改成PrintWriter out = new PrintWriter(res.getOutputStream())就可以了？

public void doGet(HttpServletRequest request, HttpServletResponse response)
?? ??? ??? ?throws ServletException, IOException {
?? ??? ?System.out.println("!");? // 檢驗
?? ??? ?String piccode =(String)request.getSession().getAttribute("piccode");
?? ??? ?String checkcode =request.getParameter("checkcode");
?? ??? ?checkcode =checkcode.toUpperCase();
?? ??? ?System.out.println(checkcode+" "+piccode);? // 檢驗

??????? response.setCharacterEncoding("text/html;charset=utf-8");
?? ??? ?System.out.println("!!");?? // 檢驗
?? ??? ?//PrintWriter out =response.getWriter(); //錯誤
?? ??? ?PrintWriter out =new PrintWriter(response.getOutputStream()); //正確
?? ??? ?System.out.println("!!!");?? // 檢驗
?? ??? ?if(checkcode.equals(piccode))
?? ??? ?{
?? ??? ??? ?out.println("驗證碼輸入正確");
?? ??? ??? ?
?? ??? ?}
?? ??? ?else
?? ??? ?{
?? ??? ??? ?out.println("驗證碼輸入錯誤");
?? ??? ?}
?? ??? ?out.flush();
?? ??? ?out.close();
?? ?}