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@Component Annotation in Spring

1. Overview

@Component is a stereotype annotation used to tell Spring that a class should be managed as a bean.

When Spring scans the classpath, it detects @Component classes and registers them inside the application context.

This is one of the simplest ways to create Spring-managed objects without writing explicit XML or @Bean methods.

2. What @Component Means

@Component marks a class as a generic Spring bean.

In simple words:

“Spring, create an object of this class and manage its lifecycle.”

Spring can then inject that bean into other classes using @Autowired.

3. Basic Example

@Component
public class Engine {

    public void start() {
        System.out.println("Engine started");
    }
}
@Component
public class Car {

    private final Engine engine;

    public Car(Engine engine) {
        this.engine = engine;
    }
}

If component scanning is enabled, Spring creates both beans automatically.

4. Component Scanning

@Component works only when Spring is told to scan the package.

Java configuration

@Configuration
@ComponentScan("com.example")
public class AppConfig {
}

Spring Boot

Spring Boot usually enables component scanning automatically through @SpringBootApplication.

5. @Component and Stereotype Annotations

@Component is the base annotation for other specialized annotations.

These annotations are built on top of it:

  • @Service
  • @Repository
  • @Controller

They all register beans, but each one expresses a different application role.

6. @Component vs @Bean

@Component

Used on the class itself.

@Component
public class Engine {
}

@Bean

Used on a method inside a @Configuration class.

@Bean
public Engine engine() {
    return new Engine();
}

Main difference

  • @Component is discovered automatically
  • @Bean is declared explicitly

7. When to Use @Component

Use @Component when:

  • the class is a regular application component
  • the object should be discovered automatically
  • you want less configuration
  • there is no need for special semantic meaning like service or repository

8. Bean Name of @Component

By default, Spring creates a bean name from the class name.

@Component
public class EmailSender {
}

Default bean name:

emailSender

You can also specify a custom name:

@Component("mailSender")
public class EmailSender {
}

9. Scope Note

By default, a @Component bean is a singleton.

That means Spring creates one instance for the application context unless another scope is configured.

Example:

@Component
@Scope("prototype")
public class TaskProcessor {
}

10. Common Mistakes

  • forgetting to enable component scanning

  • placing components outside the scanned package

  • using @Component when a more specific stereotype would be clearer

  • assuming @Component automatically makes a class a service or repository

  • mixing manual object creation with Spring-managed beans

11. Interview Questions

Q1. What does @Component do?

It marks a class as a Spring-managed bean.

Q2. What is component scanning?

The process by which Spring searches for classes annotated with @Component and registers them.

Q3. How is @Component different from @Bean?

@Component is class-based and discovered automatically, while @Bean is method-based and declared explicitly.

Q4. What annotations are built on top of @Component?

@Service, @Repository, and @Controller.

Key Takeaways

  • @Component turns a class into a Spring bean

  • It depends on component scanning

  • It is the base stereotype annotation in Spring

  • Prefer specific stereotypes when the class has a clear role

  • Default scope is singleton