To draw borders we have to understand the basics of layer-list drawable component. An exhaustive guide is provided by Android Developers Guide.
Code snippet to draw top and bottom borders:
#How layer list works?
Above code snippet results in a layer with border on all sides. Stroke tag defines the border and Solid tag defines the background colour.
This snippet is drawn over the first layer which has top offset 2dp and bottom offset 2dp (border thickness)