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Berkeley DB Java Edition is a open source, transactional storage solution for Java applications. The Direct Persistence Layer (DPL) API is faster and easier to develop, deploy, and manage than serialized object files or ORM-based Java persistence solutions. The Collections API enhances the standard java.util.collections classes allowing them to be persisted to a local file system and accessed concurrently while protected by ACID transactions. Data is stored by serializing objects and managing class and instance data separately so as not to waste space. Berkeley DB Java Edition is the reliable drop-in solution for complex, fast, and scalable storage. Source for this release is in 'je-4.0.92-sources.jar', the Javadoc is located at 'http://download.oracle.com/berkeley-db/docs/je/4.0.92/'.

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/*-
 * Copyright (C) 2002, 2018, Oracle and/or its affiliates. All rights reserved.
 *
 * This file was distributed by Oracle as part of a version of Oracle Berkeley
 * DB Java Edition made available at:
 *
 * http://www.oracle.com/technetwork/database/database-technologies/berkeleydb/downloads/index.html
 *
 * Please see the LICENSE file included in the top-level directory of the
 * appropriate version of Oracle Berkeley DB Java Edition for a copy of the
 * license and additional information.
 */

package com.sleepycat.bind.serial;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamClass;
import java.io.ObjectStreamConstants;
import java.io.OutputStream;

import com.sleepycat.je.DatabaseException;
import com.sleepycat.util.RuntimeExceptionWrapper;

/**
 * A specialized ObjectOutputStream that stores class description
 * information in a ClassCatalog.  It is used by
 * SerialBinding.
 *
 * This class is used instead of an {@link ObjectOutputStream}, which it
 * extends, to write a compact object stream.  For writing objects to a
 * database normally one of the serial binding classes is used.  {@link
 * SerialOutput} is used when an {@link ObjectOutputStream} is needed along
 * with compact storage.  A {@link ClassCatalog} must be supplied, however, to
 * stored shared class descriptions.
 *
 * The {@link ClassCatalog} is used to store class definitions rather than
 * embedding these into the stream.  Instead, a class format identifier is
 * embedded into the stream.  This identifier is then used by {@link
 * SerialInput} to load the class format to deserialize the object.
 *
 * @see Class Evolution
 *
 * @author Mark Hayes
 */
public class SerialOutput extends ObjectOutputStream {

    /*
     * Serialization version constants. Instead of hardcoding these we get them
     * by creating a SerialOutput, which itself guarantees that we'll always
     * use a PROTOCOL_VERSION_2 header.
     */
    private final static byte[] STREAM_HEADER;
    static {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            new SerialOutput(baos, null);
        } catch (IOException e) {
            throw RuntimeExceptionWrapper.wrapIfNeeded(e);
        }
        STREAM_HEADER = baos.toByteArray();
    }

    private ClassCatalog classCatalog;

    /**
     * Creates a serial output stream.
     *
     * @param out is the output stream to which the compact serialized objects
     * will be written.
     *
     * @param classCatalog is the catalog to which the class descriptions for
     * the serialized objects will be written.
     *
     * @throws IOException if an I/O error occurs while writing stream header.
     */
    public SerialOutput(OutputStream out, ClassCatalog classCatalog)
        throws IOException {

        super(out);
        this.classCatalog = classCatalog;

        /* guarantee that we'll always use the same serialization format */

        useProtocolVersion(ObjectStreamConstants.PROTOCOL_VERSION_2);
    }

    // javadoc is inherited
    protected void writeClassDescriptor(ObjectStreamClass classdesc)
        throws IOException {

        try {
            byte[] id = classCatalog.getClassID(classdesc);
            writeByte(id.length);
            write(id);
        } catch (DatabaseException e) {

            /*
             * Do not throw IOException from here since ObjectOutputStream
             * will write the exception to the stream, which causes another
             * call here, etc.
             */
            throw RuntimeExceptionWrapper.wrapIfNeeded(e);
        } catch (ClassNotFoundException e) {
            throw RuntimeExceptionWrapper.wrapIfNeeded(e);
        }
    }

    /**
     * Returns the fixed stream header used for all serialized streams in
     * PROTOCOL_VERSION_2 format.  To save space this header can be removed and
     * serialized streams before storage and inserted before deserializing.
     * {@link SerialOutput} always uses PROTOCOL_VERSION_2 serialization format
     * to guarantee that this header is fixed.  {@link SerialBinding} removes
     * this header from serialized streams automatically.
     *
     * @return the fixed stream header.
     */
    public static byte[] getStreamHeader() {

        return STREAM_HEADER;
    }
}