Is it possible to get source codes of all implemented wps processes? I want to create one big chained process in Java instead of using WPS builder.
You can find the GeoServer source at https://github.com/geoserver/geoserver
Some community contributions are in https://github.com/geoserver/geoserver/tree/master/src/community
You will be able to find the free and open-source plugins in there.