What is DI lifecycle management?

What is lifecycle management?

Manage instance creation (new) and destruction
To destroy the instance created by new, put null in the variable and free the memory
However! ** For fields with @Autowired, Spring will do it for you, even if it's not null! ** **
Moreover, when using the Servlet ** Spring will also register the scope of the instance! ** (Servlet is a function to register an instance in Session scope or Request scope)
Note: Make sure you know when the instance will be destroyed

Instance expiration date
Example: Variables declared in an if statement as Java local variables cannot be used outside the if statement because the scope is inside the if statement.
Session scope
Expiration date from user login to log out
Request scope
One HTTP request expires
Example: Request scope range from user registration screen to registration result screen

Specify which scope to register in the annotation with @Scope annotation as shown below.
In addition to @Component, @Scope annotation can be used for @Bean, @Controller, etc.
** Easy to create and destroy instances **

@Component
@Scope("prototype")
public class SampleComponent{

}

singleton
Default configuration
Create only one instance when Spring starts,
Share and use one instance after creation
prototype
An instance is created every time you get a bean
session
An instance is created for each HTTP session. Used only for web applications
request
An instance is created for each HTTP request. Used only for web applications
globalSession
Instance is generated for each GrobalSession in the portlet environment
Used only for web applications that support portlets
application
Instance is created for each context of Servlet. Only available for web applications.

If @Scope is not added, the instance will be created as a singleton.
With a singleton, only one instance of an object can be created, and you cannot even create a second or more instance.
- A singleton is usually sufficient for the scope of @Controller, @Service, and @Repository.

If an instance of singleton scope has an object of prototype scope, ** Bean with prototype scope (hereinafter referred to as PrototypeComponent) becomes singleton scope **

//It becomes a singleton scope
@Component
@Scope("prototype")
public class PrototypeComponent{

}

@Component
public class SingletonComponent{	
    @Autowired
    private PrototypeComponent component;
}