1.MQTT是什么?
MQTT(Message Queuing Telemetry Transport,消息队列遥测传输协议),是一种基于发布/订阅(publish/subscribe)模式的“轻量级”通讯协议,该协议构建于TCP/IP协议上,由IBM在1999年发布。MQTT最大优点在于,可以以极少的代码和有限的带宽,为连接远程设备提供实时可靠的消息服务。作为一种低开销、低带宽占用的即时通讯协议,使其在物联网、小型设备、移动应用等方面有较广泛的应用。
MQTT是一个基于客户端-服务器的消息发布/订阅传输协议。MQTT协议是轻量、简单、开放和易于实现的,这些特点使它适用范围非常广泛。在很多情况下,包括受限的环境中,如:机器与机器(M2M)通信和物联网(IoT)。其在,通过卫星链路通信传感器、偶尔拨号的医疗设备、智能家居、及一些小型化设备中已广泛使用。
2.代码实现
先引入jar包
<dependency>
<groupId>org.eclipse.paho</groupId>
<artifactId>org.eclipse.paho.client.mqttv3</artifactId>
<version>1.2.0</version>
</dependency>
<!-- 引入另一种mqtt的client -->
<dependency>
<groupId>org.fusesource.mqtt-client</groupId>
<artifactId>mqtt-client</artifactId>
<version>1.14</version>
</dependency>
本例子使用第二个依赖实现的
/**
* @Auther: 18030501
* @Date: 2018/10/25 17:15
* @Description: 发布端/接收端
*/
@Slf4j
public class PublishAndSubscribeClient {
// mqtt服务
public static String HOST = "tcp://host:port";
// 客户端id
public static String CLIENT_ID = "test_clientId";
// 用户名
public static String USERNAME = "whale";
// 密码
public static String PASSWORD = "123456";
// 客户端与服务端消息传递的最大间隔。它能够使服务器检测到客户端的网络是否已经丢失,而无需等待TCP/IP超时
public static short KEEP_ALIVE = 20;
public static void main(String[] args) throws Exception {
// 配置MQTT连接
MQTT mqtt = new MQTT();
mqtt.setHost(HOST);
mqtt.setClientId(CLIENT_ID);
mqtt.setUserName(USERNAME);
mqtt.setPassword(PASSWORD);
// 是否清除session,false:MQTT服务器保存于客户端会话的的主题与确认位置,true:MQTT服务器不保存于客户端会话的的主题与确认位置
mqtt.setCleanSession(true);
mqtt.setKeepAlive(KEEP_ALIVE);
// 设置重新连接的次数
mqtt.setConnectAttemptsMax(1);
// 设置重新连接的间隔
mqtt.setReconnectDelay(4);
// 获取mqtt的连接对象BlockingConnection
CallbackConnection connection = mqtt.callbackConnection();
// 添加接收消息的监听
connection.listener(new Listener() {
@Override
public void onConnected() {
System.out.println("----onConnected----");
}
@Override
public void onDisconnected() {
System.out.println("----onDisconnected----");
}
@Override
public void onPublish(UTF8Buffer topic, Buffer payload, Runnable ack) {
// 处理来自topic的消息
log.info("receive topic:{} and message:{}", topic.toString(), new String(payload.getData()));
ack.run();
}
@Override
public void onFailure(Throwable throwable) {
System.out.println("----onFailure----");
}
});
// 添加连接的事件,并在连接成功时候订阅主题,发送消息
connection.connect(new Callback<Void>() {
// 连接成功时执行的方法
@Override
public void onSuccess(Void aVoid) {
final String topic = "mqtt/test";
// 订阅主题
connection.subscribe(new Topic[]{new Topic(topic, QoS.AT_LEAST_ONCE)}, null);
final String message = "hello everyone!";
log.info("MQTT CallbackServer publish topic={},message:{}", topic, message);
// 参数说明:1.主题 2.消息 3.服务质量(0,1,2) 4.发布保留标识,表示服务器是否要保留发布的消息 5.发布成功回调
// 服务质量:
// 0:最多一次,即:<=1 ; 1:至少一次,即:>=1; 2:一次,即:=1
// 发布消息
connection.publish(topic, message.getBytes(), QoS.AT_LEAST_ONCE, false, new Callback<Void>() {
public void onSuccess(Void v) {
// the publish operation completed successfully.
