Eclipse uses its own compiler (see What is the difference between javac and the Eclipse compiler?), so you won't find it if you use an old version of Eclipse (as probably your RSA is based on). Java 7 support is available for Eclipse 3.7.1 or higher (at the moment current stable is 4.2).
However, if you want to keep that version of Eclipse, you can create a new Builder using your JDK7 as base. To do this, go to Project and add a new Builder specifying where the javac is and the other options.
Look also at this question: Eclipse 3.5 and Java 7