上面两篇文章介绍了mqtt服务的安装，
https://www.jianshu.com/p/d421bb32fe4c
https://www.jianshu.com/p/879bd7f2db92
这里介绍一下用java来实现mqtt的订阅和消息分发，我们采用eclipse paho的jar包。
1、创建java工程，添加依赖
org.eclipse.paho
org.eclipse.paho.client.mqttv3
1.2.0
2、订阅者
package com.chen.mqtt.mosquitto;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttTopic;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
import java.util.concurrent.ScheduledExecutorService;
/**
* @author: ChenJie
* @date 2018/8/10
*/
public class Subscriber {
public static final StringHOST ="tcp://172.16.1.86:1883";
public static final StringTOPIC ="speedTopic";
private static final Stringclientid ="client83";
private MqttClientclient;
private MqttConnectOptionsoptions;
// private String userName = "admin";
// private String passWord = "password";
private ScheduledExecutorServicescheduler;
public static void main(String[] args) {
Subscriber client =new Subscriber();
client.start();
}
private void start() {
try {
client =new MqttClient(HOST,clientid,new MemoryPersistence());
options =new MqttConnectOptions();
options.setCleanSession(true);
options.setConnectionTimeout(10);
options.setKeepAliveInterval(20);
client.setCallback(new PushCallback());
MqttTopic topic =client.getTopic(TOPIC);
//遗言
options.setWill(topic,"close".getBytes(),2,true);
client.connect(options);
int [] qos = {1};
String [] topics = {TOPIC};
client.subscribe(topics,qos);
}catch (MqttException e) {
e.printStackTrace();
}
}
}
3、消息发布者
package com.chen.mqtt.mosquitto;
import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
/**
* @author: ChenJie
* @date 2018/8/10
*/
public class Publisher {
//tcp://MQTT安装的服务器地址:MQTT定义的端口号
public static final StringHOST ="tcp://172.16.1.86:1883";
//定义一个主题
public static final StringTOPIC ="speedTopic";
//定义MQTT的ID，可以在MQTT服务配置中指定
private static final Stringclientid ="server84";
private MqttClientclient;
private MqttTopictopic;
private StringuserName ="mosquitto";
private Stringpassword ="";
private MqttMessagemessage;
/**
* 构造函数
* @throws MqttException
*/
public Publisher()throws MqttException {
// MemoryPersistence设置clientid的保存形式，默认为以内存保存
client =new MqttClient(HOST, clientid, new MemoryPersistence());
connect();
}
private void connect() {
MqttConnectOptions options =new MqttConnectOptions();
options.setCleanSession(false);
// options.setUserName(userName);
// options.setPassword(password.toCharArray());
//超时时长
options.setConnectionTimeout(100);
//心跳时长
options.setKeepAliveInterval(20);
options.setServerURIs(new String[]{HOST} );
try{
client.setCallback(new PushCallback() );
client.connect(options);
topic =client.getTopic(TOPIC);
}
catch(Exception e){
e.printStackTrace();
}
}
public void publish(MqttTopic topic,MqttMessage message)throws MqttException {
MqttDeliveryToken token = topic.publish(message);
System.out.println("等待发送成功:"+token.isComplete());
token.waitForCompletion();
System.out.println("已经发送成功:"+token.isComplete());
}
public static void main(String[] args)throws MqttException {
Publisher server =new Publisher();
server.message =new MqttMessage();
server.message.setQos(1);
server.message.setRetained(true);
for(int i=0;i<10;i++){
server.message.setPayload(("hello,topic speed "+i).getBytes());
server.publish(server.topic,server.message);
}
}
}
4、PushCallback
package com.chen.mqtt.mosquitto;
import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import java.time.LocalDateTime;
/**
* 发布消息的回调类
*
* 必须实现MqttCallback的接口并实现对应的相关接口方法CallBack 类将实现 MqttCallBack。
* 每个客户机标识都需要一个回调实例。在此示例中，构造函数传递客户机标识以另存为实例数据。
* 在回调中，将它用来标识已经启动了该回调的哪个实例。
* 必须在回调类中实现三个方法：
*
* public void messageArrived(MqttTopic topic, MqttMessage message)接收已经预订的发布。
*
* public void connectionLost(Throwable cause)在断开连接时调用。
*
* public void deliveryComplete(MqttDeliveryToken token))
* 接收到已经发布的 QoS 1 或 QoS 2 消息的传递令牌时调用。
* 由 MqttClient.connect 激活此回调。
*/
public class PushCallbackimplements MqttCallback{
@Override
public void connectionLost(Throwable throwable) {
System.out.println("连接断开！");
System.out.println(LocalDateTime.now());
}
@Override
public void messageArrived(String topic, MqttMessage message)throws Exception {
System.out.println("接收消息主题 : " + topic);
System.out.println("接收消息Qos : " + message.getQos());
System.out.println("接收消息内容 : " +new String(message.getPayload()));
}
@Override
public void deliveryComplete(IMqttDeliveryToken token) {
System.out.println("分发完成---------" + token.isComplete());
System.out.println(LocalDateTime.now());
}
}