how to do a file chooser for Android mode.

Hello, I am very new to Android and Processing. The thing I am trying to do is. 1: App start on Android physical device with a default image. 2: User tap or press a button to choose an imag from Android device and replace the image from step 1, then, draw this selected image on Android device.

I am stuck here, since, Processing build in selectInput() does not work with Android mode, hence, I have to cook my own file chooser. Google the Android development, found something:

            private static final int READ_REQUEST_CODE = 42;
            /**
             * Fires an intent to spin up the "file chooser" UI and select an image.
             */

            public void performFileSearch() {

              // ACTION_OPEN_DOCUMENT is the intent to choose a file via the system's file
              // browser.
              Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
              // Filter to only show results that can be "opened", such as a
              // file (as opposed to a list of contacts or timezones)
              intent.addCategory(Intent.CATEGORY_OPENABLE);

              // Filter to show only images, using the image MIME data type.
              // If one wanted to search for ogg vorbis files, the type would be "audio/ogg".
              // To search for all documents available via installed storage providers,
              // it would be "*/*".
              intent.setType("image/*");

              startActivityForResult(intent, READ_REQUEST_CODE);

              //Uri selectedImageUri = intent.getData();
              //docUri = DocumentsContract.buildDocumentUriUsingTree(selectedImageUri, DocumentsContract.getTreeDocumentId(selectedImageUri));

            }

but, when I paste this into processing (3.2.3) window, and imported the suggested lib, processing still gives me errors "The global variable "ACTION_OPEN_DOCUMENT" does not exit.

further reading android dev article,

            @Override
            public void onActivityResult(int requestCode, int resultCode,
                    Intent resultData) {

                // The ACTION_OPEN_DOCUMENT intent was sent with the request code
                // READ_REQUEST_CODE. If the request code seen here doesn't match, it's the
                // response to some other intent, and the code below shouldn't run at all.

                if (requestCode == READ_REQUEST_CODE && resultCode == Activity.RESULT_OK) {
                    // The document selected by the user won't be returned in the intent.
                    // Instead, a URI to that document will be contained in the return intent
                    // provided to this method as a parameter.
                    // Pull that URI using resultData.getData().
                    Uri uri = null;
                    if (resultData != null) {
                        uri = resultData.getData();
                        //Log.i(TAG, "Uri: " + uri.toString());
                        //showImage(uri);
                        path = uri.toString();//my edit
                        img = loadImage(path);// this is what I want.
                    }
                }
            }

how can I put above codes into a function processing sketch which can run on Android device?

I have been struggling with this "file chooser" for 3 days, please help.

Thank you for your help.