Question

我对春天来说有点新鲜，而且我已经遇到了Null Pointer Exception。我相信@Autowired不适用于我的MongoRepository。出于某种原因，当我尝试一些例子时，它正在运作。（运行函数中注释掉的代码有效）

这是我得到的错误：

2016-05-20 02：31：20.877 ERROR 6272 --- [nio-8080-exec-2]   o.a.c.c.C。[。[。[/]。[dispatcherServlet]：Servlet.service（）for   在path []的上下文中的servlet [dispatcherServlet]引发了异常   [请求处理失败;嵌套异常是   带根本原因的java.lang.NullPointerException]

java.lang.NullPointerException：null at   com.applesauce.service.CustomerService.addCustomer（CustomerService.java:24）   〜[类/：NA]

你们可以看看并指导我吗？另外，如果我为最佳做法做错了，请告诉我。如果您需要更多信息，请询问！

com.applesauce.controller

@RestController 
@RequestMapping("/customer")
public class CustomerController {

private CustomerService customerService = new CustomerService();

@RequestMapping(value = "/addcustomer", method = RequestMethod.GET)
public Customer addCustomer(@RequestParam("firstName") String fName,
                         @RequestParam("lastName") String lName,
                         @RequestParam("email") String email,
                         @RequestParam("phoneNumber") String phoneNumber,
                         @RequestParam("source") String source){
    return customerService.addCustomer(new Customer(fName,lName,email,phoneNumber,source));
}
}

com.applesauce.repository

@Repository
public interface CustomerRepository extends MongoRepository<Customer, String> {

public Customer findByFirstName(String firstName);
public List<Customer> findByLastName(String lastName);
}

com.applesauce.service

@EnableMongoRepositories(basePackages = "com.applesauce.repository")
public class CustomerService {

@Autowired
private CustomerRepository repository;

public Customer addCustomer(Customer customer){

    repository.save(customer);

    return customer;
}
}

Answer 1

Xtreme Biker意味着你应该为你的CustomerService添加@Service注释，如下所示：

@EnableMongoRepositories(basePackages = "com.applesauce.repository")
@Service
public class CustomerService {
...
}

此外，如果您希望Spring关注它，您永远不想使用new运算符创建服务。在CustomerController中，更改初始化行：

private CustomerService customerService = new CustomerService();

为：

@Autowired
private CustomerService customerService;

必须解决NullPointerException。

Answer 2

I had the same issue and I solved this way (explanation is generic)

Repository.class

def move_perimeter(a, n, direction='clockwise'):
    # a : input array
    # n : number of elements to be moved
    # direction : 'clockwise' or 'counterclockwise'

    # Dictionary to map for number of elements rolling later
    dirn_map = {'clockwise':n,'counterclockwise':-n}

    # Store size
    m,n = a.shape
    r0 = np.arange(m-1)
    r1 = np.arange(n-1)

    # Get Top, Right, Bottom and Left side linear indices. Store those.
    T = r1
    R = n-1+r0*n
    B = a.size-r1-1
    L = n+r0[::-1]*n
    idx = np.r_[T,R,B,L]

    # Make a copy of input array
    out = a.copy()

    # Linearly index into output array with those original indices
    # and extract rolled values from input array.
    out.ravel()[idx] = a.ravel()[np.roll(idx, dirn_map[direction])]
    return out

Service.class

In [233]: a
Out[233]: 
array([[83, 13, 27, 13],
       [90, 78, 57, 68],
       [66, 47, 44, 53],
       [13, 98, 95, 46],
       [29, 87, 80, 92],
       [91, 19, 86, 26],
       [31, 27, 75, 72]])

In [234]: move_perimeter(a, n=1, direction='clockwise')
Out[234]: 
array([[90, 83, 13, 27],
       [66, 78, 57, 13],
       [13, 47, 44, 68],
       [29, 98, 95, 53],
       [91, 87, 80, 46],
       [31, 19, 86, 92],
       [27, 75, 72, 26]])

In [235]: move_perimeter(a, n=2, direction='counterclockwise')
Out[235]: 
array([[27, 13, 68, 53],
       [13, 78, 57, 46],
       [83, 47, 44, 92],
       [90, 98, 95, 26],
       [66, 87, 80, 72],
       [13, 19, 86, 75],
       [29, 91, 31, 27]])

Application.class

import play.api.libs.json.{Json, OFormat}

case class ResponseModel(content: NestedCaseClassModel)

object ResponseModel {
  implicit val format: OFormat[ResponseModel] = Json.format
}

case class NestedCaseClassModel(value: String)

object NestedCaseClassModel {
  implicit val format: OFormat[NestedCaseClassModel] = Json.format
}

Answer 3

检查您是否已创建具有@Service批注的类的对象（使用new）。替代地，该类也应该自动装配，在这里您已经自动装配了存储库bean。

Spring Boot MongoRepository空指针异常

3 个答案: