Netty之源代码解析

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#bootstrap #bootstrap #源代码 #架构

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Netty始终要写一篇来作为终结的，但是到了写的时候才发现无从下手，了解的还是不够吧。无奈，从四处摘录了一大片东西，很多都是官网下来的，没有什么文字说明，权当参考了。

首先来一张总体架构图，这个是从Neety官网上摘下来的，描述了Netty的核心架构和总体功能。

1. BootStrap

Bootstrap : ChannelFactory, ChannelPipeline, ChannelPipelineFactory	初始化channel的辅助类为具体的子类提供公共数据结构
ServerBootstrap: bind()	创建服务器端channel的辅助类接收connection请求
ClientBootstrap: connect()	创建客户端channel的辅助类发起connection请求
ConnectionlessBootstrap: connect() , bind()	创建无连接传输channel的辅助类（UDP）包括Client 和Server

2. Buffer

Buffer的作用在于取代nio中的Java.nio.ByteBuffer，相比ByteBuffer，可以根据需要自定义buffertype。内置混合的buffertype, 以实现zero-copy。提供类似StringBuffer的动态dynamic buffer；不需要调用flip方法;推荐使用ChannelBuffers的静态工厂创建ChannelBuffer.

3. channel

org.jboss.netty.channel	channel核心api，包括异步和事件驱动等各种传送接口
org.jboss.netty.channel.group	channel group，帮助用户维护channel列表
org.jboss.netty.channel.local	一种虚拟传输方式，允许同一个虚拟机上的两个部分可以互相通信
org.jboss.netty.channel.socket	TCP, UDP接口，继承了核心的channel API
org.jboss.netty.channel.socket.nio	基于nio的Socket channel实现
org.jboss.netty.channel.socket.oio	基于老io的Socket channel实现
org.jboss.netty.channel.socket.http	基于http的客户端和相应的server端的实现，工作在有防火墙的情况

Channel的核心包结构如下图所示：

4. handler

org.jboss.netty.handler	处理器
org.jboss.netty.handler.codec	编码解码器
org.jboss.netty.handler.execution	基于Executor的实现
org.jboss.netty.handler.queue	将event存入内部队列的处理
org.jboss.netty.handler.ssl	基于SSLEngine的SSL以及TLS实现
org.jboss.netty.handler.stream	异步写入大数据，不会产生outOfMemory也不会花费很多内存
org.jboss.netty.handler.timeout	通过Timer来对读写超时或者闲置链接进行通知

5. Netty的事件模型

5.1. Netty Pipline

                                      I/O Request

                                     via Channel or

                                 ChannelHandlerContext

  +----------------------------------------+---------------+

  |                  ChannelPipeline       |               |

  |                                       \|/              |

  |  +----------------------+  +-----------+------------+  |

  |  | Upstream Handler  N  |  | Downstream Handler  1  |  |

  |  +----------+-----------+  +-----------+------------+  |

  |            /|\                         |               |

  |             |                         \|/              |

  |  +----------+-----------+  +-----------+------------+  |

  |  | Upstream Handler N-1 |  | Downstream Handler  2  |  |

  |  +----------+-----------+  +-----------+------------+  |

  |            /|\                         .               |

  |             .                          .               |

  |     [ sendUpstream() ]        [ sendDownstream() ]     |

  |     [ + INBOUND data ]        [ + OUTBOUND data  ]     |

  |             .                          .               |

  |             .                         \|/              |

  |  +----------+-----------+  +-----------+------------+  |

  |  | Upstream Handler  2  |  | Downstream Handler M-1 |  |

  |  +----------+-----------+  +-----------+------------+  |

  |            /|\                         |               |

  |             |                         \|/              |

  |  +----------+-----------+  +-----------+------------+  |

  |  | Upstream Handler  1  |  | Downstream Handler  M  |  |

  |  +----------+-----------+  +-----------+------------+  |

  |            /|\                         |               |

  +-------------+--------------------------+---------------+

                |                         \|/

  +-------------+--------------------------+---------------+

  |             |                          |               |

  |     [ Socket.read() ]          [ Socket.write() ]      |

  |                                                        |

  |  Netty Internal I/O Threads (Transport Implementation) |

  +--------------------------------------------------------+

处理方式：

ChannelPipelinep = Channels.pipeline();

p.addLast(“1”, newUpstreamHandlerA());

p.addLast(“2”, newUpstreamHandlerB());

p.addLast(“3”, newDownstreamHandlerA());

p.addLast(“4”, newDownstreamHandlerB());

p.addLast(“5”, newUpstreamHandlerX());

Upstream: 1 –> 2 –> 5 顺序处理

Downstream: 4 –> 3 逆序处理

5.2. ChannelState

Direction	State	Value	Meaning
Upstream	OPEN	true	The channel is open.
Upstream	OPEN	false	The channel is closed.
Upstream	BOUND	SocketAddress	The channel is bound to a local address.
Upstream	BOUND	null	The channel is unbound to a local address.
Upstream	CONNECTED	SocketAddress	The channel is connected to a remote address.
Upstream	CONNECTED	null	The channel is disconnected from a remote address.
Upstream	INTEREST_OPS	an integer	The channel interestOps has been changed.
Downstream	OPEN	true	N/A
Downstream	OPEN	false	Close the channel.
Downstream	BOUND	SocketAddress	Bind the channel to the specified local address.
Downstream	BOUND	null	Unbind the channel from the current local address.
Downstream	CONNECTED	SocketAddress	Connect the channel to the specified remote address.
Downstream	CONNECTED	null	Disconnect the channel from the current remote address.
Downstream	INTEREST_OPS	an integer	Change the interestOps of the channel.

5.3. Upstreamevents

Event name	Event type and condition	Meaning
“messageReceived”	MessageEvent	a message object (e.g. ChannelBuffer) was received from a remote peer
“exceptionCaught”	ExceptionEvent	an exception was raised by an I/O thread or a ChannelHandler
“channelOpen”	ChannelStateEvent (state = OPEN, value = true)	a Channel is open, but not bound nor connected
“channelClosed”	ChannelStateEvent (state = OPEN, value = false)	a Channel was closed and all its related resources were released
“channelBound”	ChannelStateEvent (state = BOUND, value = SocketAddress)	a Channel is open and bound to a local address, but not connected
“channelUnbound”	ChannelStateEvent (state = BOUND, value = null)	a Channel was unbound from the current local address
“channelConnected”	ChannelStateEvent (state = CONNECTED, value =SocketAddress)	a Channel is open, bound to a local address, and connected to a remote address
“writeComplete”	WriteCompletionEvent	something has been written to a remote peer
“channelDisconnected”	ChannelStateEvent (state = CONNECTED, value = null)	a Channel was disconnected from its remote peer
“channelInterestChanged”	ChannelStateEvent (state = INTEREST_OPS, no value)	a Channel’s interestOps was changed

5.4. Downstreamevents

Event name	Event type and condition	Meaning
“write”	MessageEvent	Send a message to the Channel.
“bind”	ChannelStateEvent (state = BOUND, value = SocketAddress)	Bind the Channel to the specified local address.
“unbind”	ChannelStateEvent (state = BOUND, value = null)	Unbind the Channel from the current local address.
“connect”	ChannelStateEvent (state = CONNECTED, value = SocketAddress)	Connect the Channel to the specified remote address.
“disconnect”	ChannelStateEvent (state = CONNECTED, value = null)	Disconnect the Channel from the current remote address.
“close”	ChannelStateEvent (state = OPEN, value = false)	Close the Channel.