Question

我正在使用JSP和servlet制作购物车，我正在通过数据库中的arraylist将这些项目添加到购物车。我通过设置和获取session的属性值来做到这一点。但是它只添加了1个值，之后输出为null。请告诉我如何解决这个问题。这是我的Cart.java页面，其中元素被添加到ArrayList

ArrayList al=null;
        HttpSession session=request.getSession(false);
        try (PrintWriter out = response.getWriter()) {


            String id=request.getParameter("xyz");
            int i=Integer.parseInt(id);
            if (session.getAttribute("Il")==null)
            {

                al=new ArrayList();

            try{
            Class.forName("com.mysql.jdbc.Driver");
            Connection con=DriverManager.getConnection("jdbc:mysql://127.0.0.1:3307/cart","root","password");
            Statement st=con.createStatement();
            ResultSet rs=st.executeQuery("select * from cake where id="+i+"");
            while(rs.next())
            {
                Item item=new Item();
                item.itemid=rs.getInt(1);
                String name=rs.getString(2);
                item.itemname=rs.getString(2);
                item.itemprice=rs.getString(3);
                al.add(item);


        }
            session.setAttribute("Il", al);
            con.close();
            RequestDispatcher rd=request.getRequestDispatcher("select.jsp");
            rd.forward(request, response);
            }
            catch(Exception e)
            {
                out.println(e.getMessage());
    }
        }
            else
            {


                try{
            Class.forName("com.mysql.jdbc.Driver");
            Connection con=DriverManager.getConnection("jdbc:mysql://127.0.0.1:3307/cart","root","password");
            Statement st=con.createStatement();
            ResultSet rs=st.executeQuery("select * from cake where id="+i+"");
            while(rs.next())
            {
                Item item=new Item();
                item.itemid=rs.getInt(1);
                String name=rs.getString(2);
                item.itemname=rs.getString(2);
                item.itemprice=rs.getString(3);
                al.add(item);


        }
            session.setAttribute("Il", al);
            con.close();
            RequestDispatcher rd=request.getRequestDispatcher("select.jsp");
            rd.forward(request, response);
            }
            catch(Exception e)
            {
                out.println(e.getMessage());
    }
            }

这是我的Cart.jsp页面，其中显示了所有值。

    <%-- 
    Document   : Cart
    Created on : Jul 1, 2017, 10:36:09 AM
    Author     : hp-pc
--%>

<%@page import="java.util.Iterator"%>
<%@page import="java.util.ArrayList"%>
<%@page import="p1.Item"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<%@ page import="java.util.*" %>

<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Cart</title>
        <style>
            h1{
                float: right;
            }
          </style>

    </head>
    <body>
        <%
          String name=(String)session.getAttribute("username");
            %>
            <h1>
                <%=name%>
            </h1>

                 <table>
                <tr>
                    <th> Select</th>
                    <th>Id</th>
                    <th> Name</th>
                    <th> Price</th>
                </tr>
                <form>
                  <%
                      System.out.println("testing.......................");
        ArrayList items=(ArrayList)session.getAttribute("Il");
        System.out.println("success........................"+items);
        Iterator it=items.iterator();

        while(it.hasNext())
        {
            Item i=(Item)it.next();
    %>   
    <tr>
        <td>
                 <div class="radio">
                     <label><input type="radio" name="optradio"></label>
                 </div>
            </td>
        <td><%=i.itemid%></td>
        <td><%=i.itemname%></td>
        <td><%=i.itemprice%></td>
    </tr>
    <%
        }
      %>                 
                </form>
                 </table>



    </body>
</html>

Answer 1

您需要在al = (ArrayList) session.getAttribute("Il");之后添加} else {：

        } else {
            al = (ArrayList) session.getAttribute("Il"); // add this line
            try {
                Class.forName("com.mysql.jdbc.Driver");

至少。

如何在使用jsp和servlet时在数组列表中添加项目

1 个答案: