Introduction 👋

Welcome to java-bindgen, an easy-to-use Java JNI (Java Native Interface) bindings generator and CLI tool for building Java JARs. This tool simplifies the process of integrating Rust and Java, enabling you to leverage Rust's performance and safety in your Java applications.

Goal 🚀

Develop a robust and safe framework that facilitates seamless and secure integration between Java and Rust using JNI, minimizing the complexity and risks associated with native code interoperability.

Features 🎖️

• Convenient error handling using JResult<T, JException> with propagation to the Java layer.
• Automatic type conversion for Java primitives like String, byte[], int, long, float, boolean, etc.
• Custom types with #[derive(JavaClass)] for seamless integration.
• Integrated Logger #[derive(JLogger)] for better debugging and logging support.
• Rust error stack trace attached to Java Exceptions for improved error diagnostics.
• Support for Java java.util.List<E> with Rust JList<E>.
• Support for Java nullable types in Rust using Option<T>.

Prerequisites

Install Rust and Cargo:

• Linux/MacOS/Unix
• Windows

Rust Project Setup 🦀

Install java-pack CLI 🛠️

cargo install java-pack --version <version>

Example:

cargo install java-pack --version 0.1.0-alpha.4

Add java-bindgen dependency

cargo add java-bindgen

Add Cargo.toml configuration:

[package.metadata.java-bindgen]
package = "your.java.package"

Set crate-type:

[lib]
crate-type = ["cdylib"]

Verify Your Configuration 🔦

To confirm your setup, run the following command:

java-pack info

Example

☢️ The following examples do not compile due to missing configurations in the Cargo.toml file. ☢️

lib.rs

use java_bindgen::prelude::*;

#[derive(Default, JavaClass)]
struct User {
    name: String,
}

#[java_bindgen]
fn getUser() -> JResult<User> {
    Ok(User {
        name: "Tom".to_string(),
    })
}

Building jar 🫙

java-pack build

Produces the following Java interface and User class:

public static native User getUser();

@ToString
@Getter
@Setter
@AllArgsConstructor
public class User {
	String name;
}

Testing 💯

Create Java test project:

java-pack new-test

Add Test:

@Test
public void should_get_user() {
    UserClass user = TestMacro.getUser();
    assertEquals("Tom", user.getName());
}

Run tests:

java-pack test

Cross-Platform Build

Legend

• ✅ Supported

• 🚫 Unsupported

• ❔ No Data

*Linux -> Windows

Install linker: x86_64-w64-mingw32-gcc

sudo apt install mingw-w64`

Build .dll and .so

cargo build --target=x86_64-pc-windows-gnu --target=x86_64-unknown-linux-gnu

Safety 🛡️

Although this crate forbids unsafe code, the underlying JNI (Java Native Interface) itself is not inherently safe. Therefore, thorough testing is required to ensure that your software is safe to run.

🚨 Any Rust panic that is not handled on the Rust side will cause the JVM to crash. 🚨

Project 📦

Project structure 📌

• java-bindgen - lib

• java-pack - cli tool

• java-bindgen-macro - macro system

• java-bindgen-core - shared lib

Project status 🚧

Project is in early state of development. Each release is prior tested but api changes will most likely to happen in the future as the project progress.

Roadmap 📆

To be determined. If you like the project, please consider giving it a ⭐, filing an issue ❗, or submitting a pull request (PR) ✅. Your feedback and contributions are highly appreciated!

• GitHub

Alpha ❗

This crate was developed and tested on Linux so more tests are needed to ensure that it works on all platforms. Multiplatform jar support allso needs more testing.

More Examples 🤖

Logger

lib.rs

use java_bindgen::prelude::*;

#[derive(JLogger)]
struct Log();

#[java_bindgen]
fn test_logger<'a>(env: &mut JNIEnv<'a>, name: String) -> JResult<()> {
    let logger = Log::init(env);
    let msg = format!("Hello {name}, Welcome to Rust!");
    logger.info(msg, env);
    Ok(())
}

output

[main] INFO  com.test.macro.TestMacro  - Hello Java Bindgen, Welcome to Rust!

Exception Handling

Rust

#[java_bindgen]
fn raw_object_to_string<'a>(env: &mut JNIEnv<'a>, input: JObject<'a>) -> JResult<String> {
    let input_str: String = input.into_rust(env)?;
    Ok(input_str)
}

Java signature:

String raw_object_to_string(Object input)

When Java pass non String Object

java.lang.UnsupportedOperationException:
Rust Error:  JNI call failed
   Cause: Cast failed [JObject -> String]
Rust Backtrace:
   0: <core::result::Result<T,E> as java_bindgen::exception::JavaCatch<T>>::j_catch_cause
             at /Projects/java_bindgen/src/exception.rs:145:17
   1: <jni::wrapper::objects::jobject::JObject as java_bindgen::interop::java_to_rust::IntoRustType<alloc::string::String>>::into_rust
             at /Projects/java_bindgen/src/interop.rs:87:13
   2: test_macro::raw_input_type::raw_input_type_2
             at /Projects/java_bindgen/examples/test-macro/src/lib.rs:390:33
   3: Java_com_test_macro_TestMacro_raw_1input_1type_12
             at /Projects/java_bindgen/examples/test-macro/src/lib.rs:388:5
   4: <unknown>

Complex Types

Rust

#[derive(Default, JavaClass)]
struct Element {
    parent: Node,
    children: JList<Node>,
}

#[derive(Default, JavaClass)]
struct Node {
    node_id: i32,
}

#[java_bindgen]
fn add_new_node(node: Node, element: Element) -> JResult<Element> {
    let mut update = element;
    update.children.add(node);
    Ok(update)
}

Java

Node parent = new Node(1);
Node child = new Node(2);
Element element = Element.builder().children(new LinkedList<>()).parent(parent).build();

Element updated = Lib.add_new_node(child, element);
System.out.println("Updated: " + updated);

output

Updated: Element(parent=Node(node_id=1), children=[Node(node_id=2)])

Full Examples 🧭

For full examples visit: github.com/java-bindgen/examples

Acknowledgments 💌

Thank you to the jni team!

This project strongly relies on the jni crate, and without your hard work, it would not have been possible.