12-Java Configuration

Question 1

Overrides of ApplicationContext.getBean

Answer 1

1. getBean(Class)

2. getBean(id, Class)

Question 2

How to combine multiple configuration classes?

Answer 2

@Configuration
@Import({ Config1.class, Config2.class })
public class Combine {}

Question 3

What does Spring use Objenesis lib for?

Answer 3

Prior to Spring 4.3, we cannot use constructor injection i.e. pass in dependency to the constructor, all beans need to have a default constructor. This is a CGLIB restriction

Use Objenesis to overcome this.

Question 4

What is “tramp data”?

Answer 4

Tramp Data in this case are variables passed from one method to another until they are used.
Dependency injection is designed to avoid this in Spring Beans

Question 5

List out bean scopes

Answer 5

1. singleton
2. prototype: A new instance is created each time the bean is referenced
3. session:(web-aware) per session. Used in web env
4. request:(web-aware) per request. Used in web env
5. application:(web-aware) last as long as the ServletContext
6. global: last as long as a global HttpSession in a Portlet application (obsoleted)
7. websocket:(web-aware) per web-socket connection
8. refresh scope
9. thread scope (defined but not registered by default)

Question 6

What is the implementation of ApplicationContext in a web app?

Answer 6

WebApplicationContext

Question 7

How to create a custom scope?

Answer 7

Create a bean of type CustomScopeConfigurer

Question 8

How to enable the last bean to override the one with the same name?

Answer 8

spring.main.allow-bean-definition-overriding=true

Question 9

What happens if defining 2 beans with the same name?

Answer 9

No exception thrown. Spring will pick the first one it found