NPE在CrudRepository中声明新的查询方法时

Question

我正在实现一项功能，该功能可以在天气监视中使用的现有应用程序中从数据库返回最高记录。 我正在使用Spring，Hibernate，Spring Data JPA。

Spring版本是4.1.1 RELEASE 。 这是最小的示例：

Reading实体：

@Entity
public class Reading {
    @Id
    @GeneratedValue
    private Long id;

    private Date time;
    private double temperature;

    //getters, setters
}

ReadingController ：

@Controller
@RequestMapping("/reading")
public class ReadingController {
    @Autowired
    private ReadingDao readingDao;

    //controller logic
}

我正在使用的DAO：

public interface ReadingDao extends CrudRepository<Reading, Long>{
    Reading findTopByOrderByTemperatureDesc();

    //other methods
}

我还配置了Spring在mvc-dispatcher-servlet.xml文件中寻找组件：

<context:component-scan base-package="org.mycompany"/>
<mvc:annotation-driven/>

问题 ：添加findTopByOrderByTemperatureDesc()方法将ReadingDao引起NullPointerException而自动装配的ReadingDao在ReadingController 。

根据Spring Data JPA文档（第3.4.5章），该方法应该有效。

另外，该方法的名称似乎是正确的（请参阅此处 ）。 我尝试使用findTopOrderByTemperatureDesc和findTopByTemperatureDesc ，但No property desc found for type double 。

堆栈跟踪：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'readingController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private org.mycompany.dao.ReadingDao org.mycompany.controller.ReadingController.readingDao; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'readingDao': FactoryBean threw exception on object creation; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1204)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:538)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:302)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:229)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:725)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:663)
    at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:629)
    at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:677)
    at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:548)
    at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:489)
    at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
    at javax.servlet.GenericServlet.init(GenericServlet.java:158)
    at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1279)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1192)
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1087)
    at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:5210)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5493)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:632)
    at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1740)
    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.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:301)
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
    at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
    at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:618)
    at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:565)
    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.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:301)
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)
    at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)
    at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1471)
    at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76)
    at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1312)
    at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1404)
    at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:832)
    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 sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:323)
    at sun.rmi.transport.Transport$1.run(Transport.java:200)
    at sun.rmi.transport.Transport$1.run(Transport.java:197)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$79(TCPTransport.java:683)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

请注意 ，当未声明该方法时，应用程序将正常运行，并且在自动装配过程中没有问题。

如何解决这个问题呢？ 或者如何以其他方式实现相同功能？

编辑：我也有

<jpa:repositories base-package="org.mycompany.dao"/>

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>

在配置数据库和存储库的Datasource.xml文件中。

EDIT2：我也按照建议将double更改为Double ，但这并没有改变任何内容。

Answer 1

<jpa:repositories base-package="com.company.product.repository" entity-manager-factory-ref="entityManagerFactory" transaction-manager-ref="transactionManager" />

要么

@EnableJpaRepositories(basePackages = "com.company.product.repository", entityManagerFactoryRef = "entityManager", transactionManagerRef = "transactionManager")

您必须配置jpa存储库，并且此软件包应包含所有回购类。 在您的情况下，应将ReadingDao放在repo包示例（com.company.product.repository）中

<context:component-scan base-package="org.mycompany"/>
<jpa:repositories base-package="com.company.product.repository" entity-manager-factory-ref="entityManagerFactory" transaction-manager-ref="transactionManager" />
<mvc:annotation-driven/>