Simple Java Version Manager (sjvm)

sjvm is a minimalist, cross-platform Rust-based CLI tool for managing multiple Java JDK installations using symlink indirection. Similar to tools like jenv or sdkman, but with a simpler, more focused approach.

Motivation

A few years ago, I created a project to manage the Java version currently used on my machine and within a specific terminal prompt: blazingly-fast-java-version-manager. At the time, I was just starting to learn Rust and wanted to try a different approach than the classic symlink indirection everyone uses. It worked for most use cases, but the code was messy and overly complicated. I didn't improve it much after that.

However, I kept using that tool over the years and wanted to build something better for myself.

This project aims to be a minimalist, simple, and cross-platform Java version manager using symlink indirection, built with modern Rust best practices.

Prerequisites and Permissions

To use sjvm, you must have permission to read, execute, and create symlinks for the JDK folders you want to manage.

Windows

On Windows, you need to have Developer Mode enabled: enable-your-device-for-development

Default JDK folder:

C:\Java

Linux

On Linux, if you install JDKs via a package manager and your user cannot create symlinks in those locations, you’ll need to copy the JDKs to a folder you own.

Default JDK folder:

/usr/lib/jvm

macOS

This is not tested. If you try it and it doesn't work, feel free to open an issue.

Default JDK folder:

/Library/Java/JavaVirtualMachines

Configuration

sjvm uses JSON for its configuration. A simple example:

{
  "jdks_dirs": [
    "C:\\dev\\compilers\\java"
  ]
}

You can also specify the folder sjvm will use as the main symlink destination:

{
  "symlink_dir": "C:\\dev\\sjvm\\java"
}

The configuration folder depends on your system. To find the path sjvm uses, run:

sjvm config path

Setup

To load all your JDKs into memory and create the symlink folder, run:

sjvm setup

Commands

List

List Java installations managed by sjvm on your device:

sjvm list

Example output:

C:\dev\compilers\Java\jdk-17.0.1  
C:\dev\compilers\Java\jdk-20.0.1  
C:\dev\compilers\Java\jdk-21.0.1

Use

To change the Java installation for your user:

sjvm use jdk-21

Example output:

✅ Now using JDK: C:\dev\compilers\Java\jdk-21.0.1

sjvm will match the name of the folder resolved by the list command. It will use the first match, so name your folders accordingly.

Local Mode

Set Java version for the current project only (creates .java-version file):

sjvm use jdk-21 --local

⚠️ Windows Note: Local mode is not yet supported on Windows. The command will show the manual steps to set the JAVA_HOME for the current session.

Config

Show configuration path:

sjvm config path

Development

Building

# Build the project
cargo build

# Build for release
cargo build --release

# Run the CLI
./target/release/sjvm --help

Testing

# Run unit tests
cargo test

# Run specific test
cargo test test_name

# Run all tests including integration tests
cargo test -- --ignored

# Run clippy lints
cargo clippy

# Format code
cargo fmt

End-to-End Testing with Docker

The project includes comprehensive e2e tests that run in a Docker environment with multiple Java versions (11, 17, 21) pre-installed:

# Run e2e tests (Docker image builds automatically)
docker compose -f ./docker/it-ubuntu-compose.yaml up

# Run in detached mode
docker compose -f ./docker/it-ubuntu-compose.yaml up -d

# Force rebuild of the Docker image
docker compose -f ./docker/it-ubuntu-compose.yaml up --build

# View logs
docker compose -f ./docker/it-ubuntu-compose.yaml logs -f

# Stop containers
docker compose -f ./docker/it-ubuntu-compose.yaml down

The Docker setup includes:

• Ubuntu 22.04 with Java 11, 17, and 21 installed
• Rust toolchain for building and testing
• Volume mounts for live code updates during development

Architecture

Core Components

• CLI Interface (main.rs) - Command-line parsing and routing using clap
• Configuration (config.rs) - JSON-based configuration management with cross-platform directories
• JDK Resolution (jdk_resolver.rs) - Automatic JDK discovery and version detection
• Symlink Management (symlinks.rs) - Cross-platform symlink operations
• Memory Management (memory.rs) - In-memory JDK caching and management
• Commands - Individual CLI command implementations (setup_command.rs, use_command.rs, list_command.rs)

Configuration

Configuration is stored in platform-specific directories using the directories crate:

• Linux: ~/.config/sjvm/config.json
• macOS: ~/Library/Application Support/sjvm/config.json
• Windows: %APPDATA%\sjvm\config.json

Example configuration:

{
  "jdks_dirs": [
    "C:\\dev\\compilers\\java",
    "/usr/lib/jvm",
    "/Library/Java/JavaVirtualMachines"
  ],
  "symlink_dir": "C:\\dev\\sjvm\\java"
}

Requirements

• Rust 1.85+ (Edition 2024)
• Permission to create symlinks in JDK directories
• Windows: Developer Mode enabled for symlink creation
• Docker (for e2e testing)

License

This project is open source. Feel free to contribute or report issues!