The package manager is just that - a manager for package information, it doesn't really know whats on your system, just what packages it installed and thus what it assumes is on your system.
The obvious problem with this design is that the two can become out of sync, say, if you installed JRE by hand by downloading it from oracle, then the package manager has no clue that its there and hence does its job of pointing out the failed dependancy chain.
There are multiple options, assuming this is the problem (check your rpm package list, i forget rpm's parameters) in order of uglyness: (1) You can install your distributions version of JRE, which will make the package manager happy, (2) You can fudge the package manager so it thinks said dependancy "jre version 1.7.0" is actually installed, with or without installing it, then subvert the java binaries to use your installed version, or (3) you can just install tomcat with the --nodeps option to ignore dependancies. Be aware (3) is a slippery slope and you'll end up skipping more dependancies and sub dependancies over time.