Why did Servlet.service() for servlet jsp throw this exception?

Question

I get the following error, what could be the problem?

My context descriptor:

Answer 1

If your project is Maven-based, remember to set scope to provided for such dependencies as servlet-api, jsp-api. Otherwise, these jars will be exported to WEB-INF/lib and hence contaminate with those in Tomcat server. That causes painful problems.

  javax.servlet
  servlet-api
  2.5
  provided


  javax.servlet.jsp
  jsp-api
  2.1
  provided