SpringBoot启动流程

• run方法启动时传入了当前类 ContractApplication.class,传入当前类的作用主要是为了解析当前类上面的注解(不一定传递当前类，也可以自己写一个类，在写的类上添加对应的注解)

@SpringBootApplication
@ComponentScan("com.example")
public class ContractApplication {
    public static void main(String[] args) {
        SpringApplication.run(ContractApplication.class);
    }
}

• 将传入的类封装成一个Class类型的数组

    public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
        return run(new Class[]{primarySource}, args);
    }

• 生成一个SpringApplication对象，在调用SpringApplication的run方法

    public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
        return (new SpringApplication(primarySources)).run(args);
    }

• new SpringApplication()构造方法，主要是给SpringApplication对象中的属性赋值

	public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
                //资源加载器
		this.resourceLoader = resourceLoader;
                //判断传进来的类是否为空
		Assert.notNull(primarySources, "PrimarySources must not be null");
		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
                //1.推测项目的应用类型（通过项目目录结构，和类），NONE(不是Web项目)，REACTIVE(Web应用，响应式)，SERVLET(Web应用，springmvc)
		this.webApplicationType = WebApplicationType.deduceFromClasspath();
                //2.从spring.factories中获取需要加载的BootstrapRegistryInitializer类型的的实现类
		this.bootstrapRegistryInitializers = new ArrayList<>(
				getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
                //3.从spring.factories中获取需要加载的AppliationContextInitializer(初始化器)类型的实现类
		setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
                //4.从spring.factories中获取需要加载的ApplicationListener(应用监听器)类型的实现类
		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
                //5.推测出Main类（main()方法所在的类）
		this.mainApplicationClass = deduceMainApplicationClass();
	}

• spring.factories

# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer