Groovy Script for reading prefix value of the xml file name

I have done a script for taking xml files from local machine. It's working good but I need a script for taking only prefix/suffix of the file name. this is my script.

Can You please help me on this..

def soNumber  = holder.getNodeValue("//*:employees/*:employee/*:id")//

def file = new File (groovyUtils.projectPath+"/${soNumber}.xml")//
log.info(file)
def fileToLoad = '888888'// default file name is 888888
if(file.exists())
{
  fileToLoad   = soNumber
}