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.buffer.ByteBuf; import io.netty.buffer.ByteBufAllocator; import io.netty.util.Attribute; import io.netty.util.AttributeKey; import io.netty.util.AttributeMap; import io.netty.util.concurrent.EventExecutor; import java.nio.channels.Channels; /** * Enables a {@link ChannelHandler} to interact with its {@link ChannelPipeline} * and other handlers. Among other things a handler can notify the next {@link ChannelHandler} in the * {@link ChannelPipeline} as well as modify the {@link ChannelPipeline} it belongs to dynamically. * * <h3>Notify</h3> * * You can notify the closest handler in the same {@link ChannelPipeline} by calling one of the various methods * provided here. * * Please refer to {@link ChannelPipeline} to understand how an event flows. * * <h3>Modifying a pipeline</h3> * * You can get the {@link ChannelPipeline} your handler belongs to by calling * {@link #pipeline()}. A non-trivial application could insert, remove, or * replace handlers in the pipeline dynamically at runtime. * * <h3>Retrieving for later use</h3> * * You can keep the {@link ChannelHandlerContext} for later use, such as * triggering an event outside the handler methods, even from a different thread. * <pre> * public class MyHandler extends {@link ChannelDuplexHandler} { * * <b>private {@link ChannelHandlerContext} ctx;</b> * * public void beforeAdd({@link ChannelHandlerContext} ctx) { * <b>this.ctx = ctx;</b> * } * * public void login(String username, password) { * ctx.write(new LoginMessage(username, password)); * } * ... * } * </pre> * * <h3>Storing stateful information</h3> * * {@link #attr(AttributeKey)} allow you to * store and access stateful information that is related with a handler and its * context. Please refer to {@link ChannelHandler} to learn various recommended * ways to manage stateful information. * * <h3>A handler can have more than one context</h3> * * Please note that a {@link ChannelHandler} instance can be added to more than * one {@link ChannelPipeline}. It means a single {@link ChannelHandler} * instance can have more than one {@link ChannelHandlerContext} and therefore * the single instance can be invoked with different * {@link ChannelHandlerContext}s if it is added to one or more * {@link ChannelPipeline}s more than once. * <p> * For example, the following handler will have as many independent {@link AttributeKey}s * as how many times it is added to pipelines, regardless if it is added to the * same pipeline multiple times or added to different pipelines multiple times: * <pre> * public class FactorialHandler extends {@link ChannelInboundHandlerAdapter} { * * private final {@link AttributeKey}<{@link Integer}> counter = {@link AttributeKey}.valueOf("counter"); * * // This handler will receive a sequence of increasing integers starting * // from 1. * {@code @Override} * public void channelRead({@link ChannelHandlerContext} ctx, Object msg) { * Integer a = ctx.attr(counter).get(); * * if (a == null) { * a = 1; * } * * attr.set(a * (Integer) msg); * } * } * * // Different context objects are given to "f1", "f2", "f3", and "f4" even if * // they refer to the same handler instance. Because the FactorialHandler * // stores its state in a context object (using an {@link AttributeKey}), the factorial is * // calculated correctly 4 times once the two pipelines (p1 and p2) are active. * FactorialHandler fh = new FactorialHandler(); * * {@link ChannelPipeline} p1 = {@link Channels}.pipeline(); * p1.addLast("f1", fh); * p1.addLast("f2", fh); * * {@link ChannelPipeline} p2 = {@link Channels}.pipeline(); * p2.addLast("f3", fh); * p2.addLast("f4", fh); * </pre> * * <h3>Additional resources worth reading</h3> * <p> * Please refer to the {@link ChannelHandler}, and * {@link ChannelPipeline} to find out more about inbound and outbound operations, * what fundamental differences they have, how they flow in a pipeline, and how to handle * the operation in your application. */ public interface ChannelHandlerContext extends AttributeMap, ChannelInboundInvoker, ChannelOutboundInvoker { /** * Return the {@link Channel} which is bound to the {@link ChannelHandlerContext}. */ Channel channel(); /** * Returns the {@link EventExecutor} which is used to execute an arbitrary task. */ EventExecutor executor(); /** * The unique name of the {@link ChannelHandlerContext}.The name was used when then {@link ChannelHandler} * was added to the {@link ChannelPipeline}. This name can also be used to access the registered * {@link ChannelHandler} from the {@link ChannelPipeline}. */ String name(); /** * The {@link ChannelHandler} that is bound this {@link ChannelHandlerContext}. */ ChannelHandler handler(); /** * Return {@code true} if the {@link ChannelHandler} which belongs to this context was removed * from the {@link ChannelPipeline}. Note that this method is only meant to be called from with in the * {@link EventLoop}. */ boolean isRemoved(); @Override ChannelHandlerContext fireChannelRegistered(); @Override ChannelHandlerContext fireChannelUnregistered(); @Override ChannelHandlerContext fireChannelActive(); @Override ChannelHandlerContext fireChannelInactive(); @Override ChannelHandlerContext fireExceptionCaught(Throwable cause); @Override ChannelHandlerContext fireUserEventTriggered(Object evt); @Override ChannelHandlerContext fireChannelRead(Object msg); @Override ChannelHandlerContext fireChannelReadComplete(); @Override ChannelHandlerContext fireChannelWritabilityChanged(); @Override ChannelHandlerContext read(); @Override ChannelHandlerContext flush(); /** * Return the assigned {@link ChannelPipeline} */ ChannelPipeline pipeline(); /** * Return the assigned {@link ByteBufAllocator} which will be used to allocate {@link ByteBuf}s. */ ByteBufAllocator alloc(); /** * @deprecated Use {@link Channel#attr(AttributeKey)} */ @Deprecated @Override <T> Attribute<T> attr(AttributeKey<T> key); /** * @deprecated Use {@link Channel#hasAttr(AttributeKey)} */ @Deprecated @Override <T> boolean hasAttr(AttributeKey<T> key); }