Question

我是JAVA EE中使用框架的新手所以当我试图调用实体管理器的方法时它抛出一个java.lang.NullPointerException 所以我想写我写的东西这是我的dao实现的一个例子

@Repository
@Transactional
public class IUserDAOImpl implements IUserDAO{

    @PersistenceContext
    private EntityManager em;

    public void addUser(User u) {
        em.persist(u);
    }   
}

这是我的服务

@Service
public class IUserServiceImpl implements IUserService {

@Autowired
private IUserDAO dao = new IUserDAOImpl();

public void setDao(IUserDAO dao) {
    this.dao = dao;
}

public void addUser(User u) {
    dao.addUser(u);     
}

这是我的动作类

public class ConnectionAction extends ActionSupport {

User c = new User("a","b","c",11,"d",true);

@Autowired
public IUserService service;


public String execute() throws Exception {
    service.addUser(c);
        return SUCCESS;
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="struts_blank" version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee         http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 <display-name>Struts Blank</display-name>

<filter>
<filter-name>struts2</filter-name>
<filter-class>
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

<context-param>
<param-name>contextConfiguration</param-name>
<param-value>classpath:applicationContext.xml</param-value>
</context-param>

<listener>
<listener-class>
org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>
</web-app>

applicationContext.xml（虽然它真的搞砸了所以如果你注意到某些错误的plz告诉）

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns:tx="http://www.springframework.org/schema/tx"     xmlns="http://www.springframework.org/schema/beans"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"     xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="
http://www.springframework.org/schema/beans         http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
http://www.springframework.org/schema/context     http://www.springframework.org/schema/context/spring-context-2.5.xsd
http://www.springframework.org/schema/util     http://www.springframework.org/schema/util/spring-util-2.0.xsd
http://www.springframework.org/schema/tx     http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">

<bean id="dao"
class="com.iticsys.GBO.dao.IUserDAOImpl">
</bean>

<bean id="service"
class="com.iticsys.GBO.services.IUserServiceImpl">
<property name="dao" ref="dao"></property>
</bean>

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/GBO1" />
<property name="username" value="root" />
<property name="password" value="" />
</bean>

<bean id="persistenceUnitManager"
    class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager">
<property name="persistenceXmlLocations">
<value>classpath*:META-INF/persistence.xml</value>
</property>
<property name="defaultDataSource" ref="dataSource"> </property>
</bean>

<bean id="entityManagerFactory"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="persistenceUnitManager" ref="persistenceUnitManager"></property>
<property name="persistenceXmlLocation" value="classpath*:META-INF/persistence.xml" />
<property name="persistenceUnitName" value="persistenceUnit" /> 
</bean>

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory"></property>
</bean> 
<tx:annotation-driven transaction-manager="transactionManager" /> 
<context:annotation-config></context:annotation-config>
<context:component-scan base-package="com.iticsys.GBO.dao" />
</beans>

的persistence.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="persistenceUnit"
    transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>


    <properties>
        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/GBO1" />
        <property name="javax.persistence.jdbc.user" value="root" />
        <property name="javax.persistence.jdbc.password" value="" />

        <property name="hibernate.show_sql" value="true" />
        <property name="hibernate.hbm2ddl.auto" value="update" />
    </properties>
</persistence-unit>

非常感谢你提前

Answer 1

在 IUserDAOImpl 类的实现中，您应该实例化EntityManager的对象

private EntityManager em = new EntityManager(/*constructor parameter if any*/);

或者您可以指定您可以在其他子类中创建的EntityManager对象的引用，例如IUserServiceImpl，ConnectionAction。

为此，您可以在课程 IUserDAOImpl 中添加一个接收该引用的方法。

public void setEntityManager(EntityManager em_ref ){ em = em_ref;}

Answer 2

public class HibernateUtil {

static Logger logger = Logger.getLogger(HibernateUtil.class);

private static final String FAILED_TO_CREATE_SESSION_FACTORY_OBJECT = "Failed to create sessionFactory object.";
private static final SessionFactory sessionFactory = buildSessionFactory();
private static ServiceRegistry serviceRegistry;

private static SessionFactory buildSessionFactory() {

try {
    Configuration configuration = new Configuration();
    configuration.configure("./hibernate.cfg.xml");

    configuration.addAnnotatedClass(Calzz.class);

    serviceRegistry = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build();

    return configuration.buildSessionFactory(serviceRegistry);

} catch (Throwable ex) {

    logger.debug(FAILED_TO_CREATE_SESSION_FACTORY_OBJECT + ex);
    throw new ExceptionInInitializerError(ex);
}
}

public static SessionFactory getSessionFactory() {
return sessionFactory;
}

}

实体管理器没有被spring正确注入并给出了java.lang.NullPointerException

2 个答案: