@ComponentScan

1. @Component 어노테이션이 적용된 클래스를 검색하여 빈으로 등록합니다.
2. XML이나 Annotation 두 가지 방법 중 하나를 선택할 수 있습니다.
   XML : <context:component-scan>
   Annotation : @ComponentScan
3. base 패키지를 지정할 수 있습니다. 


//=================================원문=================================//

org.springframework.context.annotation

Annotation Type ComponentScan

• ---

  
  

  @Retention(value=RUNTIME)
   @Target(value=TYPE)
   @Documented
   @Repeatable(value=ComponentScans.class)
  public @interface ComponentScan

  Configures component scanning directives for use with @Configuration classes. Provides support parallel with Spring XML's <context:component-scan> element.Either basePackageClasses() or basePackages() (or its alias value()) may be specified to define specific packages to scan. If specific packages are not defined, scanning will occur from the package of the class that declares this annotation.
  Note that the <context:component-scan> element has an annotation-config attribute; however, this annotation does not. This is because in almost all cases when using @ComponentScan, default annotation config processing (e.g. processing @Autowired and friends) is assumed. Furthermore, when using AnnotationConfigApplicationContext, annotation config processors are always registered, meaning that any attempt to disable them at the @ComponentScan level would be ignored.
  See @Configuration's Javadoc for usage examples.

  Since:

  3.1

  Author:

  Chris Beams, Juergen Hoeller, Sam Brannen

  link:

  http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/annotation/ComponentScan.html

@EnableAutoConfiguration

1.  원하는 class에 Spring Application Context를 auto-configuration 합니다. 

    (사용자가 원하는 bean을 추측하여 configure)

2. configure 되길 원하지 않는 클래스를  manually exclude 할 수 있습니다.

3. @EnableAutoConfiguration를 사용한 클래스의 패키지는 sub-package에 있는 

 @Entity 클래스들을 scan합니다. (따라서 root package의 classdㅔ서 사용하길 권장)

//===================================원문===================================//

org.springframework.boot.autoconfigure

Annotation Type EnableAutoConfiguration

• ---

  
  

  @Target(value=TYPE)
   @Retention(value=RUNTIME)
   @Documented
   @Inherited
   @AutoConfigurationPackage
   @Import(value=EnableAutoConfigurationImportSelector.class)
  public @interface EnableAutoConfiguration

  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. For example, If you have tomcat-embedded.jar on your classpath you are likely to want a TomcatEmbeddedServletContainerFactory (unless you have defined your own EmbeddedServletContainerFactory bean).Auto-configuration tries to be as intelligent as possible and will back-away as you define more of your own configuration. You can always manually exclude() any configuration that you never want to apply (use excludeName() if you don't have access to them). You can also exclude them via the spring.autoconfigure.exclude property. Auto-configuration is always applied after user-defined beans have been registered.
  The package of the class that is annotated with @EnableAutoConfiguration has specific significance and is often used as a 'default'. For example, it will be used when scanning for @Entityclasses. It is generally recommended that you place @EnableAutoConfiguration in a root package so that all sub-packages and classes can be searched.
  Auto-configuration classes are regular Spring Configuration beans. They are located using the SpringFactoriesLoader mechanism (keyed against this class). Generally auto-configuration beans are @Conditional beans (most often using @ConditionalOnClass and @ConditionalOnMissingBean annotations).

  Author:

  Phillip Webb, Stephane Nicoll

  link:

  http://docs.spring.io/spring-boot/docs/current/api/org/springframework/boot/autoconfigure/EnableAutoConfiguration.html

"Java 8의 lambda"만 계속 에러를 낼 경우

다음과 같은 에러 메세지를 보여줍니다.
    Method references are allowed only at source level 1.8 or above


이럴 경우 프로젝트의 properties -> Java compiler -> compliance level 을 1.8로 맞춰주면 됩니다.