@Autowired 的 sessionFactory 对象为空。

Question

在UserDAO类中出现空指针异常，因为sessionFactory对象始终为空。如果有帮助的话，我发现如果DAO是手动使用'new'创建而不是让Spring处理，则会发生这种情况。虽然我没有这样做，而是在service类中注入了UserDAO，但仍然获取到空的sessionFactory。

非常感谢任何帮助。

以下是相关文件的内容：

hibernate.cfg.xml

<?xml version='1.0' encoding='utf-8'?>
<beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.1.xsd">

    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="location">
            <value>/WEB-INF/properties/database.properties</value>
        </property>
    </bean>
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="${jdbc.driverClassName}" />
        <property name="url" value="${jdbc.url}" />
        <property name="username" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />
    </bean>
    <bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource">
            <ref bean="dataSource"/>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
                <prop key="hibernate.show_sql">true</prop>
            </props>
        </property>
        <property name="packagesToScan">
            <list>
                <value>org.questionbank.dto</value>
            </list>
        </property>
    </bean>
</beans>

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:security="http://www.springframework.org/schema/security"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:context="http://www.springframework.org/schema/context"
  xmlns:tx="http://www.springframework.org/schema/tx"
  xmlns:mvc="http://www.springframework.org/schema/mvc"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
  http://www.springframework.org/schema/security
  http://www.springframework.org/schema/security/spring-security-3.2.xsd
  http://www.springframework.org/schema/context 
  http://www.springframework.org/schema/context/spring-context-3.2.xsd
  http://www.springframework.org/schema/tx 
  http://www.springframework.org/schema/tx/spring-tx.xsd
  http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd">

    <import resource="hibernate.cfg.xml"/>
    <mvc:annotation-driven />
    <tx:annotation-driven />
    <context:annotation-config />
    <!--  To scan the components -->
    <context:component-scan base-package="org.questionbank"/>
    <bean id = "transactionManager" class = "org.springframework.orm.hibernate4.HibernateTransactionManager">
        <property name = "sessionFactory" ref = "sessionFactory" />
    </bean> 
</beans>    

DAO类：

public class UserDAO 
{
    protected static Logger logger = Logger.getLogger("dao");

    @Autowired
    private SessionFactory sessionFactory;

    public UserDTO searchDatabase(String username) 
    {
        logger.debug("Seraching for user in DB");
        UserDTO user=new UserDTO();
        Query query = sessionFactory.getCurrentSession().createQuery("FROM UserDTO u WHERE u.userName = :userName");
        query.setParameter("userName", username);
        user = (UserDTO) query.uniqueResult();
        if(user!=null)
            return user;
        logger.error("User does not exist!");
        throw new RuntimeException("User does not exist!");
    }
}

服务类：

@Transactional(readOnly = true)
public class CustomUserDetailsService implements UserDetailsService 
{
    protected static Logger logger = Logger.getLogger("service");
    @Autowired
    private UserDAO userDAO;
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException, DataAccessException 
    {
        UserDetails user = null;
        try 
        {
            UserDTO dbUser = userDAO.searchDatabase(username);
            user =  new User(
                    dbUser.getUserName(), 
                    dbUser.getPassword().toLowerCase(),
                    true,
                    true,
                    true,
                    true,
                    getAuthorities(Integer.parseInt(dbUser.getAccess())));
            } catch (Exception e) {
            logger.error("Error in retrieving user");
            e.printStackTrace();
            throw new UsernameNotFoundException("Error in retrieving user");
        }
        return user;
    }

- usercpd

---

这两个组件都有用@Component进行注释吗（或者类似的注释，如@Repository、@Service等）？另外，它们是否都声明在org.questionbank或其子包中？ - Anthony Accioly

你能贴出堆栈跟踪吗？ - Sotirios Delimanolis

问题已解决，我在xml中没有UserDAO bean，也没有添加注释，添加注释就解决了。感谢@AnthonyAccioly指出这一点。 - usercpd

好的，usercpd。欢迎来到Stack Overflow。我会把它转化为一个答案，可以吗？ - Anthony Accioly

Answer 1

您当前的配置，包括 <context:annotation-config /> 和 <context:component-scan base-package="org.questionbank"/>，使得Spring能够正确识别和注入您的bean的前半部分功能。

另一半是将bean声明为Spring管理的组件。

您可以通过两种方式之一来实现这一点。要么在 applicationContext.xml 中使用 <bean /> 标签声明bean（就像您对 transactionManager 所做的那样），要么使用一种注释（例如 stereotype annotation，如 @Component、@Repository、@Service 或 @Controller）。

@Repository
public class UserDAO { // ... 

并且

@Service
public class CustomUserDetailsService { // ...

- Anthony Accioly