code: private static String getFileTypeIconClass(String resourceTypeName, String fileName, boolean small) {
  
          if ((fileName != null) && fileName.contains(".")) {
              int last = fileName.lastIndexOf(".");
              if (fileName.length() > (last + 1)) {
                  String suffix = fileName.substring(fileName.lastIndexOf(".") + 1);
                  return getResourceSubTypeIconClass(resourceTypeName, suffix, small);
              }
          }
          return "";
  
      }
docs: Returns the CSS class for the given filename.<p>
  
  @param resourceTypeName the resource type name
  @param fileName the filename
  @param small if true, get the CSS class for the small icon, else for the biggest one available
  
  @return the CSS class