CODEWITHSUNDEEP
javaregex
megablue
megablue

Reputation: 155

Java's regex confusion

Basically i want to match filename with .json extension but not file that start with . and excluding list.json.

This is what i come out with (without java string escapes)

(?i)^([^\.][^list].+|list.+)\.json$

I had use an online regex tester, Regexplanet to try my regex http://fiddle.re/x9g86

Everything works fine with the regex tester, however when i tried it in Java. Everything that has the letter l,i,s,t will be excluded... which is very confusing for me.

Can anyone give me some clues?

Many thanks in advance.

Upvotes: 2

Views: 140

Answers (3)

FThompson
FThompson

Reputation: 28687

You're using a character exclusion class, [^list], which ignores character order and instead of excluding list, excludes any cases of l, i, s, or t.

Instead, you want to use a negative lookahead:

(?i)(?!^list\.json$)[^\.].*\.json

Upvotes: 1

Bernhard Barker
Bernhard Barker

Reputation: 55609

A negative look-ahead will do it.

(?i)(?!\.|list\.json$).*\.json

(?!\.|list\.json$) is a negative look-ahead checking that the characters following is not either list.json followed by the end of the string, or ..

Code:

String regex = "(?i)(?!\\.|list\\.json$).*\\.json";
System.out.println("list.json".matches(regex)); // false
System.out.println(".json".matches(regex));     // false
System.out.println("a.Json".matches(regex));    // true
System.out.println("abc.json".matches(regex));  // true

But NPE's more readable solution is probably preferred.

Upvotes: 1

NPE
NPE

Reputation: 500357

I want to match filename with .json extension but not file that start with . and excluding list.json.

I am not sure you need regular expressions for this. I find the following much easier on the eye:

boolean match = s.endsWith(".json") && !s.startsWith(".") && !s.equals("list.json");

Upvotes: 8

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