Java string replace is slow

Java String.replace uses regular expressions and can be slow, especially for large strings requiring many replacements.

If you don't need regular expression replacement, you can use this function I wrote that performs better.

static public String replaceString(String orig, String search, String replace) {
  int cap = replace.length() > search.length() ? orig.length() + (replace.length() - search.length())*20 : orig.length();
  StringBuilder out = new StringBuilder(cap);

  int prev = 0;
  CharSequence okPart;
  for (int i=orig.indexOf(search); i!=-1; i=orig.indexOf(search, prev)) {
    okPart = orig.subSequence(prev, i);
    out.append(okPart).append(replace);
    prev = i + search.length();
  }
  if (prev < orig.length()) {
    okPart = orig.subSequence(prev, orig.length());
    out.append(okPart);
  }
  return out.toString();
}

Here is the performance data with Java String.replace:



Here is the performance data with the new function:



Interpreting the data:

With String.replace, time inside doFlowAction() was broken down 71/29% for enQueueWBImpression/getCPCWidgetCache. The hottest function inside getCPCWidgetCache was String.replace that accounted for 93% of the time.

With the new replacement function,
With String.replace, time inside doFlowAction() was broken down 89/11% for enQueueWBImpression/getCPCWidgetCache. This reduction of time spent inside getCPCWidgetCache (a 62% gain) is due to the replacement of the String.replace with the new string function.