How to inject Spring bean into Java code?

[eugenebalt]

Spring newbie here.

I've read comments that it's not a good idea to use ApplicationContext.getBean() to retrieve beans, because that violates Inversion of Control. Instead, you should just declaratively "inject" your bean where you need it.

So how do I do it?

Let's say I have my Spring MVC Controller class, and I want to inject my bean here:

public class HelloController implements Controller {

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
    {
         // use my DAO bean here
    }
}

And the bean that I want to inject is a DAO bean, defined in my applicationContext.xml as follows (I'm using Hibernate to connect to the DB):

    <bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="mappingResources">
            <list>
                <value>Movie.hbm.xml</value>
            </list>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.HSQLDialect</prop>
                <prop key="show_sql">true</prop>
            </props>
        </property>
    </bean>

    <bean id="MainDao" class="MyApp.dao.MainDao">
        <property name="sessionFactory">
            <ref bean="sessionFactory" />
        </property>
    </bean>

So my MainDao bean is defined and created by Spring, and now I need to inject it into my Controller class above, that handles the page. How do I do it? Is it enough to just create a member MainDao variable in my Controller, and assume it will be populated? Thanks.

[dr_pompeii]

I've read comments that it's not a good idea to use ApplicationContext.getBean() to retrieve beans, because that violates Inversion of Control. Instead, you should just declaratively "inject" your bean where you need it.

Yes, is not recommendable that the application has knowledge about Spring itself, but some times would required

So my MainDao bean is defined and created by Spring, and now I need to inject it into my Controller class above, that handles the page.

An important rule you must consider is the MVC pattern, is not wise that the Controller call directly a DAO object, bad practice, should be

Controller -> BO (Business Object or Service) -> DAO

How do I do it? Is it enough to just create a member MainDao variable in my Controller, and assume it will be populated? Thanks.

your MainDao must implement some interface MainDaoService (due Proxy pattern used by Spring), and such interface must be declared in your BO (controller for your case, recall it is wrong)

private MainDaoService mainDaoService

//setter for your Variable

Then Spring offer you two forms to inject, by XML or by annotations, it is the magic of Spring

I suggest you read more documentation for more details about this

[eugenebalt]

thanks Dr Pompeii,

But suppose I have a Service like you said, can you give a quick example of how I would inject with annotations?

[dr_pompeii]

But suppose I have a Service like you said, can you give a quick example of how I would inject with annotations?

In Spring documentation has good information about this, read about @Autowired and @Qualifier, like plus you must read about @Repository, @Controller and @Service to get all the piece working together