Why my JDBC not working in servlet

My JDBC connection with MySQL has been always working on general java classes on command line, but when I call a class(JDBC) from servlet, there is always a connection problem. I check all classpath, it was right. I don't know if I should do sth with web.xml file, I use Tomcat 4.0.
Anybody know how?
Thanks

I have solved this problem.
I add MySQL driver mm.mysql-2.0.4-bin.jar file on the tomcat folder:
D:\Apache Tomcat 4.0\common\lib, restart tomcat server, it then works.

Glad you solved it

This is quite a common problem when connecting databases to Servlet Engines.
(but)
"Ming",
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Thanks.
Dave