adding variables in a regular expression to make it dynamic in java

Question

I need to form a regular expression in order to check the outputs of a response log. The log file will always be different based on the input. Thus, I want to create a dynamic regular expression based on the input to the function. I may need to pass variable number of variables at a time for comparison, so how can that 'or' factor be inserted in the regex?

Is it possible to create such a regular expression in Java, and how should I go about it?

Yes, it's possible. Just use string concatenation, though you'll probably want to escape the variable parts to be safe. — Matt Ball
– Matt Ball, Commented Apr 16, 2012 at 10:57

Community · Accepted Answer · 2017-05-23 11:59:05Z

4

Yes, the regex is only a string, you can concatenate your user input to constant parts and then create a pattern from it.

If you want to match the user input literally, you should use Pattern.quote("UserString") to regex escape it.

Example:

String UserInput = "Bar()";
String Prefix = "Foo";

Pattern p = Pattern.compile(Prefix + Pattern.quote(UserInput));

String s1 = "FooBar()";
String s2 = "FooBarNo";

String[] s = { s1, s2};

for (String a : s) {
    Matcher m = p.matcher(a);
    if (m.find())
        System.out.println(a + " ==> Success");
    else
        System.out.println(a + " ==> Failure");
}

Output:

FooBar() ==> Success
FooBarNo ==> Failure

edited May 23, 2017 at 11:59

CommunityBot

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answered Apr 16, 2012 at 11:00

stema

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4 Comments

ashfaq Over a year ago

thanks for the reply, that was pretty easy stuff, but the main problem for me is that it is not necessary that each time I need to add the same number of variables ... sometimes it may be 4 and sometimes 6 or more ... what to do in that case ?

Matt Ball Over a year ago

@ashfaq then you're going to have to edit your question to be more specific, because we're not mind readers.

stema Over a year ago

Thanks MДΓΓ БДLL, @ashfaq What about a loop where you add all the strings you want?

ashfaq Over a year ago

@stema thanks for the snippet, very near to my need... i'll build upon it.:-)

Matthieu · Accepted Answer · 2020-08-28 02:36:45Z

0

I think you can do that by concatenating. e.g: "your regex" + "{" + input + "}".

edited Aug 28, 2020 at 2:36

Matthieu

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answered Aug 27, 2020 at 21:30

HUNTER_X

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