Spring bean

Understand the idea

Component scanning finds annotated classes such as @Service and @Controller. @Bean methods register objects you create explicitly, often library objects. The default singleton scope means one instance per application context, shared across requests.

A concrete example

@Bean
PasswordEncoder passwordEncoder() {
    return new BCryptPasswordEncoder(12);
}

In the application

Services and controllers are discovered by scanning; SecurityConfig registers the password encoder and JWT components.

Do not store the current request or current user in singleton controller instance fields.

See it in a working stage

• Stage 2: let a controller handle a request
• Stage 8: Let Spring supply a product-file reader
• Stage 12: Create beans with explicit factory methods

Related concepts

• ApplicationContext
• Dependency injection
• Service layer
• Controller