MessageToMessageDecoder.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.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandler;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelPipeline;
import io.netty.util.ReferenceCountUtil;
import io.netty.util.ReferenceCounted;
import io.netty.util.internal.TypeParameterMatcher;

import java.util.List;

/**
 * {@link ChannelInboundHandlerAdapter} which decodes from one message to an other message.
 *
 *
 * For example here is an implementation which decodes a {@link String} to an {@link Integer} which represent
 * the length of the {@link String}.
 *
 * <pre>
 *     public class StringToIntegerDecoder extends
 *             {@link MessageToMessageDecoder}&lt;{@link String}&gt; {
 *
 *         {@code @Override}
 *         public void decode({@link ChannelHandlerContext} ctx, {@link String} message,
 *                            List&lt;Object&gt; out) throws {@link Exception} {
 *             out.add(message.length());
 *         }
 *     }
 * </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 MessageToMessageDecoder} will call
 * {@link ReferenceCounted#release()} on decoded messages.
 *
 */
public abstract class MessageToMessageDecoder<I> extends ChannelInboundHandlerAdapter {

    private final TypeParameterMatcher matcher;
    private boolean decodeCalled;
    private boolean messageProduced;

    /**
     * Create a new instance which will try to detect the types to match out of the type parameter of the class.
     */
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