Stateful EJB not retaining information.

Question

Hello,

I have created a simple shopping cart. It stores an item ok and I can return the the page and the item remains there but as soon as I add another item to the cart however, it resets and just stores that one item. Any ideas?

Thanks

@Stateful(name="CartSessionBean")
@Remote(CartSession.class)
public class CartSessionBean implements CartSession, java.io.Serializable {

    private Cart items;

    @Init
    public void create() {
        items = new Cart();
    }

    public void add(Book item, int qty) {

        items.addItem(item, qty);

    }

Cart.java

@Entity

@Table(name = "Cart") public class Cart implements java.io.Serializable {

@Id @GeneratedValue
@Column(name="id")
private int id;

@Column(name = "total")
private Double total;

@OneToMany(mappedBy="cart")
private Set<Item> items;

public Cart(){
    // not valid?

}

//setters and getters

public int getOrder(){
    return id;
}

public void setOrder(int order){
    this.id = order;
}

public Double getTotal(){
    return total;
}

public void setTotal(Double q){
    this.total = q;
}

public Set<Item> getItems(){
    return this.items;
}

public void setItems(Set<Item> i){
    this.items = i;
}

public void addItem(Book b, int qty) {

    if(items == null) {
        items = new HashSet();
    }

    Item i = new Item();
    i.setBook(b);
    i.setQty(qty);

    this.items.add(i);
}

public void removeItem(Item id) {
    this.items.remove(id);
}

public void emptyCart() {
    this.items.clear();
}

}

Servlet

public class ServletCart extends HttpServlet {

    private Set<Item> items;

    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {

        // NO need.

        // DO WE HAVE A REMOVE REQUEST??

        if (items == null) {

            try {
                InitialContext context = new InitialContext();
                CartSession cartitems = (CartSession) context.lookup("CartSessionBean/remote");
                items = cartitems.getItems();
            } catch (NamingException e) {
                throw new ServletException("JNDI problem", e);
            }

        }

        RequestDispatcher view = request.getRequestDispatcher("cart.jsp");
        request.setAttribute("items", items);
        request.setAttribute("size", items.size());
        view.forward(request, response);
    }

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

        // Add a book :s/

        String isbn = request.getParameter("isbn"); // Does this ISBN exsit?
        int quantity = Integer.parseInt(request.getParameter("qty")); // Is this a number ?

        Book bk;

        try {
            InitialContext context = new InitialContext();
            BookSession guestbookSession = (BookSession) context.lookup("BookSessionBean/remote");
            bk = guestbookSession.getBook(isbn);

            CartSession cartitems = (CartSession) context.lookup("CartSessionBean/remote");
            cartitems.add(bk, quantity);

            this.items = cartitems.getItems();

        } catch (NamingException e) {
            throw new ServletException("JNDI problem", e);
        }

        request.setAttribute("response", bk.getBookTitle() + " Added.");

        doGet(request, response);

    }
}

Answer 1

There are several issues with the code as presented:

1. You cannot store instance variables in a servlet without synchronization. All requests to the servlet share the same instance, so instance variables would be shared.
2. CartSession.getItems is a remote method call, so the list of returned items is copied and passed by value. It looks like you might have been trying to work around this?
3. Each call to context.lookup("CartSessionBean/remote") will create a new instance of the stateful session bean.

You need to do something like: find or create an HttpSession from your HttpServletRequest, find or create a cart instance on the session, and then work with the cart session bean.