What in the world are Spring beans?

java

singleton

ioc

bean-lifecycle

byAnton Shumikhin·Oct 18, 2024

Spring beans are pivotal components encapsulated within the vast ecosystem of the Spring Framework. These entities, under the vigilant management of the Spring IoC (Inversion of Control) container, are autonomously instantiated and employed, bypassing the need for you to manually breathe life into these objects. Using the @Component annotation tags beans for Spring gardeners (IoC container), whereas @Bean in a config class grants you the divine power to create life yourself. For instance:

@Component
public class KnightBean {
  // Spring sees this and goes "Ah, time to raise a knight!"
}

You can request the service of your knight (bean instance) at any point in your application like so:

@Autowired
KnightBean knightBean; // Spring heeds your call and sends the knight on his steed.

Consider beans as modular building blocks for your kingdom, err...application, maintained and run efficiently by the humble Spring folks.

Grasping bean scope and lifecycle

Scope related decisions are the epitome of Spring beans' flexibility. While their default nature is to be singleton beans, you can alter this by declaring them to be prototype, request, session, or application scoped. Observing and understanding a bean's lifecycle is essentially tracing its footprints from creation to destruction.

Third-party folks in action

Ever felt stuck with third-party libraries that do not come as beans? That's where @Bean makes an entrance. It turns those foreign components into Spring beans, enabling them to join the party:

@Configuration
public class AppConfig {
  @Bean
  public ThirdPartyGuest thirdPartyGuest() {
    // "Welcome! Welcome! Our castle is your castle!"
    return new ThirdPartyGuest();
  }
}

Decoupling for a better tomorrow

The primary benefits of Spring beans are to maximize decoupling and ensure a clear separation of concerns for more maintainable code. You just declare your dependencies, and Spring becomes your genie, resolving them at runtime.

Advanced bean usage: strategies and practices

Configuration metadata and reflection

Beans aren't just tied to the physical realm; they transcend into metadata, detailing their properties, dependencies, and management blueprint. Your decrees and declaration about these aspects can be captured in Java annotations, Java code or XML configurations.

Inversion of Control? Over to you, Spring!

IoC is a principle where control is inverted - akin to you sitting back while Spring Framework drives. It's manifested when Spring dictates the lifecycle of beans, the way they're created and destroyed, and their dependencies wired together.

Detailed documentation – Dig deeper

Want to challenge the depths of your knowledge pool? The Spring core technologies documentation offers you a deep dive into the world of Spring beans. It's an invaluable treasure trove for anyone yearning for complete mastery over this topic.

explain-codes / Java / What in the world are Spring beans?

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