# jnat
A wrapper around the [jni](https://crates.io/crates/jni) crate
View the [documentation](https://docs.rs/jnat)
## Example
Create a new Cargo lib project with `cargo new --lib mylib` and add the following to `Cargo.toml`:
```toml
[dependencies]
jnat = [latest version]
[lib]
crate-type = ["cdylib"]
```
Add the following to `src/lib.rs`:
```rust
use jnat::{
jnat_macros::jnat,
jni::{objects::JClass, JNIEnv}, // jni crate, re-exported by jnat
Class,
Env,
Signature,
Type,
};
#[jnat(HelloWorld)]
fn caller(env: JNIEnv, class: JClass) {
let mut env = env;
let mut env = Env::new(&mut env);
let mut class = Class::new(&mut env, class);
class
.call_static_method("hello", Signature::new(&[], Type::Void), &[])
.unwrap();
}
```
Then, run `cargo build`. Create a new file called `HelloWorld.java` and add the following:
```java
public class HelloWorld {
private static native void caller();
static {
System.loadLibrary("mylib");
}
public static void main(String[] args) {
HelloWorld.caller();
}
public static void hello() {
System.out.println("Hello, world!");
}
}
```
Compile the java file with `javac -h . HelloWorld.java`. Then, run `java -Djava.library.path=path/to/target/debug HelloWorld`. You should see `Hello, world!` printed to the console.
## Notes
- Jnat re-exports jni by default. If you want to use a different version of jni, you can disable either the default features or the `jni` feature.
- Jnat exports a macro, `jnat::jnat_macros::jnat` (seen in the example above), which is used to generate the `Java_HelloWorld_caller` function. This macro can be disabled by disabling either the default features or the `jni-macros` feature. Note that the macro keeps the original function to prevent unintuitive behavior (so you can, in your Rust code, call just `example()` instead of `Java_org_example_Class_example()` while still allowing Java to call it).