currentClass,
                         currentClassDesc.getFieldSequence());
                setBlockData(prevmode);
            }
            }

            /*
             * If the source class (stream) had a write object method
             * it may have written more data and will have written the
             * TC_ENDBLOCKDATA.  Skip anything up to that and read it.
             */
            if (currentClassDesc.hasWriteObject()) {
            SkipToEndOfBlockData();
            }
            setBlockData(false);
        }
        } finally {
        // Make sure we exit at the same stack level as when we started.
        spClass = spBase;
        }
    }
    return handle;
    }

    /*
     * Skip any unread block data and objects up to the next
     * TC_ENDBLOCKDATA.  Anybody can do this because readObject
     * handles the details of reporting if there is data left.
     * Try reading objects.  If it throws optional data
     * skip over it and try again.
     */
    private void SkipToEndOfBlockData()
    throws IOException, ClassNotFoundException
    {
    while (peekCode() != TC_ENDBLOCKDATA) {
        try {
        Object ignore = readObject();
        } catch (OptionalDataException data) {
        if (data.length > 0)
            skip(data.length);
        }
    }
    readCode();            /* Consume TC_ENDBLOCKDATA */
    }

    /*
     * Reset the stream to be just like it was after the constructor.
     */
    private void resetStream() throws IOException {
    wireHandle2Object = new Vector(100,100);
    nextWireOffset = 0;
    classes = new Class[20];
    classdesc = new ObjectStreamClass[20];
    spClass = 0;
    setBlockData(true);        // Re-enable buffering
    callbacks = null;        // discard any pending callbacks
    }

    /* Allocate a handle for an object.
     * The Vector is indexed by the wireHandleOffset
     * and contains the object.
     */
    private int assignWireOffset(Object obj)
    throws IOException
    {
    wireHandle2Object.addElement(obj);
    if (++nextWireOffset != wireHandle2Object.size())
      throw new StreamCorruptedException("Elements not assigned in order");;
    return nextWireOffset-1;
    }

    /*
     * Peek at the next control code in the stream.
     * If the code has not been peeked at yet, read it from the stream.
     */
    private byte peekCode() throws IOException, StreamCorruptedException{
    while (currCode == 0) {

        int newcode = in.read();    // Read byte from the underlying stream
        if (newcode < 0)
        throw new EOFException("Expecting code");

        currCode = (byte)newcode;
        if (currCode < TC_BASE || currCode > TC_MAX)
        throw new StreamCorruptedException("Type code out of range, is " + currCode);

        /*
         * Handle reset as a hidden code and reset the stream.
         */
        if (currCode == TC_RESET) {
        if (recursionDepth != 0 ||
            currentObject != null ||
            currentClassDesc != null)
            throw new StreamCorruptedException("Illegal stream state for reset");

        /* Reset the stream, and repeat the peek at the next code
         */
        resetStream();
        currCode = 0;
        }
    }
    return currCode;
    }

    /*
     * Return the next control code in the stream.
     * peekCode gets the next code.  readCode just consumes it.
     */
    private byte readCode()
    throws IOException, StreamCorruptedException
    {
    byte tc = peekCode();
    currCode = 0;
    return tc;
    }

    /*
     * Put back the specified code to be peeked at next time.
     */
    private void pushbackCode(byte code) {
    currCode = code;
    }
    /* -----------------------------------------------------*/
    /*
     * Implement the InputStream methods.  The stream has
     * two modes used internally to ObjectInputStream.  When
     * in BlockData mode, all reads are only from datablocks
     * as original written. End of data (-1) is returned
     * if something other than a datablock is next in the stream.
     * When not in BlockData mode (false), reads pass directly
     * through to the underlying stream.
     * The BlockData mode is used to encapsulate data written
     * by class specific writeObject methods that is intended
     * only to be read by corresponding readObject method of the
     * same class.  The blocking of data allows it to be skipped
     * if necessary.
     *
     * The setBlockData method is used to switch buffering
     * on and off.  When switching between on and off
     * there must be no data pending to be read. This is
     * an internal consistency check that will throw an exception.
     *
     */
    private InputStream in;

    /*
     * Count of bytes available from blockData, if zero, call refill
     * to look for more.  If -1 always return eof (-1)
     */
    private int count;

    private boolean blockDataMode;

    private byte[] buffer;    // buffer for reading array data

    /*
     * Set the blockdata buffering mode.
     * If it is being set to false after being true there must
     * be no pending data. If count > 0 a corrupted exception is thrown.
     */
    private boolean setBlockData(boolean mode) throws IOException {
    if (blockDataMode == mode)
        return mode;
    if (blockDataMode && count > 0)
        throw new StreamCorruptedException("Unread data");

