[short url] #java #sort url

base62.java

package nice.shorturl.utils;

import com.google.common.base.Charsets;
import com.google.common.hash.Hashing;

public class ShortUrlGenerator {
    private static final String ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    private static final int    BASE     = ALPHABET.length();
  
    public static String encode(int num) {
        StringBuilder sb = new StringBuilder();
        while ( num > 0 ) {
            sb.append( ALPHABET.charAt( num % BASE ) );
            num /= BASE;
        }
        return sb.reverse().toString();
    }

    public static int decode(String str) {
        int num = 0;
        for ( int i = 0; i < str.length(); i++ ) {
            num = num * BASE + ALPHABET.indexOf(str.charAt(i));
        }
        return num;
    }
}

md5hash.java

package nice.shorturl.utils;

import com.google.common.base.Charsets;
import com.google.common.hash.Hashing;

public class ShortUrlGenerator {
    private static final String[] chars = new String[] { "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" ,
            "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"

    };
    public static String[] shortUrl(String url) {
        // 可以自定义生成 MD5 加密字符传前的混合 KEY
        String key = "nice" ;
        // 要使用生成 URL 的字符

        // 对传入网址进行 MD5 加密
        String sMD5EncryptResult = Hashing.md5().hashString(key + url, Charsets.UTF_8).toString();
        String hex = sMD5EncryptResult;

        String[] resUrl = new String[4];
        for ( int i = 0; i < 4; i++) {

            // 把加密字符按照 8 位一组 16 进制与 0x3FFFFFFF 进行位与运算
            String sTempSubString = hex.substring(i * 8, i * 8 + 8);

            // 这里需要使用 long 型来转换，因为 Inteper .parseInt() 只能处理 31 位 , 首位为符号位 , 如果不用 long ，则会越界
            long lHexLong = 0x3FFFFFFF & Long.parseLong (sTempSubString, 16);
            String outChars = "" ;
            for ( int j = 0; j < 6; j++) {
                // 把得到的值与 0x0000003D 进行位与运算，取得字符数组 chars 索引
                long index = 0x0000003D & lHexLong;
                // 把取得的字符相加
                outChars += chars[( int ) index];
                // 每次循环按位右移 5 位
                lHexLong = lHexLong >> 5;
            }
            // 把字符串存入对应索引的输出数组
            resUrl[i] = outChars;
        }
        return resUrl;
    }
}