Spring in Depth 1

#

Auto wiring

#

Auto wiring looks for a dependency that implements the interface that is auto-wired. Let’s just look at a sample case below

@Component
public class ClientApp{
    @Autowired
    Service reqService;
}

@Component
public class SplService implements Service{
}

@Component
public class NormService implements Service{
}

Now, we have looked already what happens if there are 2 dependencies. It will throw an error as its not able to define a dependency as nothing is defined as primary.

So, we can mark one of the implementation with @Primary.

@Component
@Primary
public class NormService implements Service{
}

Another way to do this is auto-wiring by name.

@Component
public class ClientApp{
    @Autowired
    Service normService;
}

Now, it looks at NormService as the service is named with a implementing class name. But what if both types of auto wiring is present. Then @Primary will take precedence over auto wiring by name.

Another way is to auto wire by @Qualifier.

@Component
public class ClientApp{
    @Autowired
    @Qualifier("spl")
    Service reqService;
}

@Component
@Qualifier("Spl")
public class SplService implements Service{
}

@Qualifier takes precedence over @Primary and auto wiring by name

Bean Scope

#

Spring creates all the beans and maintains them. By default, the scope of the bean is singleton.

• singleton - One instance per Spring Context
• prototype - One instance per request
• request - One bean per HTTP request
• session - One bean per HTTP session

To configure a bean as prototype, we can use the following annotation.

@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)

Singleton vs Prototype Scope

#

We will look at further concepts like Life Cycle of a bean, Application context, etc in future posts