Java Regex ReplaceAll with grouping

Question

I want to surround all tokens in a text with tags in the following manner:

Input: " abc fg asd "

Output:" <token>abc</token> <token>fg</token> <token>asd</token> "

This is the code I tried so far:

String regex = "(\\s)([a-zA-Z]+)(\\s)";
String text = " abc fg      asd ";
text = text.replaceAll(regex, "$1<token>$2</token>$3");
System.out.println(text);

Output:" <token>abc</token> fg <token>asd</token> "

Note: for simplicity we can assume that the input starts and ends with whitespaces

Toto · Accepted Answer · 2014-11-24 14:48:30Z

2

Use lookaround:

String regex = "(?<=\\s)([a-zA-Z]+)(?=\\s)";
...
text = text.replaceAll(regex, "<token>$1</token>");

answered Nov 24, 2014 at 14:48

Toto

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1 Comment

Joop Eggen Over a year ago

And text = text.replaceAll(regex, "<token>$1</token>"); In fact why not text = text.replaceAll("\\w+", "<token>$0</token>");?

Casimir et Hippolyte · Accepted Answer · 2014-11-24 14:55:20Z

0

If your tokens are only defined with a character class you don't need to describe what characters are around. So this should suffice since the regex engine walks from left to right and since the quantifier is greedy:

String regex = "[a-zA-Z]+";
text = text.replaceAll(regex, "<token>$0</token>");

answered Nov 24, 2014 at 14:55

Casimir et Hippolyte

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Comments

Attila Neparáczki · Accepted Answer · 2014-11-24 15:09:32Z

0

                                 // meaning not a space, 1+ times
String result = input.replaceAll("([^\\s]+)", "<token>$1</token>");

this matches everything that isn't a space. Prolly the best fit for what you need. Also it's greedy meaning it will never leave out a character that it shouldn't ( it will never find the string "as" in the string "asd" when there is another character with which it matches)

answered Nov 24, 2014 at 15:09

Attila Neparáczki

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1 Comment

Pshemo Over a year ago

\\S==[^\\s]. Also you don't need to wrap entire regex with parenthesis to create group matching entire regex because group 0 already does it for you. So try replaceAll("\\S+", "<token>$0</token>");

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