ChannelHandler.java — netty Source File

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/*
 * 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:
 *
 *   https://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.Attribute;
import io.netty.util.AttributeKey;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Handles an I/O event or intercepts an I/O operation, and forwards it to its next handler in
 * its {@link ChannelPipeline}.
 *
 * <h3>Sub-types</h3>
 * <p>
 * {@link ChannelHandler} itself does not provide many methods, but you usually have to implement one of its subtypes:
 * <ul>
 * <li>{@link ChannelInboundHandler} to handle inbound I/O events, and</li>
 * <li>{@link ChannelOutboundHandler} to handle outbound I/O operations.</li>
 * </ul>
 * </p>
 * <p>
 * Alternatively, the following adapter classes are provided for your convenience:
 * <ul>
 * <li>{@link ChannelInboundHandlerAdapter} to handle inbound I/O events,</li>
 * <li>{@link ChannelOutboundHandlerAdapter} to handle outbound I/O operations, and</li>
 * <li>{@link ChannelDuplexHandler} to handle both inbound and outbound events</li>
 * </ul>
 * </p>
 * <p>
 * For more information, please refer to the documentation of each subtype.
 * </p>
 *
 * <h3>The context object</h3>
 * <p>
 * A {@link ChannelHandler} is provided with a {@link ChannelHandlerContext}
 * object.  A {@link ChannelHandler} is supposed to interact with the
 * {@link ChannelPipeline} it belongs to via a context object.  Using the
 * context object, the {@link ChannelHandler} can pass events upstream or
 * downstream, modify the pipeline dynamically, or store the information
 * (using {@link AttributeKey}s) which is specific to the handler.
 *
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