regex - java regular expressions: performance and alternative

Question

Recently I have been had to search a number of string values to see which one matches a certain pattern. Neither the number of string values nor the pattern itself is clear until a search term has been entered by the user. The problem is I have noticed each time my application runs the following line:

    if (stringValue.matches (rexExPattern))
    {
        // do something so simple
    }

it takes about 40 micro second. No need to say when the number of string values exceeds a few thousands, it'll be too slow.

The pattern is something like:

    "A*B*C*D*E*F*"

where A~F are just examples here, but the pattern is some thing like the above. Please note* that the pattern actually changes per search. For example "A*B*C*" may change to W*D*G*A*".

I wonder if there is a better substitution for the above pattern or, more generally, an alternative for java regular expressions.

Answer 1

Regular expressions in Java are compiled into an internal data structure. This compilation is the time-consuming process. Each time you invoke the method String.matches(String regex), the specified regular expression is compiled again.

So you should compile your regular expression only once and reuse it:

Pattern pattern = Pattern.compile(regexPattern);
for(String value : values) {
    Matcher matcher = pattern.matcher(value);
    if (matcher.matches()) {
        // your code here
    }
}