In Java, how do I check if a string contains a substring (ignoring case)?

str1.toUpperCase().contains(str2.toUpperCase())

UPD:

Original answer was using toLowerCase() method. But as some people correctly noticed, there are some exceptions in Unicode and it's better to use toUpperCase(). Because:

There are languages knowing more than one lower case variant for one upper case variant.

You can use the toLowerCase() method:

public boolean contains( String haystack, String needle ) {
  haystack = haystack == null ? "" : haystack;
  needle = needle == null ? "" : needle;

  // Works, but is not the best.
  //return haystack.toLowerCase().indexOf( needle.toLowerCase() ) > -1

  return haystack.toLowerCase().contains( needle.toLowerCase() )
}

Then call it using:

if( contains( str1, str2 ) ) {
  System.out.println( "Found " + str2 + " within " + str1 + "." );
}

Notice that by creating your own method, you can reuse it. Then, when someone points out that you should use contains instead of indexOf, you have only a single line of code to change.

I'd use a combination of the contains method and the toUpper method that are part of the String class. An example is below:

String string1 = "AAABBBCCC"; 
String string2 = "DDDEEEFFF";
String searchForThis = "AABB";

System.out.println("Search1="+string1.toUpperCase().contains(searchForThis.toUpperCase()));

System.out.println("Search2="+string2.toUpperCase().contains(searchForThis.toUpperCase()));

This will return:

Search1=true
Search2=false