Java tutorial
/* * 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: * * 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.bootstrap.Bootstrap; import io.netty.bootstrap.ServerBootstrap; import io.netty.channel.ChannelHandler.Sharable; import io.netty.util.internal.logging.InternalLogger; import io.netty.util.internal.logging.InternalLoggerFactory; import java.util.Collections; import java.util.Set; import java.util.concurrent.ConcurrentHashMap; /** * A special {@link ChannelInboundHandler} which offers an easy way to initialize a {@link Channel} once it was * registered to its {@link EventLoop}. * * Implementations are most often used in the context of {@link Bootstrap#handler(ChannelHandler)} , * {@link ServerBootstrap#handler(ChannelHandler)} and {@link ServerBootstrap#childHandler(ChannelHandler)} to * setup the {@link ChannelPipeline} of a {@link Channel}. * * <pre> * * public class MyChannelInitializer extends {@link ChannelInitializer} { * public void initChannel({@link Channel} channel) { * channel.pipeline().addLast("myHandler", new MyHandler()); * } * } * * {@link ServerBootstrap} bootstrap = ...; * ... * bootstrap.childHandler(new MyChannelInitializer()); * ... * </pre> * Be aware that this class is marked as {@link Sharable} and so the implementation must be safe to be re-used. * * @param <C> A sub-type of {@link Channel} */ @Sharable public abstract class ChannelInitializer<C extends Channel> extends ChannelInboundHandlerAdapter { private static final InternalLogger logger = InternalLoggerFactory.getInstance(ChannelInitializer.class); // We use a Set as a ChannelInitializer is usually shared between all Channels in a Bootstrap / // ServerBootstrap. This way we can reduce the memory usage compared to use Attributes. private final Set<ChannelHandlerContext> initMap = Collections .newSetFromMap(new ConcurrentHashMap<ChannelHandlerContext, Boolean>()); /** * This method will be called once the {@link Channel} was registered. After the method returns this instance * will be removed from the {@link ChannelPipeline} of the {@link Channel}. * * @param ch the {@link Channel} which was registered. * @throws Exception is thrown if an error occurs. In that case it will be handled by * {@link #exceptionCaught(ChannelHandlerContext, Throwable)} which will by default close * the {@link Channel}. */ protected abstract void initChannel(C ch) throws Exception; @Override @SuppressWarnings("unchecked") public final void channelRegistered(ChannelHandlerContext ctx) throws Exception { // Normally this method will never be called as handlerAdded(...) should call initChannel(...) and remove // the handler. if (initChannel(ctx)) { // we called initChannel(...) so we need to call now pipeline.fireChannelRegistered() to ensure we not // miss an event. ctx.pipeline().fireChannelRegistered(); // We are done with init the Channel, removing all the state for the Channel now. removeState(ctx); } else { // Called initChannel(...) before which is the expected behavior, so just forward the event. ctx.fireChannelRegistered(); } } /** * Handle the {@link Throwable} by logging and closing the {@link Channel}. Sub-classes may override this. */ @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { if (logger.isWarnEnabled()) { logger.warn("Failed to initialize a channel. Closing: " + ctx.channel(), cause); } ctx.close(); } /** * {@inheritDoc} If override this method ensure you call super! */ @Override public void handlerAdded(ChannelHandlerContext ctx) throws Exception { if (ctx.channel().isRegistered()) { // This should always be true with our current DefaultChannelPipeline implementation. // The good thing about calling initChannel(...) in handlerAdded(...) is that there will be no ordering // surprises if a ChannelInitializer will add another ChannelInitializer. This is as all handlers // will be added in the expected order. if (initChannel(ctx)) { // We are done with init the Channel, removing the initializer now. removeState(ctx); } } } @Override public void handlerRemoved(ChannelHandlerContext ctx) throws Exception { initMap.remove(ctx); } @SuppressWarnings("unchecked") private boolean initChannel(ChannelHandlerContext ctx) throws Exception { if (initMap.add(ctx)) { // Guard against re-entrance. try { initChannel((C) ctx.channel()); } catch (Throwable cause) { // Explicitly call exceptionCaught(...) as we removed the handler before calling initChannel(...). // We do so to prevent multiple calls to initChannel(...). exceptionCaught(ctx, cause); } finally { ChannelPipeline pipeline = ctx.pipeline(); if (pipeline.context(this) != null) { pipeline.remove(this); } } return true; } return false; } private void removeState(final ChannelHandlerContext ctx) { // The removal may happen in an async fashion if the EventExecutor we use does something funky. if (ctx.isRemoved()) { initMap.remove(ctx); } else { // The context is not removed yet which is most likely the case because a custom EventExecutor is used. // Let's schedule it on the EventExecutor to give it some more time to be completed in case it is offloaded. ctx.executor().execute(new Runnable() { @Override public void run() { initMap.remove(ctx); } }); } } }