feat: 订阅上下线状态主题，处理设备上下线信息

ruoyi-modules/ruoyi-hazard/src/main/java/org/dromara/hazard/config/HazardMqttConfig.java

@@ -47,7 +47,7 @@ public class HazardMqttConfig {
         try {
             // 订阅一个主题，QoS=1
             mqttGateway.subscribe("iot-hazard-server", 1);
-
+            mqttGateway.subscribe("status/online", 1);
             log.info("危险源模块已订阅MQTT主题: iot-hazard-server");
         } catch (Exception e) {
             log.error("订阅MQTT主题失败", e);

ruoyi-modules/ruoyi-hazard/src/main/java/org/dromara/hazard/handler/HazardMqttMessageHandler.java

@@ -1,5 +1,6 @@
 package org.dromara.hazard.handler;
 
+import org.dromara.common.core.utils.StringUtils;
 import org.dromara.common.mqtt.handler.MqttMessageHandler;
 import org.dromara.common.mqtt.server.MqttGateway;
 import org.eclipse.paho.client.mqttv3.MqttMessage;
@@ -8,6 +9,8 @@ import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
 
+import java.util.List;
+
 /**
  * 危险源模块的MQTT消息处理器
  *
@@ -32,6 +35,8 @@ public class HazardMqttMessageHandler implements MqttMessageHandler {
         // TODO: 根据不同的主题分发到不同的业务处理方法
         if (topic.equals("iot-hazard-server")) {
             handleHazardMessage(topic, payload);
+        } else if (topic.equals("status/online")){
+            handleOnlineMessage(topic, payload);
         } else {
             log.warn("未知的消息主题: {}", topic);
         }
@@ -71,4 +76,21 @@ public class HazardMqttMessageHandler implements MqttMessageHandler {
         // TODO: 实现你的业务逻辑
         // 例如: 解析JSON、保存数据库、触发业务流程等
     }
+
+    /**
+     * 处理设备上下线通知
+     * @param topic
+     * @param payload
+     */
+    private void handleOnlineMessage(String topic, String payload) {
+        log.info("处理设备上下线通知 - Topic: {}, Payload: {}", topic, payload);
+        List<String> strings = StringUtils.str2List(payload, ":", false, true);
+        if (strings.size() != 2) return;
+        String sign = strings.get(0);
+        if ("OFFLINE".equals(sign)) {
+            log.info("设备 {} 下线。", strings.get(1));
+        }else if ("ONLINE".equals(sign)) {
+            log.info("设备 {} 上线。", strings.get(1));
+        }
+    }
 }