Netty ChannelPipeline

Netty 使用ChannelPipeline来实现拦截链路调用

*                                                 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)            |
*  +-------------------------------------------------------------------+

例如 fireChannelRead为例
1.1 AbstractChannelHandlerContext#fireChannelRead

@Override
    public ChannelHandlerContext fireChannelRead(final Object msg) {
　　　　　　//findContextInbound方法负责寻找next Context
        invokeChannelRead(findContextInbound(), msg);
        return this;
    }

  1.2  AbstractChannelHandlerContext#invokeChannelRead(io.netty.channel.AbstractChannelHandlerContext, java.lang.Object)

    static void invokeChannelRead(final AbstractChannelHandlerContext next, final Object msg) {
        ObjectUtil.checkNotNull(msg, "msg");
        EventExecutor executor = next.executor();
        if (executor.inEventLoop()) {
            next.invokeChannelRead(msg);
        } else {
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    next.invokeChannelRead(msg);
                }
            });
        }
    }

 1.3 AbstractChannelHandlerContext#invokeChannelRead(java.lang.Object)

    private void invokeChannelRead(Object msg) {
        if (invokeHandler()) {
            try {//Context中handler实际处理逻辑
                ((ChannelInboundHandler) handler()).channelRead(this, msg);
            } catch (Throwable t) {
                notifyHandlerException(t);
            }
        } else {
            fireChannelRead(msg);
        }
    }

1.4 以LoggingHandler为例  io.netty.handler.logging.LoggingHandler#channelRead

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
　　　　　　//这一行代码 是LoggerHandler的实际处理逻辑
        logMessage(ctx, "RECEIVED", msg);
　　　　　　//这一行代码是链路调用的关键，调用1.1，形成链路调用
        ctx.fireChannelRead(msg);
    }

参考 https://blog.csdn.net/zxhoo/article/details/17264263