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JNA seems the industry standard of what you want, “provides Java programs easy access to native shared libraries (DLLs on Windows) without writing anything but Java code—no JNI or native code is required”
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There is also Java Foreign Function Interface –
example usage
If is ok for you, you could embed the JRuby interpreter and call winapi via jruby-ffi wich is a lot easier, see here, here, and here