订阅emqx的线上代码，可直接使用

package com.tyjt.ccpparking.config; import lombok.Data; import lombok.extern.slf4j.Slf4j; import org.eclipse.paho.client.mqttv3.MqttClient; import org.eclipse.paho.client.mqttv3.MqttClientPersistence; import org.eclipse.paho.client.mqttv3.MqttConnectOptions; import org.eclipse.paho.client.mqttv3.MqttException; import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence; import org.springframework.beans.factory.annotation.Value; import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; /** */ @Slf4j @Data @Configuration public class MqttConfig { @Value("${mqtt.client.username}") private String username; @Value("${mqtt.client.password}") private String password; @Value("${mqtt.client.serverURI}") private String serverURI; @Value("${mqtt.client.clientId}") private String clientId; @Bean("tyjt") public MqttClient mqttClient(MqttClientPersistence persistence) throws MqttException { try { MqttClient mqttClient = new MqttClient(serverURI, clientId, persistence); // QoS0，At most once，至多一次； // QoS1，At least once，至少一次； // QoS2，Exactly once，确保只有一次。 MqttConnectOptions connectOptions = getMqttConnectOptions(); MqttCallBack mqttCallBack = new MqttCallBack(mqttClient); mqttClient.setCallback(mqttCallBack); mqttClient.connect(connectOptions); return mqttClient; } catch (MqttException mqttException) { log.error("初始化mqtt client失败！", mqttException); throw mqttException; } } private MqttConnectOptions getMqttConnectOptions() { MqttConnectOptions connectOptions = new MqttConnectOptions(); connectOptions.setUserName(username); connectOptions.setPassword(password.toCharArray()); connectOptions.setCleanSession(true); connectOptions.setAutomaticReconnect(true); return connectOptions; } @Bean @ConditionalOnMissingBean(MqttClientPersistence.class) public MqttClientPersistence mqttClientPersistence() { return new MemoryPersistence(); } @Bean public MqttListenerAnnotationBeanPostProcessor mqttListenerAnnotationBeanPostProcessor() { return new MqttListenerAnnotationBeanPostProcessor(); } }