getWriter() has already been called,该怎么解决

public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        response.setContentType("text/html;charset=UTF-8");        PrintWriter out = response.getWriter();        out.print( " <script> alert( 'Booking successfully ') </script> ");        ByteArrayOutputStream out1 = QRCode.from(all).to(ImageType.PNG).stream();            response.setContentType("image/png");            response.setContentLength(out1.size());                       OutputStream outStream = response.getOutputStream();            outStream.write(out1.toByteArray());            outStream.flush();                                    outStream.close();