Java Spring Data JPA 存储库抛出空指针

Spring Data JPA repository throws null pointer

提问by James Millner

I've been working with Spring Data with Spring Boot. With the JavaConfig documentation I have set up a Spring JPA configuration, but when calling the save method in my repository a null pointer is thrown.

我一直在使用 Spring Boot 处理 Spring Data。使用 JavaConfig 文档，我设置了 Spring JPA 配置，但是在我的存储库中调用 save 方法时，会抛出空指针。

My repository:

我的存储库：

import org.springframework.data.jpa.repository.JpaRepository;

public interface HouseRepository extends JpaRepository<House, Long> {
}

My POJO's:

我的POJO：

AbstractHouse

抽象屋

@MappedSuperclass
@Table(name="houses")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
public abstract class AbstractHouse implements Serializable {

@NotEmpty
private String houseName;

@NotEmpty
private String houseNumber;

House

房子

@Entity
public class SmallHouse extends AbstractHouse {

@Id
@GeneratedValue
private Long id;

private Date created;

private Date updated;

I've then got a service object that takes an Autowired repository and attempts to save using methods obtained through JPA:

然后我有一个服务对象，它接受一个 Autowired 存储库并尝试使用通过 JPA 获得的方法进行保存：

@Service
public class HouseService {

@Autowired
protected HouseRepository houseRepository;

public void save(House house) {
    houseRepository.save(house);
} 

My application class contains:

我的应用程序类包含：

@SpringBootApplication
@EnableScheduling
@EnableJpaRepositories
public class Application {

public static void main(String[] args) throws Exception {
    SpringApplication.run(Application.class, args);
}
}

I am fairly new to Spring Data, so I do think its something within the configuration that I am missing, any advice would be greatly appreciated!

我对 Spring Data 相当陌生，所以我确实认为它在我缺少的配置中的某些东西，任何建议将不胜感激！

--Update--

- 更新 -

Stack Trace:

堆栈跟踪：

java.lang.NullPointerException
    at com.jm.service.HouseService.save(HouseService.java:15)
    at com.jm.service.HouseClass.gatherHouses(HouseClass.java:43)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:775)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:967)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:858)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:843)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

And I call the method as such:

我这样称呼该方法：

public class HouseMain {

    @Autowired
    public HouseService houseService;

    public void gatherHouse() {
    houseService = new HouseService();
    House h = new House();
    h.setHouseName("House1");
    h.setHouseNumber("12");
    try {

        HouseService.save(vmComp);          
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}
}

Then in my controller I am calling house.gatherHouse

然后在我的控制器中我调用 house.gatherHouse

采纳答案by Nikem

You currently instantiate HouseServiceby hand, not through Spring. In the houseServiceobject that you created you have field HouseRepository houseRepositorywhich is null, because you don't initialize it in any way. If you use Spring and its Autowiredfunctionality, then you should get the instance of HouseServicefrom Spring context. E.g. you can @Autowiredit into your controller class.

您目前HouseService手动实例化，而不是通过 Spring。在houseService您创建的对象中，您有一个字段HouseRepository houseRepositoryis null，因为您没有以任何方式对其进行初始化。如果您使用 Spring 及其Autowired功能，那么您应该HouseService从 Spring 上下文中获取 的实例。例如，您可以将@Autowired其添加到您的控制器类中。

回答by shankarsh15

This is not correct:

这是不正确的：

 houseService = new HouseService();

since you are using Spring, you should allow Spring to create all the beans ,that's the reason of using @Autowired, which in this case is not getting executed and houseRepository is initialisedas null.

由于您正在使用Spring，您应该允许 Spring 创建所有 bean，这就是 using 的原因@Autowired，在这种情况下，它没有被执行并且 houseRepository 是initialisedas null。