netty5/transport/src/main/java/io/netty/channel/SimpleChannelInboundHandler.java

/*
 * Copyright 2013 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:
 *
 *   http://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.channel;

import io.netty.util.ReferenceCountUtil;
import io.netty.util.internal.TypeParameterMatcher;

/**
 * {@link ChannelHandler} which allows to explicit only handle a specific type of messages.
 *
 * For example here is an implementation which only handle {@link String} messages.
 *
 * <pre>
 *     public class StringHandler extends
 *             {@link SimpleChannelInboundHandler}&lt;{@link String}&gt; {
 *
 *         {@code @Override}
 *         protected void messageReceived({@link ChannelHandlerContext} ctx, {@link String} message)
 *                 throws {@link Exception} {
 *             System.out.println(message);
 *         }
 *     }
 * </pre>
 *
 * Be aware that depending of the constructor parameters it will release all handled messages by passing them to
 * {@link ReferenceCountUtil#release(Object)}. In this case you may need to use
 * {@link ReferenceCountUtil#retain(Object)} if you pass the object to the next handler in the {@link ChannelPipeline}.
 */
public abstract class SimpleChannelInboundHandler<I> implements ChannelHandler {

    private final TypeParameterMatcher matcher;
    private final boolean autoRelease;

    /**
     * see {@link #SimpleChannelInboundHandler(boolean)} with {@code true} as boolean parameter.
     */
    protected SimpleChannelInboundHandler() {
        this(true);
    }

    /**
     * Create a new instance which will try to detect the types to match out of the type parameter of the class.
     *
     * @param autoRelease   {@code true} if handled messages should be released automatically by passing them to
     *                      {@link ReferenceCountUtil#release(Object)}.
     */
    protected SimpleChannelInboundHandler(boolean autoRelease) {
        matcher = TypeParameterMatcher.find(this, SimpleChannelInboundHandler.class, "I");
        this.autoRelease = autoRelease;
    }

    /**
     * see {@link #SimpleChannelInboundHandler(Class, boolean)} with {@code true} as boolean value.
     */
    protected SimpleChannelInboundHandler(Class<? extends I> inboundMessageType) {
        this(inboundMessageType, true);
    }

    /**
     * Create a new instance
     *
     * @param inboundMessageType    The type of messages to match
     * @param autoRelease           {@code true} if handled messages should be released automatically by passing them to
     *                              {@link ReferenceCountUtil#release(Object)}.
     */
    protected SimpleChannelInboundHandler(Class<? extends I> inboundMessageType, boolean autoRelease) {
        matcher = TypeParameterMatcher.get(inboundMessageType);
        this.autoRelease = autoRelease;
    }

    /**
     * Returns {@code true} if the given message should be handled. If {@code false} it will be passed to the next
     * {@link ChannelHandler} in the {@link ChannelPipeline}.
     */
    public boolean acceptInboundMessage(Object msg) throws Exception {
        return matcher.match(msg);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        boolean release = true;
        try {
            if (acceptInboundMessage(msg)) {
                @SuppressWarnings("unchecked")
                I imsg = (I) msg;
                messageReceived(ctx, imsg);
            } else {
                release = false;
                ctx.fireChannelRead(msg);
            }
        } finally {
            if (autoRelease && release) {
                ReferenceCountUtil.release(msg);
            }
        }
    }

    /**
     * Is called for each message of type {@link I}.
     *
     * @param ctx           the {@link ChannelHandlerContext} which this {@link SimpleChannelInboundHandler}
     *                      belongs to
     * @param msg           the message to handle
     * @throws Exception    is thrown if an error occurred
     */
    protected abstract void messageReceived(ChannelHandlerContext ctx, I msg) throws Exception;
}