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Kiwi is a utility library. We really like Google's Guava, and also use Apache Commons. But if they don't have something we need, and we think it is useful, this is where we put it.

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package org.kiwiproject.base;

import lombok.experimental.UtilityClass;

import java.util.UUID;
import java.util.regex.Pattern;

/**
 * Utility class for working with {@link UUID} instances.
 */
@UtilityClass
public class UUIDs {

    private static final String NIL_UUID = "00000000-0000-0000-0000-000000000000";

    private static final Pattern RFC4122_PATTERN =
            Pattern.compile("^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-5][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}");

    /**
     * Creates a new type 4 (pseudo randomly generated) UUID, and then returns it as a string.
     *
     * @return a new random UUID as a String
     * @see UUID#randomUUID()
     */
    public static String randomUUIDString() {
        return UUID.randomUUID().toString();
    }

    /**
     * Checks if the {@code value} is a valid UUID conforming to RFC 4122. The general form is 8-4-4-4-12 where all the
     * digits are hexadecimal. Example: {@code e94c302e-e684-4d72-9060-a66461f858d6}
     * 
     * Note specifically that this method does not support the Nil UUID
     * and will always return false if given a Nil UUID.
     * 

     * This method has been tested with UUIDs generated using {@link UUID#randomUUID()} and
     * {@link UUID#nameUUIDFromBytes(byte[])}. It has also been tested with UUIDs created using the constructor
     * {@link UUID#UUID(long, long)} with the caveat that the most and least significant bits came from valid
     * type 3 and 4 UUIDs.
     *
     * @param value the string to check
     * @return {@code true} if a valid UUID, {@code false} otherwise
     * @see UUID
     */
    public static boolean isValidUUID(String value) {
        return RFC4122_PATTERN.matcher(value).matches();
    }

    /**
     * Checks if the {@code value} is a valid UUID conforming to RFC 4122 (including the Nil UUID). The general form is
     * 8-4-4-4-12 where all the digits are hexadecimal. Example: {@code e94c302e-e684-4d72-9060-a66461f858d6}, or the
     * nil UUID {@code 00000000-0000-0000-0000-000000000000}.
     * 
     * This method has been tested with UUIDs generated using {@link UUID#randomUUID()} and
     * {@link UUID#nameUUIDFromBytes(byte[])}. It has also been tested with UUIDs created using the constructor
     * {@link UUID#UUID(long, long)} with the caveat that the most and least significant bits came from valid
     * type 3 and 4 UUIDs.
     *
     * @param value the string to check
     * @return {@code true} if a valid UUID, {@code false} otherwise
     * @see UUID
     */
    public static boolean isValidUUIDAllowingNil(String value) {
        return NIL_UUID.equals(value) || isValidUUID(value);
    }
}