how to invoke java class from soap UI

Read through this and see if it applies to what you are doing:
http://www.soapui.org/Developers-Corner ... oapui.html

One thing hinted at in the article above but not spelled out is how to write a generic java class that can be used from Groovy Scripts within soapUI.
Have a look here for a basic example of this here:
viewtopic.php?f=2&t=7052

Short simple answer is:
1. Compile java code into a JAR file.
2. Place JAR file in <soapui_program_dir>/bin/ext/
3. (re)start soapUI.
4. From groovy script import your java package and access your class(es).