/* * Copyright (c) 1997, 2001, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package sun.rmi.log; import java.io.*;import sun.rmi.server.MarshalOutputStream;import sun.rmi.server.MarshalInputStream; /** * A LogHandler represents snapshots and update records as serializable * objects. * * This implementation does not know how to create an initial snaphot or * apply an update to a snapshot.  The client must specifiy these methods * via a subclass. * * @see ReliableLog * * @author Ann Wollrath */public abstractclass LogHandler {     /**     * Creates a LogHandler for a ReliableLog.     */    public LogHandler() {}     /**     * Creates and returns the initial state of data structure that needs     * to be stably stored. This method is called when a ReliableLog is     * created.     * @return the initial state     * @exception Exception can raise any exception     */    public abstract    Object initialSnapshot() throws Exception;     /**     * Writes the snapshot object to a stream.  This callback is     * invoked when the client calls the snaphot method of ReliableLog.     * @param out the output stream     * @param value the snapshot     * @exception Exception can raise any exception     */    public    void snapshot(OutputStream out, Object value) throws Exception {        MarshalOutputStream s = new MarshalOutputStream(out);        s.writeObject(value);        s.flush();    }     /**     * Read the snapshot object from a stream and returns the snapshot.     * This callback is invoked when the client calls the recover method     * of ReliableLog.     * @param in the input stream     * @return the state (snapshot)     * @exception Exception can raise any exception     */     public    Object recover(InputStream in) throws Exception {        MarshalInputStream s = new MarshalInputStream(in);        return s.readObject();    }     /**     * Writes the representation (a serializable object) of an update     * to a stream.  This callback is invoked when the client calls the     * update method of ReliableLog.     * @param out the output stream     * @param value the snapshot     * @exception Exception can raise any exception     */    public    void writeUpdate(LogOutputStream out, Object value) throws Exception {         MarshalOutputStream s = new MarshalOutputStream(out);        s.writeObject(value);        s.flush();    }     /**     * Reads a stably logged update (a serializable object) from a     * stream.  This callback is invoked during recovery, once for     * every record in the log.  After reading the update, this method     * invokes the applyUpdate (abstract) method in order to obtain     * the new snapshot value.  It then returns the new snapshot.     *     * @param in the input stream     * @param state the current state     * @return the new state     * @exception Exception can raise any exception     */    public    Object readUpdate(LogInputStream in, Object state) throws Exception {        MarshalInputStream  s = new MarshalInputStream(in);        return applyUpdate(s.readObject(), state);    }     /**     * Reads a stably logged update (a serializable object) from a stream.     * This callback is invoked during recovery, once for every record in the     * log.  After reading the update, this method is invoked in order to     * obtain the new snapshot value.  The method should apply the update     * object to the current state <code>state</code> and return the new     * state (the new snapshot value).     * @param update the update object     * @param state the current state     * @return the new state     * @exception Exception can raise any exception     */    public abstract    Object applyUpdate(Object update, Object state) throws Exception; }