UUIDShort-java

import java.security.SecureRandom;
import java.util.UUID;

/**
 * 长度为16的 UUID 字符串生成器， 仿 java.util.UUID 实现，修改内容如下： 将16位byte数组缩短为10位，将16进制字符转换改为32进制转换
 */
public class UUIDShort {

    private static char[] digits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z' };

    private static String toUnsignedString(long i, int shift) {
        char[] buf = new char[64];
        int charPos = 64;
        int radix = 1 << shift;
        long mask = radix - 1;
        do {
            buf[--charPos] = digits[(int) (i & mask)];
            i >>>= shift;
        } while (i != 0);
        return new String(buf, charPos, (64 - charPos));
    }

    private static SecureRandom ng = new SecureRandom();

    /**
     * 生成一个长度为16的随机字符串
     *
     * @return
     */
    public static String random16() {
        byte[] data = new byte[10];
        ng.nextBytes(data);
        long msb = 0;
        long lsb = 0;
        for (int i = 0; i < 5; i++) {
            msb = (msb << 8) | (data[i] & 0xff);
        }
        for (int i = 5; i < 10; i++) {
            lsb = (lsb << 8) | (data[i] & 0xff);
        }
        String random = toUnsignedString(msb, 5) + toUnsignedString(lsb, 5);
        if (random.length() < 16) {
            for (int i = 0; i < 16 - random.length(); i++) {
                random = digits[ng.nextInt(36)] + random;
            }
        }
        return random;
    }

    public static String random32() {
        return UUID.randomUUID().toString();
    }

}