Where does the output of System.out and System.err go in a servlet?
Maxim Senin out and err should go to console for Java-based servlet engines. Some servlet engines (a.k.a. containers in Servlets 2.2) block System.out and System.err for servlets, so you may want to use ServletContext.log() or use your own log function.
Some servlet engines have a special property to disable/enable output to standard streams for servlets.
Read your servlet engine documentation to find out where it stores its log files.