Can't configure Camera2 API for a preview

I need to set a preview for camera, to use it to scan a QR code, using Camera2 API. My problem is to configure camera. This is my code:

//setting the preview surface layout file

<?xml version="1.0" encoding="utf-8"?>

<SurfaceView
    android:layout_width="250dp"
    android:layout_height="250dp"
    android:id="@+id/surfaceView"
    android:layout_gravity="center"
    android:layout_centerVertical="true"
    android:layout_centerHorizontal="true" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:text="@string/scanqr"
    android:id="@+id/textView"
    android:gravity="center_horizontal"
    android:layout_above="@+id/surfaceView"
    android:layout_centerHorizontal="true" />

In code:

//After I get my CameraDevice...
CameraCharacteristics caracteristicas=cManager.getCameraCharacteristics(chosenCam);
StreamConfigurationMap map = caracteristicas.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
Size[] mPreviewSize = map.getOutputSizes(WHAT TO PUT HERE);
surfaceViewCamera = (SurfaceView)dCamera.findViewById(R.id.surfaceView);       
surfaceViewCamera.getHolder().addCallback(this);

mPreviewRequestBuilder= cDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
Surface surface=surfaceViewCamera.getHolder().getSurface();
mPreviewRequestBuilder.addTarget(surface);
cDevice.createCaptureSession(Arrays.asList(surface),
new CameraCaptureSession.StateCallback(){...onConfigured, onCaptureFailed and onConfigureFailed methods...}

My problem is that I don't know how to configure properly the camera, as always enters the onConfigurationFailed method. Any help to do that? Someone knows any good specific tutorial about that topic?

Thank you.

EDIT:

No luck. My code now looks like this:

CameraCharacteristics caracteristicas=cManager.getCameraCharacteristics(chosenCam);
StreamConfigurationMap map = caracteristicas.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
Size[] mPreviewSize = map.getOutputSizes(ImageFormat.JPEG);
iReader=ImageReader.newInstance(mPreviewSize[0].getWidth(), mPreviewSize[0].getHeight(),ImageFormat.JPEG, 1);
iReader.setOnImageAvailableListener(new ImageReader.OnImageAvailableListener() {
       @Override
       public void onImageAvailable(ImageReader reader) {

               Log.i("TAG", "We have image. Yay!");
                        }
                    }, backgroundHandler);

I don't receive any exception, it only goes to onConfigurationFailed, and says:

06-29 08:20:50.377    1410-1410/my.package E/Legacy-CameraDevice-JNI﹕ LegacyCameraDevice_nativeDetectSurfaceDimens: Could not retrieve native window from surface.
06-29 08:20:50.388    1410-1410/my.package W/CameraDevice-JV-0﹕ Stream configuration failed
06-29 08:20:51.283    1410-1410/my.package E/CameraCaptureSession﹕ Session 0: Failed to create capture session; configuration failed
06-29 08:21:12.179    1410-1410/my.package I/Choreographer﹕ Skipped 26759 frames!  The application may be doing too much work on its main thread.
06-29 08:21:13.424    1410-1416/my.package W/art﹕ Suspending all threads took: 13.264ms
06-29 08:21:20.458    1410-1416/my.package W/art﹕ Suspending all threads took: 12.178ms
06-29 08:21:24.481    1410-1416/my.package W/art﹕ Suspending all threads took: 7.194ms
06-29 08:21:28.496    1410-1416/my.package W/art﹕ Suspending all threads took: 5.281ms
06-29 08:21:34.031    1410-1416/my.package W/art﹕ Suspending all threads took: 7.869ms
06-29 08:21:39.923    1410-1477/my.package I/OpenGLRenderer﹕ Initialized EGL, version 1.4
06-29 08:21:39.989    1410-1477/my.package W/EGL_emulation﹕ eglSurfaceAttrib not implemented
06-29 08:21:39.989    1410-1477/my.package W/OpenGLRenderer﹕ Failed to set EGL_SWAP_BEHAVIOR on surface 0xb4ba9b60, error=EGL_SUCCESS

PD: Im debugging with emulator, just in case it helps