This is probably obvious to everyone, but it took me looking at javadocs to figure out how to make tomcat give me more information than just a generic "ServletException" with no context, no message and a useless (in this case) stack trace.

Thread-45[1] dump e.getRootCause().printStackTrace();

Where e is the exception, RootCause is a java.lang.Throwable

java.lang.NoClassDefFoundError
        at xxx._jspService(_xxx_0.java:262)

Much better than

javax.servlet.ServletException
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:508)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)