Expiration Date Validation Example

Here is a simple example of a utility that can validate expirations dates like '0609' or '0710' as being valid expiration dates (i.e., is the date before the current month or not).

/**
 * Utility function to determine if a four character expiration date is valid OR not!
 * 
 * @param s
 * <p>Date string in format MMyy.  e.g., '0609' as date 'June 2009'.</p>
 * @return <code>boolean</code> flag indicating if expiration date is valid or not.
 */
public static boolean isValidExpiration(String s) {

    // use SimpleDateFormat to parse values like '0609' as date 'June 2009'
    java.text.DateFormat sdf = new java.text.SimpleDateFormat("MMyy");
    
    // establish current date as last day of previous month at 23:59:59
    java.util.Calendar now = java.util.Calendar.getInstance(); 
    now.set(now.get(java.util.Calendar.YEAR), now.get(java.util.Calendar.MONTH), 0, 23, 59, 59);

    try {
        // actual parsing of the date, wrapped in try/catch 
        // parses as 1st day of month at midnight since only providing month and year
        // e.g., '0609' becomes 'June 01, 2009 00:00:00'
        java.util.Date exp = sdf.parse(s);

        // if parsed date is before current month, then return invalid!
        if (exp.before(now.getTime())) return false;
    } catch (java.text.ParseException e) {
        return false;  // if not MMYY then reject
    }

    // valid if made it this far, can do in reverse by using !exp.before and return true above.
    return true; 
}

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