How to find if a Java String contains X or Y and contains Z

Question

I'm pretty sure regular expressions are the way to go, but my head hurts whenever I try to work out the specific regular expression.

What regular expression do I need to find if a Java String (contains the text "ERROR" or the text "WARNING") AND (contains the text "parsing"), where all matches are case-insensitive?

EDIT: I've presented a specific case, but my problem is more general. There may be other clauses, but they all involve matching a specific word, ignoring case. There may be 1, 2, 3 or more clauses.

Answer 1

If you're not 100% comfortable with regular expressions, don't try to use them for something like this. Just do this instead:

string s = test_string.toLowerCase();
if (s.contains("parsing") && (s.contains("error") || s.contains("warning")) {
    ....

because when you come back to your code in six months time you'll understand it at a glance.

Edit: Here's a regular expression to do it:

(?i)(?=.*parsing)(.*(error|warning).*)

but it's rather inefficient. For cases where you have an OR condition, a hybrid approach where you search for several simple regular expressions and combine the results programmatically with Java is usually best, both in terms of readability and efficiency.

Answer 2

If you really want to use regular expressions, you can use the positive lookahead operator:

(?i)(?=.*?(?:ERROR|WARNING))(?=.*?parsing).*

Examples:

Pattern p = Pattern.compile("(?=.*?(?:ERROR|WARNING))(?=.*?parsing).*", Pattern.CASE_INSENSITIVE); // you can also use (?i) at the beginning
System.out.println(p.matcher("WARNING at line X doing parsing of Y").matches()); // true
System.out.println(p.matcher("An error at line X doing parsing of Y").matches()); // true
System.out.println(p.matcher("ERROR Hello parsing world").matches()); // true       
System.out.println(p.matcher("A problem at line X doing parsing of Y").matches()); // false