replace substring using regex

Question

I have a string which contains many <xxx> values.

I want to retrive the value inside <>, do some manipulation and re-insert the new value into the string.

What I did is

input = This is <abc_d> a sample <ea1_j> input <lmk_02> string
while(input.matches(".*<.+[\S][^<]>.*"))
{
   value = input.substring(input.indexOf("<") + 1, input.indexOf(">"));
   //calculate manipulatedValue from value
   input = input.replaceFirst("<.+>", manipulatedValue);
}

but after the first iteration, value contains abc_d> a sample <ea1_j> input <lmk_02. I believe indexOf(">") will give the first index of ">". Where did I go wrong?

Keppil · Accepted Answer · 2012-07-12 08:04:22Z

2

This is a slightly easier way of accomplishing what you are trying to do:

String input = "This is <abc_d> a sample <ea1_j> input <lmk_02> string";
Matcher matcher = Pattern.compile("<([^>]*)>").matcher(input);
StringBuffer sb = new StringBuffer();
while(matcher.find()) {
    matcher.appendReplacement(sb, manipulateValue(matcher.group(1)));
}
matcher.appendTail(sb);
System.out.println(sb.toString());

answered Jul 12, 2012 at 8:04

Keppil

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5 Comments

Michael Schmeißer Over a year ago

StringBuilder would be the better option to use here, but otherwise your solution looks good, upvote.

Keppil Over a year ago

@MichaelSchmeißer: I would use it if matcher.appendReplacement() accepted a StringBuilder as parameter.

Michael Schmeißer Over a year ago

Oh, I see. I wasn't aware of that (I think it is kinda weird too), so there is nothing to improve in your answer I guess. :)

Keppil Over a year ago

@MichaelSchmeißer: Yeah, it is kind of weird, this seems like a perfect place to use StringBuilder, but I guess they didn't want to expand the Matcher API.

Ian Roberts Over a year ago

As per my answer, you may need to use Matcher.quoteReplacement on your replacement string - appendReplacement allows backreferences like $1 to include groups from the match in the replacement (e.g. a pattern of <([^>]*)> and a replacement string of =$1= would change <foo> into =foo=). If you want a literal $ in the replacement string you have to escape it as \$, and thus if you want a literal backslash that has to be doubled. The quoteReplacement method does these substitutions for you.

Ian Roberts · Accepted Answer · 2012-07-12 08:09:20Z

0

This is a good use case for the appendReplacement and appendTail idiom:

Pattern p = Pattern.compile("<([^>]+)>");
Matcher m = p.matcher(input);
StringBuffer out = new StringBuffer():
while(m.find()) {
  String value = m.group(1);
  // calculate manipulatedValue
  m.appendReplacement(out, Matcher.quoteReplacement(manipulatedValue));
}
m.appendTail(out);

answered Jul 12, 2012 at 8:09

Ian Roberts

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Comments

bluish · Accepted Answer · 2012-07-12 15:48:17Z

-1

Try using an escape character \\ to the regex.

edited Jul 12, 2012 at 15:48

bluish

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answered Jul 12, 2012 at 7:54

Stanley Mungai

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1 Comment

Michael Schmeißer Over a year ago

At which point should an escape character help in the regex? Also, you should mention that escape characters must occur in pairs in Java regexes.

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