Spring Boot源码解析

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Spring Boot核心源码讲解：启动、装配、运行、配置

启动过程

1、springboot的入口程序

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@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

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//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：

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	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

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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。

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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

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

3、设置系统属性java.awt.headless的值：

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/*
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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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

18、返回应用上下文

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return context;

注意：

整个springboot框架中获取factorys文件的方式统一如下：

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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：

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# PropertySource Loaders 属性文件加载器
org.springframework.boot.env.PropertySourceLoader=\
# properties文件加载器
org.springframework.boot.env.PropertiesPropertySourceLoader,\
# yaml文件加载器
org.springframework.boot.env.YamlPropertySourceLoader

# Run Listeners 运行时的监听器
org.springframework.boot.SpringApplicationRunListener=\
# 程序运行过程中所有监听通知都是通过此类来进行回调
org.springframework.boot.context.event.EventPublishingRunListener

# Error Reporters	错误报告器
org.springframework.boot.SpringBootExceptionReporter=\
org.springframework.boot.diagnostics.FailureAnalyzers

# Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
# 报告spring容器的一些常见的错误配置
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
# 设置spring应用上下文的ID
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
# 使用环境属性context.initializer.classes指定初始化器进行初始化规则
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.rsocket.context.RSocketPortInfoApplicationContextInitializer,\
# 将内置servlet容器实际使用的监听端口写入到environment环境属性中
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer

# Application Listeners
org.springframework.context.ApplicationListener=\
# 应用上下文加载完成后对缓存做清除工作，响应事件ContextRefreshEvent
org.springframework.boot.ClearCachesApplicationListener,\
# 监听双亲应用上下文的关闭事件并往自己的孩子应用上下文中传播，相关事件ParentContextAvailableEvent/ContextClosedEvent
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
# 如果系统文件编码和环境变量中指定的不同则终止应用启动。具体的方法是比较系统属性file.encoding和环境变量spring.mandatory-file-encoding是否相等(大小写不敏感)。
org.springframework.boot.context.FileEncodingApplicationListener,\
# 根据spring.output.ansi.enabled参数配置AnsiOutput
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
# EnvironmentPostProcessor，从常见的那些约定的位置读取配置文件，比如从以下目录读取#application.properties,application.yml等配置文件：
# classpath:
# file:.
# classpath:config
# file:./config/:
# 也可以配置成从其他指定的位置读取配置文件
org.springframework.boot.context.config.ConfigFileApplicationListener,\
# 监听到事件后转发给环境变量context.listener.classes指定的那些事件监听器
org.springframework.boot.context.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

自动装配

​ 在之前的课程中我们讲解了springboot的启动过程，其实在面试过程中问的最多的可能是自动装配的原理，而自动装配是在启动过程中完成，只不过在刚开始的时候我们选择性的跳过了，下面详细讲解自动装配的过程。

1、在springboot的启动过程中，有一个步骤是创建上下文，如果不记得可以看下面的代码：
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public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting();
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
            //此处完成自动装配的过程
			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
			}
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}
2、在prepareContext方法中查找load方法，一层一层向内点击，找到最终的load方法
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//prepareContext方法
	private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
			SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
		context.setEnvironment(environment);
		postProcessApplicationContext(context);
		applyInitializers(context);
		listeners.contextPrepared(context);
		if (this.logStartupInfo) {
			logStartupInfo(context.getParent() == null);
			logStartupProfileInfo(context);
		}
		// Add boot specific singleton beans
		ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
		beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
		if (printedBanner != null) {
			beanFactory.registerSingleton("springBootBanner", printedBanner);
		}
		if (beanFactory instanceof DefaultListableBeanFactory) {
			((DefaultListableBeanFactory) beanFactory)
					.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
		}
		if (this.lazyInitialization) {
			context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
		}
		// Load the sources
		Set<Object> sources = getAllSources();
		Assert.notEmpty(sources, "Sources must not be empty");
        //load方法完成该功能
		load(context, sources.toArray(new Object[0]));
		listeners.contextLoaded(context);
	}


