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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License.
18   *
19   */
20  package org.apache.mina.handler.demux;
21  
22  import org.apache.mina.core.session.IoSession;
23  
24  /**
25   * A handler interface that {@link DemuxingIoHandler} forwards
26   * <tt>messageReceived</tt> or <tt>messageSent</tt> events to.  You have to
27   * register your handler with the type of the message you want to get notified
28   * using {@link DemuxingIoHandler#addReceivedMessageHandler(Class, MessageHandler)}
29   * or {@link DemuxingIoHandler#addSentMessageHandler(Class, MessageHandler)}.
30   *
31   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
32   */
33  public interface MessageHandler<E> {
34      /**
35       * A {@link MessageHandler} that does nothing.  This is useful when
36       * you want to ignore a message of a specific type silently.
37       */
38      static MessageHandler<Object> NOOP = new MessageHandler<Object>() {
39          public void handleMessage(IoSession session, Object message) {
40              // Do nothing
41          }
42      };
43  
44      /**
45       * Invoked when the specific type of message is received from or sent to
46       * the specified <code>session</code>.
47       * 
48       * @param session the associated {@link IoSession}
49       * @param message the message to decode. Its type is set by the implementation
50       * @throws Exception if there is an error during the message processing
51       */
52      void handleMessage(IoSession session, E message) throws Exception;
53  }