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1   /*
2    * Copyright 2012 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the 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 org.jboss.netty.buffer.ChannelBuffers;
19  import org.jboss.netty.channel.Channel;
20  import org.jboss.netty.channel.ChannelDownstreamHandler;
21  import org.jboss.netty.channel.ChannelEvent;
22  import org.jboss.netty.channel.ChannelHandlerContext;
23  import org.jboss.netty.channel.ChannelPipeline;
24  import org.jboss.netty.channel.MessageEvent;
25  import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
26  import org.jboss.netty.handler.codec.frame.Delimiters;
27  
28  import static org.jboss.netty.channel.Channels.*;
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   * @apiviz.landmark
45   */
46  public abstract class OneToOneEncoder implements ChannelDownstreamHandler {
47  
48      protected OneToOneEncoder() {
49      }
50  
51      public void handleDownstream(
52              ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
53          if (!(evt instanceof MessageEvent)) {
54              ctx.sendDownstream(evt);
55              return;
56          }
57  
58          MessageEvent e = (MessageEvent) evt;
59          if (!doEncode(ctx, e)) {
60              ctx.sendDownstream(e);
61          }
62      }
63  
64      protected boolean doEncode(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
65          Object originalMessage = e.getMessage();
66          Object encodedMessage = encode(ctx, e.getChannel(), originalMessage);
67          if (originalMessage == encodedMessage) {
68              return false;
69          }
70          if (encodedMessage != null) {
71              write(ctx, e.getFuture(), encodedMessage, e.getRemoteAddress());
72          }
73          return true;
74      }
75  
76      /**
77       * Transforms the specified message into another message and return the
78       * transformed message.  Note that you can not return {@code null}, unlike
79       * you can in {@link OneToOneDecoder#decode(ChannelHandlerContext, Channel, Object)};
80       * you must return something, at least {@link ChannelBuffers#EMPTY_BUFFER}.
81       */
82      protected abstract Object encode(
83              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
84  }