三.netty学习之ChannelPipeline

官方的文档里一直推荐看看这三个类之间的关系. public interface ChannelPipeline extends java.lang.Iterable<java.util.Map.Entry<java.lang.String, io.netty.channel.ChannelHandler>>

能够看出,他里面存的是ChannelHandler的集合 他就是一个责任链的设计模式实现

1.pipeline的建立 每个channel都有本身的pipeline, 而且当channel建立的时候自动建立 2.一个event是怎么在pipeline里流动的

![pipeline中事件的流动](https://static.oschina.net/uploads/img/201510/31014503_tbRZ.png "pipeline中event的流动")

3.传递一个事件到下一个handler ChannelHandler要想event传递到下一个handler,他必须调用ChannelHandlerContext的方法 1. ** Inbound event propagation methods:**

ChannelHandlerContext.fireChannelRegistered()
        ChannelHandlerContext.fireChannelActive()
        ChannelHandlerContext.fireChannelRead(Object)
        ChannelHandlerContext.fireChannelReadComplete()
        ChannelHandlerContext.fireExceptionCaught(Throwable)
        ChannelHandlerContext.fireUserEventTriggered(Object)
        ChannelHandlerContext.fireChannelWritabilityChanged()
        ChannelHandlerContext.fireChannelInactive()
   2.
        **Outbound event propagation methods:**
        ChannelHandlerContext.bind(SocketAddress, ChannelPromise)
        ChannelHandlerContext.connect(SocketAddress, SocketAddress, ChannelPromise)
        ChannelHandlerContext.write(Object, ChannelPromise)
        ChannelHandlerContext.flush()
        ChannelHandlerContext.read()
        ChannelHandlerContext.disconnect(ChannelPromise)
        ChannelHandlerContext.close(ChannelPromise)

下面有一个例子

public class MyInboundHandler extends ChannelHandlerAdapter {
        @Override
       public void channelActive(ChannelHandlerContext ctx) {
           System.out.println("Connected!");
           ctx.fireChannelActive();
       }
   }
  
   public clas MyOutboundHandler extends ChannelHandlerAdapter {
        @Override
       public void close(ChannelHandlerContext ctx, ChannelPromise promise) {
           System.out.println("Closing ..");
           ctx.close(promise);
       }
   }

构建一个pipeline

如下是代码

static final EventExecutorGroup group = new DefaultEventExecutorGroup(16);
   ...
  
   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());

线程安全的

pipeline是线程安全的,因此一个handler能够被添加或者删除在任意时刻. 好比,要传输一些敏感的信息时,咱们能够add一个加密的handler,用完以后remove,很方便