Spring 3，带有通用 DAO 的 Hibernate 4 AutoWired sessionFactory

Question

使用 Spring MVC 3 和 Hibernate 4 我得到：

java.lang.NullPointerException

com.daniel.rr.dao.common.DAOImpl.getSession(DAOImpl.java:22)
com.daniel.rr.dao.common.DAOImpl.save(DAOImpl.java:27)
com.daniel.rr.controller.HelloController.printWelcome(HelloController.java:30)

这是相关的spring配置：

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


<bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
    <property name="packagesToScan">
        <list>
            <value>com.daniel.rr.model</value>
            <value>com.daniel.rr.dao</value>
            <value>com.daniel.rr.dao.common</value>
            <value>com.daniel.rr.controller</value>
        </list>
    </property>

    <property name="hibernateProperties">
        <props>
            <prop key="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</prop>
            <prop key="hibernate.show_sql">true</prop>
            <prop key="hibernate.hbm2ddl.auto">update</prop>
        </props>
    </property>

    <property name="dataSource" ref="dataSource" />
</bean>


<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">

    <property name="url" value="jdbc:mysql://localhost:3306/rr" />
    <property name="driverClassName" value="com.mysql.jdbc.Driver" />
    <property name="username" value="root" />
    <property name="password" value="" />

</bean>



<bean name="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
    <property name="sessionFactory" ref="sessionFactory" />
</bean>

通用 DAO：

public interface DAO<T> {

    T save(T t);
    void delete(T t);
} 

@Transactional
public abstract class DAOImpl<T> implements DAO<T> {

    @Autowired
    private SessionFactory sessionFactory;

    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    public Session getSession() {
        return sessionFactory.getCurrentSession();
    }

    @Override
    public T save(T t) {
        getSession().persist(t);
        return t;
    }

    @Override
    public void delete(T t) {
        getSession().delete(t);
    }
}

AccountDAO：

public class AccountDAO extends DAOImpl<Account> implements DAO<Account> {

} 

MVC 控制器：

public class HelloController {

    @RequestMapping(method = RequestMethod.GET)
    public String printWelcome(ModelMap model) {

        //System.out.println("is null? " + sessionFactory);

        AccountDAO dao = new AccountDAO();
        Account account = new Account();

        account.setUsername("hello");
        account.setPassword("test");

        dao.save(account);

        model.addAttribute("message", "Hello world!");
        return "hello";
    }
}

我已经通过 StackOverflow 和 Google 进行了搜索，但找不到任何有用的信息。 我尝试在 DAOImpl.save(T t) 上使用事务，但仍然存在同样的问题。

public T save(T t) {
        Transaction tr = getSession().getTransaction();
        tr.begin();

        getSession().persist(t);

        tr.commit();
        return t;
    }

Answer 1

注解不会被继承。

将事务注释添加到具体 dao，而不是抽象类。

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