RainAPI
Core library for RainJava featuring embedded ECJ compiler, Javassist bytecode tools, and ASM transformation pipeline. Enables dynamic Java compilation and class modification at runtime.
- Loaders
- Forge
- Downloads on Modrinth
- 463
- Followers on Modrinth
- 2
- versions
- 3
- Updated
- February 27, 2026Feb 27
- Published
- in 2026
At a glance
Needed both in the game and on the server
RainJava 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
FAQ
How to install RainAPI?
Install Forge for your Minecraft version, download RainAPI for the same version and loader, put the file into the mods folder and launch the game with the loader profile.
Which Minecraft versions does RainAPI support?
RainAPI has builds for Minecraft 1.20.1.
Is RainAPI needed on the server?
Needed in the game and on the server