当wifi断开连接且无法重新连接时，java应用程序、服务和mqtt崩溃

2 月，3 周 Questions & Answers 990

我正在制作一个带有mqtt客户端和后台服务的应用程序，当我收到某个mqtt消息时，后台服务会发出通知

我使用泛美卫生组织图书馆和服务作为客户，只要我连接到wifi，并且经纪人处于开启状态，一切都能完美运行

我不想通过互联网访问代理，因此当没有可用的wifi时，客户端会断开连接，问题是当wifi再次连接时，mqtt客户端不会重新连接

我尝试了很多方法，但最新的测试是让处理程序检查是否有互联网，是否通过wifi，如果是，我再次启动mqtt服务器

我在清单中有以下权限：

    安卓.permission.INTERNET"
    安卓:name="安卓.permission.ACCESS_NETWORK_STATE"
    安卓.permission.WAKE_LOCK"

当我运行模拟器并断开wifi连接时，整个应用程序以及服务崩溃，错误如下

这是我正在使用的处理程序：

    handler.postDelayed(new Runnable(){
        public void run(){
            if (isWifiConnected()) {
                startMqtt();
            }

            handler.postDelayed(this, delay);
        }
    }, delay);

以下是isWifiConnected（如果我没有在应用程序中添加^{，context.getSystemService就无法工作，我不知道这是否也是一个问题）：

    private boolean isWifiConnected() {
        boolean isWifi;
        ConnectivityManager cm = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
        boolean isConnected = activeNetwork != null && activeNetwork.isConnectedOrConnecting();

        return isWifi = activeNetwork.getType() == ConnectivityManager.TYPE_WIFI;
    }

D/AlarmPingSender: Unregister alarmreceiver to MqttServicephone
W/Mqtt: Failed to connect to: tcp://192.168.1.39:1883Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /192.168.1.39 (port 1883) from /:: (port 0) after 30000ms: connect failed: ENETUNREACH (Network is unreachable)
I/chatty: uid=10085(com.iteda.nome) identical 85 lines
W/Mqtt: Failed to connect to: tcp://192.168.1.39:1883Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /192.168.1.39 (port 1883) from /:: (port 0) after 30000ms: connect failed: ENETUNREACH (Network is unreachable)
W/Mqtt: Failed to connect to: tcp://192.168.1.39:1883Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /192.168.1.39 (port 1883) from /:: (port 0) after 30000ms: connect failed: ENETUNREACH (Network is unreachable)
I/chatty: uid=10085(com.iteda.nome) identical 4 lines
W/Mqtt: Failed to connect to: tcp://192.168.1.39:1883Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /192.168.1.39 (port 1883) from /:: (port 0) after 30000ms: connect failed: ENETUNREACH (Network is unreachable)
W/Mqtt: Failed to connect to: tcp://192.168.1.39:1883Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /192.168.1.39 (port 1883) from /:: (port 0) after 30000ms: connect failed: ENETUNREACH (Network is unreachable)
I/chatty: uid=10085(com.iteda.nome) identical 36 lines
W/Mqtt: Failed to connect to: tcp://192.168.1.39:1883Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /192.168.1.39 (port 1883) from /:: (port 0) after 30000ms: connect failed: ENETUNREACH (Network is unreachable)
W/Mqtt: Failed to connect to: tcp://192.168.1.39:1883Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /192.168.1.39 (port 1883) from /:: (port 0) after 30000ms: connect failed: ENETUNREACH (Network is unreachable)
I/chatty: uid=10085(com.iteda.nome) identical 17 lines
W/Mqtt: Failed to connect to: tcp://192.168.1.39:1883Unable to connect to server (32103) - java.net.ConnectException: failed to connect to /192.168.1.39 (port 1883) from /:: (port 0) after 30000ms: connect failed: ENETUNREACH (Network is unreachable)
I/MqttConnection: Requesting Automatic reconnect using New Java AC
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.iteda.nome, PID: 7394
    java.lang.RuntimeException: Error receiving broadcast Intent { act=安卓.net.conn.CONNECTIVITY_CHANGE flg=0x4200010 (has extras) } in org.eclipse.paho.安卓.service.MqttService$NetworkConnectionIntentReceiver@5224905
        at 安卓.app.LoadedApk$ReceiverDispatcher$Args.lambda$getRunnable$0(LoadedApk.java:1401)
        at 安卓.app.-$$Lambda$LoadedApk$ReceiverDispatcher$Args$_BumDX2UKsnxLVrE6UJsJZkotuA.run(Unknown Source:2)
        at 安卓.os.Handler.handleCallback(Handler.java:873)
        at 安卓.os.Handler.dispatchMessage(Handler.java:99)
        at 安卓.os.Looper.loop(Looper.java:193)
        at 安卓.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.安卓.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void java.util.Timer.cancel()' on a null object reference
        at org.eclipse.paho.client.mqttv3.MqttAsyncClient.stopReconnectCycle(MqttAsyncClient.java:1120)
        at org.eclipse.paho.client.mqttv3.MqttAsyncClient.reconnect(MqttAsyncClient.java:1057)
        at org.eclipse.paho.安卓.service.MqttConnection.reconnect(MqttConnection.java:1049)
        at org.eclipse.paho.安卓.service.MqttService.reconnect(MqttService.java:342)
        at org.eclipse.paho.安卓.service.MqttService$NetworkConnectionIntentReceiver.onReceive(MqttService.java:827)
        at 安卓.app.LoadedApk$ReceiverDispatcher$Args.lambda$getRunnable$0(LoadedApk.java:1391)
        at 安卓.app.-$$Lambda$LoadedApk$ReceiverDispatcher$Args$_BumDX2UKsnxLVrE6UJsJZkotuA.run(Unknown Source:2) 
        at 安卓.os.Handler.handleCallback(Handler.java:873) 
        at 安卓.os.Handler.dispatchMessage(Handler.java:99) 
        at 安卓.os.Looper.loop(Looper.java:193) 
        at 安卓.app.ActivityThread.main(ActivityThread.java:6669) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.安卓.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:858) 
I/Process: Sending signal. PID: 7394 SIG: 9
Application terminated.

