Beans & IoC Container

Introduction

A Spring bean is any object Spring manages. The IoC (Inversion of Control) container is the registry that creates beans, injects them, manages their lifecycle and tears them down. Inversion of control means you don't control object creation — Spring does.

Understanding the topic

How beans are registered:

• @Component — generic bean.
• @Service, @Repository, @Controller — semantic flavours of @Component.
• @Bean on a method inside @Configuration — manual registration (use for 3rd-party classes).
• Scopes: singleton (default), prototype, request, session.

Informative example

Bean from a 3rd-party library:

@Configuration
public class HttpClientConfig {
  @Bean
  public RestClient stripeClient(@Value("${stripe.api-key}") String key) {
    return RestClient.builder()
        .baseUrl("https://api.stripe.com")
        .defaultHeader("Authorization", "Bearer " + key)
        .build();
  }
}