一、emqtt安装

使用rpm安装emqtt并进行简单的测试：以下是在虚拟机centos7下安装的emqtt。
https://blog.csdn.net/lxw983520/article/details/89442373

二、相关配置

1. 在pom文件下添加以下maven依赖：

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

2. 在yml文件中进行mqtt的连接配置

  spring:
   mqtt:
    username: admin							# 账号
    password: public						# 密码
    host-url: tcp://ip:1883					# mqtt连接tcp地址
    client-id: test							# 客户端Id，每个启动的id要不同
    default-topic: test						# 默认主题
    timeout: 100							# 超时时间
    keepalive: 100							# 保持连接数

三、springboot-emqtt的整合

1. 获取配置

package com.modules.common.mqtt;

import lombok.Getter;
import lombok.Setter;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;

/**
 * @Classname MtqqEntity
 * @Description mqtt相关配置信息
 * @Date 2019/4/11 23:00
 * @Created by Jack
 */
@Component
@ConfigurationProperties("spring.mqtt")
@Setter
@Getter
public class MqttConfig {
    @Autowired
    private MqttPushClient mqttPushClient;

    /**
     * 用户名
     */
    private String username;
    /**
     * 密码
     */
    private String password;
    /**
     * 连接地址
     */
    private String hostUrl;
    /**
     * 客户Id
     */
    private String clientId;
    /**
     * 默认连接话题
     */
    private String defaultTopic;
    /**
     * 超时时间
     */
    private int timeout;
    /**
     * 保持连接数
     */
    private int keepalive;

    @Bean
    public MqttPushClient getMqttPushClient() {
        mqttPushClient.connect(hostUrl, clientId, username, password, timeout, keepalive);
        // 以/#结尾表示订阅所有以test开头的主题
        mqttPushClient.subscribe("test/#", 0);
        return mqttPushClient;
    }
}

2. mqtt推送客户端

package com.modules.common.mqtt;

import org.eclipse.paho.client.mqttv3.*;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;

/**
 * @Classname MqttPushClient
 * @Description mqtt推送客户端
 * @Date 2019/4/11 23:22
 * @Created by Jack
 */
@Component
public class MqttPushClient {
    private static final Logger logger = LoggerFactory.getLogger(MqttPushClient.class);

    @Autowired
    private PushCallback pushCallback;

    private static MqttClient client;

    private static MqttClient getClient() {
        return client;
    }

    private static void setClient(MqttClient client) {
        MqttPushClient.client = client;
    }

    /**
     * 客户端连接
     *
     * @param host      ip+端口
     * @param clientID  客户端Id
     * @param username  用户名
     * @param password  密码
     * @param timeout   超时时间
     * @param keepalive 保留数
     */
    public void connect(String host, String clientID, String username, String password, int timeout, int keepalive) {
        MqttClient client;
        try {
            client = new MqttClient(host, clientID, new MemoryPersistence());
            MqttConnectOptions options = new MqttConnectOptions();
            options.setCleanSession(true);
            options.setUserName(username);
            options.setPassword(password.toCharArray());
            options.setConnectionTimeout(timeout);
            options.setKeepAliveInterval(keepalive);
            MqttPushClient.setClient(client);
            try {
                client.setCallback(pushCallback);
                client.connect(options);
            } catch (Exception e) {
                e.printStackTrace();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 发布
     *
     * @param qos         连接方式
     * @param retained    是否保留
     * @param topic       主题
     * @param pushMessage 消息体
     */
    public void publish(int qos, boolean retained, String topic, String pushMessage) {
        MqttMessage message = new MqttMessage();
        message.setQos(qos);
        message.setRetained(retained);
        message.setPayload(pushMessage.getBytes());
        MqttTopic mTopic = MqttPushClient.getClient().getTopic(topic);
        if (null == mTopic) {
            logger.error("topic not exist");
        }
        MqttDeliveryToken token;
        try {
            token = mTopic.publish(message);
            token.waitForCompletion();
        } catch (MqttPersistenceException e) {
            e.printStackTrace();
        } catch (MqttException e) {
            e.printStackTrace();
        }
    }

    /**
     * 订阅某个主题
     *
     * @param topic 主题
     * @param qos   连接方式
     */
    public void subscribe(String topic, int qos) {
        logger.info("开始订阅主题" + topic);
        try {
            MqttPushClient.getClient().subscribe(topic, qos);
        } catch (MqttException e) {
            e.printStackTrace();
        }
    }
}

3. 消费监听类

package com.modules.common.mqtt;

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

/**
 * @Classname PushCallback
 * @Description 消费监听类
 * @Date 2019/4/11 23:31
 * @Created by Jack
 */
@Component
public class PushCallback implements MqttCallback {
    private static final Logger logger = LoggerFactory.getLogger(MqttPushClient.class);

    @Autowired
    private MqttConfig mqttConfig;

    private static MqttClient client;

    @Override
    public void connectionLost(Throwable throwable) {
        // 连接丢失后，一般在这里面进行重连
        logger.info("连接断开，可以做重连");
        if (client == null || !client.isConnected()) {
            mqttConfig.getMqttPushClient();
        }
    }

    @Override
    public void messageArrived(String topic, MqttMessage mqttMessage) throws Exception {
        // subscribe后得到的消息会执行到这里面
        logger.info("接收消息主题 : " + topic);
        logger.info("接收消息Qos : " + mqttMessage.getQos());
        logger.info("接收消息内容 : " + new String(mqttMessage.getPayload()));
    }

    @Override
    public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
        logger.info("deliveryComplete---------" + iMqttDeliveryToken.isComplete());
    }
}

4. 测试服务

package com.test.controller;

import com.modules.common.exception.ExceptionUtils;
import com.modules.common.mqtt.MqttPushClient;
import com.modules.common.utils.RUtils;
import com.modules.common.validator.ValidatorUtils;
import com.test.entity.TestUser;
import com.test.form.TestForm;
import com.test.service.TestService;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiImplicitParam;
import io.swagger.annotations.ApiImplicitParams;
import io.swagger.annotations.ApiOperation;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.*;

import javax.validation.Valid;

/**
 * @author: lxw
 * @Date: 2018/10/19 19:36
 * @email: 1229703575@qq.com
 * @Description: 测试文件
 */
@RestController
@RequestMapping("/")
@Api("测试")
public class TestController {
 
    @Autowired
    private MqttPushClient mqttPushClient;

    @ApiOperation(value = "发布主题", notes = "测试发布主题")
    @GetMapping(value = "/publishTopic")
    public RUtils publishTopic() {
        mqttPushClient.publish(0,false,"test/test","测试一下发布消息");
        return RUtils.ok();
    }
}

三、测试成果

1. 进入后台订阅“test/test”主题，注意要进行连接。
   
2. 接口发送相关信息。
   
3. 后台接收到相应的信息。
   
   此时项目中的客户端也订阅了test/下的主题，因此也会收到相应的消息。