How should I store the content read from intent into a string using java in android studio?

Question

I am developing an app that consists of a button to read a file from android device with java on click and then I want to use that input file for further process. I want to store that file as string.

I tried several methods with InputStream and BufferedReader but none of them worked!

Below is my intent part to read text/ csv file:

//Button for choosing file from device
Button button = (Button) findViewById(R.id.button);
InputStream inputstream = null;
button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        //Onclick action of the button
        Intent intent = new Intent(MainActivity.this, FilePickerActivity.class);
        intent.putExtra(FilePickerActivity.CONFIGS,new Configurations.Builder()
        .setCheckPermission(true)
        .setShowFiles(true)
        .setShowImages(false)
        .setShowVideos(false)
        .setMaxSelection(1)
        .setSuffixes("txt","csv")
        .setSkipZeroSizeFiles(true)
        .build());
        startActivityForResult(intent,102);

    }

});

Then i used code below for getting path of file selected;

protected void onActivityResult(int requestCode, int resultCode, @Nullable @org.jetbrains.annotations.Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (resultCode == RESULT_OK && data!=null){
        ArrayList<MediaFile> mediaFiles = data.getParcelableArrayListExtra(
                FilePickerActivity.MEDIA_FILES
        );
        String path = mediaFiles.get(0).getPath();
        TextView tv1 = (TextView) findViewById(R.id.textView9);

        tv1.setText("File Path: "+path);

        Toast.makeText(MainActivity.this, "File Selected", Toast.LENGTH_SHORT).show();
    }
}

I want to store the content of this file chosen in a string str.