简述

之前写过一篇SpringBoot通过Netty实现TCP服务的文章，本篇与之前那篇实现的场景类似，都是服务器与客户端之间双向交互，但个人觉得MQTT的方式实现更好，优雅。

基础

MQTT协议是通过MQTT服务器转发消息，MQTT服务器作为三方，为每个客户端转发消息。与TCP不同的是，TCP编码，java大部分场景是作为服务端，设备作为客户端，而MQTT是一台单独的服务器，java跟设备都作为客户端与之保持长连接。

准备

下载EMQX，对应有windows、mac、linux的版本

下载网址：EMQX下载网址

解压，启动

bin文件夹下执行：（稍等五秒钟，出现两行英文时表示启动完成）

emqx start

浏览器打开

http://localhost:18083/

启动成功。

账号密码：admin/public

若代码里连接MQTT服务时带上用户名密码需要如下操作：

创建客户端认证

编码

maven依赖

        <dependency>
            <groupId>org.springframework.integration</groupId>
            <artifactId>spring-integration-mqtt</artifactId>
        </dependency>

监听器

package com.dpkj.mqtt.mqtt;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.dpkj.mqtt.service.DpDeviceService;
import com.mdd.common.entity.DpDevice;
import com.mdd.common.enums.CtrlTypeEnum;
import com.mdd.common.enums.MqttTopicEnum;
import lombok.extern.slf4j.Slf4j;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.jetbrains.annotations.NotNull;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.Lazy;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Component;

import javax.annotation.Resource;
import java.util.List;

/**
 * 项目启动 连接mqtt服务器 订阅指定主题
 * 此处为项目启动就订阅主题，这种情况是主题已经明确的情况，
 * 若项目启动时主题不明确，需要在代码里动态订阅，
可直接在类中注入MQTTConnect server，之后执行server.sub("xxxx")
 */
@Slf4j
@Component
public class MQTTListener implements ApplicationListener<ContextRefreshedEvent> {

    private final MQTTConnect server;

    @Autowired
    public MQTTListener(MQTTConnect server) {
        this.server = server;
    }

    @Override
    public void onApplicationEvent(@NotNull ContextRefreshedEvent contextRefreshedEvent) {
        try {
            server.setMqttClient(new Callback());

            //订阅主题
            server.sub(“test/test/test”);

        } catch (MqttException e) {
            log.error(e.getMessage(), e);
        }
    }
}
 
 

发布及订阅主题

package com.dpkj.mqtt.mqtt;

import com.dpkj.mqtt.config.async.AsyncTaskService;
import lombok.extern.slf4j.Slf4j;
import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import javax.annotation.Resource;

import java.io.UnsupportedEncodingException;

import static org.eclipse.paho.client.mqttv3.MqttConnectOptions.MQTT_VERSION_3_1_1;

/**
 * WQ
 * 2023/2/14 17:10
 * MQTT工具类操作
 */
@Slf4j
@Component
public class MQTTConnect {

    @Value("${mqtt.host}")
    private String mqttHost;
    @Value("${mqtt.port}")
    private String mqttPort;
    @Value("${mqtt.username}")
    private String mqttUsername;
    @Value("${mqtt.password}")
    private String mqttPassword;

    //唯一标识
    private final String clientId = "MqttClient" + (int) (Math.random() * 100000000);

    private MqttClient mqttClient;

    @Resource
    private AsyncTaskService asyncTaskService;

    /**
     * 客户端connect连接mqtt服务器
     **/
    public void setMqttClient(MqttCallback mqttCallback) {
        MqttConnectOptions options = mqttConnectOptions();
        if (mqttCallback == null) {
            mqttClient.setCallback(new Callback());
        } else {
            mqttClient.setCallback(mqttCallback);
        }
        try {
            mqttClient.connect(options);
            log.error("MQTT服务连接成功。tcp://{}:{},clientId:{},username:{},password:{}", mqttHost, mqttPort, clientId, mqttUsername, mqttPassword);
        } catch (MqttException e) {
            e.printStackTrace();
            log.error("MQTT服务连接失败,{}。tcp://{}:{},clientId:{},username:{},password:{}", e.getMessage(), mqttHost, mqttPort, clientId, mqttUsername, mqttPassword);
        }
    }

    /**
     * MQTT连接参数设置
     */
    public MqttConnectOptions mqttConnectOptions() {
        try {
            mqttClient = new MqttClient("tcp://" + mqttHost + ":" + mqttPort, clientId, new MemoryPersistence());
        } catch (MqttException e) {
            log.error("建立mqtt客户端出错。{}", e.getMessage());
            e.printStackTrace();
        }
        MqttConnectOptions options = new MqttConnectOptions();
        options.setUserName(mqttUsername);
        options.setPassword(mqttPassword.toCharArray());
        options.setConnectionTimeout(0);
        options.setAutomaticReconnect(true);
        options.setKeepAliveInterval(90);
        return options;
    }

    /**
     * 关闭MQTT连接
     */
    public void close() throws MqttException {
        mqttClient.disconnect();
        mqttClient.close();
    }

    /**
     * 向某个主题发布消息 默认qos：1
     *
     * @param sn:道品云泊控制卡设备的唯一标识
     * @param msg：发布的消息
     * @param msgId：发布的消息唯一标识
     */
    public void pub(String sn, String msg, String msgId) {
        MqttMessage mqttMessage = new MqttMessage();
        try {
            //GBK格式下发
            mqttMessage.setPayload(msg.getBytes("GBK"));
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        String topic = "/test/" + sn + "/demo";
        log.error("向主题[{}]，发送消息 {}", topic, msg);
        MqttTopic mqttTopic = mqttClient.getTopic(topic);
        MqttDeliveryToken token;
        try {
            token = mqttTopic.publish(mqttMessage);
            token.waitForCompletion();
        } catch (MqttException e) {
            e.printStackTrace();
        }
    }

    /**
     * 订阅某一个主题 ，此方法默认的的Qos等级为：1
     *
     * @param topic 主题
     */
    public void sub(String topic) throws MqttException {
        log.error("主题订阅：{}", topic);
        mqttClient.subscribe(topic);
    }

//    /**
//     * 订阅某一个主题，可携带Qos
//     *
//     * @param topic 所要订阅的主题
//     * @param qos   消息质量：0、1、2
//     */
//    public void sub(String topic, int qos) throws MqttException {
//        mqttClient.subscribe(topic, qos);
//    }
}

yml

mqtt:
  host: 127.0.0.1
  port: 1883
  username: xxx
  password: 'xxx'