	/**
	 * Load beans into the application context.
	 * @param context the context to load beans into
	 * @param sources the sources to load
	 * 加载bean对象到context中
	 */
	protected void load(ApplicationContext context, Object[] sources) {
		if (logger.isDebugEnabled()) {
			logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
		}
        //获取bean对象定义的加载器
		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();
	}

	/**
	 * Load the sources into the reader.
	 * @return the number of loaded beans
	 */
	int load() {
		int count = 0;
		for (Object source : this.sources) {
			count += load(source);
		}
		return count;
	}
3、实际执行load的是BeanDefinitionLoader中的load方法，如下：
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//实际记载bean的方法
private int load(Object source) {
	Assert.notNull(source, "Source must not be null");
       //如果是class类型，启用注解类型
	if (source instanceof Class<?>) {
		return load((Class<?>) source);
	}
       //如果是resource类型，启动xml解析
	if (source instanceof Resource) {
		return load((Resource) source);
	}
       //如果是package类型，启用扫描包，例如@ComponentScan
	if (source instanceof Package) {
		return load((Package) source);
	}
       //如果是字符串类型，直接加载
	if (source instanceof CharSequence) {
		return load((CharSequence) source);
	}
	throw new IllegalArgumentException("Invalid source type " + source.getClass());
}
4、下面方法将用来判断是否资源的类型，是使用groovy加载还是使用注解的方式
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private int load(Class<?> source) {
       //判断使用groovy脚本
	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);
	}
       //使用注解加载
	if (isComponent(source)) {
		this.annotatedReader.register(source);
		return 1;
	}
	return 0;
}
5、下面方法判断启动类中是否包含@Component注解，但是会神奇的发现我们的启动类中并没有该注解，继续更进发现MergedAnnotations类传入了一个参数SearchStrategy.TYPE_HIERARCHY，会查找继承关系中是否包含这个注解，@SpringBootApplication–>@SpringBootConfiguration–>@Configuration–>@Component,当找到@Component注解之后，会把该对象注册到AnnotatedBeanDefinitionReader对象中
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private boolean isComponent(Class<?> type) {
   // This has to be a bit of a guess. The only way to be sure that this type is
   // eligible is to make a bean definition out of it and try to instantiate it.
   if (MergedAnnotations.from(type, SearchStrategy.TYPE_HIERARCHY).isPresent(Component.class)) {
      return true;
   }
   // Nested anonymous classes are not eligible for registration, nor are groovy
   // closures
   return !type.getName().matches(".*\\$_.*closure.*") && !type.isAnonymousClass()
         && type.getConstructors() != null && type.getConstructors().length != 0;
}

	/**
	 * Register a bean from the given bean class, deriving its metadata from
	 * class-declared annotations.
	 * 从给定的bean class中注册一个bean对象，从注解中找到相关的元数据
	 */
	private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
			@Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
			@Nullable BeanDefinitionCustomizer[] customizers) {

		AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
		if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
			return;
		}

		abd.setInstanceSupplier(supplier);
		ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
		abd.setScope(scopeMetadata.getScopeName());
		String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));

		AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
		if (qualifiers != null) {
			for (Class<? extends Annotation> qualifier : qualifiers) {
				if (Primary.class == qualifier) {
					abd.setPrimary(true);
				}
				else if (Lazy.class == qualifier) {
					abd.setLazyInit(true);
				}
				else {
					abd.addQualifier(new AutowireCandidateQualifier(qualifier));
				}
			}
		}
		if (customizers != null) {
			for (BeanDefinitionCustomizer customizer : customizers) {
				customizer.customize(abd);
			}
		}

		BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
		definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
		BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
	}

	/**
	 * Register the given bean definition with the given bean factory.
	 * 注册主类，如果有别名可以设置别名
	 */
	public static void registerBeanDefinition(
			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
			throws BeanDefinitionStoreException {

