The method getInputStream in the HttpURLConnection class throws a FileNotFoundException for a protected servlet or a protected file which is aliased. Since the response code for a protected file or servlet is 401 and since it is aliased the code at line 359 in HttpURLConnection.java throws a FileNotFoundException and doesnt return a valid input stream. Maybe a fix could be to throw the exception if the response code is not 401 followed by the rest of the logic.