05_Spring_Container.md

Spring Container

The core of Spring!

Manages Beans (objects) that constitute a program using DI (Dependency Injection)

Types

BeanFactory

Loads Beans when they are used (Lazy-loading)

• A class that creates and manages Bean objects
• Responsible for managing Beans, including creating, looking up, and returning Beans
• BeanFactory loads Bean definitions immediately, but does not instantiate the Bean itself until it is called
  • When getBean() is called, only then does the Factory instantiate the received Bean using Dependency Injection (DI) and set the Bean's properties → On-demand approach
• Focuses on the basic IoC functionality of creating Beans and configuring relationships
• How Beans are created and loaded
  • BeanFactory uses Lazy-loading
  • Instances are created and loaded at the point when a method or class receives a Bean loading request
    • Therefore, instances are created and loaded at the point when requested by the .getBean() method

ApplicationContext

Loads all Beans at runtime startup (Pre-loading)

• Similar to BeanFactory, but a more enhanced form of container
• Focuses on overseeing the overall control of Bean creation, relationship configuration, etc., by referencing separate information
• How Beans are created and loaded
  • ApplicationContext uses Pre-loading
  • All Beans and configuration files are instantiated and loaded when a load request is made by the ApplicationContext

BeanFactory vs ApplicationContext

• The reason they are divided into two approaches is because of the relationship between usage frequency and resources used
  • If a Bean is not frequently used, it should be loaded only when actually requested to save consumed resources (Lazy-loading) → Use BeanFactory
  • If a Bean is frequently used, it is better to load it all at once (Pre-loading) → Use ApplicationContext