MessageToMessageCodec.java — netty Source File

Source Code

/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.codec;

import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;
import io.netty.util.ReferenceCounted;
import io.netty.util.internal.TypeParameterMatcher;

import java.util.List;

/**
 * A Codec for on-the-fly encoding/decoding of message.
 *
 * This can be thought of as a combination of {@link MessageToMessageDecoder} and {@link MessageToMessageEncoder}.
 *
 * Here is an example of a {@link MessageToMessageCodec} which just decode from {@link Integer} to {@link Long}
 * and encode from {@link Long} to {@link Integer}.
 *
 * <pre>
 *     public class NumberCodec extends
 *             {@link MessageToMessageCodec}&lt;{@link Integer}, {@link Long}&gt; {
 *         {@code @Override}
 *         public {@link Long} decode({@link ChannelHandlerContext} ctx, {@link Integer} msg, List&lt;Object&gt; out)
 *                 throws {@link Exception} {
 *             out.add(msg.longValue());
 *         }
 *
 *         {@code @Override}
 *         public {@link Integer} encode({@link ChannelHandlerContext} ctx, {@link Long} msg, List&lt;Object&gt; out)
 *                 throws {@link Exception} {
 *             out.add(msg.intValue());
 *         }
 *     }
 * </pre>
 *
 * Be aware that you need to call {@link ReferenceCounted#retain()} on messages that are just passed through if they
 * are of type {@link ReferenceCounted}. This is needed as the {@link MessageToMessageCodec} will call
 * {@link ReferenceCounted#release()} on encoded / decoded messages.
 */
public abstract class MessageToMessageCodec<INBOUND_IN, OUTBOUND_IN> extends ChannelDuplexHandler {

    private final MessageToMessageDecoder<Object> decoder = new MessageToMessageDecoder<Object>(Object.class) {

        @Override
        public boolean acceptInboundMessage(Object msg) throws Exception {
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