Java 11 Generic Regex to parse a given String value

Question

I'm working on a side project for which I need to parse String to obtain substrings

I have a REST API containing a String parameter in the payload. This String value's pattern can vary across any of the enlisted patterns:

[Name]
[Name 1], [Name 2]
[Name 1] and [Name 2]
[Name 1], [Name 2] and [Name 3]
[Name 1], [Name 2] and [Name 3], [Role]

Options I tried:

Including another parameter in the request payload that describes the format of the String value. For Ex: If a string value of pattern #4 is to be passed as input, here is the payload I would expect:

{
"Value" : "Name 1, Name 2 and Name 3",
"Format": 4
}

Here, it's a burden on the client to determine the format and set the format value accordingly, which is definitely not a good approach

Somehow determine the format (For Ex: count the number of commas and AND keyword) and accordingly use a Reg-ex dedicated for that format For Ex: If the string contains at least one comma, an occurrence of the AND keyword and a comma after the AND keyword, it could be pattern #5 (described in the list above). So use the Reg-ex pattern: ([a-zA-Z]+( [a-zA-Z]+)+),([a-zA-Z]+( [a-zA-Z]+)+),[a-zA-Z]+
This approach does work, but still is far too rigid to be practical. For Ex: Consider 4 names (rather than 3) being a part of the value, the said pattern won't work

Is there a more generic reg-ex pattern possible that could satisfy each of the aforementioned patterns?

"Is there a more generic reg-ex pattern possible that could satisfy each of the aforementioned patterns?" - Seems to me that "and" serves the exact same purpose as the comma in your patterns. Replace " and " with comma, split the string on commas. — Tomalak
– Tomalak, Commented Feb 22, 2022 at 9:31

Tim Biegeleisen · Accepted Answer · 2022-02-22 09:33:03Z

2

Here is a generic regex pattern which covers all 5 types of inputs:

^\[.*?\](?:(?:,|\s+and\s+)\s*\[.*?\](?:\s+and\s+\[.*?\])*)*$

Demo

Explanation of regex:

^                    start of string
\[.*?\]              match [Name]
(?:
    (?:,|\s+and\s+)  match either comma or "and" separator
    \s*              optional whitespace
    \[.*?\]          another [Name 2]
    (?:
        \s+and\s+    "and" separator
        \[.*?\]      more [Name] terms
    )*               zero or more
)*                   zero or more
$                    end of string

answered Feb 22, 2022 at 9:33

Tim Biegeleisen

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The fourth bird · Accepted Answer · 2022-02-22 10:45:11Z

1

You could write the pattern repeatedly matching all between the square brackets:

^\[[^\]\[]*](?:(?:,| and) \[[^\]\[]*])*$

In parts, the pattern matches:

^ Start of string
\[[^\]\[]*] Match from [....]
(?: Non capture group
- (?:,| and) Match either a comma followed by a space or and followed by a space
- \[[^\]\[]*] Match from [....]
)* Close the non capture group and optionally repeat
$ End of string

Regex demo

In Java with the doubled escaped backslashes:

String regex = "^\\[[^\\]\\[]*](?:(?:,| and) \\[[^\\]\\[]*])*$"

answered Feb 22, 2022 at 10:45

The fourth bird

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