文本是否包含日期格式？

Question

Suppose I have this text:

how are you? ok, I'm fine and how are you 08-01-20. Nice.

How to check if it contains substring in a specific format? In this case this is a date format: dd-MM-yy

 how are you? ok, I'm fine and how are you 08-01-20. Nice.  

This case must return 08-01-20 .

But this text:

 how are you? ok, I'm fine and how are you 18:01:21. Nice.

must return null .

So I need method that return 08-01-20 in first case and return null in second case.

Answer 1

You can use match with regex .*?\\d{2}-\\d{2}-\\d{2}.* like so :

".*?\\d{2}-\\d{2}-\\d{2}.*".toRegex().matches(str)

---

Edit

After OP edit, You can extract the date with the previews regex, then use a formatter to check if the date is valid or not, if yes return it, else return null :

fun check(str: String): LocalDate? {
    var formatter = DateTimeFormatter.ofPattern("dd-MM-yy");
    var v = str.replace(".*?(\\b\\d{2}-\\d{2}-\\d{2}\\b).*".toRegex(), "$1");
    try{
        return LocalDate.parse(v, formatter);
    }catch(e: DateTimeParseException) {
        return null;
    }
}

Check kotlin demo

Or if you want to get the same value and not a LocalDate you can return the extracted date as a String like so :

fun check(str: String): String? {
    var formatter = DateTimeFormatter.ofPattern("dd-MM-yy");
    var v = str.replace(".*?(\\b\\d{2}-\\d{2}-\\d{2}\\b).*".toRegex(), "$1");
    try{
        LocalDate.parse(v, formatter);
        return v;
    }catch(e: DateTimeParseException) {
        return null;
    }
}

Note: in the second part I changed the regex and I used boundaries to avoid some case like 321-12-4321

Edit

@Andreas put a good point in comment, so if you have many dates with that format, and at least one of them is valid, in this case you have to loop over all the matches and check one by one like so :

fun check(str: String): LocalDate? {
    var formatter = DateTimeFormatter.ofPattern("dd-MM-yy")
    val regex = Regex("\\b\\d{2}-\\d{2}-\\d{2}\\b")

    for (match in regex.findAll(str)) {
        try{
            return LocalDate.parse(match.value, formatter);
        }catch(e: DateTimeParseException) { }
    }
    return null
}

This will return the first valid date in your date