MQTT Java 客户端

￡神魔★判官ぃ 2022-10-10 04:49 233阅读 0赞

### MQTT Java 客户端库 ###

[Eclipse Paho Java Clien][]t 是用 Java 编写的 MQTT 客户端库（MQTT Java Client），可用于 JVM 或其他 Java 兼容平台（例如Android）。

Eclipse Paho Java Client 提供了MqttAsyncClient 和 MqttClient 异步和同步 API。

### 通过 Maven 安装 Paho Java ###

--------------------

通过包管理工具 Maven 可以方便地安装 Paho Java 客户端库，截止目前最新版本安装如下：

<dependency>
      <groupId>org.eclipse.paho</groupId>
    	<artifactId>org.eclipse.paho.client.mqttv3</artifactId>
    	<version>1.2.2</version>
    </dependency>

### Paho Java 使用示例 ###

Java 体系中 Paho Java 是比较稳定、广泛应用的 MQTT 客户端库，本示例包含 Java 语言的 Paho Java 连接 EMQ X Broker，并进行消息收发完整代码：  
App.java

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.MqttMessage;
    import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
    
    
    public class App {
        public static void main(String[] args) {
            String subTopic = "testtopic/#";
            String pubTopic = "testtopic/1";
            String content = "Hello World";
            int qos = 2;
            String broker = "tcp://127.0.0.1:1883";
            String clientId = "mqtt_test";
            MemoryPersistence persistence = new MemoryPersistence();
    
            try {
                MqttClient client = new MqttClient(broker, clientId, persistence);
    
                // MQTT 连接选项
                MqttConnectOptions connOpts = new MqttConnectOptions();
               // connOpts.setUserName("mqtt_test");
               // connOpts.setPassword("mqtt_test_password".toCharArray());
                // 保留会话
                connOpts.setCleanSession(true);
    
                // 设置回调
                //client.setCallback(new PushCallback());
                client.setCallback(new OnMessageCallback());
                // 建立连接
                System.out.println("Connecting to broker: " + broker);
                client.connect(connOpts);
    
                System.out.println("Connected");
                System.out.println("Publishing message: " + content);
    
                // 订阅
                client.subscribe(subTopic);
    
                // 消息发布所需参数
                MqttMessage message = new MqttMessage(content.getBytes());
                message.setQos(qos);
                client.publish(pubTopic, message);
                System.out.println("Message published");
    
           /*     client.disconnect();
                System.out.println("Disconnected");
                client.close();
                System.exit(0);*/
    
            } catch (MqttException me) {
                System.out.println("reason " + me.getReasonCode());
                System.out.println("msg " + me.getMessage());
                System.out.println("loc " + me.getLocalizedMessage());
                System.out.println("cause " + me.getCause());
                System.out.println("excep " + me);
                me.printStackTrace();
            }
        }
    }

###### 回调消息处理类 OnMessageCallback.java ######

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
    import org.eclipse.paho.client.mqttv3.MqttCallback;
    import org.eclipse.paho.client.mqttv3.MqttMessage;
    
    public class OnMessageCallback implements MqttCallback {
        public void connectionLost(Throwable cause) {
            // 连接丢失后，一般在这里面进行重连
            System.out.println("连接断开，可以做重连");
        }
    
        public void messageArrived(String topic, MqttMessage message) throws Exception {
            // subscribe后得到的消息会执行到这里面
            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()));
        }
    
        public void deliveryComplete(IMqttDeliveryToken token) {
            System.out.println("deliveryComplete---------" + token.isComplete());
        }
    }

##### Paho Java MQTT 5.0 支持 #####

目前 Paho Java 还在适配 MQTT 5.0，尚未全面支持。

[Eclipse Paho Java Clien]: https://www.eclipse.org/paho/index.php?page=clients/java/index.php