我知道你可能想要更多的信息，所以与其让我用错误的代码轰炸，不如告诉我你需要什么来证明我做错了什么：）

错误代码似乎给出了答案，但因为我对安卓和java非常陌生。我不知道如何改变方法使其正确

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共 (1) 个答案

# 1 楼答案

你说：

the problem is that when the wifi connects again the mqtt client wont reconnect.

您只需在Service#onCreate()方法中使用一个BroadcastReceiver来监听WIFI_STATE_CHANGED_ACTION操作，如下所示
你还必须在Service#onStartCommand()中使用return START_STICKY，这样，服务类将在应用程序关闭后运行

服务类别：

public class MQTTService extends Service {

private MqttAndroidClient clientPhone;

@Override
  public void onCreate() {
    super.onCreate();
    registerReceiver();
    new Thread(() -> init()).start();
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    //do something
    return START_STICKY;
}

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

private void registerReceiver(){
    m_ScreenOffReceiver = new BroadcastReceiver(){
        @Override
        public void onReceive(final Context context, Intent intent){
            //Log.d(TAG,"onReceive of Wifi_State_Change called");
            if(intent.getAction().equals(WifiManager.WIFI_STATE_CHANGED_ACTION))
            {
                int wifiState = intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE, WifiManager.WIFI_STATE_UNKNOWN);
                if(wifiState != WifiManager.WIFI_STATE_ENABLED)
                    return;

                final WifiManager wifiManager = (WifiManager) context.getApplicationContext().getSystemService(Context.WIFI_SERVICE);
                new Handler().postDelayed(() -> {
                        WifiInfo wifiInfo = wifiManager.getConnectionInfo();
                        String ssid = wifiInfo.getSSID();
                        //Toast.makeText(context, "active wifi:"+ssid, Toast.LENGTH_SHORT).show();

                        //You can connect to the your mqtt broker again:
                        connectMQTT();
                }, 10000);
            }
        }
    };

    IntentFilter intentFilter = new IntentFilter();
    intentFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);
    registerReceiver(m_ScreenOffReceiver, intentFilter);
}

private void init() {

    clientPhone = new MqttAndroidClient(this, "tcp://IP:PORT", "Your-CLIENT-ID");       
    //clientPhone = new MqttAndroidClient(this, "ssl://IP:PORT", "Your-CLIENT-ID");

    clientPhone.setCallback(new MqttCallback() {
        @Override
        public void connectionLost(Throwable cause) {
            //do something - for example reconnnect again
        }

        @Override
        public void messageArrived(String topic, MqttMessage message) throws Exception {
            //you can do everything with the received message from broker here
        }

        @Override
        public void deliveryComplete(IMqttDeliveryToken token) {
            //do something
        }
    });
}

private MqttConnectOptions getOptions(){

    if(clientPhone.getServerURI().contains("ssl")) {
        //set ssl config.for example:
                //options.setSocketFactory(clientPhone.getSSLSocketFactory(YOUR_KEYSTORE_FILE, "YOUR_KEYSTORE_PASSWORD"));
                //...
    }
    options.setKeepAliveInterval(...);
    options.setMqttVersion(MqttConnectOptions.MQTT_VERSION_3_1_1);
    options.setAutomaticReconnect(true);
    options.setCleanSession(...);
    //options.setWill(...);
    options.setUserName(...));
    options.setPassword(...);
    return options;
}

private void connectMQTT() {
    try {
        //getOptions is a method that returns your MqttConnectOptions object
        IMqttToken token = clientPhone.connect(getOptions());
        token.setActionCallback(new IMqttActionListener() {
            @Override
            public void onSuccess(IMqttToken asyncActionToken) {
                //do something
            }
            @SuppressWarnings("ThrowableResultOfMethodCallIgnored")
            @Override
            public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
                //do something
            }
        });
    } catch (MqttException e) {
                //do something
        e.printStackTrace();
    }
}


@Override
public void onDestroy() {
    if(clientPhone!=null) {
        /*unregisterResources is needed,otherwise receive this error:
          has leaked ServiceConnection org.eclipse.paho.android.service.MqttAndroidClient*/
        try {
            clientPhone.unregisterResources();
            clientPhone.close();
            clientPhone.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    unregisterReceiver(m_ScreenOffReceiver);
    m_ScreenOffReceiver = null;
        ...
    super.onDestroy();
}

}

您必须在清单文件中声明org.eclipse.paho.android.service.MqttService和Your Service Class：

<service
            android:name="org.eclipse.paho.android.service.MqttService"
            android:enabled="true" />
<service
            android:name="YOUR-MQTT-SERVICE-CLASS"
            android:enabled="true"
            android:exported="false" />

我希望这对你有帮助
祝福

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当wifi断开连接且无法重新连接时，java应用程序、服务和mqtt崩溃

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# 1 楼答案