Stress - Load testing a web application

I have a web application deployed on a tomcat server. I upload files via a POST method and then the uploaded files are transcoded to another type (e.g. 3gp to flv). How can I test, how many concurrent uploads an开发者_StackOverflowd transcodings my web application can handle?

Any thoughts or any examples? Don't know a thing about stress or load testing

I've never used it, but look into JMeter. It does load testing for Java.