java - Web application crashes after a few requests, how to debug? -

my vaadin web application running on tomcat server using netbeans crashes when following in selenium test:

org.openqa.selenium.webdriver webdriver = new firefoxdriver(); //or: org.openqa.selenium.webdriver webdriver = new chromedriver();   for(int = 0; < 10; ++i) {     driver.get("http://localhost:8084/myapp/"); } 

when running test application becomes unresponsive , need restart tomcat. not error messages (maybe not looking @ right places, log shows nothing). happy know how can find out goes wrong.

edit: opening database connection inside vaadin ui class, caused pool size overflow. after became aware of used jconsole analyze problem.