java 短链接生成

1. package shorurl;
   import org.apache.commons.codec.digest.DigestUtils;
   import org.apache.commons.lang.StringUtils;
   publicclassShortUrl{
   privatestaticfinalint BINARY =0x2;
   privatestaticfinalint NUMBER_61 =0x0000003d;
   staticfinalchar[] 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','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'};
   protectedString shorten(String longUrl){
   String shortUrl = shorten(longUrl,5);
   if(StringUtils.isEmpty(shortUrl)){
   shortUrl = shorten(longUrl,6);
   }
   return shortUrl;
   }
   publicString shorten(String longUrl,int urlLength){
   if(urlLength <0|| urlLength >6){
   thrownewIllegalArgumentException("the length of url must be between 0 and 6");
   }
   String md5Hex =DigestUtils.md5Hex(longUrl);
   // 6 digit binary can indicate 62 letter & number from 0-9a-zA-Z
   int binaryLength = urlLength *6;
   long binaryLengthFixer =Long.valueOf(StringUtils.repeat("1", binaryLength), BINARY);
   for(int i =0; i <4; i++){
   String subString =StringUtils.substring(md5Hex, i *8,(i +1)*8);
   subString =Long.toBinaryString(Long.valueOf(subString,16)& binaryLengthFixer);
   subString =StringUtils.leftPad(subString, binaryLength,"0");
   StringBuilder sbBuilder =newStringBuilder();
   for(int j =0; j < urlLength; j++){
   String subString2 =StringUtils.substring(subString, j *6,(j +1)*6);
   int charIndex =Integer.valueOf(subString2, BINARY)& NUMBER_61;
   sbBuilder.append(DIGITS[charIndex]);
   }
   String shortUrl = sbBuilder.toString();
   return shortUrl;
   }
   returnnull;
   }
   }