@SpringBootApplication
public class Start {

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

}

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

 public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        this.sources = new LinkedHashSet(); // 
        this.bannerMode = Mode.CONSOLE;// 控制banner
        this.logStartupInfo = true;// 是否啟動(dòng)日志
        this.addCommandLineProperties = true; // 讀取命令行配置
        this.addConversionService = true; //添加轉(zhuǎn)換器
        this.headless = true; // 
        this.registerShutdownHook = true; // 注冊(cè)重啟
        this.additionalProfiles = Collections.emptySet();// 讀取配置環(huán)境
        this.isCustomEnvironment = false;// 是否是自定義環(huán)境
        this.lazyInitialization = false; // 是否懶加載
        this.applicationContextFactory = ApplicationContextFactory.DEFAULT;
        this.applicationStartup = ApplicationStartup.DEFAULT; // ApplicationStartup DEFAULT = new DefaultApplicationStartup();
        this.resourceLoader = resourceLoader;// 資源加載器
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet(Arrays.asList(primarySources)); // 主程序
        this.webApplicationType = WebApplicationType.deduceFromClasspath();//  SERVLET||REACTIVE; 是servlet還是reactive環(huán)境
        // BootstrapRegistryInitializer
	this.bootstrapRegistryInitializers = new ArrayList(this.getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
        // ApplicationContextInitializer
	this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
	// ApplicationListener        
	this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = this.deduceMainApplicationClass();
    }

this.bootstrapRegistryInitializers = new ArrayList(this.getSpringFactoriesInstances(BootstrapRegistryInitializer.class));

// 
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
        ClassLoader classLoader = this.getClassLoader();
        // 1、從配置文件讀取名稱(chēng)加載
        Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
        // 2、獲取構(gòu)造器實(shí)例
 	List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
        // 3、排序
	 AnnotationAwareOrderComparator.sort(instances);
        return instances;
}

// 1、加載配置
 private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
        Map<String, List<String>> result = (Map)cache.get(classLoader);
        if (result != null) {
            return result;
        } else {
            HashMap result = new HashMap();

            try {
                 //核心 從這里知道讀取配置文件位置 默認(rèn)
                Enumeration urls = classLoader.getResources("META-INF/spring.factories");
		// ... 這里省略迭代器遍歷注冊(cè)
                result.replaceAll((factoryType, implementations) -> {
                    return (List)implementations.stream().distinct().collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
                });
		// 添加到緩存中，下次讀取。根據(jù)類(lèi)名讀取
                cache.put(classLoader, result);
                return result;
            } catch (IOException var14) {
                throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var14);
            }
        }
    }

// 2、獲取構(gòu)造器實(shí)例
private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, Set<String> names) {
        List<T> instances = new ArrayList(names.size());
        Iterator var7 = names.iterator();

        while(var7.hasNext()) {
            String name = (String)var7.next();

            try {
                // 通過(guò)類(lèi)名反射機(jī)制調(diào)用，讀取Class<T> class
                Class<?> instanceClass = ClassUtils.forName(name, classLoader);
                Assert.isAssignable(type, instanceClass);
                Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
                // 獲取構(gòu)造器實(shí)例
 		T instance = BeanUtils.instantiateClass(constructor, args);
                // 添加到構(gòu)造器中
                instances.add(instance);
            } catch (Throwable var12) {
                throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, var12);
            }
        }
	// 返回
        return instances;
    }


// 排序 通過(guò)debug這里調(diào)用的是Integer類(lèi)型排序方法 List<Integer> list
  public static void sort(List<?> list) {
        if (list.size() > 1) {
            list.sort(INSTANCE);
        }

    }

org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.rsocket.context.RSocketPortInfoApplicationContextInitializer,\
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer

public ConfigurableApplicationContext run(String... args) {
        long startTime = System.nanoTime();
        DefaultBootstrapContext bootstrapContext = this.createBootstrapContext();
        ConfigurableApplicationContext context = null;
        this.configureHeadlessProperty();
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting(bootstrapContext, this.mainApplicationClass);

