This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
This can be achieved using EJB session beans. EJB3 session beans can be exposed as web service, remote method or local method. Use servlet as EJB client. Using web service, client can be any application .NET application, remote think client application in any language or any web application or mobile application. In case of Remote EJB, client can be any client in java.