masking a creditcard number in java

Question

I tried to mask the characters in a creditcard number string using character 'X'.I wrote two functions as below .The second function uses commons.lang.StringUtils class .I tried to find the time it takes in both cases

public static String maskCCNumber(String ccnum){
        long starttime = System.currentTimeMillis();
        int total = ccnum.length();
        int startlen=4,endlen = 4;
        int masklen = total-(startlen + endlen) ;
        StringBuffer maskedbuf = new StringBuffer(ccnum.substring(0,startlen));
        for(int i=0;i<masklen;i++) {
            maskedbuf.append('X');
        }
        maskedbuf.append(ccnum.substring(startlen+masklen, total));
        String masked = maskedbuf.toString();
        long endtime = System.currentTimeMillis();
        System.out.println("maskCCNumber:="+masked+" of :"+masked.length()+" size");
        System.out.println("using StringBuffer="+ (endtime-starttime)+" millis");
        return masked;
    }

    public static String maskCCNumberCommons(String ccnum){
        long starttime = System.currentTimeMillis();
        int total = ccnum.length();
        int startlen=4,endlen = 4;
        int masklen = total-(startlen + endlen) ;
        String start = ccnum.substring(0,startlen);
        String end = ccnum.substring(startlen+masklen, total);
        String padded = StringUtils.rightPad(start, startlen+masklen,'X'); 
        String masked = padded.concat(end);
        long endtime = System.currentTimeMillis();
        System.out.println("maskCCNumber:="+masked+" of :"+masked.length()+" size");
        System.out.println("using Stringutils="+(endtime-starttime)+" millis");
        return masked;
    }

public static void ccNumberMaskingDemo() {
   String mcard1="5555555555554444";
   maskCCNumber(mcard1);
   maskCCNumberCommons(mcard1);
}

When I ran this ,I got this result

maskCCNumber:=5555XXXXXXXX4444 of :16 size
using StringBuffer=0 millis
maskCCNumber:=5555XXXXXXXX4444 of :16 size
using Stringutils=25 millis

I can't understand why commons.StringUtils is taking more time than the for loop+StringBuffer in the first function.Obviously I am using the api ,the wrong way..

Can someone advise how to use this api correctly, in this case?

Answer 1

Here you go. Clean and reusable:

/**
 * Applies the specified mask to the card number.
 *
 * @param cardNumber The card number in plain format
 * @param mask The number mask pattern. Use # to include a digit from the
 * card number at that position, use x to skip the digit at that position
 *
 * @return The masked card number
 */
public static String maskCardNumber(String cardNumber, String mask) {

    // format the number
    int index = 0;
    StringBuilder maskedNumber = new StringBuilder();
    for (int i = 0; i < mask.length(); i++) {
        char c = mask.charAt(i);
        if (c == '#') {
            maskedNumber.append(cardNumber.charAt(index));
            index++;
        } else if (c == 'x') {
            maskedNumber.append(c);
            index++;
        } else {
            maskedNumber.append(c);
        }
    }

    // return the masked number
    return maskedNumber.toString();
}

Sample Calls:

System.out.println(maskCardNumber("1234123412341234", "xxxx-xxxx-xxxx-####"));
> xxxx-xxxx-xxxx-1234

System.out.println(maskCardNumber("1234123412341234", "##xx-xxxx-xxxx-xx##"));
> 12xx-xxxx-xxxx-xx34

Good luck.

Answer 2

I know this is not an answer but you can use regular expression and solve this in one step

String replaced = originalCreditCardNo.replaceAll("\\b(\\d{4})(\\d{8})(\\d{4})", "$1XXXXXXXX$3");

Explanation:

• The \b boundary helps check that we are the start of the digits (there are other ways to do this, but here this will do).
• (\d{4}) captures four digits to Group 1 and Group 3
• (\d{8}) captures eight digits to Group 2
• In the replacement, $1 and $3 contain the content matched by Groups 1 and 3

Answer 3

Using Apache StringUtils...

String ccNumber = "123232323767"; 

StringUtils.overlay(ccNumber, StringUtils.repeat("X", ccNumber.length()-4), 0, ccNumber.length()-4);

Answer 4

Here's a slightly cleaner implementation based on StringUtils, though I am not sure how it would perform in comparison to your implementations. At any rate, the 'premature optimization' comments remain very valid.

    public static String maskNumber(final String creditCardNumber) {
    final String s = creditCardNumber.replaceAll("\\D", "");

    final int start = 4;
    final int end = s.length() - 4;
    final String overlay = StringUtils.repeat(MASK_CHAR, end - start);

    return StringUtils.overlay(s, overlay, start, end);
}

Answer 5

Firstly, if you make measurements of such a short-running code, you often do not get accurate results due to the minimal timing resolution your CPU/library/whatever provides (which means you usually get to see 0ms or the same small value over and over).

Second and more importantly, do not optimize this! "Premature optimization is the root of all evil" and in a case where you have only a few ms that you want to optimize the effort is thoroughly wasted. You would have to mask millions of credit cards before you should even remotely think about optimizing this simple mask method.