a start logic analysis springboot ------- new SpringApplication ()

	SpringApplication public (<?> the ResourceLoader ResourceLoader, Class ... primarySources) { 
		this.resourceLoader = ResourceLoader; 
		Assert.notNull (primarySources, "Not PrimarySources MUST BE null"); 
　　　　　　　　　 this.primarySources a LinkedHashSet new new = <> (Arrays.asList ( primarySources)); 
. // (. 1) application type inferred based on the class of the classpath present 
		this.webApplicationType WebApplicationType.deduceFromClasspath = (); 
　　　　　　　　　　. // (2) Get ApplicationContextInitializer, and to set the Initializers 
		setInitializers ((Collection) getSpringFactoriesInstances ( 
				ApplicationContextInitializer.class)); 
　　　　　　　　　　// (.. 3) acquires ApplicationContextInitializer, and to set the Initializers 
		setListeners ((Collection) getSpringFactoriesInstances (ApplicationListener.class ));
　　　　　　　　　　// (4) concluded the main class 
		this.mainApplicationClass deduceMainApplicationClass = (); 
	}

(1). Inferential type

		this.webApplicationType = WebApplicationType.deduceFromClasspath();

　　

	static WebApplicationType deduceFromClasspath() {

　　　　　　　　　　//springframework.web.reactive.DispatcherHandler class
　　　　　　　　　　// But org.springframework.web.servlet.DispatcherServlet and org.glassfish.jersey.servlet.ServletContainer class does not exist
　　　　　　　　　　// return type WebApplicationType.REACTIVE

		if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null)
				&& !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
				&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
			return WebApplicationType.REACTIVE;
		}
　　　　　　　　　　//不存在javax.servlet.Servlet和org.springframework.web.context.ConfigurableWebApplicationContext

　　　　　　　　　　// returns WebApplicationType.NONE

		for (String className : SERVLET_INDICATOR_CLASSES) {
			if (!ClassUtils.isPresent(className, null)) {
				return WebApplicationType.NONE;
			}
		}
		return WebApplicationType.SERVLET;
	}

　　

static WebApplicationType deduceFromClasspath() {

　　//springframework.web.reactive.DispatcherHandler class 
　　// but org.springframework.web.servlet.DispatcherServlet class does not exist and org.glassfish.jersey.servlet.ServletContainer 
　　// return WebApplicationType.REACTIVE type 
　　if (ClassUtils.isPresent (WEBFLUX_INDICATOR_CLASS, null)

　　　　&& !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null) 
　　　　&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) 
　　{ 
　　　　return WebApplicationType.REACTIVE; 
　　} 
　　//不存在javax.servlet.Servlet和org.springframework.web.context.ConfigurableWebApplicationContext
　　//返回WebApplicationType.NONE
　　for (String className : SERVLET_INDICATOR_CLASSES) 
　　{ 
　　　　if (!ClassUtils.isPresent(className, null)) 
　　　　{ 

　　　　　　return WebApplicationType.NONE; 
　　　　} 
　　} 
　　//否则返回WebApplicationType.SERVLET
　　return WebApplicationType.SERVLET; 

} 

(2) disposed Initializers

		setInitializers((Collection) getSpringFactoriesInstances(
				ApplicationContextInitializer.class));

 

	private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
		return getSpringFactoriesInstances(type, new Class<?>[] {});
	}

	private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
			Class<?>[] parameterTypes, Object... args) {
		ClassLoader classLoader = getClassLoader();
		// Use names and ensure unique to protect against duplicates
		Set<String> names = new LinkedHashSet<>(
				SpringFactoriesLoader.loadFactoryNames(type, classLoader));
		List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
				classLoader, args, names);
		AnnotationAwareOrderComparator.sort(instances);
		return instances;
	}

　　

setInitializers ((Collection) getSpringFactoriesInstances (// (2) Initial ApplicationContextInitializer.
ApplicationContextInitializer.class));
setListeners ((Collection) getSpringFactoriesInstances (ApplicationListener.class)); // (. 3) determines the ApplicationListener.
this.mainApplicationClass deduceMainApplicationClass = (); // (4) determining mainApplicationClass
(. 1) to infer the type of application is determined based on whether there classPath.
this.webApplicationType WebApplicationType.deduceFromClasspath = ();
. (2) determining ApplicationContextInitializer, determined object focusing the classpath read META- INF / spring.factories, and cached
setInitializers ((Collection) getSpringFactoriesInstances (
ApplicationContextInitializer.class));
. (. 3) determines the ApplicationListener, object determined, focus is META-INF / spring.factories the CLASSPATH read, and the cache
setListeners ((Collection) getSpringFactoriesInstances (ApplicationListener.class));
. (. 4) determines mainApplicationClass, focus on new RuntimeException () getStackTrace () can be acquired stack.
this.mainApplicationClass deduceMainApplicationClass = ();