Netty中定長解碼器的使用

有了前面的基礎，定長解碼器的使用相對就比較簡單了，所以這裏只使用服務端的代碼，測試時，用telnet作為客戶客戶端，數據只作單向的發送，即從客戶端到服務端。

服務端

EchoServer.java

package cn.xpleaf.netty02;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
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;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;

public class EchoServer {
    public void bind(int port) throws Exception {
        // 配置服務端的NIO線程組
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class)
                .option(ChannelOption.SO_BACKLOG, 1024)
                .childHandler(new ChannelInitializer<SocketChannel>() {

                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        // 添加定長分隔符解碼器到pipeline中，長度設置為20
                        ch.pipeline().addLast(new FixedLengthFrameDecoder(20));
                        // 添加StringDecoder解碼器，將ByteBuf解碼成字符串對象
                        ch.pipeline().addLast(new StringDecoder());
                        // 添加業務處理handler
                        ch.pipeline().addLast(new EchoServerHandler());
                    }
                });

            // 綁定端口，同步等待成功
            ChannelFuture f = b.bind(port).sync();

            // 等待服務端監聽端口關閉
            f.channel().closeFuture().sync();
        } finally {
            // 優雅退出，釋放線程池資源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port = 8080;
        if(args != null && args.length > 0) {
            try {
                port = Integer.valueOf(port);
            } catch (NumberFormatException e) {
                // TODO: handle exception
            }
        }
        new EchoServer().bind(port);
    }
}
 

EchoServerHandler.java

package cn.xpleaf.netty02;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    private int counter = 0;

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String body = (String) msg;
        System.out.println("Receive client : [" + body + "]");
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        // 發生異常，關閉鏈路
        ctx.close();
    }
}
 

測試

啟動服務端，在telnet客戶端中輸入相應字符串：

yeyonghao@yeyonghaodeMacBook-Pro:~$ telnet localhost 8080
Trying ::1...
Connected to localhost.
Escape character is ‘^]‘.
Ye Yonghao welcome to Beijing

此時查看服務端的輸出：

Receive client : [Ye Yonghao welcome t]

可以看到中括號時字符數剛好是20個，因為在pipeline中設置定長解碼器時，設置的長度就是20。

可以嘗試再發送消息：

yeyonghao@yeyonghaodeMacBook-Pro:~$ telnet localhost 8080
Trying ::1...
Connected to localhost.
Escape character is ‘^]‘.
Ye Yonghao welcome to Beijing
I love you so much!
 

再查看服務端的輸出：

Receive client : [Ye Yonghao welcome t]
Receive client : [o Beijing
I love yo]

可以看到服務端把上一次的消息作為這次消息的開始，包括換行符，這說明定長解碼器確實是有效果了。

Netty中定長解碼器的使用