code: public static boolean isValidCSSURLChar (final char c)
    {
      return c == '!' ||
             c == '#' ||
             c == '$' ||
             c == '%' ||
             c == '&' ||
             (c >= '*' && c <= '[') ||
             (c >= ']' && c <= '~') ||
             (c >= '\u0080' && c <= '\uffff');
    }
docs: Check if the passed character is a valid character inside a URL. Characters
  for which this method returns <code>false</code> must be escaped!
  
  @param c
  The character to be checked.
  @return <code>true</code> if the passed character can be directly contained
  inside a URL, <code>false</code> otherwise if the character needs
  to be escaped.