Regex Pattern in Java

Question

I have a regular expression as defined

AAA_BBB_CCCC_(.*)_[0-9][0-9][0-9][0-9][0-1][0-9][0-3][0-9]T[0-2][0-9][0-5][0-9][0-5][0-9].

There is a string defined as --> **AAA_BBB_CCCC_DDD_EEEE_19710101T123456** and in the code, we have matcher.group(1) which can filter out what is desired as (DDD_EEEE). Now, I've a new string coming in as --> **AAA_BBB_ATCCCC_DDD_EEEE_19710101T123456**. Is there a way that I can change the regex to satisfy both old and new string? I tried few solutions that came up from Stackoverflow questions like this and others but that didn't work quite right for me.

See https://regex101.com/r/Mx9pCx/1, just add `(?:AT)?` before `CCCC`. — Wiktor Stribiżew, Sep 19 '17 at 16:32
@WiktorStribiżew - Worked like a charm. Can you please add it as answer so that I can accept it.? — user123, Sep 19 '17 at 16:37
You might also consider using `[0-9]{8}T[0-9]{6}` in your regex. That is a little easier to understand ("8 digits, T, 6 digits"). After all, you'd have to further validate the input anyway, to avoid the 14th month, the 37th day of the month, or the 27th hour of the day. — AJNeufeld, Sep 19 '17 at 17:06
It can be made shorter with `AAA_BBB_(?:AT)?CCCC_(.*)_\d{4}[01]\d[0-3]\dT[0-2]\d[0-5]\d[0-5]\d` — ctwheels, Sep 19 '17 at 17:22

score 1 · Accepted Answer · answered Sep 19 '17 at 17:24

You just need to add an optional group, (?:AT)?, before CCCC:

AAA_BBB_(?:AT)?CCCC_(.*)_[0-9]{4}[0-1][0-9][0-3][0-9]T[0-2][0-9][0-5][0-9][0-5][0-9]
        ^^^^^^^

See the regex demo

I also contracted the four [0-9] to [0-9]{4} to make the pattern shorter.

The (?:AT)? is a non-capturing group to which a ? quantifier is applied. The ? quantifier makes the whole sequence of letters match 1 or 0 times, making it optional in the end.

score 0 · Answer 2 · answered Sep 19 '17 at 17:17

0

Please give the following regex a try.

AAA_BBB_(ATCCCC|CCCC)_(.*)_[0-9][0-9][0-9][0-9][0-1][0-9][0-3][0-9]T[0-2][0-9][0-5][0-9][0-5][0-9].

It would only match ATCCCC or CCCC. It won't be able to support dynamic characters preceding CCCC. You would need to use wildcards for that.

Also, you would need to change your matcher.group(1) statement to matcher.group(2)

answered Sep 19 '17 at 17:17

Pravin Umamaheswaran

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Thank you for your tip. However, I didnt want to change the code and hence the ask. – user123 Sep 20 '17 at 19:37

Regex Pattern in Java

2 Answers2