Java regex URL prefix removal

I have a set of URLs. Some of them have a string www as substring and some of them haven't. I need to remove prefixes in each URL. I tried remove this prefixes using many variants of regexp:

newStr = str.replaceAll("http://|http://www.", "");
newStr = str.replaceAll("^http://|http://www.$", "");
newStr = str.replaceAll("http://|http://www.", "");

where str - is an inputted URL string, and newStr is the URL after replacement. Each of these variants replaces only http:// prefix, but www. remains in result. How I can change my regexp to remove http:// string as well as http://www. string?