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

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

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

Answer 2

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 3

Another issue with using StringBuidler.replace() is that that one can't handle capturing groups.

Answer 4

You shouldn't do it this way. The input to Matcher may be any CharSequence, but the sequence should not change. Matching like you do is like iterating over a Collection while removing elements at the same time, this can't work.

However, maybe there's a solution:

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

Answer 5

Maybe:

    int lookIndex = 0;
    while (lookIndex < builder.length() && matcher.find(lookIndex)) {
        lookIndex = matcher.start()+1;
        builder.replace(matcher.start(), matcher.end(), repl);
    }

...?

.find(n) with an integer argument claims to reset the matcher before it starts looking at the specified index. That would work around the issues raised in maartinus comment above.

Answer 6

This is already a reported bug and I'm guessing they're currently looking into a fix for it. Read more here.