Question

I have a StringBuilder object that I use to build one large string, separating the strings in the StringBuilder object using a "\n" character, how can I efficiently build a regex around that object without splitting the string and doing a loop?

For example say I have the below regex:

private static final regexPattern = "(([a-z[1-9]]+)||([1-9[a-z]]+))"

If I have this:

String[] myStringList = aStringList.split("\n");

I’m trying to build an effective regex using the regexPattern and each string in myStringList.

Pattern p = Pattern.compile(regexPattern + myStringList[i]);

Is there anyway to do this without splitting my stringBuilder into a loop and checking each and every string? Can I somehow build a large pattern around the entire StringBuilder object?

Answer 1

This will build a big “OR” regex out of your input, pre-pending regexPattern to each part of the input string:

String bigRegex = "(" + regexPattern + aStringList.replace("\n", ")|(" + regexPattern) + ")";

Here’s some code that shows what you get:

public static void main(String[] args) {
    String aStringList = "foo\nbar\nbaz";
    String bigRegex = "(" + regexPattern + aStringList.replace("\n", ")|(" + regexPattern) + ")";
    System.out.println(bigRegex);
    // Pattern p = Pattern.compile(bigRegex);
}

Output:

((([a-z[1-9]]+)||([1-9[a-z]]+))foo)|((([a-z[1-9]]+)||([1-9[a-z]]+))bar)|((([a-z[1-9]]+)||([1-9[a-z]]+))baz)