How to rapidly build a Web Application?
I would say part of the learning curve will go into understanding concepts. I have been learning about web-apps for some months now, and with my improved understanding of concepts right now, most frameworks show very much similarities. Here are my results so far:

PHP:  Great to learn about concepts for doing forms, http-post-requests, http-get-requests. easy interaction with database layer, and it is possible to obtain a working basic application in couple of hours. Almost no hassle with build-systems and web-server configuration.
Ruby-on-Rails:  Great to learn about REST and more complicated CRUD applications. Great to learn about the complexity behind MVC and especially simple and powerful interaction with the database layer by using ActiveRecord. Introduction of meta-programming (code-that-writes-code, code-scaffolding) is great. Nice opportunities for free cloud-deployment, e.g. heroku.com and there is a very active community
Java: Powerful interaction with web-server possible (Tomcat, JBoss, ...) MVC is rather complicated here, and in general many configuration-steps necessary (build systems, ORM layer, ...) Grails is a great simplifaction and introduces meta-programming for Java. Jboss Seam introduces REST for Java (but have not looked into this yet)
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!...