如何在mapview周围绘制边框

public class CustomMapView extends MapView {

    private Paint borderPaint;

    public CustomMapView(Context context) {
        super(context);
        init();
    }

    public CustomMapView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public CustomMapView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init() {
        borderPaint = new Paint();
        borderPaint.setColor(Color.BLACK);
        borderPaint.setStrokeWidth(5);
        borderPaint.setStyle(Paint.Style.STROKE);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int borderWidth = 10;
        int borderRadius = 10;
        RectF rect = new RectF(borderWidth, borderWidth, getWidth() - borderWidth, getHeight() - borderWidth);
        canvas.drawRoundRect(rect, borderRadius, borderRadius, borderPaint);
    }
}

<com.example.CustomMapView
    android:id="@+id/map_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#FFFFFF" />