Yossale Yossale - 2 months ago 8
Java Question

Java Replacing multiple different substring in a string at once (or in the most efficient way)

I need to replace many different sub-string in a string in the most efficient way.
is there another way other then the brute force way of replacing each field using string.replace ?

Answer

If the string you are operating on is very long, or you are operating on many strings, then it could be worthwhile using a java.util.regex.Matcher (this requires time up-front to compile, so it won't be efficient if your input is very small or your search pattern changes frequently).

Below is a full example, based on a list of tokens taken from a map. (Uses StringUtils from Apache Commons Lang).

Map<String,String> tokens = new HashMap<String,String>();
tokens.put("cat", "Garfield");
tokens.put("beverage", "coffee");

String template = "%cat% really needs some %beverage%.";

// Create pattern of the format "%(cat|beverage)%"
String patternString = "%(" + StringUtils.join(tokens.keySet(), "|") + ")%";
Pattern pattern = Pattern.compile(patternString);
Matcher matcher = pattern.matcher(template);

StringBuffer sb = new StringBuffer();
while(matcher.find()) {
    matcher.appendReplacement(sb, tokens.get(matcher.group(1)));
}
matcher.appendTail(sb);

System.out.println(sb.toString());

Once the regular expression is compiled, scanning the input string is generally very quick (although if your regular expression is complex or involves backtracking then you would still need to benchmark in order to confirm this!)