生成JUnit报告使用的XML文件

I want to create test reports generated by JUnit / TestNG PROGRAMMATICALLY. So, that rules out ANT. My main concern is to generate XML files which are created by Junit while executing test cases. I'have read that RunListener could help me achieve that, but i havn't been able to figure out how ? I'm using Selenium to created my test cases. I want to create test reports generated by JUni