Netty入门实例及分析

什么是netty？以下是官方文档的简单介绍：
The Netty project is an effort to provide
an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is
a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP/IP
socket server.

以下写一个简单的实例：
1.client细节分析

ChannelFactory是创建一个通道（和一次详细的通信实体关联如网络套接字）的主要接口。比方NioServerSocketChannelFactory 会创建一个Channel，有基于NIO的服务套接字作为底层的通信实体。一旦一个新的通道创建。那么相应的ChannelPipeline就会開始处理相关的ChannelEvents。



NioClientSocketChannelFactory会创建一个client的基于NIO的SocketChannel。利用非堵塞IO模型来高效处理这些并发的连接。当中有两种类型的线程， boss thread 和 worker thread，每一个NioClientSocketChannelFactory
有一个boss thread。它主要是有请求要发出时试图进行一次连接。连接成功后，将这个连接的通道交付给一个worker thread。接下来这个worker thread 为一个或多个通道运行非堵塞的读写服务。

[align=left]ClientBootstrap仅仅是一个辅助函数，不会分配或者管理不论什么资源，管理资源是由构造器中指定的ChannelFactory完毕的。所以从同一个ChannelFactory衍生出多个ClientBootstrap是能够的。从而为不同的Channel应用不同的设置。connect（）方法会依据指定的SocketAddress试图建立连接，假设本地地址没有设置，就会自己主动分配，等价于：[/align]
[align=left]ClientBootstrap b = ....;[/align]
[align=left]b.connect(remoteAddress, b.getOption("localAddress"));[/align]

静态方法 Channels.pipeline(ChannelHandler... handlers)用參数所指定的ChannelHandler 来创建一个新的ChannelPipeline，当然它们是有顺序的，我们也能够自己一个一个的加入。

public static ChannelPipeline pipeline(ChannelHandler...
handlers) {
[align=left] if (handlers == null) {[/align]
[align=left] throw new NullPointerException( "handlers");[/align]
[align=left] }[/align]

[align=left] ChannelPipeline newPipeline = pipeline ();[/align]
for (int i = 0; i < handlers. length;
i ++) {
[align=left] ChannelHandler h = handlers[i];[/align]
[align=left] if (h == null) {[/align]
[align=left] break;[/align]
[align=left] }[/align]
[align=left] newPipeline.addLast(ConversionUtil. toString(i), h);[/align]
[align=left] }[/align]
[align=left] return newPipeline;[/align]
[align=left] }[/align]

[align=left]2. server端细节分析[/align]

服务器端构建的基本流程和client类似，仅仅是这里的ChannelFactory。Bootstrap 都要满足作为server的特性。

NioServerSocketChannelFactory创建server端的，基于NIO的ServerSocketChannel。仍然是非堵塞模式。

每一个绑定的ServerSocketChannel 有自身的boos thread，比方说打开监听了两个port 80,443。那么就会有两个boss thread，各自负责各自port的连接请求，直到那个port解绑定，然后将接受的连接请求交给worker
thread去处理。

[align=left]这里是面向连接传输的ClientBootstrap 和 ServerBootstrap 。假设想用UDP的话就选 ConnectionlessBootstrap。[/align]

3. ChannelHandler的常见使用方法就会依据详细的事件类型做出详细的处理。牵扯到读写管道。并且有上下流的情况。

[align=left]一个简单的netty样例：[/align]
[align=left]TimeClientl.java[/align]

import java.net.InetSocketAddress;
import java.util.concurrent.Executors;

import org.jboss.netty.bootstrap.ClientBootstrap;
import org.jboss.netty.channel.ChannelFactory;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.ChannelPipelineFactory;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.channel.socket.nio.NioClientSocketChannelFactory;

public class TimeClient {
public static void main(String[] args) {
String host = args[0];
int port = Integer.parseInt(args[1]);

ChannelFactory factory = new NioClientSocketChannelFactory(
Executors.newCachedThreadPool(), Executors.newCachedThreadPool());
ClientBootstrap bootstrap = new ClientBootstrap(factory);
bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
@Override
public ChannelPipeline getPipeline() throws Exception {
return Channels.pipeline(new TimeClientHandler2());
}
});
bootstrap.connect(new InetSocketAddress(host, port));  //
}

}

[align=left]TimeClientHandler.java[/align]

import java.util.Date;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ExceptionEvent;
import org.jboss.netty.channel.MessageEvent;
import org.jboss.netty.channel.SimpleChannelHandler;

public class TimeClientHandler extends SimpleChannelHandler{
@Override
public void messageReceived(ChannelHandlerContext ctx, MessageEvent e)
throws Exception {
ChannelBuffer buffer = (ChannelBuffer)e.getMessage();
long currentTimeMills = buffer.readInt() * 1000L;
System.out.println(new Date(currentTimeMills));
e.getChannel().close();
}

@Override
public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e)
throws Exception {
e.getCause().printStackTrace();
Channel c = e.getChannel();
c.close();
}
}

[align=left]TimeServer.java[/align]

import java.net.InetSocketAddress;
import java.util.concurrent.Executors;

import org.jboss.netty.bootstrap.ServerBootstrap;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelFactory;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.ChannelPipelineFactory;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.channel.group.ChannelGroup;
import org.jboss.netty.channel.group.ChannelGroupFuture;
import org.jboss.netty.channel.group.DefaultChannelGroup;
import org.jboss.netty.channel.socket.nio.NioServerSocketChannelFactory;

public class TimeServer {
public static ChannelGroup allChannels = new DefaultChannelGroup("time-server");

public static void main(String[] args) {
ChannelFactory factory = new NioServerSocketChannelFactory(
Executors.newCachedThreadPool(),
Executors.newCachedThreadPool());

ServerBootstrap bootstrap = new ServerBootstrap(factory);
bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
@Override
public ChannelPipeline getPipeline() throws Exception {
return Channels.pipeline(new TimeServerHandler2(),
new TimeEncoder());
}
});

bootstrap.setOption("reuseAddr", true);
bootstrap.setOption("child.tcpNoDelay", true);
bootstrap.setOption("child.keepAlive", true);

Channel channel = bootstrap.bind(new InetSocketAddress(8080));

allChannels.add(channel);
//waitForShutdownCommand();  this is a imaginary logic:for instance
//when there is accepted connection we close this server ;
if(allChannels.size() >=2){
ChannelGroupFuture f = allChannels.close();
f.awaitUninterruptibly();
factory.releaseExternalResources();
}
}
}

[align=left]TimeServerHandler.java[/align]

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelFuture;
import org.jboss.netty.channel.ChannelFutureListener;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ChannelStateEvent;
import org.jboss.netty.channel.ExceptionEvent;
import org.jboss.netty.channel.SimpleChannelHandler;

public class TimeServerHandler extends SimpleChannelHandler{
@Override
public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e)
throws Exception {
Channel ch = e.getChannel();
ChannelBuffer time = ChannelBuffers.buffer(4); //sizeof int
time.writeInt((int)(System.currentTimeMillis()/1000L + 2208988800L));

ChannelFuture cf = ch.write(time);
cf.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
Channel ch = future.getChannel();
ch.close();
}
});
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e)
throws Exception {
e.getCause().printStackTrace();
Channel c = e.getChannel();
c.close();
}
}