You can install multiple JDKs in Tomcat and assign them to projects on a per-project basis.
However, as William has pointed out, Java has an excellent mechanism for providing legacy support for older versions of Java from newer JDKs. That's a feature that has been part of Java since the beginning, and one of the reasons why I pretty much abandoned less civilized development platforms.
An IDE is no substitute for an Intelligent Developer.
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com
subject: jdk 1.6 but I need to compiler with jdk 1.5