Foreign Linker API (JDK 16 Incubator)

Sandbox.java

/*
 * Demonstration of the Foreign Linker API (JDK 16 Incubator)
 *
 * The following code shows a message box using Win32 API with caption and text taken from CLI arguments 0 and 1.
 *
 * Incubator Warning: To compile this code, write a module-info.java file containing `requires jdk.incubator.foreign`.
 *
 * Incubator Warning: To execute this code, use `--add-modules jdk.incubator.foreign -Dforeign.restricted=permit`.
 */

package eu.headcrashing;

import static java.nio.charset.StandardCharsets.UTF_16LE;

import static jdk.incubator.foreign.CLinker.C_INT;
import static jdk.incubator.foreign.CLinker.C_POINTER;
import static jdk.incubator.foreign.MemoryAddress.NULL;

import java.lang.invoke.MethodType;

import jdk.incubator.foreign.LibraryLookup;
import jdk.incubator.foreign.FunctionDescriptor;
import jdk.incubator.foreign.CLinker;
import jdk.incubator.foreign.MemoryAddress;

public class Sandbox {
    public static void main(String[] args) {
        System.out.println(messageBox(args[0], args[1]));
    }

    private static int messageBox(String text, String caption) {
        try {
            var user32 = LibraryLookup.ofLibrary("user32");
            var messageBoxFunction = user32.lookup("MessageBoxW");
            var messageBoxLayout = FunctionDescriptor.of(C_INT, C_POINTER, C_POINTER, C_POINTER, C_INT);
            var javaMethodType = MethodType.methodType(int.class, MemoryAddress.class, MemoryAddress.class, MemoryAddress.class, int.class);
            var methodHandle = CLinker.getInstance().downcallHandle(messageBoxFunction.get(), javaMethodType, messageBoxLayout);
            try (var str1 = CLinker.toCString(text, UTF_16LE); var str2 = CLinker.toCString(caption, UTF_16LE)) {
                return (int) methodHandle.invokeExact(NULL, str1.address(), str2.address(), 0);
            }
        } catch (RuntimeException e) {
            throw e;
        } catch (Throwable t) {
            throw new RuntimeException(t);
        }
    }
}