		// Register bean definition under primary name.
		String beanName = definitionHolder.getBeanName();
		registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

		// Register aliases for bean name, if any.
		String[] aliases = definitionHolder.getAliases();
		if (aliases != null) {
			for (String alias : aliases) {
				registry.registerAlias(beanName, alias);
			}
		}
	}

//@SpringBootApplication
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {}

//@SpringBootConfiguration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {}

//@Configuration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {}

当看完上述代码之后，只是完成了启动对象的注入，自动装配还没有开始，下面开始进入到自动装配。

6、自动装配入口，从刷新容器开始
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@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
                // 此处是自动装配的入口
				invokeBeanFactoryPostProcessors(beanFactory);
            }
7、在invokeBeanFactoryPostProcessors方法中完成bean的实例化和执行
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/**
	 * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
	 * respecting explicit order if given.
	 * <p>Must be called before singleton instantiation.
	 */
	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        //开始执行beanFactoryPostProcessor对应实现类,需要知道的是beanFactoryPostProcessor是spring的扩展接口，在刷新容器之前，该接口可以用来修改bean元数据信息
		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

		// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
		// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
		if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}
	}
8、查看invokeBeanFactoryPostProcessors的具体执行方法
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public static void invokeBeanFactoryPostProcessors(
		ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

	// Invoke BeanDefinitionRegistryPostProcessors first, if any.
	Set<String> processedBeans = new HashSet<>();

	if (beanFactory instanceof BeanDefinitionRegistry) {
		BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
		List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
		List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
		//开始遍历三个内部类，如果属于BeanDefinitionRegistryPostProcessor子类，加入到bean注册的集合，否则加入到regularPostProcessors
		for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
			if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
				BeanDefinitionRegistryPostProcessor registryProcessor =
						(BeanDefinitionRegistryPostProcessor) postProcessor;
				registryProcessor.postProcessBeanDefinitionRegistry(registry);
				registryProcessors.add(registryProcessor);
			}
			else {
				regularPostProcessors.add(postProcessor);
			}
		}

		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let the bean factory post-processors apply to them!
		// Separate between BeanDefinitionRegistryPostProcessors that implement
		// PriorityOrdered, Ordered, and the rest.
		List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

		// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
           //通过BeanDefinitionRegistryPostProcessor获取到对应的处理类“org.springframework.context.annotation.internalConfigurationAnnotationProcessor”，但是需要注意的是这个类在springboot中搜索不到，这个类的完全限定名在AnnotationConfigEmbeddedWebApplicationContext中，在进行初始化的时候会装配几个类，在创建AnnotatedBeanDefinitionReader对象的时候会将该类注册到bean对象中，此处可以看到internalConfigurationAnnotationProcessor为bean名称，容器中真正的类是ConfigurationClassPostProcessor
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
           //首先执行类型为PriorityOrdered的BeanDefinitionRegistryPostProcessor
           //PriorityOrdered类型表明为优先执行
		for (String ppName : postProcessorNames) {
			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                   //获取对应的bean
				currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                   //用来存储已经执行过的BeanDefinitionRegistryPostProcessor
				processedBeans.add(ppName);
			}
		}
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		registryProcessors.addAll(currentRegistryProcessors);
           //开始执行装配逻辑
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
		currentRegistryProcessors.clear();

		// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
           //其次执行类型为Ordered的BeanDefinitionRegistryPostProcessor
           //Ordered表明按顺序执行
		postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
		for (String ppName : postProcessorNames) {
			if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
				currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
				processedBeans.add(ppName);
			}
		}
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		registryProcessors.addAll(currentRegistryProcessors);
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
		currentRegistryProcessors.clear();

		// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
           //循环中执行类型不为PriorityOrdered，Ordered类型的BeanDefinitionRegistryPostProcessor
		boolean reiterate = true;
		while (reiterate) {
			reiterate = false;
			postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) {
				if (!processedBeans.contains(ppName)) {
					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
					processedBeans.add(ppName);
					reiterate = true;
				}
			}
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			currentRegistryProcessors.clear();
		}

