Hibernate，repository.save-java.lang.NullPointerException:null-对象存在时

我写这段代码只是为了将新数据保存到mySql db，创建了类、存储库和主控制器，它实际上适用于一个类，但不适用于这个类，请欣赏一些指针，因为我不太明白为什么使用空指针：

代码： 主控制器：

Eclipse控制台的输出错误： 下面的我的检查显示对象是从映射中拾取的： -创建Exchange构造函数 -已创建exchange构造函数，橙色 -呼气名称为，橙色 -交换[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]：路径为[]的上下文中Servlet[dispatcherServlet]的Servlet.service（）引发异常[请求处理失败；嵌套异常为java.lang.NullPointerException]，其根本原因是

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

Exchange存储库：

//接球手和接球手

卷曲

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;
}

---

我认为

exchangeRepository

为空，您可以添加

MainController

代码吗？因为我们看不到您的原始行号，请在您的code@GetMapping（path=“/addExchange”）public@ResponseBody String addNewExchange（@RequestParam String exchange）{//check1 System.out.println（“创建Exchange构造函数”）；Exchange e=new Exchange（）；//check 2 System.out.println（“创建的Exchange构造函数”+Exchange）；e.setE_name（Exchange）；//check 3 System.out.println（“Exchange name是”+e.getE_name（））；//check 4 System.out.println（e）；exchangerepositionary.save（e）；返回“已保存的Exchange”；}请在Repository类中使用@Repository annotation，然后将其自动连接到控制器中……应该可以使用了。@Eihab您可以编辑您的帖子来添加代码，请不要在注释中添加代码……我还利用了您的帮助Devratna，添加！=null很有用，我添加了这段代码以避免出现null异常。谢谢您的帮助

public interface ExchangeRepository extends CrudRepository<Exchange, Long> {

    @Entity 
public class Exchange {

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

private String e_name;

public Exchange() {}

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

@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;
}