netty5/src/main/java/org/jboss/netty/channel/ChannelHandler.java

/*
 * Copyright 2009 Red Hat, Inc.
 *
 * Red Hat 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 org.jboss.netty.channel;

/**
 * Handles or intercepts a {@link ChannelEvent}, and sends a
 * {@link ChannelEvent} to the next handler in a {@link ChannelPipeline}.
 *
 * <h3>Sub-types</h3>
 * <p>
 * {@link ChannelHandler} itself does not provide any method.  To handle a
 * {@link ChannelEvent} you need to implement its sub-interfaces.  There are
 * two sub-interfaces which handles a received event, one for upstream events
 * and the other for downstream events:
 * <ul>
 * <li>{@link ChannelUpstreamHandler} handles and intercepts an upstream {@link ChannelEvent}.</li>
 * <li>{@link ChannelDownstreamHandler} handles and intercepts a downstream {@link ChannelEvent}.</li>
 * </ul>
 *
 * You will also find more detailed explanation from the documentation of
 * each sub-interface on how an event is interpreted when it goes upstream and
 * downstream respectively.
 *
 * <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 behavior of the pipeline, or store the information
 * (attachment) which is specific to the handler.
 *
 * <h3>Additional resources worth reading</h3>
 * <p>
 * Please refer to the {@link ChannelEvent} and {@link ChannelPipeline} to find
 * out what a upstream event and a downstream event are, what fundamental
 * differences they have, and how they flow in a pipeline.
 *
 * @author The Netty Project (netty-dev@lists.jboss.org)
 * @author Trustin Lee (trustin@gmail.com)
 *
 * @version $Rev$, $Date$
 *
 * @apiviz.landmark
 * @apiviz.exclude ^org\.jboss\.netty\.handler\..*$
 */
public interface ChannelHandler {
    // This is a tag interface.
}