netty-channelpipeline

/**
* A list of {@link ChannelHandler}s which handles or intercepts inbound events and outbound operations of a
* {@link Channel}.  {@link ChannelPipeline} implements an advanced form of the
* <a href="http://www.oracle.com/technetwork/java/interceptingfilter-142169.html">Intercepting Filter</a> pattern
* to give a user full control over how an event is handled and how the {@link ChannelHandler}s in a pipeline
* interact with each other.
*
* <h3>Creation of a pipeline</h3>
*
* Each channel has its own pipeline and it is created automatically when a new channel is created.
*
* <h3>How an event flows in a pipeline</h3>
*
* The following diagram describes how I/O events are processed by {@link ChannelHandler}s in a {@link ChannelPipeline}
* typically. An I/O event is handled by either a {@link ChannelInboundHandler} or a {@link ChannelOutboundHandler}
* and be forwarded to its closest handler by calling the event propagation methods defined in
* {@link ChannelHandlerContext}, such as {@link ChannelHandlerContext#fireChannelRead(Object)} and
* {@link ChannelHandlerContext#write(Object)}.
*
* <pre>
*                                                 I/O Request
*                                            via {@link Channel} or
*                                        {@link ChannelHandlerContext}
*                                                      |
*  +---------------------------------------------------+---------------+
*  |                           ChannelPipeline         |               |
*  |                                                  \|/              |
*  |    +---------------------+            +-----------+----------+    |
*  |    | Inbound Handler  N  |            | Outbound Handler  1  |    |
*  |    +----------+----------+            +-----------+----------+    |
*  |              /|\                                  |               |
*  |               |                                  \|/              |
*  |    +----------+----------+            +-----------+----------+    |
*  |    | Inbound Handler N-1 |            | Outbound Handler  2  |    |
*  |    +----------+----------+            +-----------+----------+    |
*  |              /|\                                  .               |
*  |               .                                   .               |
*  | ChannelHandlerContext.fireIN_EVT() ChannelHandlerContext.OUT_EVT()|
*  |        [ method call]                       [method call]         |
*  |               .                                   .               |
*  |               .                                  \|/              |
*  |    +----------+----------+            +-----------+----------+    |
*  |    | Inbound Handler  2  |            | Outbound Handler M-1 |    |
*  |    +----------+----------+            +-----------+----------+    |
*  |              /|\                                  |               |
*  |               |                                  \|/              |
*  |    +----------+----------+            +-----------+----------+    |
*  |    | Inbound Handler  1  |            | Outbound Handler  M  |    |
*  |    +----------+----------+            +-----------+----------+    |
*  |              /|\                                  |               |
*  +---------------+-----------------------------------+---------------+
*                  |                                  \|/
*  +---------------+-----------------------------------+---------------+
*  |               |                                   |               |
*  |       [ Socket.read() ]                    [ Socket.write() ]     |
*  |                                                                   |
*  |  Netty Internal I/O Threads (Transport Implementation)            |
*  +-------------------------------------------------------------------+
* </pre>
* An inbound event is handled by the inbound handlers in the bottom-up direction as shown on the left side of the
* diagram.  An inbound handler usually handles the inbound data generated by the I/O thread on the bottom of the
* diagram.  The inbound data is often read from a remote peer via the actual input operation such as
* {@link SocketChannel#read(ByteBuffer)}.  If an inbound event goes beyond the top inbound handler, it is discarded
* silently, or logged if it needs your attention.
* <p>
* An outbound event is handled by the outbound handler in the top-down direction as shown on the right side of the
* diagram.  An outbound handler usually generates or transforms the outbound traffic such as write requests.
* If an outbound event goes beyond the bottom outbound handler, it is handled by an I/O thread associated with the
* {@link Channel}. The I/O thread often performs the actual output operation such as
* {@link SocketChannel#write(ByteBuffer)}.
* <p>
* For example, let us assume that we created the following pipeline:
* <pre>
* {@link ChannelPipeline} p = ...;
* p.addLast("1", new InboundHandlerA());
* p.addLast("2", new InboundHandlerB());
* p.addLast("3", new OutboundHandlerA());
* p.addLast("4", new OutboundHandlerB());
