How to check if a String contains another String in a case insensitive manner in Java?

Question

Say I have two strings,

String s1 = \"AbBaCca\";
String s2 = \"bac\";

I want to perform a check returning that s2 is contained

Answer 1

Here's some Unicode-friendly ones you can make if you pull in ICU4j. I guess "ignore case" is questionable for the method names because although primary strength comparisons do ignore case, it's described as the specifics being locale-dependent. But it's hopefully locale-dependent in a way the user would expect.

public static boolean containsIgnoreCase(String haystack, String needle) {
    return indexOfIgnoreCase(haystack, needle) >= 0;
}

public static int indexOfIgnoreCase(String haystack, String needle) {
    StringSearch stringSearch = new StringSearch(needle, haystack);
    stringSearch.getCollator().setStrength(Collator.PRIMARY);
    return stringSearch.first();
}