High performance simple Java regular expressions

Question

Part of the code I'm working on uses a bunch of regular expressions to search for some simple string patterns (e.g., patterns like "foo[0-9]{3,4} bar"). Currently, we use statically-compiled Java Patterns and then call Pattern#matcher to check whether a string has contains a match to the pattern (I don't need the match, just a boolean indicating whether there is a match). This is causing a noticeable amount of memory allocation that is affecting performance.

Is there a better option for Java regex matching that is faster or at least doesn't allocate memory every time it searches a string for a pattern?

Answer 1

Try matcher.reset("newinputtext") method to avoid creating new matchers each time you are calling Pattern.matcher.

Answer 2

If you want to avoid creating a new Matcher for each Pattern, use the usePattern() method, like so:

Pattern[] pats = {
  Pattern.compile("123"),
  Pattern.compile("abc"),
  Pattern.compile("foo")
};
String s = "123 abc";
Matcher m = Pattern.compile("dummy").matcher(s);
for (Pattern p : pats)
{
  System.out.printf("%s : %b%n", p.pattern(), m.reset().usePattern(p).find());
}

see the demo on Ideone

You have to use matcher's reset() method too, or find() will only search from the point where the previous match ended (assuming the match was successful).