How to get the correct process id of a Process

Using the jna library to get the windows process id as adviced in other questions here on stackoverflow.

String command = "cmd /c start cmd.exe";
Process process = Runtime.getRuntime().exec(command);
long pid = windowsProcessId(process);

private static Long windowsProcessId(Process process) {
    if (process.getClass().getName().equals("java.lang.Win32Process")
            || process.getClass().getName().equals("java.lang.ProcessImpl")) {
        /* determine the pid on windows plattforms */
        try {
            Field f = process.getClass().getDeclaredField("handle");
            f.setAccessible(true);
            long handl = f.getLong(process);

            Kernel32 kernel = Kernel32.INSTANCE;
            WinNT.HANDLE handle = new WinNT.HANDLE();
            handle.setPointer(Pointer.createConstant(handl));
            int ret = kernel.GetProcessId(handle);
            return Long.valueOf(ret);
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }
    return null;
}

This however never returns the correct process id of the just started process, rather something random but usually close to the actual id. How do I get the correct process id?