Netty4.0学习笔记系列之一：Server与Client的通讯

http://blog.csdn.net/u013252773/article/details/21046697

本文是学习Netty的第一篇文章，主要对Netty的Server和Client间的通讯机制进行验证。

Server与Client建立连接后，会执行以下的步骤：

1、Client向Server发送消息：Are you ok?

2、Server接收客户端发送的消息，并打印出来。

3、Server端向客户端发送消息：I am ok!

4、Client接收Server端发送的消息，并打印出来，通讯结束。

涉及到的类有4个：

1、HelloServer ：server类，启动Netty server

2、HelloServerInHandler：server的handler，接收客户端消息，并向客户端发送消息

3、HelloClient：client类，建立于Netty server的连接

4、HelloClientIntHandler：client的handler，接收server端的消息，并向服务端发送消息

1、HelloServer代码如下：

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package com.guowl.testserver;

import io.netty.bootstrap.ServerBootstrap;

import io.netty.channel.ChannelFuture;

import io.netty.channel.ChannelInitializer;

import io.netty.channel.ChannelOption;

import io.netty.channel.EventLoopGroup;

import io.netty.channel.nio.NioEventLoopGroup;

import io.netty.channel.socket.SocketChannel;

import io.netty.channel.socket.nio.NioServerSocketChannel;

public class HelloServer {

public void start(int port) throws Exception {

EventLoopGroup bossGroup = new NioEventLoopGroup();

EventLoopGroup workerGroup = new NioEventLoopGroup();

try {

ServerBootstrap b = new ServerBootstrap();

b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)

.childHandler(new ChannelInitializer<SocketChannel>() {

@Override

public void initChannel(SocketChannel ch)

throws Exception {

// 注册handler

ch.pipeline().addLast(new HelloServerInHandler());

}

}).option(ChannelOption.SO_BACKLOG, 128)

.childOption(ChannelOption.SO_KEEPALIVE, true);

ChannelFuture f = b.bind(port).sync();

f.channel().closeFuture().sync();

} finally {

workerGroup.shutdownGracefully();

bossGroup.shutdownGracefully();

}

}

public static void main(String[] args) throws Exception {

HelloServer server = new HelloServer();

server.start(8000);

}

}

2、HelloServerInHandler代码如下：

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package com.guowl.testserver;

import io.netty.buffer.ByteBuf;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

// 该handler是InboundHandler类型

public class HelloServerInHandler extends ChannelInboundHandlerAdapter {

private static Logger logger = LoggerFactory

.getLogger(HelloServerInHandler.class);

@Override

public void channelRead(ChannelHandlerContext ctx, Object msg)

throws Exception {

logger.info("HelloServerInHandler.channelRead");

ByteBuf result = (ByteBuf) msg;

byte[] result1 = new byte[result.readableBytes()];

// msg中存储的是ByteBuf类型的数据，把数据读取到byte[]中

result.readBytes(result1);

String resultStr = new String(result1);

// 接收并打印客户端的信息

System.out.println("Client said:" + resultStr);

// 释放资源，这行很关键

result.release();

// 向客户端发送消息

String response = "I am ok!";

// 在当前场景下，发送的数据必须转换成ByteBuf数组

ByteBuf encoded = ctx.alloc().buffer(4 * response.length());

encoded.writeBytes(response.getBytes());

ctx.write(encoded);

ctx.flush();

}

@Override

public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {

ctx.flush();

}

}

3、HelloClient代码如下：

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package com.guowl.testserver;

import io.netty.bootstrap.Bootstrap;

import io.netty.channel.ChannelFuture;

import io.netty.channel.ChannelInitializer;

import io.netty.channel.ChannelOption;

import io.netty.channel.EventLoopGroup;

import io.netty.channel.nio.NioEventLoopGroup;

import io.netty.channel.socket.SocketChannel;

import io.netty.channel.socket.nio.NioSocketChannel;

public class HelloClient {

public void connect(String host, int port) throws Exception {

EventLoopGroup workerGroup = new NioEventLoopGroup();

try {

Bootstrap b = new Bootstrap();

b.group(workerGroup);

b.channel(NioSocketChannel.class);

b.option(ChannelOption.SO_KEEPALIVE, true);

b.handler(new ChannelInitializer<SocketChannel>() {

@Override

public void initChannel(SocketChannel ch) throws Exception {

ch.pipeline().addLast(new HelloClientIntHandler());

}

});

// Start the client.

ChannelFuture f = b.connect(host, port).sync();

// Wait until the connection is closed.

f.channel().closeFuture().sync();

} finally {

workerGroup.shutdownGracefully();

}

}

public static void main(String[] args) throws Exception {

HelloClient client = new HelloClient();

client.connect("127.0.0.1", 8000);

}

}

4、HelloClientIntHandler代码如下：

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package com.guowl.testserver;

import io.netty.buffer.ByteBuf;

import io.netty.channel.ChannelHandlerContext;

import io.netty.channel.ChannelInboundHandlerAdapter;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

public class HelloClientIntHandler extends ChannelInboundHandlerAdapter {

private static Logger logger = LoggerFactory.getLogger(HelloClientIntHandler.class);

// 接收server端的消息，并打印出来

@Override

public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

logger.info("HelloClientIntHandler.channelRead");

ByteBuf result = (ByteBuf) msg;

byte[] result1 = new byte[result.readableBytes()];

result.readBytes(result1);

System.out.println("Server said:" + new String(result1));

result.release();

}

// 连接成功后，向server发送消息

@Override

public void channelActive(ChannelHandlerContext ctx) throws Exception {

logger.info("HelloClientIntHandler.channelActive");

String msg = "Are you ok?";

ByteBuf encoded = ctx.alloc().buffer(4 * msg.length());

encoded.writeBytes(msg.getBytes());

ctx.write(encoded);

ctx.flush();

}

}

通过上面简单的实例可以发现：

1、在没有任何encoder、decoder的情况下，Netty发送接收数据都是按照ByteBuf的形式，其它形式都是不合法的。

2、接收发送数据操作都是通过handler实现的，handler在netty中占据了非常重要的位置。

3、netty的handler是基于事件触发的，例如当client连接server成功后，client中的HelloClientIntHandler的channelActive方法会自动调用。