Injection of autowired dependencies failed while using @Transactional

Question

I testing my DAO, but it didn't work. The following error occurs:

Tests in error: 
  testAccountOperations(com.tsekhan.rssreader.dao.HibernateControllerTest): Error creating bean with name 'com.tsekhan.rssreader.dao.HibernateControllerTest': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.tsekhan.rssreader.dao.HibernateController com.tsekhan.rssreader.dao.HibernateControllerTest.hibernateController; nested exception is java.lang.IllegalArgumentException: Can not set com.tsekhan.rssreader.dao.HibernateController field com.tsekhan.rssreader.dao.HibernateControllerTest.hibernateController to $Proxy25

My DAO:

@Service
@Scope("singleton")
public class HibernateController extends HibernateDaoSupport {

    @Autowired
    public SessionFactory sessionFactory;

    @Transactional
    public void addAcount(Account account) {
        sessionFactory.getCurrentSession().saveOrUpdate(account);
    }
}

My test for this DAO:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:/applicationContext.xml")
public class HibernateControllerTest {

    @Autowired
    HibernateController hibernateController;

    private Set<Channel> getTestChannelList(String channelLink) {
        Channel testChannel = new Channel();
        testChannel.setSourceLink(channelLink);
        Set<Channel> testChannelList = new HashSet<Channel>();
        testChannelList.add(testChannel);
        return testChannelList;
    }

    private Account getTestAccount(String accountLogin, String channelLink) {
        Account testAccount = new Account();
        testAccount.setAccountLogin(accountLogin);
        testAccount.setChannelList(getTestChannelList(channelLink));
        return testAccount;
    }

    @Test
    public void testAccountOperations() {
        hibernateController
                .addAcount(getTestAccount("test_login", "test_link"));
    }
}

My applicationContext.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"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.1.xsd"
        default-autowire="byName">

    <!-- Enabling spring-transaction annotations -->
    <tx:annotation-driven transaction-manager="transactionManager"/>

    <!-- Enabling annotation-driven configurating -->
    <context:annotation-config />

    <!-- Creation of transaction manager -->

    <bean id="transactionManager" scope="singleton" 
        class="org.springframework.orm.hibernate3.HibernateTransactionManager">
        <property name="sessionFactory" ref="sessionFactory"/>
    </bean>

    <bean id="sessionFactory" scope="singleton"
        class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
        <property name="configLocation" value="classpath:/hibernate.cfg.xml"/>
        <property name="configurationClass">
            <value>org.hibernate.cfg.AnnotationConfiguration</value>
        </property>
    </bean>
    <!--
    A Spring interceptor that takes care of Hibernate session lifecycle.
    -->
    <bean id="hibernateInterceptor" 
            class="org.springframework.orm.hibernate3.HibernateInterceptor">
        <property name="sessionFactory">
            <ref bean="sessionFactory"/>
        </property>
    </bean>

    <bean name="employeeDAO" scope="prototype" 
        class="com.tsekhan.rssreader.dao.HibernateController" />

    <!-- Searching for hibernate POJO files in package com.tsekhan.rssreader.web -->
    <context:component-scan base-package="com.tsekhan.rssreader.web" />
    <bean class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" />
    <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" />

</beans>

I note, that if you comment @Transactional in DAO, bean is created correctly. What happens?

Answer 1

First of all its realy bad to give name ending in Controller to a DAO its very confusing, Controller and DAO have all together different purpose.

When you add @Transactional to a service or dao class, for spring to make it work in a transaction needs to create a proxy of that class, its a kind of wrapper where in before the execution of proxied class(class in consideration which is proxied) method spring starts the transaction and after the execution in case no exceptions completes the transaction, this can be done in spring via AOP and Annotations. To describe in code.

public class OriginalDaoImpl implements OriginalDao extends DaoSupport {

  public void save(Object o){
      manager.save(o);
  }
}

public class ProxyDaoImpl implements OriginalDao {

    private OriginalDao originalDaoImpl; //instance of OriginalDaoImpl
    public void save(Object o){
       try{
            transaction.start();
            originalDaoImpl.save(o);
            transaction.commit(); 
       }catch(Exception e){
            transaction.rollback();
       }finally{
            //clean up code
       }
    }
}

As you see this is not an exact implementation but a foundation code, how transaction magically works for you. The key point is there interface OriginalDao which makes this injection easy as OriginalDaoImpl and ProxyDaoImpl both implement same interface. Hence they can be swapped i.e. proxy taking place of original. This dynamic proxy can be created in java by Java dynamic proxy. Now, the question what if your class is not implementing an interface, it gets harder for the replacement to happen. One of the libraries CGLIB as far as I know, helps in such a scenario, whereby it generates a dynamic subclass for the class in consideration and in overriden method performs the magic as described above, by calling super.save(o) to delegate to original code.

Now to the problem of injection.

1. Create interface and make your dao implement that and spring will default to JDK proxy as it is behaving now.
2. Add proxy-target-class="true" attribute to <tx:annotation-driven transaction-manager="transactionManager"/>

As far as exception is concerned it is throwing as it is expecting injected bean to be of type 'HibernateController' but its not.

For you reference you can refer links below.

1. 10.5.6 Using @Transactional
2. Spring AOP Doc

Hope this helps !!!!!.