第一次加載頁面時，它獲取變量的數據，但重新加載後變量爲空

Question

我不知道爲什麼會話只獲得stackOfProducts一次，並且在頁面重新加載之後StackOf Products==null但此會話的另一個對象像boolean was工作正常嗎？ 屏幕短褲 獲取數據 http://s57.radikal.ru/i155/1411/74/2922b55d6887.png 不要有數據 http://s019.radikal.ru/i614/1411/d3/b4975bb3bd60.png

這裏是我的servlet：

package ua.big_market; 

import java.io.IOException; 
import java.sql.Connection; 
import java.sql.SQLException; 
import java.util.LinkedList; 

import javax.servlet.ServletConfig; 
import javax.servlet.ServletException; 
import javax.servlet.annotation.WebServlet; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 

import ua.big_market.db.connecting.DataBaseConnect; 
import ua.big_market.db.product.GetProductDataDB; 
import ua.big_market.product.Product; 
import ua.big_market.product.StackOfProducts; 

@WebServlet(asyncSupported = false, name = "ServletGetProductData", urlPatterns = { "/xmlGetProductData"}) 
public class XmlGetProductData extends HttpServlet { 
    private static final long serialVersionUID = 1L; 


    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
     //TODO: It's must have every servlet. Because russian and Ukraine words has a UTF-8 
     request.setCharacterEncoding("utf-8"); 
     response.setCharacterEncoding("utf-8"); 
     response.setContentType("text/html"); 

     Connection connection = null; 
     DataBaseConnect dataBaseConnect = new DataBaseConnect(); 

     try{ 
      connection = dataBaseConnect.getConnectToDB(); 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 

     System.out.println("Get Product Started!"); 
     Product product; 
     GetProductDataDB getProductDataDB = new GetProductDataDB(); 
     StackOfProducts stackOfProducts = new StackOfProducts(); 


     try { 
//all work fine 
      LinkedList<Integer> listofId = getProductDataDB.getAllIdFromDB(connection, "computers_notebooks"); 
      while(!listofId.isEmpty()) { 
       product = getProductDataDB.getProduct(connection, "computers_notebooks", listofId.getFirst()); 
       listofId.removeFirst(); 
       stackOfProducts.addProduct(product); 
      } 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 


     boolean was = true; 
     request.getSession().setAttribute("stackOfProducts", stackOfProducts);   
     request.getSession().setAttribute("was", was); 
    // work fine 
     response.sendRedirect("computers-notebooks.jsp"); 
    } 


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

    } 



    @Override 
    public void init(ServletConfig config) throws ServletException { 
//  this.context = config.getServletContext(); 
    } 
} 

這裏是我的HTML：

    <% 
         boolean was = false; 
         try { 
          was = (Boolean) session.getAttribute("was"); 
         } catch (Exception e) { 
          was = false; 
         } 

         if (!was) 
          response.sendRedirect("xmlGetProductData"); 

         StackOfProducts stackOfProducts = (StackOfProducts) session.getAttribute("stackOfProducts"); **// at first i have a getting data there but after reload i have null** 


         StackOfProducts stackOfProducts2 = null; 


         if (stackOfProducts != null && !stackOfProducts.isEmpty()) { 
          stackOfProducts2 = new StackOfProducts(); 
          stackOfProducts2 = stackOfProducts; 
         } 
//      stackOfProducts = stackOfProducts2; 

         Product product = new Product(); 

         if (stackOfProducts2 != null) { 
          while (!stackOfProducts2.isEmpty()) { 
           product = stackOfProducts2.getNext(); 
        %> 
           <%=product.getProductName()%> **//only once i'm there** 

        <% 
           stackOfProducts2.removeCurrent(); 
          } 
         } else { 
          int i = 0; 
        %> 
          123456789 **//and after reload i'm always here** 
        <% 
         } 
        %> 

Answer 1

的問題是在您的變量was當您重定向到xmlGetProductData時檢查。之後，您應該將其設置爲false或null，就像初始狀態一樣。

if (!was) 
    response.sendRedirect("xmlGetProductData"); 
request.getSession().setAttribute("was", false);