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 |
a Channel is open, but not bound nor connected |
"channelClosed" |
ChannelStateEvent |
a Channel was closed and all its related resources were released |
"channelBound" |
ChannelStateEvent |
a Channel is open and bound to a local address, but not connected |
"channelUnbound" |
ChannelStateEvent |
a Channel was unbound from the current local address |
"channelConnected" |
ChannelStateEvent |
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 |
a Channel was disconnected from its remote peer |
"channelInterestChanged" |
ChannelStateEvent |
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 |
Bind the Channel to the specified local address. |
"unbind" |
ChannelStateEvent |
Unbind the Channel from the current local address. |
"connect" |
ChannelStateEvent |
Connect the Channel to the specified remote address. |
"disconnect" |
ChannelStateEvent |
Disconnect the Channel from the current remote address. |
"close" |
ChannelStateEvent |
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