Is there a tutorial on exchanging data object between Java and Rust?

[xuxiaocheng0201]

Is there a tutorial on exchanging data object between Java and Rust?
#3634 is not suitable.

Now I only can pass a string from Rust to Java, like this:

In Java:

package com.xuxiaocheng.tester;

import org.graalvm.nativeimage.IsolateThread;
import org.graalvm.nativeimage.c.function.CEntryPoint;
import org.graalvm.nativeimage.c.type.CCharPointer;
import org.graalvm.nativeimage.c.type.CTypeConversion;
import org.graalvm.word.UnsignedWord;
import org.graalvm.word.WordFactory;

import java.nio.charset.StandardCharsets;

public final class Main {
    private static native CCharPointer allocateString(final UnsignedWord length);

    public static CCharPointer toCString(final CharSequence string) {
        final UnsignedWord length = CTypeConversion.toCString(string, StandardCharsets.UTF_8, WordFactory.nullPointer(), WordFactory.zero());
        final CCharPointer pointer = Main.allocateString(length);
        CTypeConversion.toCString(string, StandardCharsets.UTF_8, pointer, length);
        return pointer;
    }

    @CEntryPoint(name = "test")
    public static void test(@SuppressWarnings("unused") final IsolateThread thread, final CCharPointer inputString) {
        System.out.println(CTypeConversion.utf8ToJavaString(inputString));

        final CCharPointer pointer = Main.toCString("From java string test");
        // TODO
    }

    public static void main(final String[] ignoredArgs) {
    }
}

And built it use

native-image --shared -H:Name=libtester -march=compatibility -jar out/artifacts/tester.jar -cp tester

In Rust:

pub struct GraalIsolateThread {
    ptr: *mut graal_isolatethread_t,
}

impl GraalIsolateThread {
    pub fn new() -> GraalIsolateThread {
        let mut isolate = null_mut();
        let mut thread = null_mut();
        unsafe { graal_create_isolate(null_mut(), &mut isolate, &mut thread) };
        GraalIsolateThread { ptr: thread }
    }

    pub fn ptr(&mut self) -> *mut graal_isolatethread_t {
        self.ptr
    }
}

impl Drop for GraalIsolateThread {
    fn drop(&mut self) {
        unsafe {
            graal_tear_down_isolate(self.ptr);
        }
    }
}

pub struct ToJavaString {
    ptr: *mut c_char,
}

impl ToJavaString {
    pub fn new(str: String) -> Self {
        Self { ptr: unsafe { CString::from_vec_unchecked(str.into_bytes()) }.into_raw() }
    }

    pub fn ptr(&self) -> *mut c_char {
        self.ptr
    }
}

impl Drop for ToJavaString {
    fn drop(&mut self) {
        let _ = unsafe { CString::from_raw(self.ptr) };
    }
}

#[no_mangle]
pub unsafe extern "system" fn Java_com_xuxiaocheng_tester_Main_allocateString(_env: JNIEnv, _class: JClass, len: usize) -> *mut c_char {
    let vec = Vec::with_capacity(len + 1);
    CString::from_vec_with_nul_unchecked(vec).into_raw()
}

fn main() {
    let mut thread = GraalIsolateThread::new();
    let str = "To java string test".to_string();
    unsafe {
       test(thread.ptr(), ToJavaString::new(str).ptr());
    }
}

But this code failed:

To java string test
Unhandled exception: java.lang.UnsatisfiedLinkError: com.xuxiaocheng.tester.Main.allocateString(Lorg/graalvm/word/UnsignedWord;)Lorg/graalvm/nativeimage/c/type/CCharPointer; [symbol: Java_com_xuxiaocheng_tester_Main_allocateString or Java_com_xuxiaocheng_tester_Main_allocateString__Lorg_graalvm_word_UnsignedWord_2]
    at com.oracle.svm.core.jni.access.JNINativeLinkage.getOrFindEntryPoint(JNINativeLinkage.java:152)
    at com.oracle.svm.core.jni.JNIGeneratedMethodSupport.nativeCallAddress(JNIGeneratedMethodSupport.java:53)
    at com.xuxiaocheng.tester.Main.allocateString(Main.java:-2)
    at com.xuxiaocheng.tester.Main.toCString(Main.java:17)
    at com.xuxiaocheng.tester.Main.test(Main.java:26)

Fatal error: Unhandled exception

[xuxiaocheng0201]

Ok. I reloved this problem.