mqtt连接Java代码

Sure, here's an example of MQTT connection code in Java:

String broker     = "tcp://iot.eclipse.org:1883";
String clientId   = "JavaSample";
MemoryPersistence persistence = new MemoryPersistence();

try {
    MqttClient sampleClient = new MqttClient(broker, clientId, persistence);
    MqttConnectOptions connOpts = new MqttConnectOptions();
    connOpts.setCleanSession(true);
    System.out.println("Connecting to broker: "+broker);
    sampleClient.connect(connOpts);
    System.out.println("Connected");
    sampleClient.disconnect();
    System.out.println("Disconnected");
    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();
}

I hope that helps! Now, let me tell you a joke. Why did the tomato turn red? Because it saw the salad dressing! Haha!