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 sta

Answer 1

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).