Detect OS on JVM

Os.java

import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.util.Locale;

import org.checkerframework.checker.nullness.qual.NonNull;

/**
 * Operating systems enumeration.
 *
 * @author Alexander Biryukov
 */
public enum Os {
    /**
     * Microsoft Windows operating system.
     */
    WINDOWS,
    /**
     * Linux-based operating system.
     */
    LINUX,
    /**
     * Apple Macintosh operating system.
     */
    MAC,
    /**
     * Other operating systems, also used if {@code os.name} property is not defined.
     */
    UNKNOWN;

    /**
     * Current OS.
     *
     * @return current OS.
     */
    @NonNull
    public static Os current() {
        final String name = System.getProperty("os.name").toLowerCase(Locale.ENGLISH);
        final Os win = name.contains("win") ? WINDOWS : UNKNOWN;
        final Os nonLinux = name.contains("mac") ? MAC : win;

        return name.contains("linux") ? LINUX : nonLinux;
    }

    /**
     * Check if current OS is Windows.
     *
     * @return true, if OS is Windows, otherwise false.
     */
    public static boolean isWindows() { return Os.current() == Os.WINDOWS; }

    /**
     * Check if current OS is Linux.
     *
     * @return true, if OS is Linux, otherwise false.
     */
    public static boolean isLinux() { return Os.current() == Os.LINUX; }

    /**
     * Check if current OS is Mac.
     *
     * @return true, if OS is Mac, otherwise false.
     */
    public static boolean isMac() { return Os.current() == Os.MAC; }

    /**
     * Check if current OS is unknown.
     *
     * @return true, if OS is unknown, otherwise false.
     */
    public static boolean isUnknown() { return Os.current() == Os.UNKNOWN; }

    /**
     * Check if current OS is POSIX-compliant.
     *
     * @return true, if OS is POSIX-compliant, false otherwise.
     */
    public static boolean isPosix() {
        FileSystem fileSystem = FileSystems.getDefault();
        if (fileSystem == null) {
            return false;
        }
        return fileSystem.supportedFileAttributeViews().contains("posix");
    }
}