https://openjdk.java.net/ 
/*
 * 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.

Author:Ann Wollrath
See Also:
  • ReliableLog
/**
 * 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 abstract
class LogHandler {

    
Creates a LogHandler for a ReliableLog.

/**
     * 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.

Throws:
Returns:the initial state
/**
     * 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.

Params:
  • out – the output stream
  • value – the snapshot
Throws:
/**
     * 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.

Params:
  • in – the input stream
Throws:
Returns:the state (snapshot)
/**
     * 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.

Params:
  • out – the output stream
  • value – the snapshot
Throws:
/**
     * 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.

Params:
  • in – the input stream
  • state – the current state
Throws:
Returns:the new 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
     * 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 state and return the new
state (the new snapshot value).

Params:
  • update – the update object
  • state – the current state
Throws:
Returns:the new 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;

}