1. is there any sample show how groovy used on top of java ?
2. groovy mainly use for web application ? is groovy something like jsp ?
3. how stable of groovy ?
4. is there any good reference site for groovy ?
5. is groovy tend to improve java application performance?
1. Groovy pretty much "is" Java with an augmented and relaxed syntax and a different compiler. So you don't have to run "on top of" anything. Most anything you can code in Java you can code in Groovy. You would need to groovyc instead of javac when you want to compile. (Noting that compilation is optional.) Here's an example Groovy script:
You can run in interpreted mode and use the BeanScriptingFramework approach
towards embedding. That would give you Groovy "on top of" Java.
2. Groovy is a general purpose programming language. As such it can be used for templating (which it has lots of wild support for), web apps (see GSP or Grails), desktop GUIs (using something like SwingBuilder), or anything you need.
3. Groovy just released it's 1st released candidate about a week ago. Prior versions to that have showed problems mostly with special use cases. I'd say it's pretty stable but that's entirely subjective.
4. See the docs on its home page: http://groovy.codehaus.org/Documentation
5. Groovy is inteded to improve Java's usability. In other words it's more programmer friendly making programs easier to write and easier to maintain. Goals like this are always in opposition to performance. Consider your task. If you need nose-bleed critically high performance (which many modern apps really do not need) then you would use a lower level programming language like C. That said Groovy's performance, as far as I can tell, has been acceptable. I would say in most typical uses performance of the language would not be a concern.