You want to use java in your ECMA (.esp) script.
Here is an example where a Java object is initialized, and a method of the object is called:
var myClass = new Packages.com.myapp.MyClass(); myClass.setTitle("My Title");
For additional information, see http://docs.day.com/en/home/communique_3/docucq355/programming/ecma_script_reference/creating/differences/using0.html
Although this documentation is written for Communiqué version 3.5.5/3.5.6, it's still applicable.