Java Version Checker Mod 1.8, 1.7.10, 1.7.2 is FML coremod that shows a user-friendly message if the conditions for Java version aren't met. There is one version that checks for Java 7, and one for Java 8, make sure you download the correct one.

The 1.7.10 version of this mod should be compatible with older versions of Minecraft. It is not compatible with 1.8 because of a very special change in Forge ModLoader, however the 1.8 version is now released and should work in future versions of Minecraft.