How to debug Java Web Application in Netbeans?

I have debug Java Desktop Applications various times in Netbeans but haven't debug Java Web Application ever.

I tried to debug it the same way, but it's not working.

I have made an index.html webpage. There is a "form" on that page. After a user submits the form, the request goes to a servlet (say serv1). The servlet has been called but it is showing unexpected results.

So to debug it, I put a 开发者_运维问答breakpoint in the servlet class (serv1) and then debug the application.

But when I submitted the form, the control didn't stop at the breakpoint. I am sure that the line at which the breakpoint is set is being called.

Is there any thing I am missing?

==================EDITED===================================================

Yes, I had started the server in debug mode. I am using Apache Tomcat 6.0.20

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How did you start your web application in debug mode? On my machine, I simply select the project, click on the Debug top menu, then Debug Project, select a Server (GlassFish, WebLogic, Tomcat) if required and things just work (I can place a breakpoint in a Servlet and the execution stops there). Tested with all the mentioned containers.

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Also sometimes, I don't know why the project detaches itself from the debugger process, you just need to select the menu Debug -> Attach Debugger and attach the project again. For example in Glassfish just put localhost as the server and 9009 as the port and it will work again