Spring MVC-获取模型类的NullPointerException

Question

我面临的问题是，当客户试图将物品添加到购物车中时，在Controller的这行代码中会引发NullPointerException

CustomerCart customercart = customer.getCustomercart();

addItemToCart是我的控制器方法

@RequestMapping("/customerreqAddItemToCart/{xps_id}")
    public String addItemToCart(@PathVariable("xps_id")String xps_id,@RequestParam("qty")int qty,Principal principal,HttpSession hsession,Model m){


        System.out.println("xps_id : "+xps_id + "  qty : " + qty);

        String customerid=principal.getName();
        System.out.println(customerid);
        Customer customer =cuss.getCustomerByUserId(customerid);
        CustomerCart customercart = customer.getCustomercart();
        Xmap_ps xmap_ps = xpss.getXPSbyId(xps_id);
        CustomerCartItems cartitem = new CustomerCartItems();

        cartitem.setCustomercart(customercart);
        cartitem.setXmap_ps(xmap_ps);
        cartitem.setCus_cartquantity(qty);  
        cartitem.setCus_cartitemwisetotal(xmap_ps.getXps_price()*qty);
        /*cartitem.setProduct_id(xmap_ps.getProduct_id());
        cartitem.setSupplier_id(xmap_ps.getSupplier_id());*/

        ccis.addCartItem(cartitem);

        Customer customer1=cuss.getCustomerByUserId(customerid);
        CustomerCart cart1=customer1.getCustomercart();

        int cartsize = ccss.getCartSize(cart1);

        List<CustomerCartItems> cartitems = cart1.getCustomercartitems();
        int sum=0;
        for(CustomerCartItems critem :cartitems){
            sum+= critem.getCus_cartitemwisetotal();
        }

        cart1.setCus_cartgrandtotal(sum);
        ccss.updateCart(cart1);         

        List<VwXmapPS> xpsdata = vxpss.getBestVwPs();

        m.addAttribute("xpsdata", xpsdata);

        m.addAttribute("customername",hsession.getAttribute("customername"));
        m.addAttribute("customerid",hsession.getAttribute("customerid"));
        m.addAttribute("cartsize",hsession.getAttribute("cartsize"));

        m.addAttribute("cartmessage","Item added to cart successfully");

        hsession.setAttribute("cartsize", cartsize);

        System.out.println("cart size :" + cartsize);       

        return "redirect:/reqdisplaycustomerhomepage";


    }

让我也和大家分享我的模型课

1. CustomerCartItems模型类与CustomerCartItems模型类具有一对多关系的CustomerCart模型类

@Entity
public class CustomerCart {

    @Id
    private String cus_cartid;
    private double cus_cartgrandtotal;

    @OneToOne(mappedBy="customercart")
    private Customer customer;

    @OneToMany(mappedBy="customercart", cascade=CascadeType.ALL, fetch=FetchType.EAGER)
    private List<CustomerCartItems> customercartitems;

@Entity
public class CustomerCartItems {



    @Id
        private String cus_cartitemid;
        private int cus_cartquantity;
        private int cus_cartitemwisetotal;

        @ManyToOne
        @JoinColumn(name="cus_cartid")
        private CustomerCart customercart;

        @ManyToOne
        @JoinColumn(name="xps_id")
        private Xmap_ps xmap_ps;

3.还有Customer模型类，它具有与其他表的所有外键关系

 @Entity
public class Customer {

    @Id
    private String cus_id;
    private String cus_name;
    private String cus_emailid;
    private String cus_mobileno;

    @OneToOne(cascade=CascadeType.ALL)
    @JoinColumn(name="cus_loginid")
    private CustomerDetails customerdetails;

    @OneToOne(cascade=CascadeType.ALL)
    @JoinColumn(name="cus_billingaddressid")
    private CustomerBillingAddress customerbillingaddress;

    @OneToOne(cascade=CascadeType.ALL)
    @JoinColumn(name="cus_shippingaddressid")
    private CustomerShippingAddress customershippingaddress;

    @OneToOne(cascade=CascadeType.ALL)
    @JoinColumn(name="cus_cartid")
    private CustomerCart customercart;

谢谢你花时间帮助我<3

Answer 1

这真的像你认为的那样吗？：

String customerid=principal.getName();

它不认为它会给出数据库中的ID字段值。您可以将登录用户的Id存储在会话中，或者将其作为来自JSP的请求参数。

调试它，您将看到customer为null。