一，在app下的build.gradle中添加如下引用

    implementation 'org.eclipse.paho:org.eclipse.paho.client.mqttv3:1.1.0'//mqtt相关
    implementation 'org.eclipse.paho:org.eclipse.paho.android.service:1.1.1'//mqtt相关
    implementation 'org.greenrobot:eventbus:3.1.1'//eventBus  为了传数据会UI界面

二，AndroidManifest.xml中添加权限

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />

在application中添加如下代码

   <service android:name="org.eclipse.paho.android.service.MqttService" /> <!--MqttService-->
   <service android:name=".service.MyMqttService"/> <!--MyMqttService  自己写的服务  后面会讲-->

三，MyMqttService类

public class MyMqttService extends Service {

    public final String TAG = MyMqttService.class.getSimpleName();
    private static MqttAndroidClient mqttAndroidClient;
    private MqttConnectOptions mMqttConnectOptions;
    public String HOST = "tcp://192.168.101.115:1883";//服务器地址（协议+地址+端口号）
    public String USERNAME = "admin";//用户名
    public String PASSWORD = "admin";//密码
    public static String PUBLISH_TOPIC = "tourist_enter";//发布主题
    public static String RESPONSE_TOPIC = "message_arrived";//响应主题
    public String CLIENTID = "zhangrenwen";
//    public String CLIENTID = Build.VERSION.SDK_INT >= Build.VERSION_CODES.O
//            ? Build.getSerial() : Build.SERIAL;//客户端ID，一般以客户端唯一标识符表示，这里用设备序列号表示

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        init();
        return super.onStartCommand(intent, flags, startId);
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    /**
     * 开启服务
     */
    public static void startService(Context mContext) {
        mContext.startService(new Intent(mContext, MyMqttService.class));
    }

    /**
     * 发布 （模拟其他客户端发布消息）
     *
     * @param message 消息
     */
    public static void publish(String message) {
        String topic = PUBLISH_TOPIC;
        Integer qos = 2;
        Boolean retained = false;
        try {
            //参数分别为：主题、消息的字节数组、服务质量、是否在服务器保留断开连接后的最后一条消息
            mqttAndroidClient.publish(topic, message.getBytes("GBK"), qos.intValue(), retained.booleanValue());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 响应 （收到其他客户端的消息后，响应给对方告知消息已到达或者消息有问题等）
     *
     * @param message 消息
     */
    public void response(String message) {
        String topic = RESPONSE_TOPIC;
        Integer qos = 2;
        Boolean retained = false;
        try {
            //参数分别为：主题、消息的字节数组、服务质量、是否在服务器保留断开连接后的最后一条消息
            mqttAndroidClient.publish(topic, message.getBytes(), qos.intValue(), retained.booleanValue());
        } catch (MqttException e) {
            e.printStackTrace();
        }
    }

    /**
     * 初始化
     */
    private void init() {
        String serverURI = HOST; //服务器地址（协议+地址+端口号）
        mqttAndroidClient = new MqttAndroidClient(this, serverURI, CLIENTID);
        mqttAndroidClient.setCallback(mqttCallback); //设置监听订阅消息的回调
        mMqttConnectOptions = new MqttConnectOptions();
        mMqttConnectOptions.setCleanSession(true); //设置是否清除缓存
        mMqttConnectOptions.setConnectionTimeout(10); //设置超时时间，单位：秒
        mMqttConnectOptions.setKeepAliveInterval(20); //设置心跳包发送间隔，单位：秒
        mMqttConnectOptions.setUserName(USERNAME); //设置用户名
        mMqttConnectOptions.setPassword(PASSWORD.toCharArray()); //设置密码

        // last will message
        boolean doConnect = true;
        String message = "{\"terminal_uid\":\"" + CLIENTID + "\"}";
        String topic = PUBLISH_TOPIC;
        Integer qos = 2;
        Boolean retained = false;
        if ((!message.equals("")) || (!topic.equals(""))) {
            // 最后的遗嘱
            try {
                mMqttConnectOptions.setWill(topic, message.getBytes(), qos.intValue(), retained.booleanValue());
            } catch (Exception e) {
                Log.i(TAG, "Exception Occured", e);
                doConnect = false;
                iMqttActionListener.onFailure(null, e);
            }
        }
        if (doConnect) {
            doClientConnection();
        }
    }

    /**
     * 连接MQTT服务器
     */
    private void doClientConnection() {
        if (!mqttAndroidClient.isConnected() && isConnectIsNomarl()) {
            try {
                mqttAndroidClient.connect(mMqttConnectOptions, null, iMqttActionListener);
            } catch (MqttException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 判断网络是否连接
     */
    private boolean isConnectIsNomarl() {
        ConnectivityManager connectivityManager = (ConnectivityManager) this.getApplicationContext().getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo info = connectivityManager.getActiveNetworkInfo();
        if (info != null && info.isAvailable()) {
            String name = info.getTypeName();
            Log.i(TAG, "当前网络名称：" + name);
            return true;
        } else {
            Log.i(TAG, "没有可用网络");
            /*没有可用网络的时候，延迟3秒再尝试重连*/
            new Handler().postDelayed(new Runnable() {
                @Override
                public void run() {
                    doClientConnection();
                }
            }, 3000);
            return false;
        }
    }

    //MQTT是否连接成功的监听
    private IMqttActionListener iMqttActionListener = new IMqttActionListener() {

        @Override
        public void onSuccess(IMqttToken arg0) {
            Log.i(TAG, "连接成功 ");
            try {
                mqttAndroidClient.subscribe(PUBLISH_TOPIC, 2);//订阅主题，参数：主题、服务质量
            } catch (MqttException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onFailure(IMqttToken arg0, Throwable arg1) {
            arg1.printStackTrace();
            Log.i(TAG, "连接失败 ");
            doClientConnection();//连接失败，重连（可关闭服务器进行模拟）
        }
    };

    //订阅主题的回调
    private MqttCallback mqttCallback = new MqttCallback() {

        @Override
        public void messageArrived(String topic, MqttMessage message) throws Exception {
            Log.i(TAG, "收到消息： " + topic + new String(message.getPayload(),"GBK"));
            EventBus.getDefault().post(new UpdateTextEvent(new String(message.getPayload(),"GBK")));
            //收到消息，这里弹出Toast表示。如果需要更新UI，可以使用广播或者EventBus进行发送
//            Toast.makeText(getApplicationContext(), "messageArrived: " + new String(message.getPayload()), Toast.LENGTH_LONG).show();
            //收到其他客户端的消息后，响应给对方告知消息已到达或者消息有问题等
            response("message arrived");
        }


        @Override
        public void deliveryComplete(IMqttDeliveryToken arg0) {

        }

        @Override
        public void connectionLost(Throwable arg0) {
            Log.i(TAG, "连接断开 ");
            doClientConnection();//连接断开，重连
        }
    };

    @Override
    public void onDestroy() {
        try {
            mqttAndroidClient.disconnect(); //断开连接
            Log.i(TAG, "onDestroy: 服务关闭");
        } catch (MqttException e) {
            e.printStackTrace();
        }
        super.onDestroy();
    }
}

四，封装数据bean类

public class UpdateTextEvent {
    private static final String TAG = "AA";
    private String msg;

    public UpdateTextEvent(String msg) {
        this.msg = msg;
        Log.i(TAG, "updateTextEvent: " + msg);
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

五，activity_main.xml布局

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="发送"
        app:layout_constraintTop_toBottomOf="@+id/editText"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        />
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintTop_toBottomOf="@+id/button"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        />

</android.support.constraint.ConstraintLayout>

六，MainActivity代码

public class MainActivity extends AppCompatActivity {

    TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final EditText editText = findViewById(R.id.editText);

        textView = findViewById(R.id.textView);
        MyMqttService.startService(this); //开启服务
        findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                MyMqttService.publish(editText.getText().toString());
            }
        });
    }

    /**
     * 订阅的过程中，默认是在主线程中用到的
     */
    @Subscribe(threadMode = ThreadMode.MAIN)
    public void modifyBtn4(UpdateTextEvent msg) {
        textView.setText("收到的消息："+msg.getMsg());
    }

    @Override
    public void onStart() {
        super.onStart();
        //在事件被订阅的界面中注册EventBus
        EventBus.getDefault().register(this);
    }

    @Override
    public void onStop() {
        super.onStop();
        //注销EventBus
        EventBus.getDefault().unregister(this);
    }
}

至此 已经完毕 但是想要测试效果请联系后台
我们根据后台修改以下框框内容就好

QQ截图20190828151833.png