Regex for time in hh:mm am/pm format in java

Question

I need to make strict validation of input for my project, time in format HH:MM am/pm. So far i've got this RegEx expression:

(1[012]|[1-9]):[0-5][0-9](\\s)?(?i)(am|pm)

Above expression working fine but when I pass 09:05 AM its not working and its working when i pass 9:05 AM

Can some one suggest me please how can i solve this problem.

Code

public class SampleClass {

    public static void main(String[] args) {
        String inputTimeString = "09:05 PM";
        boolean isValidaTim = isValidTime(inputTimeString);
        if (isValidaTim) {
            System.out.println("Valid time string: " + inputTimeString);
        } else {
            System.out.println("Invalid time string: " + inputTimeString);
        }
    }

    public static boolean isValidTime(String time) {
        String regexPattern = "(1[012]|[1-9]):" + "[0-5][0-9](\\s)" + "?(?i)(am|pm)";
        Pattern compiledPattern = Pattern.compile(regexPattern);
        if (time == null) {
            return false;
        }
        Matcher m = compiledPattern.matcher(time);
        return m.matches();
    }

}

For a match only, you don't need the capturing groups. You have to add an optional zero to match 09 and you can use a character class for the am pm part (?:1[012]|0?[1-9]):[0-5][0-9]\\h?(?i)[ap]m See regex101.com/r/0ien3M/1 — The fourth bird
– The fourth bird, Commented Nov 12, 2020 at 8:56
Regex is overkill here. See the use of java.time classes shown in Answer by Ole V.V. — Basil Bourque
– Basil Bourque, Commented Nov 16, 2020 at 0:38

Anonymous · Accepted Answer · 2020-11-15 09:49:46Z

java.time

Don’t use a regular expression for this. Use java.time, the modern Java date and time API.

private static final DateTimeFormatter timeFormatter = new DateTimeFormatterBuilder()
        .parseCaseInsensitive()
        .appendPattern("h:mm a")
        .toFormatter(Locale.ENGLISH);

public static boolean isValidTime(String time) {
    try {
        LocalTime.parse(time, timeFormatter);
        return true;
    } catch (DateTimeParseException dtpe) {
        return false;
    }
}

To try it out:

    System.out.println("Is 9:05 am valid? " + isValidTime("9:05 am"));
    System.out.println("Is 09:05 PM valid? " + isValidTime("09:05 PM"));

Output:

Is 9:05 am valid? true
Is 09:05 PM valid? true

If you want to allow single-digit minutes and permit omitting the space, write your pattern like this:

        .appendPattern("h:m[ ]a")

Is 09:10PM valid? true
Is 09:5 PM valid? true

For most purposes you should also keep the LocalTime object that results from parsing rather than keep your time in a string.

Link: Oracle tutorial: Date Time explaining how to use java.time.

rzwitserloot · Accepted Answer · 2020-11-12 02:51:23Z

1

Just go through the regex. You start with 1[012]|[1-9]. So, either 10, or 11, or 12, or a single non-zero digit. Update the second part, and note that 00 is also a valid hour: 1[012]|0?[0-9] will get the job done. There are many regex tutorials and testers out there.

You then shove a question mark as first char in the final bit for am/pm - whatever is that about? That's making the last digit of minute optional, that seems bizarre; it means 10:5 matches but 10:6 won't. You presumably want to allow spaces in between, so toss a \\s* in there too.

answered Nov 12, 2020 at 2:51

rzwitserloot

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1 Comment

AbhiRam Over a year ago

Thanks working now.But if i pass 09:10PM or 09:5 PM it should allow can you suggest please

larsgrefer · Accepted Answer · 2020-11-12 03:02:51Z

0

I'd try this one (\d|0\d|1[012]):([0-5]\d)\s*(am|pm)

The hour (\d|0\d|1[012]) can be a single digit, a zero and a single digit or 10,11,12

The minute ([0-5]\d) can be a 0 to 5 followed by a second digit

answered Nov 12, 2020 at 3:02

larsgrefer

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