Pattern Matching for java using regex

Question

I have a Long string that I have to parse for different keywords. For example, I have the String:

"==References== This is a reference ==Further reading== *{{cite book|editor1-last=Lukes|editor1-first=Steven|editor2-last=Carrithers|}} * ==External links=="

And my keywords are

'==References==' '==External links==' '==Further reading=='

I have tried a lot of combination of regex but i am not able to recover all the strings.

the code i have tried:

Pattern pattern = Pattern.compile("\\=+[A-Za-z]\\=+");
Matcher matcher = pattern.matcher(textBuffer.toString());

while (matcher.find()) {
    System.out.println(matcher.group(0));
}

==External links== and ==Further reading== have space characters in them which will not be matched by [A-Za-z]. An improvement would be to change [A-Za-z] to [A-Za-z ] but I suspect there are still additional issues with your regex. — Asaph
– Asaph, Commented Sep 18, 2013 at 18:10

Rohit Jain · Accepted Answer · 2013-09-18 18:54:47Z

4

You don't need to escape the = sign. And you should also include a whitespace inside your character class.

Apart from that, you also need a quantifier on your character class to match multiple occurrences. Try with this regex:

Pattern pattern = Pattern.compile("=+[A-Za-z ]+=+");

You can also increase the flexibility to accept any characters in between two =='s, by using .+? (You need reluctant quantifier with . to stop it from matching everything till the last ==) or [^=]+:

Pattern pattern = Pattern.compile("=+[^=]+=+");

If the number of ='s are same on both sides, then you need to modify your regex to use capture group, and backreference:

"(=+)[^=]+\\1"

edited Sep 18, 2013 at 18:54

answered Sep 18, 2013 at 18:08

Rohit Jain

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4 Comments

Nikhil Over a year ago

I had used the whitespace, but i wasnt using the quantifier. Worked perfectly. Thanks.

Pshemo Over a year ago

=+ can cause mismatch. This regex will match =Lukes|editor1-first= and =Carrithers|}} * ==. Pattern.compile("==[^=]+=="); seems to be better here.

Nikhil Over a year ago

@Pshemo : I might need to match string like ===Example=== or =Example=. The number of "='s" is not fixed. i am sorry i didn't these them in the examples.

Rohit Jain Over a year ago

@Nikhil. Would you like to match - ==Example=?

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