I'm new in Android development in geoserver's WMS map.
Can I get .jar file of GeoServer's WMS layer?
I couln't open it though I tried https://github.com/shalperin/android-wms.git
You can download and compile all of GeoServer from github.com/geoserver or as a zip file from geoserver.org. However, it will probably not work on android machines as it (and the underlying GeoTools library) are not designed to work on android.