Xuanwo commented on code in PR #2209:
URL:
https://github.com/apache/incubator-opendal/pull/2209#discussion_r1185755842
##########
bindings/java/src/macros.rs:
##########
Review Comment:
The main issue is that Java uses `exception` differently from Rust's
`Result` logic. To address this, we need to create a shim between the Rust and
Java code. For example:
- `xxx_inner() -> Result<T, Error>`
- `xxx() -> T`: This would call `xxx_inner()` and raise an exception.
Additionally, why do we need to build exceptions in Rust code? Could we
instead return a new object and raise an exception in Java?
j4rs returns a `jobject` for that:
```rust
#[call_from_java("io.github.astonbitecode.j4rs.example.RustFunctionCalls.addintegers")]
fn add_integers(integer_instance1: Instance, integer_instance2: Instance) ->
Result<Instance, String> {
let jvm: Jvm = Jvm::attach_thread().unwrap();
let i1: i32 = jvm.to_rust(integer_instance1).unwrap();
let i2: i32 = jvm.to_rust(integer_instance2).unwrap();
let sum = i1 + i2;
let ia = InvocationArg::try_from(sum).map_err(|error| format!("{}",
error)).unwrap();
Instance::try_from(ia).map_err(|error| format!("{}", error))
}
```
Underhood:
```rust
// The jni function return type
let ref jni_function_output = match &user_function_signature.output {
ReturnType::Default => ReturnType::Default,
_ => {
let ret_type: ReturnType = syn::parse_str("-> jobject").unwrap();
ret_type
}
};
// The jni return value. This may be void or jobject
let return_value = match &user_function_signature.output {
ReturnType::Default => {
let ret_value: Expr = syn::parse_str("()").unwrap();
ret_value
}
_ => {
let ret_value: Expr = syn::parse_str(
r#"match instance_to_return {
Ok(i) => {
i.java_object()
// i.as_java_ptr_with_local_ref(jni_env).unwrap()
},
Err(error) => {
let message = format!("{}", error);
let _ = jvm.throw_invocation_exception(&message);
ptr::null_mut()
},
}"#).unwrap();
ret_value
}
};
```
---
Binding must be simple and easy to understand.
If we have to add those complex logic, I prefer to use `j4rs` directly.
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