How to make SimpleDateFormat.parse() fail hard?

Question

I need this below code to start failing when the provided date string doesn't match the given format 100%.

SimpleDateFormat format = new SimpleDateFormat("MM/dd/yyyy");
format.setLenient(false);
format.parse("09/10/20144");

For some reason even with setLenient(false) this call returns an actual 09/10/20144 date. I tried passing "new ParsePosition(0)" to the parse call but that doesn't help at all since the date still returns as 09/10/20144. I need any exceptions from the exact date format to fail hard. Is there any good way of doing that?

Does it fail when given `2014/10/09`? Because I think it doesn't care about the exact number of numbers - in 8000 years that code would stop working. But if you want it to only accept EXACTLY that many letters, you could always check the input string's length. — Pokechu22, Sep 15 '14 at 00:05
That's actually a very simple yet good idea and I think this will solve my issue for now. Thx — goe, Sep 15 '14 at 13:45

score 4 · Answer 1 · answered Sep 15 '14 at 06:20

the string you give SDF only informs the formatter about the order and type of the input parts (the amount of information about the intervals for each field is limited, since he applies some calculations to make it "make" sense).

To achieve what you want, you can do an initial check using regular expression. In your case:

String input = "09/10/20144";
if (input == null || !input.matches("[01]\\d/[0123]\\d/[12]\\d{3}")) {
    throw new IllegalArgumentException("Invalid value or format");
} else {
    SimpleDateFormat format = new SimpleDateFormat("MM/dd/yyyy");
    format.setLenient(false);
    format.parse(input);
}

The above regex checks that:

the month has 2 digits, first of which is either 0 or 1
the day has 2 digits with the first being one of {0,1,2,3}
the year has 4 digits with the first one 1 or 2.

More information on regular expressions in Java: http://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html

This idea is good as well but I have to be able to deal with multiple date formats coming from higher logic so I don't want to get into the business of having multiple regexs to handle all possible date formats. But thx for the suggestion. — goe, Sep 15 '14 at 13:47
Ok, how about yoda time, as suggest in this SO: http://stackoverflow.com/questions/489538/is-there-a-good-strict-date-parser-for-java ? — Adrian B., Sep 15 '14 at 14:26

score 0 · Answer 2 · answered Sep 15 '14 at 14:22

Here's one way to do this, although it's slightly odd:

public static Date parseDate(String input) {
    final String format = "MM/dd/yyyy";
    if (input.length != format.length) { //Check the length, helps to avoid the cases mentioned earlier.
        throw new ParseException("Lengths do not match", 0);
    }
    SimpleDateFormat format = new SimpleDateFormat(format);
    format.setLenient(false);
    return format.parse(input);
}

(This is what I said in the comment earlier)

How to make SimpleDateFormat.parse() fail hard?

2 Answers2