Tomcat’s RUNNING.txt which you can find in the root of the bundle states that Apache Tomcat requires Java Standard Edition Runtime Environment (JRE) to run. Minimum version of JRE depends on the version of Tomcat: for Tomcat 6.0 it is Java 5, for Tomcat 7.0 - Java 6. However you can also use JDK because, as you probably know, it includes JRE (link).
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