    /* Set count to allow reading or not */
    count =  mode ? 0 : -1;

    blockDataMode = mode;
    return !mode;
    }

    /**
     * Reads a byte of data. This method will block if no input is
     * available.
     * @return     the byte read, or -1 if the end of the
     *        stream is reached.
     * @exception IOException If an I/O error has occurred.
     * @since     JDK1.1
     */
    public int read() throws IOException {
    int data;
    if (blockDataMode) {
        while (count == 0)
        refill();
        if (count < 0)
        return -1;            /* EOF */
        data = in.read();
        if (data >= 0)
        count--;
    } else {
        data = in.read();        /* read directly from input stream */
    }
    return data;
    }

    /*
     * Expect the next thing in the stream is a datablock, If its a
     * datablock, extract the count of bytes to allow.  If data is not
     * available set the count to zero.  On error or EOF, set count to -1.
     */
    private void refill() throws IOException {
    count = -1;        /*  No more data to read, EOF */
    byte code;
    try {
        code = peekCode();
    } catch (EOFException e) {
        return;
    }
    if (code == TC_BLOCKDATA) {
        code = readCode();            /* Consume the code */
        int c = in.read();
        if (c < 0)
        throw new StreamCorruptedException("EOF expecting count");

        count = c & 0xff;
    } else if (code == TC_BLOCKDATALONG) {
        code = readCode();
        int b3 = in.read();
        int b2 = in.read();
        int b1 = in.read();
        int b0 = in.read();
        if ((b3 | b2 | b1 | b0) < 0)
        throw new StreamCorruptedException("EOF expecting count");
        int c = (b3 << 24) | (b2 << 16) | (b1 << 8) | b0;
        /*
         * The 32 bit integer size in the long block data format is
         * signed (unlike like the normal block data format), and
         * negative values are invalid.
         */
        if (c < 0)
        throw new StreamCorruptedException("Negative block data size");

        count = c;
    }
    }

    /**
     * Reads into an array of bytes.  This method will
     * block until some input is available.
     * @param b    the buffer into which the data is read
     * @param off the start offset of the data
     * @param len the maximum number of bytes read
     * @return  the actual number of bytes read, -1 is
     *         returned when the end of the stream is reached.
     * @exception IOException If an I/O error has occurred.
     * @since     JDK1.1
     */
    public int read(byte[] data, int offset, int length) throws IOException {
    int v;
    int i;

    if (length < 0)
        throw new IndexOutOfBoundsException();

    if (blockDataMode) {
        while (count == 0)
        refill();
        if (count < 0)
        return -1;
        int l = Math.min(length, count);
        i = in.read(data, offset, l);
        if (i > 0)
        count -= i;
        return i;            /* return number of bytes read */
    } else {
        /* read directly from input stream */
        return in.read(data, offset, length);
    }
    }

    /**
     * Returns the number of bytes that can be read without blocking.
     * @return the number of available bytes.
     * @since     JDK1.1
     */
    /*
     * If in blockdataMode returns the number of bytes in the
     * current block. If that is zero, it will try to read
     * another blockdata from the stream if any data is available from the
     * underlying stream..
     * If not in blockdata mode it returns zero.
     */
    public int available() throws IOException {
    if (blockDataMode) {
        if (count == 0 && in.available() > 0)
        refill();
        if (count >= 0) {
        return count;
        } else
        return 0;    /* EOF is no bytes available */
    } else {
        return 0;        /* Not blockdata, no bytes available */
    }
    }

    /**
     * Closes the input stream. Must be called
     * to release any resources associated with
     * the stream.
     * @exception IOException If an I/O error has occurred.
     * @since     JDK1.1
     */
    public void close() throws IOException {
    in.close();
    }

    /* -----------------------------------------------------*/
    /*
     * Provide the methods to implement DataInput.
     * They delegate to an Instance of DataInputStream that
     * reads its input from the ObjectInputStream.
     * This allows this stream to manage the blocked data the data
     * as necessary.
     */
    private DataInputStream dis;

    /**
     * Reads in a boolean.
     * @return the boolean read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public boolean readBoolean() throws IOException {
    return dis.readBoolean();
    }

    /**
     * Reads an 8 bit byte.
     * @return the 8 bit byte read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public byte readByte() throws IOException  {
    return dis.readByte();
    }

    /**
     * Reads an unsigned 8 bit byte.
     * @return the 8 bit byte read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public int readUnsignedByte()  throws IOException {
    return dis.readUnsignedByte();
    }

    /**
     * Reads a 16 bit short.
     * @return the 16 bit short read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public short readShort()  throws IOException {
    return dis.readShort();
    }

    /**
     * Reads an unsigned 16 bit short.
     * @return the 16 bit short read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public int readUnsignedShort() throws IOException {
    return dis.readUnsignedShort();
    }

