Netty4.0学习笔记系列之一：Server与Client的通讯

2024-04-18 00:59:02

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：

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：

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：

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：

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。

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