Anybody, please explain the differences between a SaaS App and Web App. Also how can we make a Java Web App, a SaaS App?
Short answer, a web application can be provisioned as a software service (SaaS).
I suggest reading the series of Wisdom of the Clouds to get a in-depth and time-wise developments through time on the evolution of IaaS, SaaS, and PaaS.
For me Saas (Software as a Service) is when you provide your application without any infrastructure requirement from the client, so the client could use your software without take care about the systems that support your software. A web app is a Saas application if the application runs in the provider infrastructure.