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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 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   * @apiviz.landmark
    48   */
    49  public abstract class OneToOneDecoder implements ChannelUpstreamHandler {
    50
    51      /**
    52       * Creates a new instance with the current system character set.
    53       */
    54      protected OneToOneDecoder() {
    55          super();
    56      }
    57
    58      public void handleUpstream(
    59              ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
    60          if (!(evt instanceof MessageEvent)) {
    61              ctx.sendUpstream(evt);
    62              return;
    63          }
    64
    65          MessageEvent e = (MessageEvent) evt;
    66          Object originalMessage = e.getMessage();
    67          Object decodedMessage = decode(ctx, e.getChannel(), originalMessage);
    68          if (originalMessage == decodedMessage) {
    69              ctx.sendUpstream(evt);
    70          } else if (decodedMessage != null) {
    71              fireMessageReceived(ctx, decodedMessage, e.getRemoteAddress());
    72          }
    73      }
    74
    75      /**
    76       * Transforms the specified received message into another message and return
    77       * the transformed message.  Return {@code null} if the received message
    78       * is supposed to be discarded.
    79       */
    80      protected abstract Object decode(
    81              ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
    82  }