Google App Engine: RUN JSP ERROR

I used Eclipse to try the google app engine demo project: guestbook.
when i create a *.jsp file in the WAR directory,the error information appear:
"Your Web Application Project must be configured to use a JDK in order to use JSPs."
solution:
It is because Eclipse put the JRE to the JRE directory, but not the JDK directory.
under "windows - preference", expand "Java". click on "Installed JRE":
change the location to JDK directory.
refresh the project. Done!!!