Kotlin DSL reading JSON file

I am looking to read in a file as part of the Kotlin DSL definition of my TC pipeline - i.e. read in JSON and build a parameter of tick boxes depending on the file contents. However, I am having trouble reading the file into the Kotlin code. I am behind a number of firewalls so I cant easily pull import libraries from outside my org. Is this possible? How do I do file handling? Do I need to import any specific libraries? Is there a JSON handler? 

When trying to access the file using 

var modulesJson = File("../module_def.json").bufferedReader()

I get:

Unresolved reference: File

I see the file needs to be in the .teamcity folder, which is not an issue. 

Any help would be appreciated.