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1   /*
2    * Copyright 2009 Red Hat, Inc.
3    *
4    * Red Hat licenses this file to you under the Apache License, version 2.0
5    * (the "License"); you may not use this file except in compliance with the
6    * License.  You may obtain a copy of the License at:
7    *
8    *    http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package org.jboss.netty.handler.codec.oneone;
17  
18  import static org.jboss.netty.channel.Channels.*;
19  
20  import org.jboss.netty.buffer.ChannelBuffers;
21  import org.jboss.netty.channel.Channel;
22  import org.jboss.netty.channel.ChannelDownstreamHandler;
23  import org.jboss.netty.channel.ChannelEvent;
24  import org.jboss.netty.channel.ChannelHandlerContext;
25  import org.jboss.netty.channel.ChannelPipeline;
26  import org.jboss.netty.channel.MessageEvent;
27  import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
28  import org.jboss.netty.handler.codec.frame.Delimiters;
29  
30  /**
31   * Transforms a write request into another write request.  A typical setup for
32   * TCP/IP would be:
33   * <pre>
34   * {@link ChannelPipeline} pipeline = ...;
35   *
36   * // Decoders
37   * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#nulDelimiter()}));
38   * pipeline.addLast("customDecoder", new {@link OneToOneDecoder}() { ... });
39   *
40   * // Encoder
41   * pipeline.addLast("customEncoder", new {@link OneToOneEncoder}() { ... });
42   * </pre>
43   *
44   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
45   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
46   *
47   * @version $Rev:231 $, $Date:2008-06-12 16:44:50 +0900 (목, 12 6월 2008) $
48   *
49   * @apiviz.landmark
50   */
51  public abstract class OneToOneEncoder implements ChannelDownstreamHandler {
52  
53      protected OneToOneEncoder() {
54          super();
55      }
56  
57      public void handleDownstream(
58              ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
59          if (!(evt instanceof MessageEvent)) {
60              ctx.sendDownstream(evt);
61              return;
62          }
63  
64          MessageEvent e = (MessageEvent) evt;
65          Object originalMessage = e.getMessage();
66          Object encodedMessage = encode(ctx, e.getChannel(), originalMessage);
67          if (originalMessage == encodedMessage) {
68              ctx.sendDownstream(evt);
69          } else if (encodedMessage != null) {
70              write(ctx, e.getFuture(), encodedMessage, e.getRemoteAddress());
71          }
72      }
73  
74      /**
75       * Transforms the specified message into another message and return the
76       * transformed message.  Note that you can not return {@code null}, unlike
77       * you can in {@link OneToOneDecoder#decode(ChannelHandlerContext, Channel, Object)};
78       * you must return something, at least {@link ChannelBuffers#EMPTY_BUFFER}.
79       */
80      protected abstract Object encode(
81              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
82  }