java - 带有实体类的 NullPointerException

Question

我要扔这个issue但我找到了一个解决方案，但我有一些错误，所以我问这个新问题，这是我的代码:

@Service
public class GestionAOService {

    @Autowired
    private GenericDao<AoFollow, Integer> ao_follow_dao;

    @Transactional
    public void follow_ao(Integer idcontact , Integer idao) {
        ao_follow_dao.create(new AoFollow(new AppelOffre(idao) , new Contact(idcontact)));

       ao_follow_dao.read(1);
    }
    .....

我的配置

@Configuration
@ComponentScan("service")
public class AnnotationContextConfiguration {

   @Bean(autowire = Autowire.BY_NAME)
   public GenericDaoJpaImpl<AoFollow, Integer> ao_follow_dao() {
       System.out.println("Autowire.BY_NAME");
        return new GenericDaoJpaImpl<AoFollow, Integer>(AoFollow.class);
   }

}

问题是，当我执行 ao_follow_dao.read(..); 时，什么也没发生，创建(插入)没问题，但我得到了 NullPointerException int 这个级别的返回this.entityManager.find(entityClass, id);

@Override
public T read(PK id) {
    return this.entityManager.find(entityClass, id);
}

我认为该 bean 没有使用 @Configuration 正确初始化，因为这是我第一次尝试它。

我的小鬼类(class)

@Repository
public class GenericDaoJpaImpl<T, PK extends Serializable> 
                                            implements GenericDao<T, PK> {

    protected Class<T> entityClass;

    @PersistenceContext
    protected EntityManager entityManager;



    public GenericDaoJpaImpl() {

    }

    public GenericDaoJpaImpl(Class<T> entityClass) {
        this.entityClass = entityClass;
    }

    @Override
    public T create(T t) {
        this.entityManager.persist(t);
        return t;
    }

    @Override
    public T read(PK id) {
        return this.entityManager.find(entityClass, id);
    }

    @Override
    public T update(T t) {
        return this.entityManager.merge(t);
    }

    @Override
    public void delete(T t) {
        t = this.entityManager.merge(t);
        this.entityManager.remove(t);
    }

    @Override
    public void delete(Set<T> ts) {
        for( T t : ts){
            t = this.entityManager.merge(t);
            this.entityManager.remove(t);
        }
    }
}

我的界面:

public interface GenericDao<T, PK extends Serializable> {

    T create(T t);
    T read(PK id);
    T update(T t);
    void delete(T t);
    void delete(Set<T> ts);

}

我还有一个 xml 配置文件

 <beans ... >

   <context:property-placeholder location="persistence-mysql.properties" />
   <jpa:repositories base-package="repository"/>


   <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
      ...
   </bean>

     <bean id="jpaVendorAdapter" class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
        <property name="showSql" value="true" />
    </bean>

   <bean id="dataSource" class="org.apache.tomcat.dbcp.dbcp2.BasicDataSource">
      ...
   </bean>

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

    <context:component-scan base-package="service"/>
    <context:component-scan base-package="dao"/>

    <tx:annotation-driven transaction-manager="transactionManager" />

</beans>

完整的堆栈跟踪

java.lang.NullPointerException
    at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.<init>(SessionImpl.java:2508)
    at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.<init>(SessionImpl.java:2495)
    at org.hibernate.internal.SessionImpl.byId(SessionImpl.java:1043)
    at org.hibernate.internal.SessionImpl.get(SessionImpl.java:955)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:1110)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:1068)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:262)
    at com.sun.proxy.$Proxy42.find(Unknown Source)
    at dao.GenericDaoJpaImpl.read(GenericDaoJpaImpl.java:46)
    at service.GestionAOService.follow_ao(GestionAOService.java:88)
    at service.GestionAOService$$FastClassBySpringCGLIB$$8fa00f17.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:708)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:262)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:644)
    at service.GestionAOService$$EnhancerBySpringCGLIB$$a32311b9.follow_ao(<generated>)
    at controller.GestionAO.FollowAO(GestionAO.java:64)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:749)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:689)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    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.apache.logging.log4j.web.Log4jServletFilter.doFilter(Log4jServletFilter.java:67)
    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:219)
    at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:106)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.__invoke(StandardHostValve.java:142)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:534)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1081)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
    at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

Answer 1

向您的服务添加@Transactional注释:

@Service
@Transactional
public class GestionAOService {
    ...
}

并确保您的 AnnotationContextConfiguration 类位于由 Spring 框架(例如 service 和 dao)扫描的包中。

假设您的类位于包 config 中，请将此行添加到您的 spring 配置中:

<context:component-scan base-package="config"/>