Spring MVC @Controller：由于“ component-scan”标签的“ use-default-filter”而导致的事务性问题

Question

I'm kinda new to Spring MVC, so I'm creating a small web application just to try it.

I am using Spring 4.2 and Hibernate 5.

The web app has a Spring servlet-context.xml and a Spring application-context.xml .

I have a @Controller with a method that make use of a @Service . This Service has a findAll() method marked as @Transactional .

The web.xml looks like this:

...
<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>
        classpath:*-context.xml
    </param-value>
</context-param>

<servlet>
    <servlet-name>myDispatcher</servlet-name>
    <servlet-class>
        org.springframework.web.servlet.DispatcherServlet
    </servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:servlet-context.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>myDispatcher</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>
...

Here the Controller:

@Controller
public class TestOneController
{
    @Autowired
    private UserManager userManager;

    @RequestMapping("views/test")
    public ModelAndView defaultResolution()
    {
        List<User> users = userManager.findAll();
        // here I build my String msg object
        return new ModelAndView("views/resolution", "msg", msg);
    }
}

Here the Service:

@Service("userManager")
public class UserManagerImpl implements UserManager
{
    @Autowired
    private UserDao userDao;

    @Override
    @Transactional(readOnly = true, propagation = Propagation.REQUIRED)
    public List<User> findAll()
    {
        return userDao.findAll();
    }
}

And finally the Dao used by the Service:

@Repository("userDao")
public class UserDaoImpl implements UserDao
{

    @Autowired
    private SessionFactory sessionFactory;

    @Override
    @SuppressWarnings("unchecked")
    @Transactional(readOnly = true, propagation = Propagation.SUPPORTS)
    public List<User> findAll()
    {
        Query query = sessionFactory.getCurrentSession().createQuery("from User ");
        return query.list();
    }
}

My question: I have tried several configurations, that I believed to be equivalent, but with one of them I am getting an org.hibernate.HibernateException: Could not obtain transaction-synchronized Session for current thread when I hit the mapped Controller method from a link in a page. Could someone explain me why this exception is raised when I use configuration 2, but not on configuration 1 and 3?

Configuration 1 (working)

application-context.xml

...
<tx:annotation-driven />
<context:component-scan base-package="my.package">
    <context:exclude-filter type="annotation"
        expression="org.springframework.stereotype.Controller" />
</context:component-scan>

<bean id="transactionManager"
    class="org.springframework.orm.hibernate5.HibernateTransactionManager">
    <property name="sessionFactory" ref="sessionFactory" />
</bean>

<bean id="sessionFactory"
    class="org.springframework.orm.hibernate5.LocalSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="configLocation" value="classpath:hibernate.cfg.xml" />
    <property name="packagesToScan">
        <list>
            <value>my.package.entities</value>
        </list>
    </property>
</bean>

<bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
    <property name="jndiName" value="java:comp/env/jdbc/myDb" />
</bean>
...

servlet-context.xml

...
<context:component-scan base-package="my.package.inner.package">
    <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller" />
</context:component-scan>

<mvc:annotation-driven />
<mvc:resources mapping="/resources/**" location="/resources/" />
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="viewClass"
        value="org.springframework.web.servlet.view.JstlView" />
    <property name="prefix" value="/" />
    <property name="suffix" value=".jsp" />
</bean>
...

Configuration 2 (raises the exception) Same configuration as 1, with the difference of the <context:component-scan> tag of the servlet-context.xml , that has a base-package closer to the root:

<context:component-scan base-package="my.package">
    <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller" />
</context:component-scan>

Note that this is the same base-package for the component-scan in the application-context.xml .

Configuration 3 (working) Same as 2 (thus with base-package="my.package" in the servlet-context.xml ), with the difference that instead of annotating my Service with @Service , I declare it explicitly as a bean in the application-context.xml :

...
<bean id="userManager" class="my.package.services.impl.UserManagerImpl">
</bean>
...

TL;DR Could someone explain me why I am getting an org.hibernate.HibernateException: Could not obtain transaction-synchronized Session for current thread when I hit the Controller mapped method with configuration 2 and not with configuration 1 and 3? I was believing that all those 3 configuration were equivalent.

Thank you.

Answer 1

After some hours of trial-and-error process, I found out the issue.

In all the 3 configurations, the component-scan tag of servlet-context.xml needs another attribute: use-default-filters must be set to "false".

<context:component-scan base-package="my.package" use-default-filters="false">
    <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller" />
</context:component-scan>

If it's set to "true" (as per default), it's essentially like having a default include filter like this one:

<context:include-filter type="annotation" 
                    expression="org.springframework.stereotype.Component"/>

This means that during the package scan, it loaded also the defined @Service (and the @Repository , etc.). Since the Service was loaded by the Servlet Context, that has no <tx:annotation-driven /> tag, no Transactional context was enabled for the Service, and the Exception was raised.

In configuration 1, since the base package for scanning was restricted (including only the Controller package), the issue was bypassed (the Servlet Context only loaded the Controller, so the Service used was the one loaded by the Application Context, that has Transactional context enabled).

In configuration 3, since I used a "manual definition" of the Service bean in the right "transactional" context ( application-context.xml ), the problem was bypassed too.