java - 无法实例化bean构造函数抛出异常；嵌套异常是 java.lang.NullPointerException

Question

我的基于java的配置是

@Configuration
@ComponentScan(basePackages = { "com.doly.jproject" })
@EnableTransactionManagement 
@EnableJpaRepositories (basePackages = "com.doly.jproject.repository")
public class RootConfigurer extends WebMvcConfigurerAdapter {   

    private Properties jpaProperties;   

    @Bean
    public DriverManagerDataSource dataSource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName("com.mysql.jdbc.Driver");
        dataSource.setUrl("jdbc:mysql://localhost/dbga");
        dataSource.setUsername("root");
        dataSource.setPassword("");
        return dataSource;
    } 

    @Bean
    public EntityManagerFactory entityManagerFactory() throws SQLException {

        LocalContainerEntityManagerFactoryBean entityManagerFactory = 
                new LocalContainerEntityManagerFactoryBean();
        entityManagerFactory.setPackagesToScan("com.doly.jproject.entity");
        entityManagerFactory.setDataSource(dataSource());

        jpaProperties = new Properties();       
        jpaProperties.put("hibernate.show_sql", true);
        jpaProperties.put("hibernate.hbm2ddl.auto", "create");

        entityManagerFactory.setJpaProperties(jpaProperties);
        entityManagerFactory.setPersistenceProvider(new HibernatePersistenceProvider());

        return entityManagerFactory.getObject();
    }


    @Bean
    @Qualifier(value = "entityManager")
    public EntityManager entityManager(EntityManagerFactory entityManagerFactory) {
        return entityManagerFactory.createEntityManager();
    }

    @Bean
    public JpaTransactionManager transactionManager() {
        JpaTransactionManager transactionManager = new JpaTransactionManager();
        transactionManager.setDataSource(dataSource());
        return transactionManager;
    }
}

但是当我想初始化 org.hibernate.Session 的对象时来自javax.persistence.EntityManager在我的 @Service 类中为

@Autowired
@Qualifier(value = "entityManager")
private EntityManager entityManager;    
private Session session = entityManager.unwrap(org.hibernate.Session.class);

我得到错误+堆栈跟踪为

    SEVERE: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'homeController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.doly.jproject.service.VidService com.doly.jproject.controllers.HomeController.vidService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidService' defined in file [F:\Spring Workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jobsnetwork\WEB-INF\classes\com\doly\jproject\service\VidService.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.doly.jproject.service.VidService]: Constructor threw exception; 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:1210)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:403)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:106)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:5014)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5528)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1575)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1565)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.doly.jproject.service.VidService com.doly.jproject.controllers.HomeController.vidService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidService' defined in file [F:\Spring Workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jobsnetwork\WEB-INF\classes\com\doly\jproject\service\VidService.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.doly.jproject.service.VidService]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331)
    ... 22 more
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.doly.jproject.service.VidService com.doly.jproject.controllers.HomeController.vidService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidService' defined in file [F:\Spring Workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jobsnetwork\WEB-INF\classes\com\doly\jproject\service\VidService.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.doly.jproject.service.VidService]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1101)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1046)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1120)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1044)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
    ... 24 more
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.doly.jproject.service.JobService]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:163)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1094)
    ... 35 more
Caused by: java.lang.NullPointerException
    at com.doly.jproject.service.VidService.<init>(VidService.java:42)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:147)
    ... 37 more

和com.doly.jproject.service.VidService.<init>(VidService.java:42)是

和

public void updateJobCategory(Video video) {
        Video video = (Video)session.get(Video.class, id);// Here it causes com.doly.jproject.service.VidService.<init>(VidService.java:42)
video.getCustomers().clear();//removes all the existing customers
Customer customer1 = new Customer();
customer1.getVideos().add(video)//adding video to the customer
video.getCustomers().add(customer1);
session.update(video)


    }

更新当我改变时

@Autowired
    @Qualifier(value = "entityManager")
    private EntityManager entityManager;    
    private Session session;

在更新方法中我写

public void updateJobCategory(Video video) {
    session= entityManager.unwrap(org.hibernate.Session.class);
    Video video = (Video)session.get(Video.class, id);
    video.getCustomers().clear();//removes all the existing customers
    Customer customer1 = new Customer();
    customer1.getVideos().add(video)//adding video to the customer
    video.getCustomers().add(customer1);
    session.update(video)


