I want a mechanism that will allow to dynamically load and unload jars as well as calling an activator class in the jar. I don't want to use OSGi because of the cumbersome import/export mechanism.
There's a project called the Java Plugin Framework that might be what you're looking for. On their web page it states the project is an attempt to match and extend Eclipse's pre-OSGI plugin architecture. It's a generic framework and isn't tied to SWT/desktop apps.