Spring Bean Annotation

This document summarizes Annotations related to Spring Beans.

1. @Component

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@Component
public class MyComponentA {
}

@Component("myComponentC")
public class MyComponentB {
}

[Code 1] @Component Example

A Class with @Component attached means a Class managed as a Component in Spring, as the name suggests. Being managed as a Component means that Instances of that Class are managed as Beans. Spring obtains information about Classes with @Component attached through Spring’s Component Scanner, then creates Beans based on the obtained information and performs DI (Dependency Injection) as needed. The Default name of a Bean uses the Class name with the first letter changed to lowercase. Therefore, the Bean name of the MyComponentA Class in [Code 1] becomes myComponentA. The Bean name can also be specified as the Value of @Component. The Bean name of the MyComponentB Class in [Code 1] becomes myComponentC specified in the Value of @Component.

2. @Configuration

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package com.ssup2;

@Component
public class MyBeanB {
}

[Code 2] @Configuration Example 1

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@Configuration
@ComponentScan("com.ssup2")
public class MyConfig {

    @Bean
    public Mybean myBeanA() {
        return new myBeanA();
    }
}

[Code 3] @Configuration Example 2

@Configuration is an Annotation to inform Spring that it is a Class containing Bean Methods. Also, @Configuration informs Spring’s Component Scanner of the Package of Components so that the Component Scanner can discover Components. In [Code 2], [Code 3], a Bean Method named myBeanA is defined using @Bean. Also, @ComponentScan is used to inform the Component Scanner of the Package where MyBeanB exists. Configuration inherits @Component. Therefore, Instances of Classes with @Configuration attached are also managed as Spring Beans.

2.1. @Bean

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public class MyBeanA {
}

public class MyBeanB {
}

@Configuration
public class MyConfig {

    @Bean
    public MybeanA myBeanA() {
        return new myBeanA();
    }

    @Bean("myBeanC")
    public MybeanB myBeanB() {
        return new myBeanB();
    }
}

[Code 4] @Bean Example

@Bean is attached to Bean Methods to inform Spring that the Method is a Bean Method. Bean Methods must return Instances. The Default name of Beans created through Bean Methods becomes the Method name. The Bean name created through the myBeanA() Method in [Code 4] becomes myBeanA. Also, you can specify the name of Beans created through Bean Methods through the Value of @Bean. The Bean name created through the myBeanB() Method in [Code 4] becomes myBeanC, which is the Value of @Bean.

3. @Service, @Controller, @Repository

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@Service
public class MyService {
}

@Controller
public class MyController {
}

@Repository
public class MyRepository {
}

[Code 5] @Service, @Controller, @Repository Example

@Service is attached to Classes containing Business Logic. @Controller is attached to Classes responsible for Controllers in the MVC Pattern. @Repository is attached to Classes responsible for Data Access. @Service, @Controller, and @Repository all inherit @Component. Therefore, Instances of Classes with the 3 Annotations attached are managed as Spring Beans.

4. References

React Router