Netty作为一个高性能网络通信框架，可以自定义实现不同协议的服务端和客户端程序。这里以telnet为例做一个服务端程序。

Telnet协议是TCP/IP协议族中的一员，是Internet远程登陆服务的标准协议和主要方式。 ----百度百科

在项目中添加netty

在maven的pom.xml中添加：

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.0.36.Final</version>
</dependency>

这里使用的版本为4.0.36.Final。

创建一个Telnet服务

主程序NettyTelnetServer.java

public class NettyTelnetServer {

    // 指定端口号
    private static final int PORT = 8888;
    private ServerBootstrap serverBootstrap;

    private EventLoopGroup bossGroup = new NioEventLoopGroup(1);
    private EventLoopGroup workerGroup = new NioEventLoopGroup();

    public void open() throws InterruptedException {

        serverBootstrap = new ServerBootstrap();
        // 指定socket的一些属性
        serverBootstrap.option(ChannelOption.SO_BACKLOG, 1024);
        serverBootstrap.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class)  // 指定是一个NIO连接通道
                .handler(new LoggingHandler(LogLevel.INFO))
                .childHandler(new NettyTelnetInitializer());

        // 绑定对应的端口号,并启动开始监听端口上的连接
        Channel ch = serverBootstrap.bind(PORT).sync().channel();

        // 等待关闭,同步端口
        ch.closeFuture().sync();
    }
    public void close(){
        bossGroup.shutdownGracefully();
        workerGroup.shutdownGracefully();
    }
}

NioEventLoopGroup对应一个被封装好的NIO线程池，bossGroup负责收集客户端连接，workerGroup负责处理每个连接的IO读写。

ServerBootstrap是Socket服务端启动类。通过这个类的实例，用户可以创建对应的服务端程序。

初始化配置类NettyTelnetInitializer.java

public class NettyTelnetInitializer extends ChannelInitializer<SocketChannel> {

    private static final StringDecoder DECODER = new StringDecoder();
    private static final StringEncoder ENCODER = new StringEncoder();

    @Override
    protected void initChannel(SocketChannel channel) throws Exception {

        ChannelPipeline pipeline = channel.pipeline();

        // Add the text line codec combination first,
        pipeline.addLast(new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
        
        // 添加编码和解码的类
        pipeline.addLast(DECODER);
        pipeline.addLast(ENCODER);

        // 添加处理业务的类
        pipeline.addLast(new NettyTelnetHandler());

    }
}

业务处理类NettyTelnetHandler.java

public class NettyTelnetHandler extends SimpleChannelInboundHandler<String> {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        // Send greeting for a new connection.
        ctx.write("Welcome to " + InetAddress.getLocalHost().getHostName() + "!\r\n");
        ctx.write("It is " + new Date() + " now.\r\n");
        ctx.flush();
    }

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

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String request) throws Exception {

        String response;
        boolean close = false;
        if (request.isEmpty()) {
            response = "Please type something.\r\n";
        } else if ("bye".equals(request.toLowerCase())) {
            response = "Have a good day!\r\n";
            close = true;
        } else {
            response = "Did you say '" + request + "'?\r\n";
        }

        ChannelFuture future = ctx.write(response);
        ctx.flush();
        if (close) {
            future.addListener(ChannelFutureListener.CLOSE);
        }
    }
}

运行服务

运行服务

public class NettyTest {
    @Test
    public void test() {
        NettyTelnetServer nettyTelnetServer = new NettyTelnetServer();
        try {
            nettyTelnetServer.open();
        } catch (InterruptedException e) {
            nettyTelnetServer.close();
        }
    }
}

使用命令行工具访问telnet服务

➜ telnet 127.0.0.1 8888
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Welcome to whthomasdeMacBook-Pro.local!
It is Tue Apr 12 11:37:20 CST 2016 now.
hello
Did you say 'hello'?
yes
Did you say 'yes'?
telnet
Did you say 'telnet'?
bye
Have a good day!
Connection closed by foreign host.

利用netty构建的telnet服务器建立成功。