There's an intermediate approach - use a generator to spew out tables of data that an engine-type thing uses to adapt to boilerplate style variations.

This is totally a 'C' hacker's approach but it's not bad for some things - especially serialization and the like. But it will need some generic reference mechanism - as void * is used in 'C' - to work.

On a continuum from "so robust you don't even consider it codegen" to "well, some people use it": microcode, compilers, virtualization, visual interface builders like XCode and Android Studio, dynamic HTML pages, ORMs, protobufs & other schema definition languages, autoconf & friends, compile-to-C languages like early versions of C++ and Go, ES6 transpilers like Traceur and Babel, compile-to-JS languages like CoffeeScript. Probably others I've forgotten or don't know about.

When it works, you forget that the only thing that computers understand is their native instruction set, and everything on top of that is built on some form of codegen. When it doesn't, you curse out the programmer who left you a pile of buggy scripts to maintain.

Java annotations have been used pretty successfully for several versions. Not all of them are code generating, but many (from e.g. Spring, or something smaller like Retrofit) generate tons of code for you.

Compilers, for start.