    /**
     * Reads a 16 bit char.
     * @return the 16 bit char read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public char readChar()  throws IOException {
    return dis.readChar();
    }

    /**
     * Reads a 32 bit int.
     * @return the 32 bit integer read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public int readInt()  throws IOException {
    return dis.readInt();
    }

    /**
     * Reads a 64 bit long.
     * @return the read 64 bit long.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public long readLong()  throws IOException {
    return dis.readLong();
    }

    /**
     * Reads a 32 bit float.
     * @return the 32 bit float read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public float readFloat() throws IOException {
    return dis.readFloat();
    }

    /**
     * Reads a 64 bit double.
     * @return the 64 bit double read.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public double readDouble() throws IOException {
    return dis.readDouble();
    }

    /**
     * Reads bytes, blocking until all bytes are read.
     * @param b    the buffer into which the data is read
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public void readFully(byte[] data) throws IOException {
    dis.readFully(data);
    }

    /**
     * Reads bytes, blocking until all bytes are read.
     * @param b    the buffer into which the data is read
     * @param off the start offset of the data
     * @param len the maximum number of bytes to read
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public void readFully(byte[] data, int offset, int size) throws IOException {
    if (size < 0)
        throw new IndexOutOfBoundsException();

    dis.readFully(data, offset, size);
    }

    /**
     * Skips bytes, block until all bytes are skipped.
     * @param n the number of bytes to be skipped
     * @return    the actual number of bytes skipped.
     * @exception EOFException If end of file is reached.
     * @exception IOException If other I/O error has occurred.
     * @since     JDK1.1
     */
    public int skipBytes(int len) throws IOException {
    return dis.skipBytes(len);
    }

    /**
     * Reads in a line that has been terminated by a \n, \r,
     * \r\n or EOF.
     * @return a String copy of the line.
     * @since     JDK1.1
     */
    public String readLine() throws IOException {
    return dis.readLine();
    }

    /**
     * Reads a UTF format String.
     * @return the String.
     * @since     JDK1.1
     */
     public String readUTF() throws IOException {
    return dis.readUTF();
    }

    /* Remember the first exception that stopped this stream. */
    private IOException abortIOException = null;
    private ClassNotFoundException abortClassNotFoundException = null;

    /* Read the fields of the specified class.
     * The native implementation sorts the field names to put them
     * in cononical order, ignores transient and static fields
     * and invokes the appropriate write* method on this class.
     */
    private native void inputClassFields(Object o, Class cl, int[] fieldSequence)
    throws InvalidClassException,
        StreamCorruptedException, ClassNotFoundException, IOException;

    /* Allocate a new object for the specified class
     * Native since newInstance may not be able to find a zero arg constructor.
     */
    private static native Object allocateNewObject(Class aclass, Class initclass)
    throws InstantiationException, IllegalAccessException;

    /* Allocate a new array for the specified class
     * Native since the type of the array needs to be set to the class
     */
    private static native Object allocateNewArray(Class aclass, int length);

    /* Test if readObject/Writer methods are present, if so
     * invoke the reader and return true.
     */
    private native boolean invokeObjectReader(Object o, Class aclass)
    throws InvalidClassException,
        StreamCorruptedException, ClassNotFoundException, IOException;


    /* The object is the current object and class is the the current
     * subclass of the object being read. Nesting information is kept
     * on the stack.
     */
    private Object currentObject;
    private ObjectStreamClass currentClassDesc;
    private Class currentClass;

    /* Arrays used to keep track of classes and ObjectStreamClasses
     * as they are being merged; used in inputObject.
     * spClass is the stack pointer for both.
     */
    ObjectStreamClass[] classdesc;
    Class[] classes;
    int spClass;

    /* During deserialization the objects in the stream are represented by
     * handles (ints), they need to be mapped to the objects.
     * The vector is indexed by the offset between baseWireHandle and the
     * wire handle in the stream.
     */
    private Vector wireHandle2Object;
    private int nextWireOffset;

    /* Vector of validation callback objects
     * The vector is created as needed, and ValidationCallback objects added
     * for each call to registerObject. The vector is maintained in
     * order of highest (first) priority to lowest
     */
    private Vector callbacks;

    /* Recursion level, starts at zero and is incremented for each entry
     * to readObject.  Decremented before exit.
     */
    private int recursionDepth;

    /* Last code Peek'ed, if any */
    private byte currCode;

    /*
     * Flag set to true to allow resolveObject to be called.
     * Set by enableResolveObject.
     */
    private boolean enableResolve;
}

// Internal class to hold the Callback object and priority
class ValidationCallback {
    ValidationCallback(ObjectInputValidation cb, int prio) {
    callback = cb;
    priority = prio;
    }

    int priority;            // priority of this callback
    ObjectInputValidation callback; // object to be called back
}