ConnectMQTT.java

private void connect() {
 MqttConnectOptions mqttConnectOptions = new MqttConnectOptions();
 mqttConnectOptions.setAutomaticReconnect(true);
 mqttConnectOptions.setCleanSession(false);
 mqttConnectOptions.setUserName(username);
 mqttConnectOptions.setPassword(password.toCharArray());
 try {
  mqttAndroidClient.connect(mqttConnectOptions, null, new IMqttActionListener() {
  
  @Override
  public void onSuccess(IMqttToken asyncActionToken) {
    DisconnectedBufferOptions disconnectedBufferOptions = new DisconnectedBufferOptions();
    disconnectedBufferOptions.setBufferEnabled(true);
    disconnectedBufferOptions.setBufferSize(100);
    disconnectedBufferOptions.setPersistBuffer(false);
    disconnectedBufferOptions.setDeleteOldestMessages(false);
    mqttAndroidClient.setBufferOpts(disconnectedBufferOptions);
    subscribeToTopic();
  }
  
  @Override
  public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
    Log.d(TAG, "Failed to connect to: " + serverUri + exception.toString());
  }
  
 });
} catch (Exception e) {
  e.printStackTrace();
 }
}