3、netty第二个例子，使用netty建立客户端，与服务端通讯

第一个例子中，建立了http的服务器端，可以直接使用curl命令，或者浏览器直接访问。

在第二个例子中，建立一个netty的客户端来主动发送请求，模拟浏览器发送请求。

这里先启动服务端，再启动客户端，启动客户端后，在 channelActive 方法中，主动向服务器端发送消息，服务器端channelRead0 方法中，接收到客户端的消息后，会再向客户端返回消息。客户端channelRead0方法中接收到消息再向客户端发送消息，依次往复。

同样的，按照顺序

client

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

public class MyClient {
    public static void main(String[] args) throws InterruptedException {
        //客户端只需要一个
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try{

            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup)
                    .channel(NioSocketChannel.class)
                    .handler(new MyClientInitlalizer());
            ChannelFuture channelFuture = bootstrap.connect("localhost", 8899).sync();

            //channelFuture.channel().writeAndFlush("first msg");//发送数据，其实应该写到handler的active方法中

            channelFuture.channel().closeFuture().sync();

        }finally {
            eventLoopGroup.shutdownGracefully();
        }

    }
}

 

Initlalizer

import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.util.CharsetUtil;

public class MyClientInitlalizer extends ChannelInitializer<SocketChannel> {

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline channelPipeline = ch.pipeline();

        //添加解码器的handler
        channelPipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,0,4,0,4));

        channelPipeline.addLast(new LengthFieldPrepender(4));
        //字符串的解码器
        channelPipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        //字符串的编码器
        channelPipeline.addLast( new StringEncoder(CharsetUtil.UTF_8));
        //自定义的处理器
        channelPipeline.addLast(new MyClientHandler());
    }
}

handler

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

import java.time.LocalDateTime;

public class MyClientHandler  extends SimpleChannelInboundHandler<String> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println( ctx.channel().remoteAddress() + "," + msg);
        System.out.println( "client output:" + msg);

        ctx.writeAndFlush("from client" + LocalDateTime.now());
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
        //super.exceptionCaught(ctx, cause);
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.channel().writeAndFlush("来自客户端的问候！");//通道连接之后，发送数据
        super.channelActive(ctx);
    }
}

sever中的handle

server中的server代码和第一个例子类似，initlializer和client中的一致，就不贴代码了。

public class MyServerHandler extends SimpleChannelInboundHandler<String> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println(ctx.channel().remoteAddress() + "," + msg);

        ctx.writeAndFlush("from serevber" + UUID.randomUUID());//消息返回
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
//      super.exceptionCaught(ctx, cause);
    }
}