How to save image in application files?

Question

Android

Good afternoon, dear reader!
There is a code that generates a QR code:

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

        etInput = findViewById(R.id.et_input);
        btGenerate = findViewById(R.id.bt_generate);
        ivOutput = findViewById(R.id.iv_output);

        btGenerate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String sText = etInput.getText().toString().trim();
                MultiFormatWriter writer = new MultiFormatWriter();
                try {
                    BitMatrix matrix = writer.encode(sText, BarcodeFormat.QR_CODE,
                            350, 350);
                    BarcodeEncoder encoder = new BarcodeEncoder();
                    Bitmap bitmap = encoder.createBitmap(matrix);
                    ivOutput.setImageBitmap(bitmap);
                    InputMethodManager manager = (InputMethodManager) getSystemService(
                            Context.INPUT_METHOD_SERVICE
                    );
                    manager.hideSoftInputFromWindow(etInput.getApplicationWindowToken()
                    ,0);
                    btGenerate.setVisibility(View.INVISIBLE);
                    etInput.setVisibility(View.INVISIBLE);
                } catch (WriterException e) {
                    e.printStackTrace();
                }
            }
        });

    }

I need to save the image to the application files after generation and network it to the widget when the application is reloaded. If someone came across, tell me with an example of my code. I will be very grateful!