		// Now, invoke the postProcessBeanFactory callback of all processors handled so far.	
           //执行父类方法，优先执行注册处理类
		invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
           //执行有规则处理类
		invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
	}

	else {
		// Invoke factory processors registered with the context instance.
		invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
	}

	// Do not initialize FactoryBeans here: We need to leave all regular beans
	// uninitialized to let the bean factory post-processors apply to them!
	String[] postProcessorNames =
			beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

	// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
	// Ordered, and the rest.
	List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
	List<String> orderedPostProcessorNames = new ArrayList<>();
	List<String> nonOrderedPostProcessorNames = new ArrayList<>();
	for (String ppName : postProcessorNames) {
		if (processedBeans.contains(ppName)) {
			// skip - already processed in first phase above
		}
		else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
			priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
		}
		else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
			orderedPostProcessorNames.add(ppName);
		}
		else {
			nonOrderedPostProcessorNames.add(ppName);
		}
	}

	// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

	// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
	List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
	for (String postProcessorName : orderedPostProcessorNames) {
		orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
	}
	sortPostProcessors(orderedPostProcessors, beanFactory);
	invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

	// Finally, invoke all other BeanFactoryPostProcessors.
	List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
	for (String postProcessorName : nonOrderedPostProcessorNames) {
		nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
	}
	invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

	// Clear cached merged bean definitions since the post-processors might have
	// modified the original metadata, e.g. replacing placeholders in values...
	beanFactory.clearMetadataCache();
}

9、开始执行自动配置逻辑（启动类指定的配置，非默认配置），可以通过debug的方式一层层向里进行查找，会发现最终会在ConfigurationClassParser类中，此类是所有配置类的解析类，所有的解析逻辑在parser.parse(candidates)中

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public void parse(Set<BeanDefinitionHolder> configCandidates) {
		for (BeanDefinitionHolder holder : configCandidates) {
			BeanDefinition bd = holder.getBeanDefinition();
			try {
                //是否是注解类
				if (bd instanceof AnnotatedBeanDefinition) {
					parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
				}
				else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
					parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
				}
				else {
					parse(bd.getBeanClassName(), holder.getBeanName());
				}
			}
			catch (BeanDefinitionStoreException ex) {
				throw ex;
			}
			catch (Throwable ex) {
				throw new BeanDefinitionStoreException(
						"Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);
			}
		}
    	//执行配置类
		this.deferredImportSelectorHandler.process();
	}
-------------------
    	protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException {
		processConfigurationClass(new ConfigurationClass(metadata, beanName));
	}
-------------------
    protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
		if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
			return;
		}

		ConfigurationClass existingClass = this.configurationClasses.get(configClass);
		if (existingClass != null) {
			if (configClass.isImported()) {
				if (existingClass.isImported()) {
					existingClass.mergeImportedBy(configClass);
				}
				// Otherwise ignore new imported config class; existing non-imported class overrides it.
				return;
			}
			else {
				// Explicit bean definition found, probably replacing an import.
				// Let's remove the old one and go with the new one.
				this.configurationClasses.remove(configClass);
				this.knownSuperclasses.values().removeIf(configClass::equals);
			}
		}

		// Recursively process the configuration class and its superclass hierarchy.
		SourceClass sourceClass = asSourceClass(configClass);
		do {
            //循环处理bean,如果有父类，则处理父类，直至结束
			sourceClass = doProcessConfigurationClass(configClass, sourceClass);
		}
		while (sourceClass != null);

		this.configurationClasses.put(configClass, configClass);
	}

10、继续跟进doProcessConfigurationClass方法，此方式是支持注解配置的核心逻辑

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/**
	 * Apply processing and build a complete {@link ConfigurationClass} by reading the
	 * annotations, members and methods from the source class. This method can be called
	 * multiple times as relevant sources are discovered.
	 * @param configClass the configuration class being build
	 * @param sourceClass a source class
	 * @return the superclass, or {@code null} if none found or previously processed
	 */
	@Nullable
	protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
			throws IOException {

