Is it possible to use a custom java function in a calculated expression within a domain?

I have created a jar containing a custom function. This works correctly within reports in JasperStudio

I want to use the custom function to output a calculated field within a JasperServer domain. I am struggling to make this work.

I have loaded the JAR into the webapps\jasperserver-pro\WEB-INF\lib

I can't see the correct syntax/additional configuration required to use this function in the CalculatedField expression box

I have attempted to add it to the applicationContext-el.xml, but all that happens is that JaspereServer passes the function down to the database.

Is what i am trying to do possible?