Jsp 提交响应后无法转发

我正试图通过设置属性从Servlet转发到JSP，但出现以下异常：

java.lang.IllegalStateException:在响应结束后无法转发 犯下

请帮忙

我的代码：

public class setPassword extends HttpServlet {

  protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException, ClassNotFoundException, SQLException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();

    Connection co;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        co = DriverManager.getConnection("jdbc:mysql://localhost:3306/gift", "root", "");
        Statement st = co.createStatement();
        System.out.println("setpassword...........");

        ResultSet rs = st.executeQuery("select * from generaldata");

        System.out.println("setpassword...........111");
        String userid = request.getParameter("username");

        while (rs.next()) {
            String us = rs.getString(2);
            String ps = rs.getString(3);
            System.out.println("setpassword...........222");

            System.out.println(us);
            System.out.println(userid);

            if (userid.equals(us)) {

                System.out.println(ps);
                System.out.println("setpassword...........333");

                if (ps.equals("")) {
                    String pass = request.getParameter("password");
                    String pass1 = request.getParameter("password1");
                    System.out.println("setpassword...........444");

                    if (pass.equals(pass1)) {
                        rs.updateNString(3, pass);
                        RequestDispatcher rdpassword = request.getRequestDispatcher("home.jsp");
                        rdpassword.forward(request, response);
                        System.out.println("setpassword...........555");
                    } else {
                        request.setAttribute("errorPassword", "Your Password does not match...!!!");
                        RequestDispatcher rdlogin = request.getRequestDispatcher("newuser.jsp");
                        rdlogin.forward(request, response);
                        System.out.println("setpassword...........666");
                    }
                } else {
                    request.setAttribute("err", "Please note you are not a New User...!!!");
                    System.out.println("setpassword.................777");
                    RequestDispatcher rdNotNew = request.getRequestDispatcher("login.jsp");
                    rdNotNew.forward(request, response);

                }
            } else {
                request.setAttribute("err", "Not a valid User...!!!");
                System.out.println("setpassword.................788");
                RequestDispatcher rdNotValid = request.getRequestDispatcher("login.jsp");
                rdNotValid.forward(request, response);
            }
            System.out.println("setpassword.................888");
        }
        System.out.println("setpassword.................999");

        rs.close();
        st.close();
        co.close();

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

您应该在转发后立即放置一个

返回

您应该将

response.setContentType（“text/html；charset=UTF-8”）

和

PrintWriter out=response.getWriter（）仅在不转发的分支内

在转发之前，您需要找到关闭db连接的方法

---

工作代码。。。。我已经指定了我在上述代码中进行更改的区域

公共类setPassword扩展了HttpServlet{

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException, ClassNotFoundException, SQLException {
   **// response.setContentType("text/html;charset=UTF-8");**
    PrintWriter out = response.getWriter();

    Connection co;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        co = DriverManager.getConnection("jdbc:mysql://localhost:3306/gift", "root", "");
        Statement st = co.createStatement();
        System.out.println("setpassword...........");

        ResultSet rs = st.executeQuery("select * from generaldata");

        System.out.println("setpassword...........111");
        String userid = request.getParameter("username");
        **int count = 0;**

        while (rs.next()) {
            String us = rs.getString(2);
            String ps = rs.getString(3);
            System.out.println("setpassword...........222");

            System.out.println(us);
            System.out.println(userid);

            if (userid.equals(us)) {

                **count++;**

                System.out.println(ps);
                System.out.println("setpassword...........333");

                if (ps.equals("")) {
                    String pass = request.getParameter("password");
                    String pass1 = request.getParameter("password1");
                    System.out.println("setpassword...........444");

                    if (pass.equals(pass1)) {
                        rs.updateNString(3, pass);
                        RequestDispatcher rdpassword = request.getRequestDispatcher("home.jsp");
                        rdpassword.forward(request, response);
                        System.out.println("setpassword...........555");
                    } else {
                        request.setAttribute("errorPassword", "Your Password does not match...!!!");
                        RequestDispatcher rdlogin = request.getRequestDispatcher("newuser.jsp");
                        rdlogin.forward(request, response);
                        System.out.println("setpassword...........666");
                        **return;**
                    }
                } else {
                    request.setAttribute("error", "Please note you are not a New User...!!!");
                    System.out.println("setpassword.................777");
                    RequestDispatcher rdNotNew = request.getRequestDispatcher("login.jsp");
                    rdNotNew.forward(request, response);
                    **return;**

                }
            }
            **else{
                continue;
            }**
            System.out.println("setpassword.................888");
        }

         **if(count == 0) {
                request.setAttribute("error", "Not a valid User...!!!");
                System.out.println("setpassword.................788");
                RequestDispatcher rdNotValid = request.getRequestDispatcher("login.jsp");
                rdNotValid.forward(request, response);
                return;
            }**

        System.out.println("setpassword.................999");

        rs.close();
        st.close();
        co.close();

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

---

请粘贴输出如果请求在循环终止前转发一次，则即使在转发请求后，循环仍将继续，该请求将尝试再次从另一个（或可能是相同的，取决于对其中一个条件的评估）

if-else

块，导致抛出笨拙的

java.lang.IllegalStateException

（这似乎不寻常）。您可能希望适当地使用

break

语句或

if else if

梯形图中的标志变量来指示身份验证的状态，并使用该变量在循环外转发请求。如果您正在检查用户身份验证，则可以使用带有prepare语句的单个查询，如

select*从user_表，其中user_email=？和user_password=？

，然后

如果（rs.next（））{//用户凭据正确。因此重定向到主页}否则{//显示指示凭据错误的消息}

。无需与循环共舞：）感谢您提出的“准备声明”想法………仅添加return不起作用，但我删除了“response.setContentType（“text/html；charset=UTF-8”）；”并添加了return；效果很好。