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.channel.Channel;
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.ChannelUpstreamHandler;
25 import org.jboss.netty.channel.MessageEvent;
26 import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
27 import org.jboss.netty.handler.codec.frame.Delimiters;
28 import org.jboss.netty.handler.codec.frame.FrameDecoder;
29
30 /**
31 * Transforms a received message into another message. Please note that this
32 * decoder must be used with a proper {@link FrameDecoder} such as
33 * {@link DelimiterBasedFrameDecoder} or you must implement proper framing
34 * mechanism by yourself if you are using a stream-based transport such as
35 * TCP/IP. A typical setup for TCP/IP would be:
36 * <pre>
37 * {@link ChannelPipeline} pipeline = ...;
38 *
39 * // Decoders
40 * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#nulDelimiter()}));
41 * pipeline.addLast("customDecoder", new {@link OneToOneDecoder}() { ... });
42 *
43 * // Encoder
44 * pipeline.addLast("customEncoder", new {@link OneToOneEncoder}() { ... });
45 * </pre>
46 *
47 * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
48 * @author <a href="http://gleamynode.net/">Trustin Lee</a>
49 *
50 * @version $Rev:231 $, $Date:2008-06-12 16:44:50 +0900 (목, 12 6월 2008) $
51 *
52 * @apiviz.landmark
53 */
54 public abstract class OneToOneDecoder implements ChannelUpstreamHandler {
55
56 /**
57 * Creates a new instance with the current system character set.
58 */
59 protected OneToOneDecoder() {
60 super();
61 }
62
63 public void handleUpstream(
64 ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
65 if (!(evt instanceof MessageEvent)) {
66 ctx.sendUpstream(evt);
67 return;
68 }
69
70 MessageEvent e = (MessageEvent) evt;
71 Object originalMessage = e.getMessage();
72 Object decodedMessage = decode(ctx, e.getChannel(), originalMessage);
73 if (originalMessage == decodedMessage) {
74 ctx.sendUpstream(evt);
75 } else if (decodedMessage != null) {
76 fireMessageReceived(ctx, decodedMessage, e.getRemoteAddress());
77 }
78 }
79
80 /**
81 * Transforms the specified received message into another message and return
82 * the transformed message. Return {@code null} if the received message
83 * is supposed to be discarded.
84 */
85 protected abstract Object decode(
86 ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
87 }