拨打Ajax

I have a requirement and I am stuck.

I need to create a web tool. 1.So I have created a Web project in eclipse. 2.Created a jsp file with (html,css,js ) 3.Now a click on a radio button should give call a java class and display it in the same page.So I need to make an ajax call.

how do I make an ajax call in my jsp?

how do I create a servlet and link my java class.

I do not want any coding help here, just if someone can give me an approach, I would really appreciate it.

thanks