        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, bootstrapContext, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            Banner printedBanner = this.printBanner(environment);
            context = this.createApplicationContext();
            context.setApplicationStartup(this.applicationStartup);
            this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
            // 加載所有注解使用的掃描的組件
	    this.refreshContext(context);
	    // 刷新
            this.afterRefresh(context, applicationArguments);
            Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), timeTakenToStartup);
            }

            listeners.started(context, timeTakenToStartup);
            this.callRunners(context, applicationArguments);
        } catch (Throwable var12) {
            this.handleRunFailure(context, var12, listeners);
            throw new IllegalStateException(var12);
        }

        try {
            Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);
            listeners.ready(context, timeTakenToReady);
            return context;
        } catch (Throwable var11) {
            this.handleRunFailure(context, var11, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var11);
        }
    }

private void registerBeanDefinitionForImportedConfigurationClass(ConfigurationClass configClass) {
        AnnotationMetadata metadata = configClass.getMetadata();
        AnnotatedGenericBeanDefinition configBeanDef = new AnnotatedGenericBeanDefinition(metadata);
        ScopeMetadata scopeMetadata = scopeMetadataResolver.resolveScopeMetadata(configBeanDef);
        configBeanDef.setScope(scopeMetadata.getScopeName());
        String configBeanName = this.importBeanNameGenerator.generateBeanName(configBeanDef, this.registry);
        AnnotationConfigUtils.processCommonDefinitionAnnotations(configBeanDef, metadata);
        BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(configBeanDef, configBeanName);
        definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
        // 在這里注冊(cè)
	this.registry.registerBeanDefinition(definitionHolder.getBeanName(), definitionHolder.getBeanDefinition());
        configClass.setBeanName(configBeanName);
        if (logger.isTraceEnabled()) {
            logger.trace("Registered bean definition for imported class '" + configBeanName + "'");
        }

    }

@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException {

		Assert.hasText(beanName, "Bean name must not be empty");
		Assert.notNull(beanDefinition, "BeanDefinition must not be null");

		if (beanDefinition instanceof AbstractBeanDefinition) {
			try {
				((AbstractBeanDefinition) beanDefinition).validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}

		BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
		if (existingDefinition != null) {
			if (!isAllowBeanDefinitionOverriding()) {
				throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
			}
			else if (existingDefinition.getRole() < beanDefinition.getRole()) {
				// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
				if (logger.isInfoEnabled()) {
					logger.info("Overriding user-defined bean definition for bean '" + beanName +
							"' with a framework-generated bean definition: replacing [" +
							existingDefinition + "] with [" + beanDefinition + "]");
				}
			}
			else if (!beanDefinition.equals(existingDefinition)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Overriding bean definition for bean '" + beanName +
							"' with a different definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			else {
				if (logger.isTraceEnabled()) {
					logger.trace("Overriding bean definition for bean '" + beanName +
							"' with an equivalent definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			// 注冊(cè)
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		else {
			if (hasBeanCreationStarted()) {
				// Cannot modify startup-time collection elements anymore (for stable iteration)
				synchronized (this.beanDefinitionMap) {
					this.beanDefinitionMap.put(beanName, beanDefinition);
					List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
					updatedDefinitions.addAll(this.beanDefinitionNames);
					updatedDefinitions.add(beanName);
					this.beanDefinitionNames = updatedDefinitions;
					removeManualSingletonName(beanName);
				}
			}
			else {
				// Still in startup registration phase
				this.beanDefinitionMap.put(beanName, beanDefinition);
				this.beanDefinitionNames.add(beanName);
				removeManualSingletonName(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

		if (existingDefinition != null || containsSingleton(beanName)) {
			resetBeanDefinition(beanName);
		}
		else if (isConfigurationFrozen()) {
			clearByTypeCache();
		}
	}