Hi Illyass, and welcome to JavaRanch!
We see this question from time to time and the answer really is: don't write to standard out (stdout) or standard err (stderr) from a web app. Actually, writing to stdout and stderr is almost always a bad idea.
You should be using a logging framework instead. The one recommended by Apache is, not surprisingly, Apache Commons Logging. See the
Tomcat Logging FAQ here:
http://wiki.apache.org/tomcat/FAQ/Logging
Logging isn't really that hard to configure, and it's a long-established best practice. Retrofitting all your System.print statements to log statements may be the hardest part, depending how many there are, but it'll be worth it. I promise!