Replace text in StringBuilder via regex

Question

I would like to replace some texts in StringBuilder. How to do this?

In this code I got java.lang.StringIndexOutOfBoundsException at line with matcher.find():

StringBuilder sb = new StringBuilder(input);
Pattern pattern = Pattern.compile(str_pattern);
Matcher matcher = pattern.matcher(sb);
while (matcher.find())
  sb.replace(matcher.start(), matcher.end(), "x"); 

Answer 1

Lets have a StringBuilder w/ 50 total length and you change the first 20chars to 'x'. So the StringBuilder is shrunk by 19, right - however the initial input pattern.matcher(sb) is not altered, so in the end StringIndexOutOfBoundsException.

Answer 2

I've solved this by adding matcher.reset():

    while (matcher.find())
    {
        sb.replace(matcher.start(), matcher.end(), "x");
        matcher.reset();
    }