MQTT java 实现 案例 demo
一.MQTT介绍
1.简介
MQTT(message queuing telemetry transport)是IBM开发的即时通讯协议,是一种发布/订阅极其轻量级的消息传输协议,专门为网络受限设备、低宽带以及高延迟和不可靠的网络而设计的。由于以上轻量级的特点,是实现智能家居的首选传输协议,相比于XMPP,更加轻量级而且占用宽带低。
2.特点
a.由于采用发布/订阅的消息模式,可以提供一对多的消息发布
b.轻量级,网络开销小
c.对负载内容会有屏蔽的消息传输
d.有三种消息发布质量(Qos):
qos=0:“至多一次”,这一级别会发生消息丢失或重复,消息发布依赖于TCP/IP网络
qos=1:“至少一次”,确保消息到达,但消息重复可能会发生
qos=2:“只有一次”,确保消息到达一次
e.通知机制,异常中断时会通知双方
3.原理
![](http://upload-images.jianshu.io/upload_images/16900944-a23bb5aba6f195e6.png?imageMogr2/auto-orient/strip|imageView2/2/w/826/format/webp)
MQTT协议有三种身份:发布者、代理、订阅者,发布者和订阅者都为客户端,代理为服务器,同时消息的发布者也可以是订阅者(为了节约内存和流量发布者和订阅者一般都会定义在一起)。
MQTT传输的消息分为主题(Topic,可理解为消息的类型,订阅者订阅后,就会收到该主题的消息内容(payload))和负载(payload,可以理解为消息的内容)两部分。
二.MQTT DEMO
windos下 下载并安装mqtt 服务 运行并通过浏览器打开 http://127.0.0.1:18083/#/connections
MQTT 启动说明:
进入bin目录用cmd方式启动 启动命令emqx start, 关闭 emqx stop, 注意是 bin目录下。 管理网页http://192.168.128.8:18083/#/topics 账户 admin/public
jar包:主要是paho包
java demo 代码
1.监控客户端状态:
package com.yt.mqtt.simple; import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken; import org.eclipse.paho.client.mqttv3.MqttCallback; 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; import com.alibaba.fastjson.JSON; import com.alibaba.fastjson.JSONException; import com.alibaba.fastjson.JSONObject; /** * 监控客户端状态 * * @author YT * 2020-05-08 */ public class ClientStatus { public static void main(String[] args) throws MqttException { String HOST = "tcp://127.0.0.1:11883"; // String TOPIC = "mqtt/test"; // String TOPIC = "$SYS/broker/clients/connected"; String TOPIC ="$SYS/brokers/+/clients/#"; int qos = 1; String clientid = "subClient2"; String userName = "admin"; String passWord = "test"; try { // host为主机名,test为clientid即连接MQTT的客户端ID,一般以客户端唯一标识符表示,MemoryPersistence设置clientid的保存形式,默认为以内存保存 MqttClient client = new MqttClient(HOST, clientid, new MemoryPersistence()); // MQTT的连接设置 MqttConnectOptions options = new MqttConnectOptions(); // 设置是否清空session,这里如果设置为false表示服务器会保留客户端的连接记录,这里设置为true表示每次连接到服务器都以新的身份连接 options.setCleanSession(true); // 设置连接的用户名 options.setUserName(userName); // 设置连接的密码 options.setPassword(passWord.toCharArray()); // 设置超时时间 单位为秒 options.setConnectionTimeout(10); // 设置会话心跳时间 单位为秒 服务器会每隔1.5*20秒的时间向客户端发送个消息判断客户端是否在线,但这个方法并没有重连的机制 options.setKeepAliveInterval(20); // 设置回调函数 client.setCallback(new MqttCallback() { public void connectionLost(Throwable cause) { System.out.println("connectionLost"); } // 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())); // // } public void deliveryComplete(IMqttDeliveryToken token) { System.out.println("deliveryComplete---------"+ token.isComplete()); } public void messageArrived(String topic, MqttMessage message) throws Exception { String msg = new String(message.getPayload()); // System.out.println("topic:"+topic); // System.out.println("Qos:"+message.getQos()); System.out.println("Message content:"+msg); try { JSONObject jsonObject = JSON.parseObject(msg); String clientId = String.valueOf(jsonObject.get("clientid")); if (topic.endsWith("disconnected")) { System.out.println("客户端已掉线:" +clientId); } else { System.out.println("客户端已上线:"+clientId); } } catch (JSONException e) { System.out.println("JSON Format Parsing Exception : "+ msg); } } }); client.connect(options); //订阅消息 client.subscribe(TOPIC, qos); } catch (Exception e) { e.printStackTrace(); } } }
消息发布类
