The shared server has it's own set configuration in regards to how java environments run on the server since it has to be configured in a set manner to ensure that it does not cause any resource or stability issues . Servlets are uploaded to WEB-INF directory then it is expanded by the server. You do need to make sure you have defined the classes on your servlets. Any incorrect paths to classes can cause issues.  You also want to ensure that what ever servlet is being ran meets a shared server system requirements as often development of them are done on dedicated environments. The best option is contacting support in assistance to getting the information.