在JSP中从Object ArrayList转换为Object Array

Question

I am trying to do a simple conversion from ArrayList to Object Array but I am getting an error, I have tried numerous methods as mention on the internet but none of them is working, NEED HELP

Here is what I am doing

  private List<CartItems> cartobj = new ArrayList<CartItems>();

  --- Bean (Cart) ---

  private String name;
  private float price;
  private int quantity;

  --- In Servlet ---

  Order h = new Order(String a, String b, String c);
  cartobj.add(h);

  session.setAttribute("Cart", cartobj);


  --- In JSP ---

  <tbody>
      <% ArrayList<CartItems> cartobj = new ArrayList<CartItems>();
      cartobj.add((CartItems)session.getAttribute("Cart"));
      for(int i=0;i<cartobj.size();i++)
      {%>
          <tr>
              <td><% out.println(i+1); %></td>
              <td><% cartobj.get(i).getProductName(); %></td>
              <td><% cartobj.get(i).getPrice(); %></td>
              <td><% cartobj.get(i).getSales_Address(); %></td>
              <td><% cartobj.get(i).getOrder_Date(); %></td>
              <td><% cartobj.get(i).getQuantity(); %></td>
          </tr>

      <% } %> 

I also tried this

     <% 
       CartItems[] obj = (CartItems[])session.getAttribute("Cart");
       for(int i=0;i<obj.length;i++)
       {%>
           <tr>
               <td><% out.println(i+1); %></td>
               <td><% obj[i].getProductName(); %></td>
               <td><% obj[i].getPrice(); %></td>
               <td><% obj[i].getSales_Address(); %></td>
               <td><% obj[i].getOrder_Date(); %></td>
               <td><% obj[i].getQuantity(); %></td>
           </tr>
       <% } %>

I am getting this following error

  SEVERE: Servlet.service() for servlet [jsp] in context with path [/Final_Project] threw exception [java.lang.ClassCastException: java.util.ArrayList cannot be cast to [LObjects.CartItems;] with root cause

java.lang.ClassCastException: java.util.ArrayList cannot be cast to [LObjects.CartItems; at org.apache.jsp.cart_jsp._jspService(cart_jsp.java:165)

Answer 1

You can't cast a List to an array. A List is not a type of array. But, you could use List.toArray(T[]) and change

session.setAttribute("Cart", cartobj);

to something like

session.setAttribute("Cart", cartobj.toArray(new CartItems[cartobj.size()]));

then

CartItems[] obj = (CartItems[])session.getAttribute("Cart");

would be valid.

Answer 2

You need to cast it to List like this:

List<CartItems> obj = (List<CartItems>) session.getAttribute("Cart");

Still better to use JSTL for directly iterating on your list of objects:

<c:forEach items="${Cart}" var="element"> 
 <tr>
   <td>${element.productName}</td>
   <td>${element.salesAddress}</td>
   <td>${element.quantity}</td>
 </tr>
</c:forEach>

And follow Java bean naming conventions for your setters and getters, for example, getSales_Address is not a correctly defined.

Answer 3

You are setting List<CartItems> to session, ArrayList can not be cast with Array .

Try the following:

  <% 
   List<CartItems> obj = (List<CartItems>)session.getAttribute("Cart");
   for(int i=0;i<obj.length;i++)
   {
     CartItems cartItem = obj.get(i);
   %>
       <tr>
           <td><% out.println(i+1); %></td>
           <td><% cartItem.getProductName(); %></td>
           <td><% cartItem.getPrice(); %></td>
           <td><% cartItem.getSales_Address(); %></td>
           <td><% cartItem.getOrder_Date(); %></td>
           <td><% cartItem.getQuantity(); %></td>
       </tr>
   <% } %

Avoid java code in your jsp as much as you can. You can achieve this using JSTL .

<c:forEach items="${Cart}" var="c" varStatus="loop">
    <tr>
        <td>${loop.index+1}</td>
        <td>${c.productName}</td>
        <td>${c.price}</td>
        <td>${c.sales_address}</td>
        <td>${c.quantity}</td>
    </tr>
</c:forEach>