Spring dependency Injection/IOC

Question 1

What is spring IOC container?

Answer 1

• Creates the objects
• Wire them together
• Configure them
• Manage their complete lifecycle from creation till destruction
• Uses dependency injection (DI) to manage the components that make up an application

Question 2

What is dependency injection?

Answer 2

• We don’t create objects but describe how they should be created
• We don’t directly connect components and services together in code but describe which services are needed by which components in a configuration file
• A container ( the IOC container) is then responsible for hooking it all up

Question 3

In how many ways dependency injection can be done?

Answer 3

There are three types of dependency injection:

1. constructor injection: dependencies are provided as constructors parameters
2. setters injection: dependences are assigned through java beans properties (setter methods)

Question 4

Whats is the difference between constructor injection and setter injection?

Answer 4

Constructor injection: Theres no partial injection, doesnt overrides the setter property, it will create new instance if any modification is done

Setter injection: there can be partial injection, overrides the constructor property if both are defined,
wront create new instance if modification is done

Question 5

How many types of IOC containers are there in spring?

Answer 5

Bean factory & ApplicationContext

A beanFactory is like a factory class that contains a collection of beans. It instantiates the beans whenever asked for by clients.

ApplicationContext: the applicationContext interface is built on top of BeanFactory interface. It adds some extra functionaly than bean factory

Question 6

Differentiate between BeanFactory and ApplicationContext

Answer 6

Bean factory: uses lazy initialzization

• Explicitly provided a resource object using the syntax
• doesnt support internationalization
• annotation based dependency injection is not supported

Application Context

• Uses eager/aggressive initialization
• cretes and manages resources objects on its own
• supports internationalization
• Annotation based dependency injection is supported

Question 7

List some of the benefits of IoC

Answer 7

• it minimizes the amount of code in application
• makes application easy to test
• loose coupling is promoted with minimal effort and least intrusive mechanism
• IOC containers support eager instantiation and lazy loading of services