Question

基本上，我有一个users表，并且我正在尝试通过利用Users pojo类中的getter进行表单的一些基本登录身份验证。它会引发空指针异常。

这里有一个jquery，它打包数据并将其发送到处理userlogin的控制器：

$.ajax({// defining the below function as ajax responsive//
        url:'userlogin', // the function that process the  mapped url name and matching type is going to receive the data//
        type:'POST',
        data:{user_email:email,user_password:pass},// function to get the value from jsp page and send it to mapped class function//
        success: function(response){// if the backend process is success then the function will run by getting the response as its parameter//
                alert(response.message);
                            }               
    });

这是处理该网址的控制器：

    @RequestMapping(value="/userlogin", method=RequestMethod.POST)
public @ResponseBody ModelAndView validateuser(@Valid LoginForm loginForm, BindingResult result) {


    if (result.hasErrors()) {
        ModelAndView view =new ModelAndView("users");
        return view;
    }

    boolean userExists = loginService.checkLogin(loginForm.getUser_email(),loginForm.getUser_password());
    if(userExists){
        ModelAndView view =new ModelAndView("user_loginsuccess");
         return view;
    }else{
        ModelAndView view =new ModelAndView("users");
         return view;
    }
}

这里loginform是我创建的pojo类，用于设置和获取登录凭据（user_name和user_password）。我还创建了两个接口api的“ loginapi包下的LoginDao和Login Service，并在loginimpl包下实现了它们。

这些接口的实现如下：

public class LoginServiceImpl implements LoginService{

 @Autowired
 private LoginDao loginDAO;

   public void setLoginDAO(LoginDao loginDAO) {
          this.loginDAO = loginDAO;
   }

   public boolean checkLogin(String user_email, String user_password){
          System.out.println("In Service class...Check Login");
          return loginDAO.checkLogin(user_email, user_password);
   }
}

@Repository("loginDAO")
public class LoginDaoImpl implements LoginDao{

   @Resource(name="sessionFactory")
   protected SessionFactory sessionFactory;

   public void setSessionFactory(SessionFactory sessionFactory) {
          this.sessionFactory = sessionFactory;
   }

   protected Session getSession(){
          return sessionFactory.openSession();
   }

   public boolean checkLogin(String user_email, String user_password){
        System.out.println("In Check login");
        Session session = sessionFactory.openSession();
        boolean userFound = false;
        //Query using Hibernate Query Language
        String SQL_QUERY =" from Users as o where o.user_email=? and o.user_password=?";
        Query query = session.createQuery(SQL_QUERY);
        query.setParameter(0,user_email);
        query.setParameter(1,user_password);
        List list = query.list();

        if ((list != null) && (list.size() > 0)) {
            userFound= true;
        }

        session.close();
        return userFound;              
   }
}

谁能解释为什么我得到空指针异常？是否有任何错误或我做错了什么？ Spring Servlet试图传达什么？

我真的一直在这段代码中呆了很多天，如果有人对代码感兴趣，并就我做错的事情敲了我头，谢谢！！

Answer 1

由于您没有添加异常堆栈跟踪，因此不确定它是否可以解决您的问题，但是根据您的问题，您@Service缺少了LoginServiceImpl

您将获得private LoginDao loginDAO的NullPointerException

@Service //need to add @service here
public class LoginServiceImpl implements LoginService{

 @Autowired
 private LoginDao loginDAO;//if not add @service,this line of code will throw NullPointerException

   public void setLoginDAO(LoginDao loginDAO) {
          this.loginDAO = loginDAO;
   }

   public boolean checkLogin(String user_email, String user_password){
          System.out.println("In Service class...Check Login");
          return loginDAO.checkLogin(user_email, user_password);
   }
}

有人可以解释一下为什么Spring Mvc说请求处理失败并抛出空指针异常

1 个答案: