Your project must be configured to use a JDK in order to use JSPs
Using Eclipse 3.7 + Google Plugin for Eclipse to develop GAE project, when created a .jsp file in “war” directory, Eclipse shows a cross error icon on top of the JSP file.
In Eclipse problem view, it show “Your project must be configured to use a JDK in order to use JSPs.“.
To solve it, change your Eclipse’s Installed JRE, and point it to your JDK folder. In Eclipse menu, select Windows -> Preferences -> Java -> Installed JREs, add your JDK folder and checked on it.
P.S JSP need JDK “javac” to compile, which doesn’t exist in JRE.