How to padded strings with zero`s in java?

Question

According to the requirement i want to get a unique reference according to following format.

Reference should be = 15 Chars Date Format(yyyy-MM--dd) + ZERO`s + Id ; ex 1 = 201911070000181 ex 2 = 201911070000090

In the code sample i have shown date as string and Id as string can anyone help me here? Thanks.

Date today = Utils.getCurrentDateByTimeZone(environment.getProperty(TIME_ZONE));
    String pattern = "yyyyMMdd";
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat(pattern);
    String date = simpleDateFormat.format(today);
    String merchantId = String.valueOf(transactionData.getMerchant().getMerchantId());

Answer 1

You can use String format to do this.

String.format("%s%07d", date, id);
// if date="20191107" and id=181, this will give 201911070000181

What this code does is, it appends 0's before id until its length is 7. (The first part is date and I assume that date is always 8 characters long.) It won't work if id is string so I suggest casting it to integer.

Answer 2

You can always use a StringBuilder:

StringBuilder sb = new StringBuilder(15);
sb.append(date);
for (int i = date.length() ; i < 15 - merchantId.length(); i++) {
    sb.append('0');
}
sb.append (merchantId);
String reference = sb.toString();