I have a JSP that extends a custom super class:

<@page extends="com.example.MySuperServlet" %>

My super class is defined as follows:

public abstract class MySuperServlet extends javax.servlet.GenericServlet implements javax.servlet.jsp.HttpJspPage {
  @Override public void service(....) {
    _jspService(req, res);
  }
  @Override public void jspInit() {}
  @Override public void jspDestroy() {}
}


The problem is that the generated JSP class contains a method _jspInit() which is never called.
It initializes an expression factory (_el_expressionfactory) and an instance manager (_jsp_instancemanager).
Now that both are not initialized, I get NullpointerExceptions when calling the JSP, i.e. in some generated methods there is code like
_jsp_instancemanager.newInstance(_jspx_th_my_005fcustomtag_005f0)

Usually when there is no custom super class, tomcat extends the generated JSP class from org.apache.jasper.runtime.HttpJspBase which calls _jspInit() from its init(ServletContext) method.

For my custom super class it is no option to extend org.apache.jasper.runtime.HttpJspBase instead of GenericServlet because it is tomcat specific.
It is also no option to call _jspInit() directly from my jspInit() method, because _jspInit() is not part of the servlet/JSP spec and thus it is not defined in any interface.

Note that there is no problem with tomcat 6 and 5.

I haven't tested with tomcat 8, yet.