Question

我正在尝试从数据库中获取数据并将其显示在另一个JSP上，但是出现错误

"java.lang.IllegalStateException: Cannot forward after response has been committed"

请任何人给我解决方案

代码是

  protected void doGet(HttpServletRequest request, HttpServletResponse response)
       throws ServletException, IOException {
       processRequest(request, response);

      System.out.println("Control at Question Of The day *************************************  ");
      PrintWriter out = response.getWriter();
    HttpSession session=request.getSession();
    String username= (String) session.getAttribute("username");
    System.out.println("Username from session == == = == == = ="+username);
    //Code for creation Dynamic number....

    xyz uniquecode=new xyz();
    String uni=uniquecode.UniqueCode();
    System.out.println("dynamic number creation== ==== ==== == "+uni);

   if(username!=null)
   {
        System.out.println("Session is not nulll block ... ");
        String url = null;
        DBConnector db=new DBConnector(url);
        Connection con=db.getConnection();
        System.out.println("Connection establish successfully ... ... .. .. .. ");
        String query="select Question, choiceA,choiceB,choiceC,choiceD from question_master where Question_id=?";
        try{
                PreparedStatement ps=con.prepareStatement(query);
                ps.setString(1, "92");
                java.sql.ResultSet rs= ps.executeQuery();
                List<QTD> questions = new ArrayList<QTD>();

                if(rs.next())
                {
                    QTD question = new QTD();

                    question.setQuestion(rs.getString(1));
                    System.out.println("Question ==== = "+rs.getString(1));
                    question.setOptA(rs.getString(2));
                    System.out.println("Answer A ==== = "+rs.getString(2));
                    question.setOptB(rs.getString(3));
                    System.out.println("Answer B ==== = "+rs.getString(3));
                    question.setOptC(rs.getString(4));
                    System.out.println("Answer C ==== = "+rs.getString(4));
                    question.setOptD(rs.getString(5));
                    System.out.println("Answer D ==== = "+rs.getString(5));
                    questions.add(question);
                      // System.out.println("************************************ List Data ****************************");
                     //System.out.println("************************************ List Data ****************************" +question) ;
                    RequestDispatcher rd=request.getRequestDispatcher("/html/QTD.jsp");
                    rd.forward(request, response);


                  }


                else{
                        System.out.println("there is not data ");
                     }
        //System.out.println("List from Database ========= "+questions);
        }

        catch(Exception e)
        {
            e.printStackTrace();
            System.out.println(e);
        }



   }

      else{

             System.out.println(" ********************* inside username is null block     ************************** ");
           RequestDispatcher rd=request.getRequestDispatcher("html/login.jsp");
          out.print("Sorry! Wrong Some Error is Occure, Please try again");
           rd.forward(request, response);
          }

    }

Answer 1

在方法的开头添加代码

HttpSession session=request.getSession();
String username= (String) session.getAttribute("username");
if (username==null) {
    RequestDispatcher rd=request.getRequestDispatcher("html/login.jsp");
    out.print("Sorry! Wrong Some Error is Occure, Please try again");
    rd.forward(request, response);
}

错误表明，当某些内容发送到响应时，您无法转发。

Answer 2

信息说明了一切。

基本上，当您的webapp执行导致启动写入客户端的操作时，响应将“已提交”。发生这种情况时，会写入响应头。但是，如果需要重定向请求，则不能编写头文件......因为您重定向到的servlet很可能需要在响应中输出不同的标头。

在这种情况下，当您致电response.getWriter()时，会提交回复。当您稍后致电rd.forward(request, response)时，为时已晚，您将获得例外。

您需要重新考虑doGet（）方法的逻辑......

Answer 3

在调用RequestDispatcher.forward()之前，不应提交响应。

在你的情况下，最有可能的是servlet导致响应在forward（）之前被提交。

以下是提交回复的原因：

Causes of Response getting committed.

java.lang.IllegalStateException：在提交响应后无法转发，位于com.java.QTD.QuestionOfTheDay.doGet（）

3 个答案: