There are four parts to the java gadget servers:

* java/common The common java code that both the social data server and the
  gadget rendering server rely on.

* java/gadgets This server is used for rendering gadgets.

* java/social-api This server is used to provide social data for gadgets. Long
  term, it will implement the OpenSocial RESTful apis.

* java/server This directory only contains a pom and a web.xml file. It is used
  to run both the gadget rendering code and the social data code at once. In
  order to use the samplecontainer you must run this server.

For more information, see http://incubator.apache.org/projects/shindig.html