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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.example.factorial;
17  
18  import java.math.BigInteger;
19  
20  import org.jboss.netty.buffer.ChannelBuffer;
21  import org.jboss.netty.buffer.ChannelBuffers;
22  import org.jboss.netty.channel.Channel;
23  import org.jboss.netty.channel.ChannelHandlerContext;
24  import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;
25  
26  /**
27   * Encodes a {@link Number} into the binary representation prepended with
28   * a magic number ('F' or 0x46) and a 32-bit length prefix.  For example, 42
29   * will be encoded to { 'F', 0, 0, 0, 1, 42 }.
30   *
31   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
32   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
33   *
34   * @version $Rev: 2125 $, $Date: 2010-02-02 12:13:15 +0900 (Tue, 02 Feb 2010) $
35   *
36   */
37  public class NumberEncoder extends OneToOneEncoder {
38  
39      @Override
40      protected Object encode(
41              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception {
42          if (!(msg instanceof Number)) {
43              // Ignore what this encoder can't encode.
44              return msg;
45          }
46  
47          // Convert to a BigInteger first for easier implementation.
48          BigInteger v;
49          if (msg instanceof BigInteger) {
50              v = (BigInteger) msg;
51          } else {
52              v = new BigInteger(String.valueOf(msg));
53          }
54  
55          // Convert the number into a byte array.
56          byte[] data = v.toByteArray();
57          int dataLength = data.length;
58  
59          // Construct a message.
60          ChannelBuffer buf = ChannelBuffers.dynamicBuffer();
61          buf.writeByte((byte) 'F'); // magic number
62          buf.writeInt(dataLength);  // data length
63          buf.writeBytes(data);      // data
64  
65          // Return the constructed message.
66          return buf;
67      }
68  }