How to rapidly build a Web Application?
Speaking only in terms of speed of development, Ruby on Rails is the fastest one out there.
To build a Web Application, what kind of open source web application frameworks / technologies are currently present that would be:  

Faster to learn.  
Ease of use.   
Have widgets for rapid development(From a GUI perspective).  
Database integration.

I would want this web app to communicate to a Java client.
I am not bound to Java on the server side and free to try out any good rapid application framework.
To summarize, I haven't done much work for the server side hence am not conversant with the tools and technologies for the same.
What would you suggest?
Any and every input would be welcome!...