Spring : ServiceLocatorFactoryBean Interface

This interface is used for lazy initialization of beans:

The problem with ApplicationContextAware and ObjectFactory is the component is coupled with the spring API.

Steps required

Step 1

Now to achieve 100% abstraction, we need some way by which Spring can dynamically create the instance of another bean and return it to us. So this is what we do as our first step:

//the interface implemented by various impl classes
public interface BillPaymentService {

}
//step 1
public interface BillPaymentServiceFactory {

    public BillPaymentService getService();
}

Step 2

public interface CustomerService{ 
void payBill(double amt)
}
public class CustomerServiceImpl3 implements CustomerService {

    private BillPaymentServiceFactory billPaymentServiceFactory;
    
    public void setBillPaymentServiceFactory(
            BillPaymentServiceFactory billPaymentServiceFactory) {
        this.billPaymentServiceFactory = billPaymentServiceFactory;
    }

    public void payBill(double amt) {
        BillPaymentService billService = billPaymentServiceFactory.getService();
        //we need to call some method of BillPaymentService here. Right now not required.        
    }

Step 3 :  Xml config

<!-- We are using the ServiceLocatorFactoryBean here -->
<!-- In the bean just refer to serviceLocator -->
bean id="customerService3" class="com.xxxxx.CustomerServiceImpl3">
 <property name="billPaymentServiceFactory" ref="serviceLocator"/>
/bean>

<bean id="serviceLocator"
        class="org.springframework.beans.factory.config.ServiceLocatorFactoryBean">
 <property name="serviceLocatorInterface" value="com.xxxxx.BillPaymentServiceFactory"/>
/bean>

We are injecting the ServiceLocator in CustomerService bean which implement factory interface for us and provide an instance of the target bean transparently.