使用netty 编写mqtt客户端，具体

如下： ```java import io.netty.bootstrap.Bootstrap; import io.netty.channel.*; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.SocketChannel; import io.netty.channel.socket.nio.*; import io . netty . handler . codex . mqtt . * ; // 导入mqtt 的处理器 public class NettyMqttClient { private final String host; // 服务端地址 private final int port ; // 服务端端口号 public NettyMqttClient(String host , int port ) { this . host = host ; this . port = port ; } public void run() 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 protected void initChannel(SocketChannel ch) throws Exception { ch . pipeline () // 添加mqtt的编解码器 // 注意，在Netty4中它必须放在HttpServerCodec之前 ．addLast("decoder" , new MqttDecoder ()) ．addLast("encoder" , new MqttEncoder ()) ．addLast("handler" ,new MyMqttHandler ()); } } ); ChannelFuture f = b．connect(host, port).sync(); f﹒channel().closeFuture().sync(); } finally { workerGroup﹒shutdownGracefully(); } }} class MyMqttHandler extends SimpleChannelInboundHandler<Object>{ @Override protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception{ if(msg instanceof MqttMessage){ System﹒out﹒println("客户端收到消息:"+msg); }} } public static void main(String[] args) throws Exception{ NettyMqttClient client=new Net tyMqt t Client ("127 ． 0 ． 0 ． 1 " , 8888 ); client ﹒ run (); }} ```