1 /*
2 * Copyright 2009 Red Hat, Inc.
3 *
4 * Red Hat licenses this file to you under the Apache License, version 2.0
5 * (the "License"); you may not use this file except in compliance with the
6 * License. You may obtain a copy of the License at:
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16 package org.jboss.netty.channel;
17
18 /**
19 * Handles or intercepts a downstream {@link ChannelEvent}, and sends a
20 * {@link ChannelEvent} to the next handler in a {@link ChannelPipeline}.
21 * <p>
22 * The most common use case of this interface is to intercept an I/O request
23 * such as {@link Channel#write(Object)} and {@link Channel#close()}.
24 *
25 * <h3>{@link SimpleChannelDownstreamHandler}</h3>
26 * <p>
27 * In most cases, you will get to use a {@link SimpleChannelDownstreamHandler}
28 * to implement a downstream handler because it provides an individual handler
29 * method for each event type. You might want to implement this interface
30 * directly though if you want to handle various types of events in more
31 * generic way.
32 *
33 * <h3>Firing an event to the next handler</h3>
34 * <p>
35 * You can forward the received event downstream or upstream. In most cases,
36 * {@link ChannelDownstreamHandler} will send the event downstream
37 * (i.e. outbound) although it is legal to send the event upstream (i.e. inbound):
38 *
39 * <pre>
40 * // Sending the event downstream (outbound)
41 * void handleDownstream({@link ChannelHandlerContext} ctx, {@link ChannelEvent} e) throws Exception {
42 * ...
43 * ctx.sendDownstream(e);
44 * ...
45 * }
46 *
47 * // Sending the event upstream (inbound)
48 * void handleDownstream({@link ChannelHandlerContext} ctx, {@link ChannelEvent} e) throws Exception {
49 * ...
50 * ctx.sendUpstream(new {@link UpstreamChannelStateEvent}(...));
51 * ...
52 * }
53 * </pre>
54 *
55 * <h4>Using the helper class to send an event</h4>
56 * <p>
57 * You will also find various helper methods in {@link Channels} to be useful
58 * to generate and send an artificial or manipulated event.
59 *
60 * <h3>State management</h3>
61 *
62 * Please refer to {@link ChannelHandler}.
63 *
64 * <h3>Thread safety</h3>
65 * <p>
66 * {@link #handleDownstream(ChannelHandlerContext, ChannelEvent) handleDownstream}
67 * may be invoked by more than one thread simultaneously. If the handler
68 * accesses a shared resource or stores stateful information, you might need
69 * proper synchronization in the handler implementation.
70 *
71 * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
72 * @author <a href="http://gleamynode.net/">Trustin Lee</a>
73 *
74 * @version $Rev: 2122 $, $Date: 2010-02-02 11:00:04 +0900 (Tue, 02 Feb 2010) $
75 *
76 * @apiviz.exclude ^org\.jboss\.netty\.handler\..*$
77 */
78 public interface ChannelDownstreamHandler extends ChannelHandler {
79
80 /**
81 * Handles the specified downstream event.
82 *
83 * @param ctx the context object for this handler
84 * @param e the downstream event to process or intercept
85 */
86 void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e) throws Exception;
87 }