'Android Design' site is recommending 'Boundary feedback' for scrollable view. http://developer.android.com/design/style/touch-feedback.html
https://i.sstatic.net/TuBkX.png
is there any API or library for custom view to implement that with ease and consistent? or should I implement it from the scratch?
Are you "building custom"? If you stick to the UI elements form the API you should be fine. All the scroll views can already be configured to do different things for boundry cases (such as overscroll).
If you are building UI elements from scratch, you might consider simply overriding or subclassing existing UI elements to function the way you want. If not, you can examine the source to see how different boundry cases (again overscrolling) are implemented. But, I get the feeling you're in the first category..
