benanders / rjni

Run Java code from Rust!

Java Native Interface Bindings for Rust

This library provides complete FFI bindings to the Java Native Interface, as well as a safe and intuitive wrapper around most these bindings (lacking array support for now).

Features include:

• Creating and configuring an instance of a Java Virtual Machine
• Loading classes
• Calling static methods on classes
• Setting and retrieving public static fields on classes
• Instantiating objects from a class
• Calling methods on objects
• Setting and retrieving public fields on objects
• Using all primitive Java types and other Java objects as arguments and return values (no support for arrays yet)

Documentation

Documentation can be found here.

Usage

First you'll need to compile your Java source code, either as separate .class files, or package them together as a .jar archive.

You need to make sure you target the Java compiler to the JVM version you plan to use. This is done through the -target and -source command line arguments to javac.

For example, if you have a /path/to/project/com/me/Test.java file (ie. the class com.me.Test) and you intend to target the 1.6 JVM:

$ javac -target 1.6 -source 1.6 /path/to/project/com/me/Test.java

This will create a /path/to/project/com/me/Test.class file.

Then when you create the JVM in Rust, you need to add /path/to/project (ie. the directory containing the root of your Java code) to the classpath, and specify the correct JVM version:

use rjni::{Jvm, Version, Classpath, Options};

fn main() {
	// Create a custom classpath, pointing to the directory containing the root
	// of your Java code
	let mut classpath = Classpath::new();
	classpath.add(&Path::new("/path/to/project"));

	// Create a series of configuration options for the JVM, specifying the
	// version of the JVM we want to use (1.6), and our custom classpath
	let mut options = Options::new();
	options.version(Version::V16);
	options.classpath(classpath);

	// Create the JVM with these options
	let jvm = Jvm::new(options).unwrap();

	// Get the `com.me.Test` class using the JVM
	let class = jvm.class("com/me/Test").unwrap();

	// ...
}

See the examples folder for more example code on how to call static methods on classes, instantiate objects, call methods on objects, and access object fields.