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;
}