Short url

ShortUrlUtil.java

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * 
 * @author <a href="mailto:xiaowei.hu@renren-inc.com">Xiaowei Hu</a>
 * @version 1.0 2012-8-1 下午03:17:19
 * @since 1.0
 */
public class ShortUrlUtil {

    private static final char[] hexChar = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a',
            'b', 'c', 'd', 'e', 'f' };

    private static final char[] shortChar = { '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', '0',
            '1', '2', '3', '4', '5' };

    /**
     * 
     * <pre>
     * 1)将长网址md5生成32字符签名串,分为4段, 每段8个字符;
     * 2)对这四段循环处理, 将他看成16进制串与0x3fffffff(30位1)与操作, 即超过30位的忽略处理; 
     * 3)这30位分成6段,每5位的数字作为字母表的索引取得特定字符, 依次进行获得6位字符串; 
     * 4)总的md5串可以获得4个6位串;取里面的任意一个就可作为这个长url的短url地址;
     * </pre>
     * 
     * @param src
     * @return
     */
    public static String[] shortUrl(String src) {
        String md5v = md5(src);

        String[] rs = new String[4];
        for (int i = 0; i < 4; i++) {
            StringBuilder res = new StringBuilder();
            
            long hexInt = Long.parseLong(md5v.substring(i * 8, i * 8 + 8), 16) & 0x3fffffff;

            for (int j = 0; j < 6; j++) {
                res.append(shortChar[(int) (0x000000000000001F & hexInt)]);
                hexInt = hexInt >> 5;
            }
            
            rs[i] = res.toString();
        }

        return rs;
    }

    public static String md5(String src) {
        String result = null;
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            byte[] byd = md.digest(src.getBytes("utf-8"));
            result = bytes2Hex(byd);
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return result;
    }

    private static String bytes2Hex(byte[] byd) {
        StringBuilder s = new StringBuilder();
        for (byte bt : byd) {
            char charA = hexChar[(bt >> 4) & 0x0f];
            char charB = hexChar[bt & 0x0f];

            s.append(charA).append(charB);
        }
        return s.toString();
    }

    public static void main(String[] args) {
        String[] ss = shortUrl("11");
        for (String s : ss) {
            System.out.println(s);
        }
    }
}