When creating URL objects we have a small optimization in place that avoids initializing Locale on bootstrap:

    static String toLowerCase(String protocol) {
        if (protocol.equals("jrt") || protocol.equals("file") || protocol.equals("jar")) {
            return protocol;
        } else {
            return protocol.toLowerCase(Locale.ROOT);
        }
    }

This could be improved in two ways:
- move it to sun.net.util.URLUtil to facilitate reuse
- return "jrt", "file" or "jar" respectively to get canonicalization of the protocol string for free, saving memory for any URL we hold on to for an extended time