        }

我明白

SEVERE: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'homeController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.doly.jproject.service.VidService com.doly.jproject.controllers.HomeController.vidService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.doly.jproject.repository.VidRepository com.doly.jproject.VidService.vidRepository; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidRepository': Cannot create inner bean '(inner bean)#681afbff' of type [org.springframework.orm.jpa.SharedEntityManagerCreator] while setting bean property 'entityManager'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name '(inner bean)#681afbff': Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.persistence.EntityManager]: Factory method 'createSharedEntityManager' threw exception; 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:1210)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:403)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:106)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:5014)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5528)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1575)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1565)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.doly.jproject.service.VidService com.doly.jproject.controllers.HomeController.vidService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.doly.jproject.repository.VidRepository com.doly.jproject.service.VidService.vidRepository; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidRepository': Cannot create inner bean '(inner bean)#681afbff' of type [org.springframework.orm.jpa.SharedEntityManagerCreator] while setting bean property 'entityManager'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name '(inner bean)#681afbff': Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.persistence.EntityManager]: Factory method 'createSharedEntityManager' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331)
    ... 22 more
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.rhcloud.jobsnetwork.repository.JobRepository com.doly.jproject.service.VidService.vidRepository; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidRepository': Cannot create inner bean '(inner bean)#681afbff' of type [org.springframework.orm.jpa.SharedEntityManagerCreator] while setting bean property 'entityManager'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name '(inner bean)#681afbff': Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.persistence.EntityManager]: Factory method 'createSharedEntityManager' threw exception; 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:1210)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1120)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1044)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
    ... 24 more
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.doly.jproject.repository.VidRepository com.doly.jproject.service.VidService.vidRepository; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidRepository': Cannot create inner bean '(inner bean)#681afbff' of type [org.springframework.orm.jpa.SharedEntityManagerCreator] while setting bean property 'entityManager'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name '(inner bean)#681afbff': Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.persistence.EntityManager]: Factory method 'createSharedEntityManager' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331)
    ... 35 more
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'vidRepository': Cannot create inner bean '(inner bean)#681afbff' of type [org.springframework.orm.jpa.SharedEntityManagerCreator] while setting bean property 'entityManager'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name '(inner bean)#681afbff': Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.persistence.EntityManager]: Factory method 'createSharedEntityManager' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveInnerBean(BeanDefinitionValueResolver.java:313)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:129)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1477)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1222)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1120)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1044)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
    ... 37 more
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name '(inner bean)#681afbff': Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.persistence.EntityManager]: Factory method 'createSharedEntityManager' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:599)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1119)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1014)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveInnerBean(BeanDefinitionValueResolver.java:299)
    ... 50 more
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.persistence.EntityManager]: Factory method 'createSharedEntityManager' threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:189)
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:588)
    ... 55 more
Caused by: java.lang.NullPointerException
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.initProxyClassLoader(SharedEntityManagerCreator.java:198)
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.<init>(SharedEntityManagerCreator.java:190)
    at org.springframework.orm.jpa.SharedEntityManagerCreator.createSharedEntityManager(SharedEntityManagerCreator.java:162)
    at org.springframework.orm.jpa.SharedEntityManagerCreator.createSharedEntityManager(SharedEntityManagerCreator.java:119)
    at org.springframework.orm.jpa.SharedEntityManagerCreator.createSharedEntityManager(SharedEntityManagerCreator.java:91)
    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.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:162)
    ... 56 more

如何获得 org.hibernate.Session 的一个来自javax.persistence.EntityManager在我的@Service 类中？请帮忙!

Answer 1

这对我来说似乎有问题:

@Autowired
@Qualifier(value = "entityManager")
private EntityManager entityManager;    
private Session session = entityManager.unwrap(org.hibernate.Session.class);

Autowiring 发生在对象构造之后。这意味着当您的服务被创建时，它将在设置entityManager之前尝试调用entityManager.unwrap。

此外，这样保存 session 通常不是一个好习惯。您应该为您执行的每个操作/事务创建一个新的 EntityManager/Session。按照您配置的方式，应用程序的生命周期内只会有一个 EntityManager bean，这将导致问题。您可能想要什么:

@Autowired
private EntityManagerFactory entityManagerFactory;

然后

public void doStuff() {
    EntityManager entityManager = entityManagerFactory.createEntityManager();
}

由于您已经在使用 Spring，您可能还想研究一下 @Transactional 注释。