197 lines
7.0 KiB
Java
197 lines
7.0 KiB
Java
/*
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* Copyright 2009 Red Hat, Inc.
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*
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* Red Hat licenses this file to you under the Apache License, version 2.0
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* (the "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.channel;
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/**
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* Enables a {@link ChannelHandler} to interact with its {@link ChannelPipeline}
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* and other handlers. A handler can send a {@link ChannelEvent} upstream or
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* downstream, modify the {@link ChannelPipeline} it belongs to dynamically.
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*
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* <h3>Sending an event</h3>
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*
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* You can send or forward a {@link ChannelEvent} to the closest handler in the
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* same {@link ChannelPipeline} by calling {@link #sendUpstream(ChannelEvent)}
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* or {@link #sendDownstream(ChannelEvent)}. Please refer to
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* {@link ChannelPipeline} to understand how an event flows.
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*
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* <h3>Modifying a pipeline</h3>
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*
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* You can get the {@link ChannelPipeline} your handler belongs to by calling
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* {@link #getPipeline()}. A non-trivial application could insert, remove, or
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* replace handlers in the pipeline dynamically in runtime.
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*
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* <h3>Retrieving for later use</h3>
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*
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* You can keep the {@link ChannelHandlerContext} for later use, such as
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* triggering an event outside the handler methods, even from a different thread.
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* <pre>
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* public class MyHandler extends {@link SimpleChannelHandler}
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* implements {@link LifeCycleAwareChannelHandler} {
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*
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* <b>private {@link ChannelHandlerContext} ctx;</b>
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*
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* public void beforeAdd({@link ChannelHandlerContext} ctx) {
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* <b>this.ctx = ctx;</b>
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* }
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*
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* public void login(String username, password) {
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* {@link Channels}.write(
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* <b>this.ctx</b>,
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* {@link Channels}.succeededFuture(<b>this.ctx</t>.getChannel()</b>),
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* new LoginMessage(username, password));
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* }
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* ...
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* }
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* </pre>
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*
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* <h3>Storing stateful information</h3>
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*
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* {@link #setAttachment(Object)} and {@link #getAttachment()} allow you to
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* store and access stateful information that is related with a handler and its
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* context. Please refer to {@link ChannelHandler} to learn various recommended
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* ways to manage stateful information.
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*
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* <h3>A handler can have more than one context</h3>
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*
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* Please note that a {@link ChannelHandler} instance can be added to more than
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* one {@link ChannelPipeline}. It means a single {@link ChannelHandler}
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* instance can have more than one {@link ChannelHandlerContext} and therefore
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* the single instance can be invoked with different
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* {@link ChannelHandlerContext}s if it is added to one or more
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* {@link ChannelPipeline}s more than once.
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* <p>
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* For example, the following handler will have as many independent attachments
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* as how many times it is added to pipelines, regardless if it is added to the
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* same pipeline multiple times or added to different pipelines multiple times:
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* <pre>
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* public class FactorialHandler extends {@link SimpleChannelHandler} {
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*
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* // This handler will receive a sequence of increasing integers starting
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* // from 1.
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* {@code @Override}
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* public void messageReceived({@link ChannelHandlerContext} ctx, {@link MessageEvent} evt) {
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* Integer a = (Integer) ctx.getAttachment();
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* Integer b = (Integer) evt.getMessage();
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*
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* if (a == null) {
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* a = 1;
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* }
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*
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* ctx.setAttachment(Integer.valueOf(a * b));
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* }
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* }
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*
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* // Different context objects are given to "f1", "f2", "f3", and "f4" even if
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* // they refer to the same handler instance. Because the FactorialHandler
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* // stores its state in a context object (as an attachment), the factorial is
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* // calculated correctly 4 times once the two pipelines (p1 and p2) are active.
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* FactorialHandler fh = new FactorialHandler();
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*
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* {@link ChannelPipeline} p1 = {@link Channels}.pipeline();
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* p1.addLast("f1", fh);
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* p1.addLast("f2", fh);
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*
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* {@link ChannelPipeline} p2 = {@link Channels}.pipeline();
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* p2.addLast("f3", fh);
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* p2.addLast("f4", fh);
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* </pre>
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*
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* <h3>Additional resources worth reading</h3>
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* <p>
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* Please refer to the {@link ChannelHandler}, {@link ChannelEvent}, and
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* {@link ChannelPipeline} to find out what a upstream event and a downstream
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* event are, what fundamental differences they have, how they flow in a
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* pipeline, and how to handle the event in your application.
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*
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* @author <a href="http://netty.io/">The Netty Project</a>
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* @author <a href="http://gleamynode.net/">Trustin Lee</a>
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*
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* @apiviz.owns io.netty.channel.ChannelHandler
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*/
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public interface ChannelHandlerContext {
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/**
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* Returns the {@link Channel} that the {@link ChannelPipeline} belongs to.
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* This method is a shortcut to <tt>getPipeline().getChannel()</tt>.
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*/
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Channel getChannel();
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/**
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* Returns the {@link ChannelPipeline} that the {@link ChannelHandler}
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* belongs to.
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*/
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ChannelPipeline getPipeline();
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/**
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* Returns the name of the {@link ChannelHandler} in the
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* {@link ChannelPipeline}.
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*/
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String getName();
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/**
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* Returns the {@link ChannelHandler} that this context object is
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* serving.
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*/
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ChannelHandler getHandler();
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/**
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* Returns {@code true} if and only if the {@link ChannelHandler} is an
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* instance of {@link ChannelUpstreamHandler}.
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*/
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boolean canHandleUpstream();
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/**
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* Returns {@code true} if and only if the {@link ChannelHandler} is an
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* instance of {@link ChannelDownstreamHandler}.
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*/
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boolean canHandleDownstream();
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/**
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* Sends the specified {@link ChannelEvent} to the
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* {@link ChannelUpstreamHandler} which is placed in the closest upstream
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* from the handler associated with this context. It is recommended to use
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* the shortcut methods in {@link Channels} rather than calling this method
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* directly.
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*/
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void sendUpstream(ChannelEvent e);
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/**
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* Sends the specified {@link ChannelEvent} to the
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* {@link ChannelDownstreamHandler} which is placed in the closest
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* downstream from the handler associated with this context. It is
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* recommended to use the shortcut methods in {@link Channels} rather than
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* calling this method directly.
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*/
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void sendDownstream(ChannelEvent e);
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/**
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* Retrieves an object which is {@link #setAttachment(Object) attached} to
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* this context.
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*
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* @return {@code null} if no object was attached or
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* {@code null} was attached
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*/
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Object getAttachment();
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/**
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* Attaches an object to this context to store a stateful information
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* specific to the {@link ChannelHandler} which is associated with this
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* context.
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*/
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void setAttachment(Object attachment);
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}
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