java - Hibernate，repository.save - java.lang.NullPointerException : null - while Object exist

Question

我编写这段代码只是为了将新数据保存到 mySql 数据库，创建类、存储库和主 Controller ，它实际上适用于一个类，但不适用于这个类，感谢一些指针，因为我真的不明白为什么空指针:

Code: main controller:

    @GetMapping(path = "/addExchange") 
public @ResponseBody String addNewExchange (@RequestParam String exchange)
{
    //check1
    System.out.println("creating Exchange constructor");
    Exchange e = new Exchange(); 
    //check 2
    System.out.println("created exchange constructor, " + exchange);
    e.setE_name(exchange);
    //check 3
    System.out.println("Exhange name is, " + e.getE_name());
    //check 4
    System.out.println(e);
    exchangeRepository.save(e); 
    return "Saved Exchange";
}

Output error from Eclipse Console: my checks below show object is picked up from the mapping: - creating Exchange constructor - created exchange constructor, orange - Exhange name is, orange - Exchange [idexchange=0, e_name=orange]

2018-05-21 15:59:43.528 错误 5118 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[/].[dispatcherServlet] : servlet [dispatcherServlet] 的 Servlet.service()在路径 [] 的上下文中抛出异常 [请求处理失败；嵌套异常是 java.lang.NullPointerException] 其根本原因

java.lang.NullPointerException: null 在 com.instantmoney.MoneyServices.MainController.addNewExchange(MainController.java:47) ~[classes/:na]

Exchange Repository:

public interface ExchangeRepository extends CrudRepository<Exchange, Long> {

}

Exchange class

    @Entity 
public class Exchange {

@Id
@GeneratedValue (strategy = GenerationType.AUTO)
private int idexchange; 

private String e_name;

public Exchange() {}

//getter 和 setter

Curl

http://localhost:8080/moneyservice/addExchange?exchange=orange

Answer 1

试试这个

@Controller
public class ExchangeController {    

   @RequestMapping(path = "/addExchange", method = RequestMethod.POST) 
   public @ResponseBody String addNewExchange (@RequestParam String exchange)
   {
    if (exchange != null ) {
       Exchange e = new Exchange(); 
       e.setE_name(exchange);
       exchangeRepository.save(e); 
       return "Saved Exchange";
    } else {
       return new BadRequestException("exchange name can not be null!");
    }
   }

   @Autowired
   public ExchangeController(ExchangeRepository exchangeRepository) {
       this.exchangeRepository = exchangeRepository;
   }

   private ExchangeRepository exchangeRepository;
}