正文

springboot源码解析启动过程(代码片段)

J_Newbie  J_Newbie  2022-12-11  240

关键词：

1.springboot的入口程序

@SpringBootApplication
public class StartupApplication 

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

当程序开始执行之后，会调用SpringApplication的构造方法，进行某些初始参数的设置

//创建一个新的实例，这个应用程序的上下文将要从指定的来源加载Bean
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) 
    //资源初始化资源加载器，默认为null
	this.resourceLoader = resourceLoader;
    //断言主要加载资源类不能为 null，否则报错
	Assert.notNull(primarySources, "PrimarySources must not be null");
    //初始化主要加载资源类集合并去重
	this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
    //推断当前 WEB 应用类型，一共有三种：NONE,SERVLET,REACTIVE
	this.webApplicationType = WebApplicationType.deduceFromClasspath();
    //设置应用上线文初始化器,从"META-INF/spring.factories"读取ApplicationContextInitializer类的实例名称集合并去重，并进行set去重。（一共7个）
	setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
    //设置监听器,从"META-INF/spring.factories"读取ApplicationListener类的实例名称集合并去重，并进行set去重。（一共11个）
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    //推断主入口应用类，通过当前调用栈，获取Main方法所在类，并赋值给mainApplicationClass
	this.mainApplicationClass = deduceMainApplicationClass();

在上述构造方法中，有一个判断应用类型的方法，用来判断当前应用程序的类型：

static WebApplicationType deduceFromClasspath() 
		if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
				&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) 
			return WebApplicationType.REACTIVE;
		
		for (String className : SERVLET_INDICATOR_CLASSES) 
			if (!ClassUtils.isPresent(className, null)) 
				return WebApplicationType.NONE;
			
		
		return WebApplicationType.SERVLET;
	
//WebApplicationType的类型
public enum WebApplicationType 

	/**
	 * The application should not run as a web application and should not start an
	 * embedded web server.
	 * 非web项目
	 */
	NONE,

	/**
	 * The application should run as a servlet-based web application and should start an
	 * embedded servlet web server.
	 * servlet web 项目
	 */
	SERVLET,

	/**
	 * The application should run as a reactive web application and should start an
	 * embedded reactive web server.
	 * 响应式 web 项目
	 */
	REACTIVE;

springboot启动的运行方法，可以看到主要是各种运行环境的准备工作

public ConfigurableApplicationContext run(String... args) 
    //1、创建并启动计时监控类
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
    //2、初始化应用上下文和异常报告集合
	ConfigurableApplicationContext context = null;
	Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    //3、设置系统属性“java.awt.headless”的值，默认为true，用于运行headless服务器，进行简单的图像处理，多用于在缺少显示屏、键盘或者鼠标时的系统配置，很多监控工具如jconsole 需要将该值设置为true
	configureHeadlessProperty();
    //4、创建所有spring运行监听器并发布应用启动事件，简单说的话就是获取SpringApplicationRunListener类型的实例（EventPublishingRunListener对象），并封装进SpringApplicationRunListeners对象，然后返回这个SpringApplicationRunListeners对象。说的再简单点，getRunListeners就是准备好了运行时监听器EventPublishingRunListener。
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting();
	try 
        //5、初始化默认应用参数类
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
        //6、根据运行监听器和应用参数来准备spring环境
		ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
        //将要忽略的bean的参数打开
		configureIgnoreBeanInfo(environment);
        //7、创建banner打印类
		Banner printedBanner = printBanner(environment);
        //8、创建应用上下文，可以理解为创建一个容器
		context = createApplicationContext();
        //9、准备异常报告器，用来支持报告关于启动的错误
		exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
					new Class[]  ConfigurableApplicationContext.class , context);
        //10、准备应用上下文，该步骤包含一个非常关键的操作，将启动类注入容器，为后续开启自动化提供基础
		prepareContext(context, environment, listeners, applicationArguments, printedBanner);
        //11、刷新应用上下文
		refreshContext(context);
        //12、应用上下文刷新后置处理，做一些扩展功能
		afterRefresh(context, applicationArguments);
        //13、停止计时监控类
		stopWatch.stop();
        //14、输出日志记录执行主类名、时间信息
		if (this.logStartupInfo) 
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
		
        //15、发布应用上下文启动监听事件
		listeners.started(context);
        //16、执行所有的Runner运行器
		callRunners(context, applicationArguments);
	catch (Throwable ex) 
		handleRunFailure(context, ex, exceptionReporters, listeners);
		throw new IllegalStateException(ex);
	
	try 
        //17、发布应用上下文就绪事件
		listeners.running(context);
	catch (Throwable ex) 
		handleRunFailure(context, ex, exceptionReporters, null);
		throw new IllegalStateException(ex);
	
    //18、返回应用上下文
	return context;

下面详细介绍各个启动的环节：

1、创建并启动计时监控类，可以看到记录当前任务的名称，默认是空字符串，然后记录当前springboot应用启动的开始时间。

StopWatch stopWatch = new StopWatch();
stopWatch.start();
//详细源代码
public void start() throws IllegalStateException 
	start("");

public void start(String taskName) throws IllegalStateException 
	if (this.currentTaskName != null) 
		throw new IllegalStateException("Can't start StopWatch: it's already running");
	
	this.currentTaskName = taskName;
	this.startTimeNanos = System.nanoTime();

2、初始化应用上下文和异常报告集合

ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();

3、设置系统属性java.awt.headless的值：

/*
java.awt.headless模式是在缺少显示屏、键盘或者鼠标的系统配置
当配置了如下属性之后，应用程序可以执行如下操作：
	1、创建轻量级组件
	2、收集关于可用的字体、字体指标和字体设置的信息
	3、设置颜色来渲染准备图片
	4、创造和获取图像，为渲染准备图片
	5、使用java.awt.PrintJob,java.awt.print.*和javax.print.*类里的方法进行打印
*/
private void configureHeadlessProperty() 
		System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS,
				System.getProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));

4、创建所有spring运行监听器并发布应用启动事件

SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();

//创建spring监听器
private SpringApplicationRunListeners getRunListeners(String[] args) 
	Class<?>[] types = new Class<?>[]  SpringApplication.class, String[].class ;
	return new SpringApplicationRunListeners(logger,
				getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));

SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) 
	this.log = log;
	this.listeners = new ArrayList<>(listeners);

//循环遍历获取监听器
void starting() 
	for (SpringApplicationRunListener listener : this.listeners) 
		listener.starting();
	

//此处的监听器可以看出是事件发布监听器，主要用来发布启动事件
@Override
public void starting() 
    //这里是创建application事件‘applicationStartingEvent’
	this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));

//applicationStartingEvent是springboot框架最早执行的监听器，在该监听器执行started方法时，会继续发布事件，主要是基于spring的事件机制
	@Override
	public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) 
		ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
        //获取线程池，如果为空则同步处理。这里线程池为空，还未初始化
		Executor executor = getTaskExecutor();
		for (ApplicationListener<?> listener : getApplicationListeners(event, type)) 
			if (executor != null) 
                //异步发送事件
				executor.execute(() -> invokeListener(listener, event));
			
			else 
                //同步发送事件
				invokeListener(listener, event);

5、初始化默认应用参数类

ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
public DefaultApplicationArguments(String... args) 
	Assert.notNull(args, "Args must not be null");
	this.source = new Source(args);
	this.args = args;

6、根据运行监听器和应用参数来准备spring环境

ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
//详细环境的准备
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
	ApplicationArguments applicationArguments) 
	// 获取或者创建应用环境
	ConfigurableEnvironment environment = getOrCreateEnvironment();
    // 配置应用环境，配置propertySource和activeProfiles
	configureEnvironment(environment, applicationArguments.getSourceArgs());
    //listeners环境准备，广播ApplicationEnvironmentPreparedEvent
	ConfigurationPropertySources.attach(environment);
	listeners.environmentPrepared(environment);
    //将环境绑定给当前应用程序
	bindToSpringApplication(environment);
    //对当前的环境类型进行判断，如果不一致进行转换
	if (!this.isCustomEnvironment) 
		environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
					deduceEnvironmentClass());
	
    //配置propertySource对它自己的递归依赖
	ConfigurationPropertySources.attach(environment);
	return environment;

// 获取或者创建应用环境，根据应用程序的类型可以分为servlet环境、标准环境(特殊的非web环境)和响应式环境
private ConfigurableEnvironment getOrCreateEnvironment() 
    //存在则直接返回
		if (this.environment != null) 
			return this.environment;
		
    //根据webApplicationType创建对应的Environment
		switch (this.webApplicationType) 
		case SERVLET:
			return new StandardServletEnvironment();
		case REACTIVE:
			return new StandardReactiveWebEnvironment();
		default:
			return new StandardEnvironment();
		
	
//配置应用环境
protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) 
	if (this.addConversionService) 
		ConversionService conversionService = ApplicationConversionService.getSharedInstance();
		environment.setConversionService((ConfigurableConversionService) conversionService);
	
    //配置property sources
	configurePropertySources(environment, args);
    //配置profiles
	configureProfiles(environment, args);

7、创建banner的打印类

Banner printedBanner = printBanner(environment);
//打印类的详细操作过程
private Banner printBanner(ConfigurableEnvironment environment) 
		if (this.bannerMode == Banner.Mode.OFF) 
			return null;
		
		ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader
				: new DefaultResourceLoader(getClassLoader());
		SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);
		if (this.bannerMode == Mode.LOG) 
			return bannerPrinter.print(environment, this.mainApplicationClass, logger);
		
		return bannerPrinter.print(environment, this.mainApplicationClass, System.out);

8、创建应用的上下文:根据不同哦那个的应用类型初始化不同的上下文应用类

context = createApplicationContext();
protected ConfigurableApplicationContext createApplicationContext() 
		Class<?> contextClass = this.applicationContextClass;
		if (contextClass == null) 
			try 
				switch (this.webApplicationType) 
				case SERVLET:
					contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
					break;
				case REACTIVE:
					contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
					break;
				default:
					contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
				
			
			catch (ClassNotFoundException ex) 
				throw new IllegalStateException(
						"Unable create a default ApplicationContext, please specify an ApplicationContextClass", ex);
			
		
		return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);

9、准备异常报告器

exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
					new Class[]  ConfigurableApplicationContext.class , context);
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;

10、准备应用上下文

prepareContext(context, environment, listeners, applicationArguments, printedBanner);

private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
			SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) 
    	//应用上下文的environment
		context.setEnvironment(environment);
    	//应用上下文后处理
		postProcessApplicationContext(context);
    	//为上下文应用所有初始化器，执行容器中的applicationContextInitializer(spring.factories的实例)，将所有的初始化对象放置到context对象中
		applyInitializers(context);
    	//触发所有SpringApplicationRunListener监听器的ContextPrepared事件方法。添加所有的事件监听器
		listeners.contextPrepared(context);
   	 	//记录启动日志
		if (this.logStartupInfo) 
			logStartupInfo(context.getParent() == null);
			logStartupProfileInfo(context);
		
		// 注册启动参数bean，将容器指定的参数封装成bean，注入容器
		ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
		beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
    	//设置banner
		if (printedBanner != null) 
			beanFactory.registerSingleton("springBootBanner", printedBanner);
		
		if (beanFactory instanceof DefaultListableBeanFactory) 
			((DefaultListableBeanFactory) beanFactory)
					.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
		
		if (this.lazyInitialization) 
			context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
		
		// 加载所有资源，指的是启动器指定的参数
		Set<Object> sources = getAllSources();
		Assert.notEmpty(sources, "Sources must not be empty");
    	//将bean加载到上下文中
		load(context, sources.toArray(new Object[0]));
    	//触发所有springapplicationRunListener监听器的contextLoaded事件方法，
		listeners.contextLoaded(context);
	
-------------------
    //这里没有做任何的处理过程，因为beanNameGenerator和resourceLoader默认为空，可以方便后续做扩展处理
    protected void postProcessApplicationContext(ConfigurableApplicationContext context) 
		if (this.beanNameGenerator != null) 
			context.getBeanFactory().registerSingleton(AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR,
					this.beanNameGenerator);
		
		if (this.resourceLoader != null) 
			if (context instanceof GenericApplicationContext) 
				((GenericApplicationContext) context).setResourceLoader(this.resourceLoader);
			
			if (context instanceof DefaultResourceLoader) 
				((DefaultResourceLoader) context).setClassLoader(this.resourceLoader.getClassLoader());
			
		
		if (this.addConversionService) 
			context.getBeanFactory().setConversionService(ApplicationConversionService.getSharedInstance());
		
	
---------------------
    //将启动器类加载到spring容器中，为后续的自动化配置奠定基础，之前看到的很多注解也与此相关
    protected void load(ApplicationContext context, Object[] sources) 
		if (logger.isDebugEnabled()) 
			logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
		
		BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources);
		if (this.beanNameGenerator != null) 
			loader.setBeanNameGenerator(this.beanNameGenerator);
		
		if (this.resourceLoader != null) 
			loader.setResourceLoader(this.resourceLoader);
		
		if (this.environment != null) 
			loader.setEnvironment(this.environment);
		
		loader.load();
	
---------------------
    //springboot会优先选择groovy加载方式，找不到在选择java方式
    private int load(Class<?> source) 
		if (isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) 
			// Any GroovyLoaders added in beans DSL can contribute beans here
			GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class);
			load(loader);
		
		if (isComponent(source)) 
			this.annotatedReader.register(source);
			return 1;
		
		return 0;

11、刷新应用上下文

refreshContext(context);

private void refreshContext(ConfigurableApplicationContext context) 
		refresh(context);
		if (this.registerShutdownHook) 
			try 
				context.registerShutdownHook();
			
			catch (AccessControlException ex) 
				// Not allowed in some environments.
			
		
	

------------
    public void refresh() throws BeansException, IllegalStateException 
		synchronized (this.startupShutdownMonitor) 
			// Prepare this context for refreshing.
            //刷新上下文环境，初始化上下文环境，对系统的环境变量或者系统属性进行准备和校验
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
            //初始化beanfactory，解析xml，相当于之前的xmlBeanfactory操作
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
            //为上下文准备beanfactory，对beanFactory的各种功能进行填充，如@autowired，设置spel表达式解析器，设置编辑注册器，添加applicationContextAwareprocessor处理器等等
			prepareBeanFactory(beanFactory);

			try 
				// Allows post-processing of the bean factory in context subclasses.
                //提供子类覆盖的额外处理，即子类处理自定义的beanfactorypostProcess
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
                //激活各种beanfactory处理器
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
                //注册拦截bean创建的bean处理器，即注册beanPostProcessor
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
                //初始化上下文中的资源文件如国际化文件的处理
				initMessageSource();

				// Initialize event multicaster for this context.
                //初始化上下文事件广播器
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
                //给子类扩展初始化其他bean
				onRefresh();

				// Check for listener beans and register them.
                //在所有的bean中查找listener bean,然后 注册到广播器中
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
                //初始化剩余的非懒惰的bean，即初始化非延迟加载的bean
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
                //发完成刷新过程，通知声明周期处理器刷新过程，同时发出ContextRefreshEvent通知别人
				finishRefresh();
			

			catch (BeansException ex) 
				if (logger.isWarnEnabled()) 
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				

				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			

			finally 
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();

12、应用上下文刷新后置处理

afterRefresh(context, applicationArguments);
//当前方法的代码是空的，可以做一些自定义的后置处理操作
protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args)

13、停止计时监控类：计时监听器停止，并统计一些任务执行信息

stopWatch.stop();
public void stop() throws IllegalStateException 
		if (this.currentTaskName == null) 
			throw new IllegalStateException("Can't stop StopWatch: it's not running");
		
		long lastTime = System.nanoTime() - this.startTimeNanos;
		this.totalTimeNanos += lastTime;
		this.lastTaskInfo = new TaskInfo(this.currentTaskName, lastTime);
		if (this.keepTaskList) 
			this.taskList.add(this.lastTaskInfo);
		
		++this.taskCount;
		this.currentTaskName = null;

14、输出日志记录执行主类名、时间信息

if (this.logStartupInfo) 
	new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);

15、发布应用上下文启动完成事件：触发所有SpringapplicationRunListener监听器的started事件方法

listeners.started(context);
	void started(ConfigurableApplicationContext context) 
		for (SpringApplicationRunListener listener : this.listeners) 
			listener.started(context);

16、执行所有Runner执行器：执行所有applicationRunner和CommandLineRunner两种运行器

callRunners(context, applicationArguments);
private void callRunners(ApplicationContext context, ApplicationArguments args) 
		List<Object> runners = new ArrayList<>();
		runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
		runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
		AnnotationAwareOrderComparator.sort(runners);
		for (Object runner : new LinkedHashSet<>(runners)) 
			if (runner instanceof ApplicationRunner) 
				callRunner((ApplicationRunner) runner, args);
			
			if (runner instanceof CommandLineRunner) 
				callRunner((CommandLineRunner) runner, args);

17、发布应用上下文就绪事件：触发所有springapplicationRunnListener将挺起的running事件方法

listeners.running(context);
void running(ConfigurableApplicationContext context) 
		for (SpringApplicationRunListener listener : this.listeners) 
			listener.running(context);

18、返回应用上下文

return context;

注意：

整个springboot框架中获取factorys文件的方式统一如下：

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;

-----------------------------
    public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) 
		String factoryTypeName = factoryType.getName();
		return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
	

	private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) 
		MultiValueMap<String, String> result = cache.get(classLoader);
		if (result != null) 
			return result;
		

		try 
			Enumeration<URL> urls = (classLoader != null ?
					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
			result = new LinkedMultiValueMap<>();
			while (urls.hasMoreElements()) 
				URL url = urls.nextElement();
				UrlResource resource = new UrlResource(url);
				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
				for (Map.Entry<?, ?> entry : properties.entrySet()) 
					String factoryTypeName = ((String) entry.getKey()).trim();
					for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) 
						result.add(factoryTypeName, factoryImplementationName.trim());
					
				
			
			cache.put(classLoader, result);
			return result;
		
		catch (IOException ex) 
			throw new IllegalArgumentException("Unable to load factories from location [" +
					FACTORIES_RESOURCE_LOCATION + "]", ex);
		
	
-------------------------
    private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes,
			ClassLoader classLoader, Object[] args, Set<String> names) 
		List<T> instances = new ArrayList<>(names.size());
		for (String name : names) 
			try 
                //装载class文件到内存
				Class<?> instanceClass = ClassUtils.forName(name, classLoader);
				Assert.isAssignable(type, instanceClass);
				Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
                //通过反射创建实例
				T instance = (T) BeanUtils.instantiateClass(constructor, args);
				instances.add(instance);
			
			catch (Throwable ex) 
				throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
			
		
		return instances;

spring.factory文件中的类的作用：

ontext.config.DelegatingApplicationListener,\\
# 一个SmartApplicationListener,对环境就绪事件ApplicationEnvironmentPreparedEvent/应用失败事件ApplicationFailedEvent做出响应，往日志DEBUG级别输出TCCL(thread context class loader)的classpath。
org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\\
# 检测正在使用的日志系统，默认时logback，，此时日志系统还没有初始化
org.springframework.boot.context.logging.LoggingApplicationListener,\\
# 使用一个可以和Spring Boot可执行jar包配合工作的版本替换liquibase ServiceLocator
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener

# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\\
org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor,\\
org.springframework.boot.reactor.DebugAgentEnvironmentPostProcessor

# Failure Analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\\
org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.BeanDefinitionOverrideFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.BindValidationFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.UnboundConfigurationPropertyFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.NoSuchMethodFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyNameFailureAnalyzer,\\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyValueFailureAnalyzer

# FailureAnalysisReporters
org.springframework.boot.diagnostics.FailureAnalysisReporter=\\
org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter

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

# Application Listeners
org.springframework.context.ApplicationListener=\\
# 另外单独启动一个线程实例化并调用run方法，包括验证器、消息转换器等
org.springframework.boot.autoconfigure.BackgroundPreinitializer

# Auto Configuration Import Listeners
org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\\
org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener

# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\\
org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveRestClientAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\\
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\\
org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.rsocket.RSocketSecurityAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\\
org.springframework.boot.autoconfigure.flyway.FlywayMigrationScriptMissingFailureAnalyzer,\\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\\
org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer

# Template availability providers
org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\\
org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\\
org.springframework.boot.autoconfigure.web.servlet.JspTemplateAvailabilityProvider

注：转自连鹏举老师文章

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