package com.yt.mqtt.simple; 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; /** * 消息发布 * * @author YT * 2020-05-08 */ public class PublishSample { public static void main(String[] args) { String topic = "mqtt/test"; String content = "hello 哈哈"; int qos = 1; String broker = "tcp://127.0.0.1:11883"; String userName = "admin"; String password = "test"; String clientId = "pubClient"; // 内存存储 MemoryPersistence persistence = new MemoryPersistence(); try { // 创建客户端 MqttClient sampleClient = new MqttClient(broker, clientId, persistence); // 创建链接参数 MqttConnectOptions connOpts = new MqttConnectOptions(); // 在重新启动和重新连接时记住状态 connOpts.setCleanSession(false); // 设置连接的用户名 connOpts.setUserName(userName); connOpts.setPassword(password.toCharArray()); // 建立连接 sampleClient.connect(connOpts); // 创建消息 MqttMessage message = new MqttMessage(content.getBytes()); // 设置消息的服务质量 message.setQos(qos); // 发布消息 sampleClient.publish(topic, message); // 断开连接 sampleClient.disconnect(); // 关闭客户端 sampleClient.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(); } } }
消息订阅类
package com.yt.mqtt.simple; import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken; import org.eclipse.paho.client.mqttv3.MqttCallback; 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; /** * 消息订阅 * * @param args * @throws MqttException */ public class SubscribeSample { // <dependencies> // <dependency> // <groupId>org.eclipse.paho</groupId> // <artifactId>org.eclipse.paho.client.mqttv3</artifactId> // <version>1.2.0</version> // </dependency> //</dependencies> public static void main(String[] args) throws MqttException { String HOST = "tcp://127.0.0.1:11883"; String TOPIC = "mqtt/test"; int qos = 1; String clientid = "subClient1"; String userName = "admin"; String passWord = "test"; try { // host为主机名,test为clientid即连接MQTT的客户端ID,一般以客户端唯一标识符表示,MemoryPersistence设置clientid的保存形式,默认为以内存保存 MqttClient client = new MqttClient(HOST, clientid, new MemoryPersistence()); // MQTT的连接设置 MqttConnectOptions options = new MqttConnectOptions(); // 设置是否清空session,这里如果设置为false表示服务器会保留客户端的连接记录,这里设置为true表示每次连接到服务器都以新的身份连接 options.setCleanSession(true); // 设置连接的用户名 options.setUserName(userName); // 设置连接的密码 options.setPassword(passWord.toCharArray()); // 设置超时时间 单位为秒 options.setConnectionTimeout(10); // 设置会话心跳时间 单位为秒 服务器会每隔1.5*20秒的时间向客户端发送个消息判断客户端是否在线,但这个方法并没有重连的机制 options.setKeepAliveInterval(20); // 设置回调函数 client.setCallback(new MqttCallback() { public void connectionLost(Throwable cause) { System.out.println("connectionLost"); } 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())); } public void deliveryComplete(IMqttDeliveryToken token) { System.out.println("deliveryComplete---------" + token.isComplete()); } }); client.connect(options); // 订阅消息 client.subscribe(TOPIC, qos); } catch (Exception e) { e.printStackTrace(); } } }
执行结果:
ClientStatus:
Message content:{"clean_start":true,"clientid":"subClient1","connack":0,"ipaddress":"127.0.0.1","keepalive":20,"proto_name":"MQTT","proto_ver":4,"ts":1588933626,"username":"admin"} 客户端已上线:subClient1 Message content:{"clean_start":false,"clientid":"pubClient","connack":0,"ipaddress":"127.0.0.1","keepalive":60,"proto_name":"MQTT","proto_ver":4,"ts":1588933634,"username":"admin"} 客户端已上线:pubClient Message content:{"clientid":"pubClient","username":"admin","reason":"normal","ts":1588933634} 客户端已掉线:pubClient
SubscribeSample:
topic:mqtt/test Qos:1 message content:hello 哈哈