Question

我正在尝试使用MySQL为Java Web应用程序创建登录页面。当我运行代码时，我收到此异常。 java.lang.IllegalStateException：提交响应后无法创建会话

    protected void processRequest(HttpServletRequest request,  HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        try (PrintWriter out = response.getWriter()) {
        `String email = request.getParameter("email");
        String pass = request.getParameter("pass");
        MyDb1 db = new MyDb1();
      Connection con = db.getCon();
      Statement stmt = con.createStatement();
     ResultSet rs = stmt.executeQuery("select uid,email,pass from register where email = '"+email+"' and  pass = '"+pass+"'");
    if ((rs.next())) {

        String uid = rs.getString("uid");
        response.sendRedirect("http://localhost:8080/FinalYearProjec/userprofile.jsp");  


          HttpSession session=request.getSession();  
          session.setAttribute("name",uid); } 

else {
  RequestDispatcher rd = request.getRequestDispatcher("/Incorrect.html");
                rd.forward(request, response);


 }

  } catch (SQLException ex) {
    Logger.getLogger(Logi.class.getName()).log(Level.SEVERE,   null, ex);
         }

Answer 1

您的错误是因为您在设置会话属性之前正在重定向：

  HttpSession session=request.getSession();  
  session.setAttribute("name",uid); } 

 response.sendRedirect("http://localhost:8080/FinalYearProjec/userprofile.jsp");  //put this last

每当您将用户重定向或转发到其他页面时，都需要确保在转发或重定向之前执行了要执行的任何操作。因此，只需像这样更改它：

protected void processRequest(HttpServletRequest request,  HttpServletResponse response) throws ServletException, IOException {
    String email = request.getParameter("email");
    String pass = request.getParameter("pass");
    MyDb1 db = new MyDb1();

    String url = "Incorrect.html";    
    try(Connection con = db.getCon()){

         PreparedStatement pst = con.prepareStatement("select uid,email,pass from register where email = ? and pass = ?;"); 
         pst.setString(1, email); //set first '?'
         pst.setString(2, pass); //set second '?'
         ResultSet rs = pst.executeQuery();

        while(rs.next()) {

            url = "userprofile.jsp"; //override url string

            String uid = rs.getString("uid");

            HttpSession session=request.getSession();  
            session.setAttribute("name",uid); 

        }

    } catch (SQLException e) {
        e.printStackTrace();
    }

    RequestDispatcher rd = request.getRequestDispatcher(url);
    rd.forward(request, response);

}

这是您的代码，并且不需要的东西也被清除了（在这里使用preparestatement，因为手动构建您的语句并不安全，因为已经提到了注释。）

SELECT CONCAT('A purchase with the purchase ID of' AS "Constraint",
ONLINEPURCHASE.PurchaseID AS "OLID", 'is an online purchase of type' AS "Condition", ONLINEPURCHASE.OnlineType AS "OLType", 'and also a walkin purchase of location' AS "Condition", WALKINPURCHASE.ShopLocation AS "ShopLocation") 
FROM ONLINEPURCHASE JOIN WALKINPURCHASE
    ON ONLINEPURCHASE.PurchaseID = WALKINPURCHASE.PurchaseID
WHERE WALKINPURCHASE.PurchaseID IN (SELECT PurchaseID
        FROM WALKINPURCHASE);

错误; java.lang.IllegalStateException：提交响应后无法创建会话

1 个答案: