SimpleUID.java

import org.apache.commons.codec.binary.Hex;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

/**
 * @author Ray Krueger
 */
public abstract class SimpleUID {

    public static final int MAX_LEN = 40;
    public static final int MIN_LEN = 16;

    private static final String ALGORITHM = "SHA1";
    private static final SecureRandom RANDOM = new SecureRandom();

    public static String generate() {
        byte[] bytes = new byte[64];
        RANDOM.nextBytes(bytes);
        try {
            bytes = MessageDigest.getInstance(ALGORITHM).digest(bytes);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }
        return new String(Hex.encodeHex(bytes));
    }

    public static String generate(final int length) {
        if (length < MIN_LEN) {
            throw new IllegalArgumentException("length must be greater than " + MIN_LEN + " to be useful");
        }
        if (length > MAX_LEN) {
            throw new IllegalArgumentException("length must not be greater than " + MAX_LEN);
        }
        return generate().substring(0, length);
    }
}