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Improved documentation on how an event is processed in ChannelPipeline

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Trustin Lee 2009-04-08 08:38:06 +00:00
parent 945d2ea3cd
commit 415702217b
1 changed files with 29 additions and 0 deletions
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src/main/java/org/jboss/netty/channel/ChannelPipeline.java
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@ -98,6 +98,35 @@ import org.jboss.netty.handler.ssl.SslHandler;
* to the last upstream handler (i.e. to the next) and a downstream event
* flows from the last downstream handler to the first downstream handler
* (i.e. to the previous).
* <p>
* For example, let us assume that we created the following pipeline:
* <pre>
* ChannelPipeline p = Channels.pipeline();
* p.addLast("1", new UpstreamHandlerA());
* p.addLast("2", new UpstreamHandlerB());
*.p.addLast("3", new DownstreamHandlerA());
*.p.addLast("4", new DownstreamHandlerB());
* p.addLast("5", new UpstreamHandlerX());
* </pre>
* The class whose name starts with {@code Upstream} means it is an upstream
* handler. The class whose name starts with {@code Downstream} means it is a
* downstream handler.
* <p>
* In the given example configuration, the handler evaluation order is 1, 2, 3,
* 4, 5 when an event goes upstream. When an event goes downstream, the order
* is 5, 4, 3, 2, 1. On top of this principle, {@link ChannelPipeline} skips
* the evaluation of certain handlers to shorten the stack depth:
* <ul>
* <li>3 and 4 don't implement {@link ChannelUpstreamHandler}, and therefore the
* actual evaluation order of an upstream event will be: 1, 2, and 5.</li>
* <li>1, 2, and 5 don't implement {@link ChannelDownstreamHandler}, and
* therefore the actual evaluation order of a downstream event will be:
* 4 and 3.</li>
* <li>If 5 extended {@link SimpleChannelHandler} which implements both
* {@link ChannelUpstreamHandler} and {@link ChannelDownstreamHandler}, the
* evaluation order of an upstream and a downstream event could be 125 and
* 543 respectively.</li>
* </ul>
*
* <h3>Building a pipeline</h3>
* <p>