@SpringBootApplication?

갑자기 왜 SpringBootApplication을 알아보는거죠?

• 코드 리뷰를 하는 중 SpringBootApplication이 있는데, ComponentScan , PropertySource 를 사용하는 이유가 무엇인지 질문이 들어왔을 때였다.

• 사실 난 SpringBootApplication 에 대하여 왜 이걸 쓰는지 누군가에게 설명 할 수 없단걸 깨달았고 이제 알아보려 한다.

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication { ... }

Documented

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Documented {
}

Inherited

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Inherited {
}

Retention

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Retention {
    /**
     * Returns the retention policy.
     * @return the retention policy
     */
    RetentionPolicy value();
}

Target

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Target {
    /**
     * Returns an array of the kinds of elements an annotation interface
     * can be applied to.
     * @return an array of the kinds of elements an annotation interface
     * can be applied to
     */
    ElementType[] value();
}

• TYPE_PARAMETER가 쓰이는 곳은 class name<T1, T2, ..., Tn> 에서 T1, T2다.

• TYPE_USE가 쓰이는 곳은 @C int f; 에서 int다.

ComponentScan

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Repeatable(ComponentScans.class)
public @interface ComponentScan { ... }

• 해당 어노테이션을 사용하면 스캔할 패키지를 명시할 수 있다.

• Exclude Filter, Include Filter, Filter로 필터링도 가능하다.

@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

Repeatable

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Repeatable {
    /**
     * Indicates the <em>containing annotation interface</em> for the
     * repeatable annotation interface.
     * @return the containing annotation interface
     */
    Class<? extends Annotation> value();
}

@AliasFor("classes")
		Class<?>[] value() default {};

SpringBootConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
@Indexed
public @interface SpringBootConfiguration {
	@AliasFor(annotation = Configuration.class)
		boolean proxyBeanMethods() default true;
}

Indicates that a class provides Spring Boot application @Configuration. Can be used as an alternative to the Spring's standard @Configuration annotation so that configuration can be found automatically (for example in tests).

Configuration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {
	@AliasFor(annotation = Component.class)
	String value() default "";

	boolean proxyBeanMethods() default true;
}

Indicates that a class declares one or more @Bean methods and may be processed by the Spring container to generate bean definitions and service requests for those beans at runtime

Indexed

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Indexed {
}

• Component를 붙은 어노테이션은 스프링 컨테이너에 빈으로 등록 된다.

AliasFor

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Documented
public @interface AliasFor {

	/**
	 * Alias for {@link #attribute}.
	 * <p>Intended to be used instead of {@link #attribute} when {@link #annotation}
	 * is not declared &mdash; for example: {@code @AliasFor("value")} instead of
	 * {@code @AliasFor(attribute = "value")}.
	 */
	@AliasFor("attribute")
	String value() default "";

	/**
	 * The name of the attribute that <em>this</em> attribute is an alias for.
	 * @see #value
	 */
	@AliasFor("value")
	String attribute() default "";

	/**
	 * The type of annotation in which the aliased {@link #attribute} is declared.
	 * <p>Defaults to {@link Annotation}, implying that the aliased attribute is
	 * declared in the same annotation as <em>this</em> attribute.
	 */
	Class<? extends Annotation> annotation() default Annotation.class;

}

@AliasFor is an annotation that is used to declare aliases for annotation attributes.

• 어노테이션과 함께 명시적으로 사용

public @interface ContextConfiguration {
 
     @AliasFor("locations")
     String[] value() default {};
 
     @AliasFor("value")
     String[] locations() default {};
 
     // ...
  }

• 메타 어노테이션의 Attribute에 명시적으로 사용

@ContextConfiguration
  public @interface XmlTestConfig {
 
     @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")
     String[] xmlFiles();
  }

• Implicit Aliases within an Annotation

@ContextConfiguration
  public @interface MyTestConfig {
 
     @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")
     String[] value() default {};
 
     @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")
     String[] groovyScripts() default {};
 
     @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")
     String[] xmlFiles() default {};
  }

• Transitive Implicit Aliases within an Annotation

@MyTestConfig
  public @interface GroovyOrXmlTestConfig {
 
     @AliasFor(annotation = MyTestConfig.class, attribute = "groovyScripts")
     String[] groovy() default {};
 
     @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")
     String[] xml() default {};
  }

EnableAutoConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
	String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
	Class<?>[] exclude() default {};
	String[] excludeName() default {};
}

Enable auto-configuration of the Spring Application Context, attempting to guess and configure beans that you are likely to need. Auto-configuration classes are usually applied based on your classpath and what beans you have defined.

AutoConfigurationPackage

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {
	String[] basePackages() default {};

	Class<?>[] basePackageClasses() default {};
}

Registers packages with AutoConfigurationPackages. When no base packages or base package classes are specified, the package of the annotated class is registered

Import

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
	Class<?>[] value();
}

ndicates one or more component classes to import — typically @Configuration classes.