前言
主要讲下Android如何使用MQTT通讯。用到的软件或者框架有：
EMQ：https://www.emqx.io/cn/
org.eclipse.paho的MQTT通讯框架：https://github.com/eclipse/paho.mqtt.android
如果已经有MQTT相关服务，可以跳过第一项，从第二项开始看。
一、安装EMQ及启动EMQ
1.安装所需要的依赖包
$ sudo yum install -y yum-utils device-mapper-persistent-data lvm2
2.使用以下命令设置稳定存储库，以 CentOS7 为例
$ sudo yum-config-manager --add-repo https://repos.emqx.io/emqx-ce/redhat/centos/7/emqx-ce.repo
3.安装最新版本的 EMQ X
$ sudo yum install emqx
4.安装特定版本的 EMQ X
- 查询可用版本
$ yum list emqx --showduplicates | sort -r
emqx.x86_64 3.1.0-1.el7 emqx-stable
emqx.x86_64 3.0.1-1.el7 emqx-stable
emqx.x86_64 3.0.0-1.el7 emqx-stable
- 根据第二列中的版本字符串安装特定版本，例如 3.1.0
$ sudo yum install emqx-3.1.0
5.启动 EMQ X
- 直接启动
$ emqx start
emqx 3.1.0 is started successfully!
$ emqx_ctl status
Node '[email protected]' is started
emqx v3.1.0 is running
- systemctl 启动
$ sudo systemctl start emqx
- service 启动
$ sudo service emqx start
EMQ管理后台
地址：xxx.xxx.xxx:18083，地址为服务器ip或者域名，端口为18083端口
image.png
二、Android使用MQTT
1.在Android中导入依赖
implementation 'org.eclipse.paho:org.eclipse.paho.android.service:1.1.1'
implementation 'org.eclipse.paho:org.eclipse.paho.client.mqttv3:1.2.0'
项目地址：https://github.com/eclipse/paho.mqtt.android
2.创建MQTT连接的一个Service
public class MqttMessageService extends Service {
/**
* 订阅的主题
*/
private String subTopic;
@Override
public void onCreate() {
super.onCreate();
//初始化mqtt配置
initMqtt();
//连接mqtt
connectMqtt();
}
/**
* 连接mqtt
*/
private void connectMqtt() {
try {
mqttAndroidClient.connect(mqttConnectOptions, null, new IMqttActionListener() {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
}
@Override
public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
LogUtils.e("MQTT连接失败！！！！" + exception.getCause());
new Thread(new Runnable() {
@Override
public void run() {
LogUtils.e("30s后，尝试重新连接" );
try {
Thread.sleep(1000*30);
} catch (InterruptedException e) {
e.printStackTrace();
}
connectMqtt();
}
}).start();
}
});
} catch (MqttException e) {
e.printStackTrace();
}
}
/**
* mqtt初始化
*/
private void initMqtt() {
try {
//写上自己的url
String uri = "";
subTopic = "topic_test" ;
mqttAndroidClient = new MqttAndroidClient(
getApplicationContext(),
uri, "test");
mqttAndroidClient.setCallback(new MqttCallbackExtended() {
@Override
public void connectComplete(boolean reconnect, String serverURI) {
if (reconnect) {
LogUtils.i("MQTT重新连接成功！serverURI:" + serverURI);
} else {
LogUtils.i("MQTT连接成功！serverURI:" + serverURI);
}
subscribeAllTopics();
}
@Override
public void connectionLost(Throwable cause) {
LogUtils.i("MQTT连接断开！" + cause.getCause());
}
@Override
public void messageArrived(String topic, MqttMessage message) {
LogUtils.i("收到了消息："+topic+ message.toString()+ message.getQos());
}
@Override
public void deliveryComplete(IMqttDeliveryToken token) {
try {
// MqttMessage mqttMessage = token.getMessage();
// LogUtils.i("消息发送成功:" + mqttMessage.toString());
} catch (MqttException e) {
e.printStackTrace();
}
}
});
// 新建连接设置
mqttConnectOptions = new MqttConnectOptions();
mqttConnectOptions.setUserName(MqttConfig.EMQ_USERNAME);
mqttConnectOptions.setPassword(MqttConfig.EMQ_PASSWORD.toCharArray());
//断开后，是否自动连接
mqttConnectOptions.setAutomaticReconnect(true);
//是否清空客户端的连接记录。若为true，则断开后，broker将自动清除该客户端连接信息
mqttConnectOptions.setCleanSession(true);
//设置超时时间，单位为秒
mqttConnectOptions.setConnectionTimeout(15);
//心跳时间，单位为秒。即多长时间确认一次Client端是否在线
mqttConnectOptions.setKeepAliveInterval(30);
//允许同时发送几条消息（未收到broker确认信息）
mqttConnectOptions.setMaxInflight(30);
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 订阅所有主题
*/
private void subscribeAllTopics() {
//订阅主消息主题和更新消息主题
subscribeToTopic(subTopic , 2);
}
/**
* 订阅一个主主题
*
* @param subTopic 主题名称
*/
private void subscribeToTopic(String subTopic, int qos) {
try {
mqttAndroidClient.subscribe(subTopic, qos, null, new IMqttActionListener() {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
LogUtils.i("MQTT订阅消息成功：" + subTopic);
}
@Override
public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
LogUtils.d("MQTT订阅消息失败！" + subTopic);
}
});
} catch (MqttException ex) {
LogUtils.d("subscribeToTopic: Exception whilst subscribing");
ex.printStackTrace();
}
}
/**
* 发布主题
*
* @param topic 主题
* @param msg 内容
* @param qos qos
*/
public void publishMessage(String topic, String msg, int qos) {
if (mqttAndroidClient != null && mqttAndroidClient.isConnected()) {
try {
LogUtils.d("publishMessage: 发送" + msg);
mqttAndroidClient.publish(topic, msg.getBytes(), qos, false);
} catch (Exception e) {
LogUtils.e("publishMessage: Error Publishing: " + e.getMessage());
e.printStackTrace();
}
} else {
LogUtils.e("publishMessage失败，MQTT未连接 ");
}
}
public void publishMessage(String topic, String msg) {
publishMessage(topic, msg, 2);
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
return Service.START_NOT_STICKY;
}
@Override
public void onDestroy() {
LogUtils.e("关闭MQTT");
//断开mqtt连接
try {
if (mqttAndroidClient != null && mqttAndroidClient.isConnected()) {
mqttAndroidClient.disconnect();
mqttAndroidClient.unregisterResources();
}
} catch (Exception e) {
e.printStackTrace();
}
super.onDestroy();
}
}