Groovy - How to reflect code from another groovy app to find Classes/Properties/Types within

First, I came from a .NET background so please excuse my lack of groovy lingo. Back when I was in a .NET shop, we were using TypeScript with C# to build web apps. In our controllers, we would always receive/respond with DTOs (data xfer objects). This got to be quite the headache every time you create/modify a DTO you had to update the TypeScript interface (the d.ts file) that corresponded to it.

So we created a little app (a simple exe) that loaded the dll from the webapp into it, then reflected over it to find the DTOs (filtering by specific namespaces), and parse through them to find each class name within, their properties, and their properties' data types, generate that information into a string, and finally saved as into a d.ts file.

This app was then configured to run on every build of the website. That way, when you go to run/debug/build the website, it would update your d.ts files automatically - which made working with TypeScript that much easier.

Long story short, how could I achieve this with a Grails Website if I were to write a simple groovy app to generate the d.ts that I want?

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How do I get the IDE (ex IntelliJ) to run a groovy file (that is part of the app) that does this generation post-build?