* p.addLast("5", new InboundOutboundHandlerX());
* </pre>
* In the example above, the class whose name starts with {@code Inbound} means it is an inbound handler.
* The class whose name starts with {@code Outbound} means it is a outbound handler.
* <p>
* In the given example configuration, the handler evaluation order is 1, 2, 3, 4, 5 when an event goes inbound.
* When an event goes outbound, 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 ChannelInboundHandler}, and therefore the actual evaluation order of an inbound
*     event will be: 1, 2, and 5.</li>
* <li>1 and 2 don't implement {@link ChannelOutboundHandler}, and therefore the actual evaluation order of a
*     outbound event will be: 5, 4, and 3.</li>
* <li>If 5 implements both {@link ChannelInboundHandler} and {@link ChannelOutboundHandler}, the evaluation order of
*     an inbound and a outbound event could be 125 and 543 respectively.</li>
* </ul>
*
* <h3>Forwarding an event to the next handler</h3>
*
* As you might noticed in the diagram shows, a handler has to invoke the event propagation methods in
* {@link ChannelHandlerContext} to forward an event to its next handler.  Those methods include:
* <ul>
* <li>Inbound event propagation methods:
*     <ul>
*     <li>{@link ChannelHandlerContext#fireChannelRegistered()}</li>
*     <li>{@link ChannelHandlerContext#fireChannelActive()}</li>
*     <li>{@link ChannelHandlerContext#fireChannelRead(Object)}</li>
*     <li>{@link ChannelHandlerContext#fireChannelReadComplete()}</li>
*     <li>{@link ChannelHandlerContext#fireExceptionCaught(Throwable)}</li>
*     <li>{@link ChannelHandlerContext#fireUserEventTriggered(Object)}</li>
*     <li>{@link ChannelHandlerContext#fireChannelWritabilityChanged()}</li>
*     <li>{@link ChannelHandlerContext#fireChannelInactive()}</li>
*     <li>{@link ChannelHandlerContext#fireChannelUnregistered()}</li>
*     </ul>
* </li>
* <li>Outbound event propagation methods:
*     <ul>
*     <li>{@link ChannelHandlerContext#bind(SocketAddress, ChannelPromise)}</li>
*     <li>{@link ChannelHandlerContext#connect(SocketAddress, SocketAddress, ChannelPromise)}</li>
*     <li>{@link ChannelHandlerContext#write(Object, ChannelPromise)}</li>
*     <li>{@link ChannelHandlerContext#flush()}</li>
*     <li>{@link ChannelHandlerContext#read()}</li>
*     <li>{@link ChannelHandlerContext#disconnect(ChannelPromise)}</li>
*     <li>{@link ChannelHandlerContext#close(ChannelPromise)}</li>
*     <li>{@link ChannelHandlerContext#deregister(ChannelPromise)}</li>
*     </ul>
* </li>
* </ul>
*
* and the following example shows how the event propagation is usually done:
*
* <pre>
* public class MyInboundHandler extends {@link ChannelInboundHandlerAdapter} {
*     {@code @Override}
*     public void channelActive({@link ChannelHandlerContext} ctx) {
*         System.out.println("Connected!");
*         ctx.fireChannelActive();
*     }
* }
*
* public clas MyOutboundHandler extends {@link ChannelOutboundHandlerAdapter} {
*     {@code @Override}
*     public void close({@link ChannelHandlerContext} ctx, {@link ChannelPromise} promise) {
*         System.out.println("Closing ..");
*         ctx.close(promise);
*     }
* }
* </pre>
*
* <h3>Building a pipeline</h3>
* <p>
* A user is supposed to have one or more {@link ChannelHandler}s in a pipeline to receive I/O events (e.g. read) and
* to request I/O operations (e.g. write and close).  For example, a typical server will have the following handlers
* in each channel's pipeline, but your mileage may vary depending on the complexity and characteristics of the
* protocol and business logic:
*
* <ol>
* <li>Protocol Decoder - translates binary data (e.g. {@link ByteBuf}) into a Java object.</li>
* <li>Protocol Encoder - translates a Java object into binary data.</li>
* <li>Business Logic Handler - performs the actual business logic (e.g. database access).</li>
* </ol>
*
* and it could be represented as shown in the following example:
*
* <pre>
* static final {@link EventExecutorGroup} group = new {@link DefaultEventExecutorGroup}(16);
* ...
*
* {@link ChannelPipeline} pipeline = ch.pipeline();
*
* pipeline.addLast("decoder", new MyProtocolDecoder());
* pipeline.addLast("encoder", new MyProtocolEncoder());
*
* // Tell the pipeline to run MyBusinessLogicHandler's event handler methods
* // in a different thread than an I/O thread so that the I/O thread is not blocked by
* // a time-consuming task.
* // If your business logic is fully asynchronous or finished very quickly, you don't
* // need to specify a group.
* pipeline.addLast(group, "handler", new MyBusinessLogicHandler());
* </pre>
*
* <h3>Thread safety</h3>
* <p>
* A {@link ChannelHandler} can be added or removed at any time because a {@link ChannelPipeline} is thread safe.
* For example, you can insert an encryption handler when sensitive information is about to be exchanged, and remove it
* after the exchange.
*/

以上是channelpipeline的英文注释,从中可以看出几个结论：

channelpipeline是线程安全的。

channelpipeline的实现是参照 intercepting filter 设计的，具体可以参照http://www.oracle.com/technetwork/java/interceptingfilter-142169.html

channelpipeline的运行机制可以看上述的流程图。