java - 提交响应后如何解决无法调用 sendRedirect() 的问题？

Question

这个问题在这里已经有了答案:

java.lang.IllegalStateException: Cannot (forward | sendRedirect | create session) after response has been committed (9 个回答)

关闭 6年前。

我正在尝试使用以下代码将值从 servlet 传递到 jsp 页面:

public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    PrintWriter out = response.getWriter();
    try {
        System.out.println("try");

        String taskid=request.getParameter("id");   
        convty = new Connectivity();
        con = convty.setConnection();
        st=con.createStatement();

        query="select * from task_table";

        rset=convty.getResultSet(query, con);
        while(rset.next()) {
            System.out.println("while");
            lst.add(rset.getString("task_id"));
            lst.add(rset.getString("date"));
            lst.add(rset.getString("project_name"));    
        }
        rset.close();
        System.out.println("after while");

    } catch(Exception e) {

        RequestDispatcher dd= request.getRequestDispatcher("error.jsp");
        dd.forward(request, response);

    } finally {
        System.out.println("finally1");
        HttpSession sessionvar = request.getSession();
        sessionvar.setAttribute("TaskData", "lst");

        response.sendRedirect("usertaskpage.jsp");

        lst.clear();
        out.close();            
    }
}

当我运行我的页面时，我得到:

错误:

java.lang.IllegalStateException: Cannot call sendRedirect() after the response has been committed
    org.apache.catalina.connector.ResponseFacade.sendRedirect(ResponseFacade.java:483)
    src.Taskservlet.doPost(Taskservlet.java:108)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)

我尝试使用:

RequestDispatcher dd=request.getRequestDispatcher("usertaskpage.jsp");
dd.forward(request, response);

但我遇到了同样的错误。

如何解决这个错误？

Answer 1

您已经在 catch block 中转发了响应:

RequestDispatcher dd = request.getRequestDispatcher("error.jsp");

dd.forward(request, response);

所以，你不能再次调用:

response.sendRedirect("usertaskpage.jsp");

因为它已经被转发(提交)了。

所以你可以做的是:保留一个字符串以分配您需要转发响应的位置。

    String page = "";
    try {

    } catch (Exception e) {
      page = "error.jsp";
    } finally {
      page = "usertaskpage.jsp";
    }

RequestDispatcher dd=request.getRequestDispatcher(page);
dd.forward(request, response);