netty：pipeline的执行顺序

# 假设pipeline里面有这样的handler顺序

OutBoundHandler1
InBoundHandler1
OutBoundHandler2
InBoundHandler2

• 当在【InBoundHandler1】里面执行【ctx.write()】时
  • 向上执行触发【OutBoundHandler1.write()】方法
  • 由于【OutBoundHandler2】在【InBoundHandler1】的下面，所以【OutBoundHandler1.write()】不会执行
• 当在【InBoundHandler1】里面执行【ctx.fireChannelRead()】时
  • 先执行【in】再执行【out】，所以【InBoundHandler2.channelRead0()】会比【OutBoundHandler1、OutBoundHandler2】的【read()】先执行
  • 向下执行，所以【InBoundHandler2.channelRead0()】会被触发。
  • 执行完【in】之后，开始执行【out】，【OutBoundHandler2】在【OutBoundHandler1】的下面，所以【OutBoundHandler2.read()】先执行
  • 最后执行【OutBoundHandler1.read()】
• 当在【InBoundHandler2】里面执行【ctx.fireChannelRead()】时
  • 由于【InBoundHandler1】在【InBoundHandler2】的前面，所以不执行
  • 执行【OutBoundHandler2.read()】
  • 再执行【OutBoundHandler1.read()】