MySql + Tomcat on Ubuntu 9.04

[Luigi Fonti]

I have used Mysql + Tomcat for years on different O.S. (Windows, Fedora, Ubuntu...)
On a new PC I just installed Ububtu 9.04, Tomcat 6 and Mysql 5.
Both Tomcat and Mysql work properly, but not together.
What I mean is: java applications access local Mysql server without problems.
But if I try to access it from a java servlet managed by tomcat, and using the same parameters (username, password, database, driver..) I never have it granted.
Can somebody tell me why ?
I tried to uninstall and re-install both Tomcat and Mysql, but the problem is still there.
Luigi