
RainAPI
Core library for RainJava featuring embedded ECJ compiler, Javassist bytecode tools, and ASM transformation pipeline. Enables dynamic Java compilation and…
⬇ Download on ModrinthRainJava API
Advanced Runtime Class Transformation Framework
A foundational library providing Mixin and Coremod interoperability layers, powered by enterprise-grade bytecode and compilation tools.
Overview
RainJava API establishes the critical infrastructure for runtime class transformation pipelines. It serves as a middleware bridge between dynamic compilation workflows and Minecraft's standard modification systems (Mixin & Coremod), ensuring bytecode-level compatibility without compromising game stability.
While designed as the prerequisite foundation for the upcoming RainJava ecosystem, this API functions independently as a robust toolkit for developers requiring deep class manipulation capabilities.
Embedded Libraries
This mod ships with zero-external-dependency versions of industry-standard tools:
Javassist — High-level bytecode manipulation library for runtime class engineering
ECJ (Eclipse Compiler for Java) — Full-featured Java compiler capable of runtime source-to-bytecode transformation
JavaParser — Abstract Syntax Tree (AST) analysis and code generation framework
These libraries are shaded and isolated to prevent conflicts with other mods.
Technical Scope
Transformation Bridge — Facilitates communication between runtime-generated class definitions and established bytecode modification frameworks
Mixin Compatibility Layer — Enables standardized injection patterns to recognize and process dynamically provisioned classes
Coremod Integration — Provides stable hooks for runtime class definitions to participate in Forge's transformation chain
Sandboxed Execution — Implements security boundaries for runtime code evaluation environments
For Modders
Install this API if you:
Plan to develop for or use the upcoming RainJava framework
Require embedded Javassist/ECJ/JavaParser without bundling them yourself
Need stable Mixin/Coremod interoperability for advanced bytecode operations
- Edition: Minecraft Java
- File type: .jar
- Minecraft version listed: 1.20.1
- How to install: Install the matching mod loader (Forge, Fabric or NeoForge) for your Minecraft version. → Download the .jar. → Put it in the .minecraft/mods folder and launch that loader profile.
- Where to get it: Opens on Modrinth — not every file is mirrored on our own servers.
Install steps are the general flow for this file type — How to install Minecraft Java mods & modpacks walks through it step by step.
- Ships as RainAPI-1.0.2.jar — drop this file into the mods folder
- Download size: 7.2 MB
- Download link checked 8 Sept 2026 — working
These come from our own check of the pack file, not from the source page.