Question

我创建了一个简单的购物车。它存储一个项目确定，我可以返回页面，项目仍然存在，但是一旦我将另一个项目添加到购物车，它会重置并只存储该项目。有什么想法吗？

由于

@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实现了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();
}

}

的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

所提供的代码有几个问题：

如果没有同步，则无法在servlet中存储实例变量。对servlet的所有请求共享同一个实例，因此实例变量将被共享。
CartSession.getItems是一个远程方法调用，因此返回的项列表将被复制并按值传递。看起来你可能一直试图解决这个问题？
每次调用context.lookup（“CartSessionBean / remote”）都会创建一个有状态会话bean的新实例。

您需要执行以下操作：从HttpServletRequest中查找或创建HttpSession，在会话中查找或创建购物车实例，然后使用购物车会话bean。

有状态EJB不保留信息

1 个答案: