解决JUnit下的LazyInitialization问题

我的话：

这几天在做一个小项目，我负责先实现底层的DAO与Service，用的是Spring+Hibernate，使用HibernateTemplate实现简单的增删改查功能。按理说应该很简单，但是我用JUnit测试的时候却发现很诡异的问题：1、save方法发出了sql，但数据库却没有相应记录；2、load方法获取不到对象，只有一个代理，调用任何属性就会说LazyInitialization

我们知道所谓的懒加载的原因是session被关闭了。在web环境下我们可以在web.xml里面加入OpenSessionInView的过滤器，那在junit下应该怎么办呢？

最后在网上找到了一篇文章，里面阐述了如何在各种层面上使用lazy。根据其最后一部分的指导，终于在junit里面把我的service跑通了，开心~~ 

全文摘录如下，原文地址是：http://www.jroller.com/kbaum/entry/orm_lazy_initialization_with_dao。如果上国外网比较慢，也可以看这里的转载：http://blog.csdn.net/wczwcg/archive/2008/11/01/3202535.aspx

 

Lazy Initialization and the DAO pattern with Hibernate and Spring

10:42PM Apr 06, 2005 in category Java by Karl Baum

Hibernate and Lazy Initialization

Hibernate object relational mapping offers both lazy and non-lazy modes of object initialization. Non-lazy initialization retrieves an object and all of its related objects at load time. This can result in hundreds if not thousands of select statements when retrieving one entity. The problem is compounded when bi-directional relationships are used, often causing entire databases to be loaded during the initial request. Of course one could tediously examine each object relationship and manually remove those most costly, but in the end, we may be losing the ease of use benefit sought in using the ORM tool.

The obvious solution is to employ the lazy loading mechanism provided by hibernate. This initialization strategy only loads an object's one-to-many and many-to-many relationships when these fields are accessed. The scenario is practically transparent to the developer and a minimum amount of database requests are made, resulting in major performance gains. One drawback to this technique is that lazy loading requires the Hibernate session to remain open while the data object is in use. This causes a major problem when trying to abstract the persistence layer via the Data Access Object pattern. In order to fully abstract the persistence mechanism, all database logic, including opening and closing sessions, must not be performed in the application layer. Most often, this logic is concealed behind the DAO implementation classes which implement interface stubs. The quick and dirty solution is to forget the DAO pattern and include database connection logic in the application layer. This works for small applications but in large systems this can prove to be a major design flaw, hindering application extensibility.

Being Lazy in the Web Layer

Fortunately for us, the Spring Framework has developed an out of box web solution for using the DAO pattern in combination with Hibernate lazy loading. For anyone not familiar with using the Spring Framework in combination with Hibernate, I will not go into the details here, but I encourage you to read Hibernate Data Access with the Spring Framework. In the case of a web application, Spring comes with both the OpenSessionInViewFilter and the OpenSessionInViewInterceptor. One can use either one interchangeably as both serve the same function. The only difference between the two is the interceptor runs within the Spring container and is configured within the web application context while the Filter runs in front of Spring and is configured within the web.xml. Regardless of which one is used, they both open the hibernate session during the request binding this session to the current thread. Once bound to the thread, the open hibernate session can transparently be used within the DAO implementation classes. The session will remain open for the view allowing lazy access to the database value objects. Once the view logic is complete, the hibernate session is closed either in the Filter doFilter method or the Interceptor postHandle method. Below is an example of the configuration of each component:

Interceptor Configuration

<beans> 

  <bean id="urlMapping"     

     class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">    

       <property name="interceptors">

         <list>

              <ref bean="openSessionInViewInterceptor"/>

         </list>

       </property>

       <property name="mappings">

  ...

  </bean>

  ...

  <bean name="openSessionInViewInterceptor"  

    class="org.springframework.orm.hibernate.support.OpenSessionInViewInterceptor">

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

  </bean>

</beans>

Filter Configuration

<web-app>

 ...      

  <filter>

    <filter-name>hibernateFilter</filter-name>

    <filter-class>

      org.springframework.orm.hibernate.support.OpenSessionInViewFilter

    </filter-class>

   </filter>

  ...      

  <filter-mapping>

    <filter-name>hibernateFilter</filter-name>

     <url-pattern>*.spring</url-pattern>

  </filter-mapping>

  ...

</web-app>

Implementing the Hibernate DAO's to use the open session is simple. In fact, if you are already using the Spring Framework to implement your Hibernate DAO's, most likely you will not have to change a thing. The DAO's must access Hibernate through the convenient HibernateTemplate utility, which makes database access a piece of cake. Below is an example DAO.

Example DAO

public class HibernateProductDAO extends HibernateDaoSupport implements ProductDAO  {      



       public Product getProduct(Integer productId) {

              return (Product)getHibernateTemplate().load(Product.class, productId);

       }



       public Integer saveProduct(Product product) {

              return (Integer) getHibernateTemplate().save(product);

       }       



       public void updateProduct(Product product) {

              getHibernateTemplate().update(product);

       }

 }

Being Lazy in the Business Layer

Even outside the view, the Spring Framework makes it easy to use lazy load initialization, through the AOP interceptor HibernateInterceptor. The hibernate interceptor transparently intercepts calls to any business object configured in the Spring application context, opening a hibernate session before the call, and closing the session afterward. Let's run through a quick example. Suppose we have an interface BusinessObject:

public interface BusinessObject { 

     public void doSomethingThatInvolvesDaos(); 

}

The class BusinessObjectImpl implements BusinessObject:

 

public class BusinessObjectImpl implements BusinessObject {

    public void doSomethingThatInvolvesDaos() {

        // lots of logic that calls

        // DAO classes Which access 

        // data objects lazily

    }

}

Through some configurations in the Spring application context, we can instruct the HibernateInterceptor to intercept calls to the BusinessObjectImpl allowing it's methods to lazily access data objects. Take a look at the fragment below:

<beans>

    <bean id="hibernateInterceptor" class="org.springframework.orm.hibernate.HibernateInterceptor">

         <property name="sessionFactory">

           <ref bean="sessionFactory"/>

         </property>

    </bean>

    <bean id="businessObjectTarget" class="com.acompany.BusinessObjectImpl">

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

    </bean>

    <bean id="businessObject" class="org.springframework.aop.framework.ProxyFactoryBean">

         <property name="target"><ref bean="businessObjectTarget"/></property>

         <property name="proxyInterfaces">

           <value>com.acompany.BusinessObject</value>

         </property>

         <property name="interceptorNames">

           <list>

              <value>hibernateInterceptor</value>

           </list>

         </property>

     </bean>            

</beans>

When the businessObject bean is referenced, the HibernateInterceptor opens a hibernate session and passes the call onto the BusinessObjectImpl. When the BusinessObjectImpl has finished executing, the HibernateInterceptor transparently closes the session. The application code has no knowledge of any persistence logic, yet it is still able to lazily access data objects.

Being Lazy in your Unit Tests

Last but not least, we'll need the ability to test our lazy application from J-Unit. This is easily done by overriding the setUp and tearDown methods of the TestCase class. I prefer to keep this code in a convenient abstract TestCase class for all of my tests to extend.

public abstract class MyLazyTestCase extends TestCase {





	

        public void setUp() throws Exception {

	    super.setUp();

	    SessionFactory sessionFactory = (SessionFactory) getBean("sessionFactory");

	    Session s = sessionFactory.openSession();

	    TransactionSynchronizationManager.bindResource(sessionFactory, new SessionHolder(s));



        }



        protected Object getBean(String beanName) {

            //Code to get objects from Spring application context

        }

	

        public void tearDown() throws Exception {

	    super.tearDown();

	    SessionHolder holder = (SessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);

	    Session s = holder.getSession(); 

	    s.flush();

	    TransactionSynchronizationManager.unbindResource(sessionFactory);

	    SessionFactoryUtils.closeSessionIfNecessary(s, sessionFactory);

        }

}