How to register and generate structures in 1.15 Minecraft using nbt files!
This very small Forge mod is full of comments that will help you understand what a lot of the methods do and what needs to be done to get your structure to generate. In all, this mod is really just 4 files plus 2 structure nbt files.
If you don't know how to make an nbt file for structures, it's actually fairly simple and you can do it all inside minecraft itself! Here is a video on how to make and save a structure to nbt using structure blocks:
Once saved, the structure nbt file is stored in that world's save folder within the generated folder inside. Grab those files as you'll need to put it under your mod's resource folder inside data.mod_id.structures.
Now you're ready to begin adding the structure to your mod! Take a look at StructureTutorialMain, start reading the comments, and follow the methods/classes. Don't just copy the code quickly or else you will get confuse. Take your time and try to understand how it all works before attempting to register and generate your structure in your own mod.
Good luck and I hope this helps!
[This is using MCP mapping version of: '20200521-1.15.1' but try to use the latest mappings from http://export.mcpbot.bspk.rs/. Don't download any files but just get the number like this '20200521-1.15.1' of the latest mapping release. Put that number into your mapping channel in build.gradle and rebuild your project to be able to use the latest mappings.]