Java regex String parse, trying to figure out a pattern

Question

File file = new File("file-type-string-i-want-2000-01-01-01-01-01.conf.gz");
            Matcher matcher = pattern.compile("\\-(.*)\\-\\d{4}")).matcher(fileName);
            StringBuilder sb = new StringBuilder();
            while (matcher.find()) {
                sb.append(matcher.group());
            }
            stringList = Arrays.asList(sb.toString().split("-"));
            if (stringList.size() >= 2) {
                nameFragment = stringList.get(stringList.size() - 2);
            }

Desired result is to extract

string-iwant

from strings that look like this

file-type-string-iwant-2000-01-01-01-01-01.conf.gz

Unfortunatly, the format for "string-iwant" is a non-fixed length of alpha-numeric characters that will include only ONE hyphen BUT never start with a hyphen. The date formatting is consistent, the year is always after the string, so my current approach is to match on the -year, but I'm having difficulty excluding the stuff at the beginning.

Thanks for any thoughts or ideas

Edit: updated strings

What about the file-type part, can that contain hyphen? If yes, what else makes it different from string-i-want? — Attila
– Attila, Commented Mar 27, 2012 at 14:57
You cannot exclude the part at the beginning because you did not define what it is with enough clarity. From your current description, an extra assumption is needed to tell "type-string-i-want" from "string-i-want" or even from "i-want" or "want". — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Mar 27, 2012 at 15:04
@Hoofamon - in that case you need to find another quality that differentiates the two parts (e.g. string-i-want always contains a specific amount of hyphens), otherwise there is no way to tell the difference with a regexp — Attila
– Attila, Commented Mar 27, 2012 at 15:05
@Hoofamon If file-type may or may not contain a hyphen, how do you tell apart "string-i-want" and "type-string-i-want"? — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Mar 27, 2012 at 15:06

bezmax · Accepted Answer · 2012-03-27 15:04:59Z

4

Here's the regex you need:

\\-([^-]+\\-[^-]+)\\-\\d{4}\\-

Basically it means:

- starts with minus
([^-]+\\-[^-]+) contains 1 or more non-minus symbols, then a minus, then 1 or more non-minus symbols. This part is captured.
-\d{4} a minus sign and 4 digits

However, that will only work if stuff-you-need has only one hyphen (or a constant amount of hyphens, which will need correction in regex). Otherwise, there is no way to know if given the string file-type-string-i-want the word type belongs to a sting you want or not.

Added:

In case the file-type always contains exactly one hyphen, you can capture the required part this way:

[^-]+\\-[^-]+\\-(.*)\\-\\d{4}\\-

Explanation:

[^-]+\-[^-]+\\- some amount of non-hyphen characters, then a hyphen, then more non-hyphens. This will skip the file-type string with the following hyphen.
\-\d{4}\- a hyphen, 4 digits followed by another hyphen
(.*) everything in between of previous 2 statements is captured as being the string you need to select

edited Mar 27, 2012 at 15:04

answered Mar 27, 2012 at 14:54

bezmax

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4 Comments

jpm Over a year ago

I don't get the impression that the capture should contain exactly one hyphen . . . just that hyphen is a valid character for that portion of the string.

bezmax Over a year ago

The question is a bit confusing in this part: "Unfortunatly, the format for "string-i-want" is a non-fixed length of alpha-numeric characters that will include a hyphen BUT never start with a hyphen.", is it ONE hyphen, or is it ANY amount of hyphens.

RandomUser Over a year ago

sorry, it is indeed only 1 hyphen so I should have said string-iwant

bezmax Over a year ago

@Hoofamon then the first part (before "Added:") will work for you.

inhan · Accepted Answer · 2012-03-27 15:10:54Z

0

If it were PHP I would use something like the following to capture that string.

/^(\w+\-){2}(?<string>.+?)\-\d{4}(\-\d{2}){5}(\.\w+){2}$/

answered Mar 27, 2012 at 15:10

inhan

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Comments

anubhava · Accepted Answer · 2012-03-27 15:15:53Z

0

The regex that I would use for this purpose is this with a positive lookahead:

Pattern p = Pattern.compile("[^-]+-[^-]+(?=-\\d{4})");

Which simply means match the text containing exactly one hyphen followed by one hyphen and a 4 digit year.

Then you can simply grab the matcher.group(0) as your matched text which will be string-iwant in this case.

answered Mar 27, 2012 at 15:15

anubhava

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