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

Question

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 1

How about using the replaceAll() method?

Answer 2

If you are going to be changing a String many times, then it is usually more efficient to use a StringBuilder (but measure your performance to find out):

String str = "The rain in Spain falls mainly on the plain";
StringBuilder sb = new StringBuilder(str);
// do your replacing in sb - although you'll find this trickier than simply using String
String newStr = sb.toString();

Every time you do a replace on a String, a new String object is created, because Strings are immutable. StringBuilder is mutable, that is, it can be changed as much as you want.

Answer 3

StringBuilder will perform replace more efficiently, since its character array buffer can be specified to a required length. See this question for more details. StringBuilder is designed for more than appending!

Of course the real question is whether this is an optimisation too far ? The JVM is very good at handling creation of multiple objects and the subsequent garbage collection, and like all optimisation questions, my first question is whether you've measured this and determined that it's a problem.

Answer 4

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!)