Spring Core Concepts

Inversion of Control is the foundational design principle behind Spring Framework.

Dependency Injection is the mechanism Spring uses to implement Inversion of Control.

Every Spring bean goes through a precise lifecycle — from BeanDefinition registration through instantiation, dependency injection, initialization callbacks, active use…

Bean scope determines how many instances of a bean Spring creates and how long each instance lives.

ApplicationContext is the central interface of the Spring IoC container.

BeanFactory is the root interface of Spring's IoC container — the most basic form of the container that provides dependency injection and bean management.

Component scanning is the mechanism Spring uses to automatically discover and register beans.

Java-based configuration uses @Configuration classes and @Bean methods to define Spring beans programmatically — replacing XML configuration with type-safe, IDE-friendly…

XML-based configuration was Spring's original configuration mechanism — declaring beans, dependencies, and wiring in applicationContext.xml files.

Constructor injection is the recommended dependency injection style in Spring.

Setter injection provides dependencies through setter methods after the bean is constructed.

The @Qualifier annotation resolves ambiguity when Spring finds multiple beans of the same type.

The @Primary annotation marks one bean as the default candidate when multiple beans of the same type exist in the Spring container.

By default, Spring creates all singleton beans at application startup — eager initialization.

Spring's Environment abstraction provides unified access to configuration properties from all sources — property files, environment variables, system properties, and…