測試環境為centOS 7

#安裝libwebsockets
wget https://dl.fedoraproject.org/pub/epel/7/x86_64/Packages/l/libwebsockets-1.7.5-1.el7.x86_64.rpm
rpm -ivh libwebsockets-1.7.5-1.el7.x86_64.rpm

#安裝mosquitto
wget https://download.opensuse.org/repositories/home:/oojah:/mqtt/CentOS_CentOS-7/home:oojah:mqtt.repo
mv home\:oojah\:mqtt.repo /etc/yum.repos.d/mosquitto.repo
yum install
 
 mosquitto mosquitto-clients
cd /etc/mosquitto/
cp mosquitto.conf.example conf.d/mosquitto.conf
vim conf.d/mosquitto.conf
# 修改內容為： allow_anonymous false
#password_file /etc/mosquitto/pwfile
cp pwfile.example pwfile
#建立admin使用者
mosquitto_passwd -c /etc/mosquitto/pwfile admin
#使用【mosquitto -c /etc/mosquitto/mosquitto.conf -d 】可以後臺執行，第一次啟用不要加-d，這樣如果執行出錯可以立即看到反饋
 

mosquitto -c /etc/mosquitto/mosquitto.conf
#測試
mosquitto_pub -t test -u admin -P password -m "ok"
mosquitto_sub -t test -u admin -P password
# 如果sub收到ok說明測試成功

Publisher

package server;

import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public
 
 class Publisher {

  /**
   * 代理伺服器ip地址
   */
//  public static final String MQTT_BROKER_HOST = "tcp://192.168.1.236:61613";  //apollo
  public static final String MQTT_BROKER_HOST = "tcp://192.168.1.236:1883";

  /**
   * 訂閱標識
   */
  public static final String MQTT_TOPIC = "testTopic";
  /**
   * 客戶端唯一標識
   */
  public static final String MQTT_CLIENT_ID = "publisher01";
  private static String userName = "admin";
  private static String password = "password";
  private static MqttTopic topic;
  private static MqttClient client;

  public static void main(String... args) {
    // 推送訊息

    try {
      client = new MqttClient(MQTT_BROKER_HOST, MQTT_CLIENT_ID, new MemoryPersistence());
      MqttConnectOptions options = new MqttConnectOptions();
      options.setCleanSession(false);
      options.setUserName(userName);
      options.setPassword(password.toCharArray());
      options.setConnectionTimeout(10);
      options.setKeepAliveInterval(20);

      topic = client.getTopic(MQTT_TOPIC);

      client.connect(options);
      client.setCallback(new MqttCallback() {

        @Override public void connectionLost(Throwable throwable) {
          System.out.println("連線斷開,正在重連......");
          try {
            client.connect(options);
          }catch (Exception exception){
            System.out.println(exception.getMessage());
          }
        }

        @Override public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
        }

        @Override public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
        }
      });
      int i=0;
      while (true) {
        MqttMessage message = new MqttMessage();
        //0 最多一次傳送 (只負責傳送，傳送過後就不管資料的傳送情況)
        //1 至少一次傳送 (確認資料交付)
        //2 正好一次傳送 (保證資料交付成功)
        message.setQos(2);
        message.setRetained(true);
        message.setPayload((""+i++).getBytes());
        MqttDeliveryToken token = topic.publish(message);
        token.waitForCompletion();
        System.out.println(i);
        Thread.sleep(1000);
      }

    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

Subscriber

package client;

import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class Subscriber {

  /**
   * 代理伺服器ip地址
   */
//  public static final String MQTT_BROKER_HOST = "tcp://192.168.1.236:61613";
  public static final String MQTT_BROKER_HOST = "tcp://192.168.1.236:1883";

  /**
   * 客戶端唯一標識
   */
  public static final String MQTT_CLIENT_ID = "subscriber01";

  /**
   * 訂閱標識
   */
  public static final String MQTT_TOPIC = "testTopic";

  /**
   *
   */
  public static final String USERNAME = "admin";
  /**
   * 密碼
   */
  public static final String PASSWORD = "password";

  private volatile static MqttClient mqttClient;
  private static MqttConnectOptions options;

  public static void main(String... args) {
    try {
      // host為主機名，clientid即連線MQTT的客戶端ID，一般以客戶端唯一識別符號表示，
      // MemoryPersistence設定clientid的儲存形式，預設為以記憶體儲存
      mqttClient = new MqttClient(MQTT_BROKER_HOST, MQTT_CLIENT_ID, new MemoryPersistence());
      // 配置引數資訊
      options = new MqttConnectOptions();
      // 設定是否清空session,這裡如果設定為false表示伺服器會保留客戶端的連線記錄，
      // 這裡設定為true表示每次連線到伺服器都以新的身份連線
      options.setCleanSession(false);
      // 設定使用者名稱
      options.setUserName(USERNAME);
      // 設定密碼
      options.setPassword(PASSWORD.toCharArray());
      // 設定超時時間 單位為秒
      options.setConnectionTimeout(10);
      // 設定會話心跳時間 單位為秒 伺服器會每隔1.5*20秒的時間向客戶端傳送個訊息判斷客戶端是否線上，但這個方法並沒有重連的機制
      options.setKeepAliveInterval(20);
      // 連線
      mqttClient.connect(options);
      // 訂閱
      mqttClient.subscribe(MQTT_TOPIC);
      // 設定回撥
      mqttClient.setCallback(new MqttCallback() {

        @Override public void connectionLost(Throwable throwable) {
          // 連線丟失後，一般在這裡面進行重連
          System.out.println("連線斷開,正在重連......");
          try {
            mqttClient.connect(options);
          }catch (Exception exception){
            exception.printStackTrace();
          }
        }

        @Override public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
          System.out.println("toppic:"+s+"\t message:\t"+ mqttMessage.toString());
        }

        @Override public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {

        }
      });
    } catch (Exception e) {
      e.printStackTrace();
    }

  }

}