001/*
002 *  Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *
010 *    http://www.apache.org/licenses/LICENSE-2.0
011 *
012 *  Unless required by applicable law or agreed to in writing,
013 *  software distributed under the License is distributed on an
014 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 *  KIND, either express or implied.  See the License for the
016 *  specific language governing permissions and limitations
017 *  under the License.
018 *
019 */
020package org.apache.mina.handler.demux;
021
022import org.apache.mina.core.session.IoSession;
023
024/**
025 * A handler interface that {@link DemuxingIoHandler} forwards
026 * <tt>messageReceived</tt> or <tt>messageSent</tt> events to.  You have to
027 * register your handler with the type of the message you want to get notified
028 * using {@link DemuxingIoHandler#addReceivedMessageHandler(Class, MessageHandler)}
029 * or {@link DemuxingIoHandler#addSentMessageHandler(Class, MessageHandler)}.
030 *
031 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
032 */
033public interface MessageHandler<E> {
034    /**
035     * A {@link MessageHandler} that does nothing.  This is useful when
036     * you want to ignore a message of a specific type silently.
037     */
038    MessageHandler<Object> NOOP = new MessageHandler<Object>() {
039        public void handleMessage(IoSession session, Object message) {
040            // Do nothing
041        }
042    };
043
044    /**
045     * Invoked when the specific type of message is received from or sent to
046     * the specified <code>session</code>.
047     * 
048     * @param session the associated {@link IoSession}
049     * @param message the message to decode. Its type is set by the implementation
050     * @throws Exception if there is an error during the message processing
051     */
052    void handleMessage(IoSession session, E message) throws Exception;
053}