As it says in the API
doc, this method appeared in
Servlet API 2.3, which is covered on
J2EE 1.3. Are you using an updated servlet-api.jar and servlet.jar (for example, from
Tomcat 4.1 or 5.x or 6.x)? If you're developing using an
IDE, look for the target J2EE, maybe it's configured by default to 1.2 or 1.1...