Netty之源代码解析

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.

 

6.  Netty VS Mina

Netty基于Pipeline处理，Mina基于Filter过滤

Netty的事件驱动模型具有更好的扩展性和易用性

Https，SSL，PB，RSTP，Text&Binary等协议支持

Netty中UDP传输有更好的支持

官方测试Netty比Mina性能更好