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/*
 * Copyright 2018 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 ChannelInboundHandlerAdapter} which allows to conveniently only handle a specific type of user events.
 *
 * For example, here is an implementation which only handle {@link String} user events.
 *
 * 
 *     public class StringEventHandler extends
 *             {@link SimpleUserEventChannelHandler}<{@link String}> {
 *
 *         {@code @Override}
 *         protected void eventReceived({@link ChannelHandlerContext} ctx, {@link String} evt)
 *                 throws {@link Exception} {
 *             System.out.println(evt);
 *         }
 *     }
 * 
* * Be aware that depending of the constructor parameters it will release all handled events 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 SimpleUserEventChannelHandler extends ChannelInboundHandlerAdapter { private final TypeParameterMatcher matcher; private final boolean autoRelease; /** * see {@link #SimpleUserEventChannelHandler(boolean)} with {@code true} as boolean parameter. */ protected SimpleUserEventChannelHandler() { 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 events should be released automatically by passing them to * {@link ReferenceCountUtil#release(Object)}. */ protected SimpleUserEventChannelHandler(boolean autoRelease) { matcher = TypeParameterMatcher.find(this, SimpleUserEventChannelHandler.class, "I"); this.autoRelease = autoRelease; } /** * see {@link #SimpleUserEventChannelHandler(Class, boolean)} with {@code true} as boolean value. */ protected SimpleUserEventChannelHandler(Class eventType) { this(eventType, true); } /** * Create a new instance * * @param eventType The type of events to match * @param autoRelease {@code true} if handled events should be released automatically by passing them to * {@link ReferenceCountUtil#release(Object)}. */ protected SimpleUserEventChannelHandler(Class eventType, boolean autoRelease) { matcher = TypeParameterMatcher.get(eventType); this.autoRelease = autoRelease; } /** * Returns {@code true} if the given user event should be handled. If {@code false} it will be passed to the next * {@link ChannelInboundHandler} in the {@link ChannelPipeline}. */ protected boolean acceptEvent(Object evt) throws Exception { return matcher.match(evt); } @Override public final void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception { boolean release = true; try { if (acceptEvent(evt)) { @SuppressWarnings("unchecked") I ievt = (I) evt; eventReceived(ctx, ievt); } else { release = false; ctx.fireUserEventTriggered(evt); } } finally { if (autoRelease && release) { ReferenceCountUtil.release(evt); } } } /** * Is called for each user event triggered of type {@link I}. * * @param ctx the {@link ChannelHandlerContext} which this {@link SimpleUserEventChannelHandler} belongs to * @param evt the user event to handle * * @throws Exception is thrown if an error occurred */ protected abstract void eventReceived(ChannelHandlerContext ctx, I evt) throws Exception; }




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