log.info("----publish message is success!----");
}
public void onFailure(Throwable value) {
log.info("----publish message is failure!----");
value.printStackTrace();
}
});
try {
Thread.sleep(20000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
// 连接失败时执行的方法
@Override
public void onFailure(Throwable value) {
// If we could not connect to the server.
log.info("MQTTCallbackServer.CallbackConnection.connect.onFailure 连接失败......{}", value.getMessage());
value.printStackTrace();
}
});
// 等待消息发送和处理
try {
Thread.sleep(20000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 断开连接
connection.disconnect(new Callback<Void>() {
@Override
public void onSuccess(Void aVoid) {
log.info("--------disconnect success-----------");
}
@Override
public void onFailure(Throwable throwable) {
log.info("--------disconnect failure-----------");
}
});
}
}
下面在提供一个使用第一个jar包实现发送和接收消息:
/**
* @Auther: 18030501
* @Date: 2018/10/25 15:18
* @Description: 发布端
*/
public class PublishExample {
public static String topic = "mqtt/test";
public static String content = "我在测试mqtt消息发送";
public static String broker = "tcp://host:port";
public static String userName = "test";
public static String password = "test";
public static String clientId = "pubClient";
public static int qos = 1;
// 内存存储
public static MemoryPersistence persistence = new MemoryPersistence();
public static void main(String[] args) {
try {
// 1.创建客户端
MqttClient client = new MqttClient(broker, clientId, persistence);
// 2.创建连接参数
MqttConnectOptions options = new MqttConnectOptions();
// 3.在重新启动和重新连接时记住状态
options.setCleanSession(true);
// 4.设置连接的用户名和密码
options.setUserName(userName);
options.setPassword(password.toCharArray());
// 5.建立连接
client.connect(options);
// 6.创建消息
MqttMessage message = new MqttMessage(content.getBytes());
// 7.设置消息的服务质量
message.setQos(qos);
// 8.发布消息
client.publish(topic, message);
// 9.断开连接
client.disconnect();
// 10.关闭客户端
client.close();
} 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();
}
}
}
/**
* @Auther: 18030501
* @Date: 2018/10/25 15:49
* @Description: 订阅端
*/
public class SubscribeExample {
public static String HOST = "tcp://10.245.39.91:61613";
public static String TOPIC = "mqtt/test";
public static int qos = 1;
public static String clientId = "subClient";
public static String userName = "test";
public static String password = "test";
public static void main(String[] args) throws Exception {
try {
// 1.创建客户端
MqttClient client = new MqttClient(HOST, clientId, new MemoryPersistence());
// 2.Mqtt的连接设置
MqttConnectOptions options = new MqttConnectOptions();
options.setCleanSession(true);
options.setUserName(userName);
options.setPassword(password.toCharArray());
options.setConnectionTimeout(10);
options.setKeepAliveInterval(20);
// 3.设置回调函数
client.setCallback(new MqttCallback() {
@Override
public void connectionLost(Throwable throwable) {
System.out.println("connectionLost");
}
@Override
public void messageArrived(String topic, MqttMessage message) throws Exception {
System.out.println("topic:" + topic);
System.out.println("Qos:" + message.getQos());
System.out.println("message content:" + new String(message.getPayload()));
}
@Override
public void deliveryComplete(IMqttDeliveryToken token) {
System.out.println("deliveryComplete---------" + token.isComplete());
}
});
// 4.建立连接
client.connect(options);
// 5.订阅消息
client.subscribe(TOPIC, qos);
} catch (Exception e) {
e.printStackTrace();
}
}
}