MQTT的学习研究（四）moquette-mqtt 的使用之mqtt Blocking API客户端订阅并接收主题信息

在上面两篇关于mqtt的broker的启动和mqtt的服务端发布主题信息之后，我们客户端需要订阅相关的信息并接收相关的主题信息。

package com.etrip.mqtt;

import java.net.URISyntaxException;

import org.fusesource.mqtt.client.BlockingConnection;
import org.fusesource.mqtt.client.MQTT;
import org.fusesource.mqtt.client.Message;
import org.fusesource.mqtt.client.QoS;
import org.fusesource.mqtt.client.Topic;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
 *
 * MQTT moquette 的Client 段用于订阅主题，并接收主题信息
 *
 * 采用阻塞式 订阅主题
 *
 * @author longgangbai
 */
public class MQTTClient {
      private static final Logger LOG = LoggerFactory.getLogger(MQTTClient.class);
        private final static String CONNECTION_STRING = "tcp://192.168.208.46:1883";
        private final static boolean CLEAN_START = true;
        private final static short KEEP_ALIVE = 30;// 低耗网络，但是又需要及时获取数据，心跳30s
        private final static String CLIENT_ID = "publishService";
        public  static Topic[] topics = {
                        new Topic("china/beijing", QoS.EXACTLY_ONCE),
                        new Topic("china/tianjin", QoS.AT_LEAST_ONCE),
                        new Topic("china/henan", QoS.AT_MOST_ONCE)};
        public final  static long RECONNECTION_ATTEMPT_MAX=6;
        public final  static long RECONNECTION_DELAY=2000;

        public final static int SEND_BUFFER_SIZE=2*1024*1024;//发送最大缓冲为2M


      public static void main(String[] args)   {
        //创建MQTT对象
        MQTT mqtt = new MQTT();
        BlockingConnection connection=null;
        try {
            //设置mqtt broker的ip和端口
            mqtt.setHost(CONNECTION_STRING);
            //连接前清空会话信息
            mqtt.setCleanSession(CLEAN_START);
            //设置重新连接的次数
            mqtt.setReconnectAttemptsMax(RECONNECTION_ATTEMPT_MAX);
            //设置重连的间隔时间
            mqtt.setReconnectDelay(RECONNECTION_DELAY);
            //设置心跳时间
            mqtt.setKeepAlive(KEEP_ALIVE);
            //设置缓冲的大小
            mqtt.setSendBufferSize(SEND_BUFFER_SIZE);


            //获取mqtt的连接对象BlockingConnection
            connection = mqtt.blockingConnection();
            //MQTT连接的创建
            connection.connect();
            //创建相关的MQTT 的主题列表
            Topic[] topics = {new Topic("china/beijing", QoS.AT_LEAST_ONCE)};
            //订阅相关的主题信息
            byte[] qoses = connection.subscribe(topics);
            //
            while(true){
                //接收订阅的消息内容
                Message message = connection.receive();
                //获取订阅的消息内容
                byte[] payload = message.getPayload();
                // process the message then:
                LOG.info("MQTTClient Message  Topic="+message.getTopic()+" Content :"+new String(payload));
                //签收消息的回执
                message.ack();

                Thread.sleep(2000);
            }
        } catch (URISyntaxException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                connection.disconnect();
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}