Setting Up Rust

Step 1: Exporting Rust Functions

To make Rust functions callable from Java, we need to do two things:

• Use #[no_mangle] to prevent Rust from renaming (mangling) the function name internally. This ensures Java can find the function by its exact name.
• Declare the function with extern "C" to make sure it uses the C Application Binary Interface (ABI), which Java understands.

Rust Example:

#![allow(unused)]
fn main() {
#[no_mangle]
pub extern "C" fn create_point(x: i32, y: i32) -> *mut Point {
    Box::into_raw(Box::new(Point { x, y }))
}

#[no_mangle]
pub extern "C" fn get_x(point: *mut Point) -> i32 {
    unsafe { (*point).x }
}

#[no_mangle]
pub extern "C" fn free_point(point: *mut Point) {
    unsafe { Box::from_raw(point); } // Frees the allocated memory
}

struct Point {
    x: i32,
    y: i32,
}
}

Explanation:

• *mut Point: The function returns a raw pointer (*mut Point), which Java can manage using the FFM API.

Step 2: Compiling Rust into a Shared Library

To compile the Rust code into a format Java can load, modify the Cargo.toml file:

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

Then, compile the Rust project into a shared library:

cargo build --release

This command will generate a shared library file (e.g., libmyrustlib.so or myrustlib.dll) in the target/release/ directory, which Java can dynamically load.