You can use a hammer to bang in a screw, and you can drive on the wrong side of the road if you like. Neither is smart.
Using the right tool for the job, and following accepted conventions and best practices
is smart.
Servlets and JSP are intended, and best suited, to be used as part of the Presentation Layer of web applications. As such
neither should be used for business logic, which should be ensconced in its own UI-agnostic layer.
Perhaps
this article can help.