ChannelHandler原理

1. 创建ChannelPipeline的方法是实现接口  ChannelPipelineFactory 中的那个 getPipeline() 方法，然后根据自己的业务需要加入相应的 ChannelHandler。

 

2. 

接口 ChannelHandlerContext 提供的功能是统一管理这些ChannelHandler，使其能够和这个ChannelPipeline及其他Handler进行交互，一个handler可以往上流或者下流发送一个ChannelEvent，动态修改其所属的Channelpipeline。

充当链表节点的 DefaultChannelHandlerContext 里面的重要成员有： 链表指针next , prev, 以及是否能够处理downStream，upStream事件的布尔变量。

private   final  class  DefaultChannelHandlerContext  implements  ChannelHandlerContext {

     volatile  DefaultChannelHandlerContext  next ;

     volatile  DefaultChannelHandlerContext  prev ;

     private   final  String  name  ;

     private   final  ChannelHandler  handler ;

     private   final   boolean  canHandleUpstream  ;

     private   final   boolean  canHandleDownstream  ;

     private   volatile  Object  attachment  ;

    DefaultChannelHandlerContext(

            DefaultChannelHandlerContext prev, DefaultChannelHandlerContext next,

            String name, ChannelHandler handler) {

         if  (name ==  null ) {

             throw   new  NullPointerException(  "name" );

        }

         if  (handler ==  null ) {

             throw   new  NullPointerException(  "handler" );

        }

         canHandleUpstream  = handler  instanceof  ChannelUpstreamHandler;

         canHandleDownstream  = handler  instanceof  ChannelDownstreamHandler;

         if  (! canHandleUpstream  && !  canHandleDownstream ) {

             throw   new  IllegalArgumentException(

                     "handler must be either "  +

                    ChannelUpstreamHandler.  class .getName() +  " or "  +

                    ChannelDownstreamHandler.  class .getName() +  '.' );

        }

         this  . prev  = prev;

         this  . next  = next;

         this  . name  = name;

         this  . handler  = handler;

    }

     public  Channel getChannel() {

         return  getPipeline().getChannel();

    }

     public  ChannelPipeline getPipeline() {

         return  DefaultChannelPipeline.  this  ;

    }

     public   boolean  canHandleDownstream() {

         return   canHandleDownstream  ;

    }

     public   boolean  canHandleUpstream() {

         return   canHandleUpstream  ;

    }

     public  ChannelHandler getHandler() {

         return   handler  ;

    }

     public  String getName() {

         return   name  ;

    }

     public  Object getAttachment() {

         return   attachment  ;

    }

     public   void  setAttachment(Object attachment) {

         this  . attachment  = attachment;

    }

     public   void  sendDownstream(ChannelEvent e) {

        DefaultChannelHandlerContext prev = getActualDownstreamContext(  this .  prev );

         if  (prev ==  null ) {

             try  {

                getSink().eventSunk( DefaultChannelPipeline.  this , e);

            }  catch  (Throwable t) {

                notifyHandlerException(e, t);

            }

        }  else  {

            DefaultChannelPipeline.  this .sendDownstream(prev, e);

        }

    }

     public   void  sendUpstream(ChannelEvent e) {

        DefaultChannelHandlerContext next = getActualUpstreamContext(  this .  next );

         if  (next !=  null ) {

            DefaultChannelPipeline.  this .sendUpstream(next, e);

        }

    }

}