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.string;
17
18 import java.nio.charset.Charset;
19
20 import org.jboss.netty.buffer.ChannelBuffer;
21 import org.jboss.netty.channel.Channel;
22 import org.jboss.netty.channel.ChannelHandler.Sharable;
23 import org.jboss.netty.channel.ChannelHandlerContext;
24 import org.jboss.netty.channel.ChannelPipeline;
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 import org.jboss.netty.handler.codec.oneone.OneToOneDecoder;
30
31 /**
32 * Decodes a received {@link ChannelBuffer} into a {@link String}. Please
33 * note that this decoder must be used with a proper {@link FrameDecoder}
34 * such as {@link DelimiterBasedFrameDecoder} if you are using a stream-based
35 * transport such as TCP/IP. A typical setup for a text-based line protocol
36 * in a TCP/IP socket would be:
37 * <pre>
38 * {@link ChannelPipeline} pipeline = ...;
39 *
40 * // Decoders
41 * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#lineDelimiter()}));
42 * pipeline.addLast("stringDecoder", new {@link StringDecoder}(CharsetUtil.UTF_8));
43 *
44 * // Encoder
45 * pipeline.addLast("stringEncoder", new {@link StringEncoder}(CharsetUtil.UTF_8));
46 * </pre>
47 * and then you can use a {@link String} instead of a {@link ChannelBuffer}
48 * as a message:
49 * <pre>
50 * void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} e) {
51 * String msg = (String) e.getMessage();
52 * ch.write("Did you say '" + msg + "'?\n");
53 * }
54 * </pre>
55 *
56 * @apiviz.landmark
57 */
58 @Sharable
59 public class StringDecoder extends OneToOneDecoder {
60
61 // TODO Use CharsetDecoder instead.
62 private final Charset charset;
63
64 /**
65 * Creates a new instance with the current system character set.
66 */
67 public StringDecoder() {
68 this(Charset.defaultCharset());
69 }
70
71 /**
72 * Creates a new instance with the specified character set.
73 */
74 public StringDecoder(Charset charset) {
75 if (charset == null) {
76 throw new NullPointerException("charset");
77 }
78 this.charset = charset;
79 }
80
81 @Override
82 protected Object decode(
83 ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
84 if (!(msg instanceof ChannelBuffer)) {
85 return msg;
86 }
87 return ((ChannelBuffer) msg).toString(charset);
88 }
89 }