How to get the trigger Buttons of a PS4 Controller into Android?

I am trying to get my PS4 Controller as a model into an Android App. Exampels from Androids Developer Page (joysticks and digital buttons) work fine for me. Ichecked this with the Log.e outputs. I don't get the point how to get the values of R2 and L2. On the developers page it is describe this way:

Handle shoulder trigger presses (but provide alternative input methods). Some controllers have left and right shoulder triggers. If these triggers are present, Android reports a left trigger press as an AXIS_LTRIGGER event and a right trigger press as an AXIS_RTRIGGER event. On Android 4.3 (API level 18), a controller that produces a AXIS_LTRIGGER also reports an identical value for the AXIS_BRAKE axis. The same is true for AXIS_RTRIGGER and AXIS_GAS. Android reports all analog trigger presses with a normalized value from 0.0 (released) to 1.0 (fully pressed). Not all controllers have triggers, so consider allowing players to perform those game actions with other buttons.

Adding this line:

float rTrigger = historyPos < 0 ? event.getAxisValue(MotionEvent.AXIS_RTRIGGER) : event.getHistoricalAxisValue(MotionEvent.AXIS_RTRIGGER, historyPos);

to the processJoystickInput(): float rtrigger is alwas 0.0

Really looking forward to get things done.

Thanks

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.InputDevice;
import android.view.KeyEvent;
import android.view.MotionEvent;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        boolean handled = false;
        if ((event.getSource() & InputDevice.SOURCE_GAMEPAD)
                == InputDevice.SOURCE_GAMEPAD) {
            if (event.getRepeatCount() == 0) {

                if (keyCode == 96)
                    Log.e("Taste:", "Square pressed");

                if (keyCode == 97)
                    Log.e("Taste:", "Cross pressed");

                if (keyCode == 98)
                    Log.e("Taste:", "Circle pressed");
            }
            if (handled) {
                return true;
            }
        }
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        boolean handled = false;
        if ((event.getSource() & InputDevice.SOURCE_GAMEPAD)
                == InputDevice.SOURCE_GAMEPAD) {
            if (event.getRepeatCount() == 0) {

                if (keyCode == 96)
                    Log.e("Taste:", "Square released");

                if (keyCode == 97)
                    Log.e("Taste:", "X released");

                if (keyCode == 98)
                    Log.e("Taste:", "Circle released");
            }
            if (handled) {
                return true;
            }
        }
        return super.onKeyDown(keyCode, event);
    }


    @Override
    public boolean onGenericMotionEvent(MotionEvent event) {


        // Check that the event came from a game controller
        if ((event.getSource() & InputDevice.SOURCE_JOYSTICK) ==
                InputDevice.SOURCE_JOYSTICK &&
                event.getAction() == MotionEvent.ACTION_MOVE) {


            // Process all historical movement samples in the batch
            final int historySize = event.getHistorySize();

            // Process the movements starting from the
            // earliest historical position in the batch
            for (int i = 0; i < historySize; i++) {
                // Process the event at historical position i
                processJoystickInput(event, i);
            }

            // Process the current movement sample in the batch (position -1)
            processJoystickInput(event, -1);
            return true;
        }
        return super.onGenericMotionEvent(event);
    }


    private void processJoystickInput(MotionEvent event,
                                      int historyPos) {

        InputDevice mInputDevice = event.getDevice();

        // Calculate the horizontal distance to move by
        // using the input value from one of these physical controls:
        // the left control stick, hat axis, or the right control stick.
        float lx = getCenteredAxis(event, mInputDevice,
                MotionEvent.AXIS_X, historyPos);

        float rx = getCenteredAxis(event, mInputDevice,
                MotionEvent.AXIS_Z, historyPos);

        float ly = getCenteredAxis(event, mInputDevice,
                MotionEvent.AXIS_Y, historyPos);

        float ry = getCenteredAxis(event, mInputDevice,
                MotionEvent.AXIS_RZ, historyPos);


        Log.e("LX:", lx + "");
        Log.e("LY:", ly + "");
        Log.e("RX:", rx + "");
        Log.e("RY:", ry + "");
    }

    private static float getCenteredAxis(MotionEvent event,
                                         InputDevice device, int axis, int historyPos) {
        final InputDevice.MotionRange range =
                device.getMotionRange(axis, event.getSource());

        // A joystick at rest does not always report an absolute position of
        // (0,0). Use the getFlat() method to determine the range of values
        // bounding the joystick axis center.
        if (range != null) {
            final float flat = range.getFlat();
            final float value =
                    historyPos < 0 ? event.getAxisValue(axis) :
                            event.getHistoricalAxisValue(axis, historyPos);

            // Ignore axis values that are within the 'flat' region of the
            // joystick axis center.
            if (Math.abs(value) > flat) {
                return value;
            }
        }
        return 0;
    }
}

Solved the problem myself. The trigger buttons are matched to Axis_RX and Axis_RY