This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
The relative path concept varies from context to context.
Whenever you are talking about File, the path is relative to the current directory from where you are running the web-server. Like, if you run the tomcat from c:\tomcat\bin and try to use new File("abc.jar"), you must place the "abc.jar" file in "c:\tomcat\bin".
But, in case of any response.sendRidirect(), the relative path is as you specified.