SpringBoot automatic assembly principle learning

1. Automatic configuration of
pom.xml

• spring-boot-dependencies: The core is in the parent project
• When we write or introduce some Springboot dependencies, we don't need to specify the version because there are these version repositories.

2. Launcher

	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter</artifactId>
	</dependency>

• Starter: To put it bluntly, it is the startup scene of springboot
• For example, spring-boot-starter-web will help us automatically import all the dependencies of the web environment
• springboot will turn all the functional scenarios into one starter
• What function we want to use, we only need to find the corresponding launcher

3. The main program

//@SpringBootApplication 标注这个类是一个springboot的应用
@SpringBootApplication
public class BlogApplication {
    
    

	public static void main(String[] args) {
    
    
		SpringApplication.run(BlogApplication.class, args);
	}
}

• annotation

@SpringBootConfiguration : springboot的配置
	@Configuration
	@Component : 说明也是一个spring的组件
@EnableAutoConfiguration : 自动配置
	@AutoConfigurationPackage : 自动配置包
		@Import(AutoConfigurationPackages.Registrar.class) : 自动配置包注册
	@Import(EnableAutoConfigurationImportSelector.class) : 自动配置导入选择
//获取所有的配置
List<String> configurations = getCandidateConfigurations(annotationMetadata,
attributes);

Get candidate configurations

	protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
			AnnotationAttributes attributes) {
    
    
		List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
				getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
		Assert.notEmpty(configurations,
				"No auto configuration classes found in META-INF/spring.factories. If you "
						+ "are using a custom packaging, make sure that file is correct.");
		return configurations;
	}

META-INF/spring.factories

//所有的类加载到配置类中
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));