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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  }