        //处理内部类逻辑，由于传来的参数是启动类，并不包含内部类，所以跳过
		if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
			// Recursively process any member (nested) classes first
			processMemberClasses(configClass, sourceClass);
		}

		// Process any @PropertySource annotations
        //针对属性配置的解析
		for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
				sourceClass.getMetadata(), PropertySources.class,
				org.springframework.context.annotation.PropertySource.class)) {
			if (this.environment instanceof ConfigurableEnvironment) {
				processPropertySource(propertySource);
			}
			else {
				logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
						"]. Reason: Environment must implement ConfigurableEnvironment");
			}
		}

		// Process any @ComponentScan annotations
        // 这里是根据启动类@ComponentScan注解来扫描项目中的bean
		Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
				sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
		if (!componentScans.isEmpty() &&
				!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
            
			for (AnnotationAttributes componentScan : componentScans) {
				// The config class is annotated with @ComponentScan -> perform the scan immediately
                //遍历项目中的bean，如果是注解定义的bean，则进一步解析
				Set<BeanDefinitionHolder> scannedBeanDefinitions =
						this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
				// Check the set of scanned definitions for any further config classes and parse recursively if needed
				for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
					BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
					if (bdCand == null) {
						bdCand = holder.getBeanDefinition();
					}
					if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
                        //递归解析，所有的bean,如果有注解，会进一步解析注解中包含的bean
						parse(bdCand.getBeanClassName(), holder.getBeanName());
					}
				}
			}
		}

		// Process any @Import annotations
        //递归解析，获取导入的配置类，很多情况下，导入的配置类中会同样包含导入类注解
		processImports(configClass, sourceClass, getImports(sourceClass), true);

		// Process any @ImportResource annotations
        //解析@ImportResource配置类
		AnnotationAttributes importResource =
				AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
		if (importResource != null) {
			String[] resources = importResource.getStringArray("locations");
			Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
			for (String resource : resources) {
				String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
				configClass.addImportedResource(resolvedResource, readerClass);
			}
		}

		// Process individual @Bean methods
        //处理@Bean注解修饰的类
		Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
		for (MethodMetadata methodMetadata : beanMethods) {
			configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
		}

		// Process default methods on interfaces
        // 处理接口中的默认方法
		processInterfaces(configClass, sourceClass);

		// Process superclass, if any
        //如果该类有父类，则继续返回，上层方法判断不为空，则继续递归执行
		if (sourceClass.getMetadata().hasSuperClass()) {
			String superclass = sourceClass.getMetadata().getSuperClassName();
			if (superclass != null && !superclass.startsWith("java") &&
					!this.knownSuperclasses.containsKey(superclass)) {
				this.knownSuperclasses.put(superclass, configClass);
				// Superclass found, return its annotation metadata and recurse
				return sourceClass.getSuperClass();
			}
		}

		// No superclass -> processing is complete
		return null;
	}

11、查看获取配置类的逻辑

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processImports(configClass, sourceClass, getImports(sourceClass), true);

	/**
	 * Returns {@code @Import} class, considering all meta-annotations.
	 */
	private Set<SourceClass> getImports(SourceClass sourceClass) throws IOException {
		Set<SourceClass> imports = new LinkedHashSet<>();
		Set<SourceClass> visited = new LinkedHashSet<>();
		collectImports(sourceClass, imports, visited);
		return imports;
	}
------------------
    	/**
	 * Recursively collect all declared {@code @Import} values. Unlike most
	 * meta-annotations it is valid to have several {@code @Import}s declared with
	 * different values; the usual process of returning values from the first
	 * meta-annotation on a class is not sufficient.
	 * <p>For example, it is common for a {@code @Configuration} class to declare direct
	 * {@code @Import}s in addition to meta-imports originating from an {@code @Enable}
	 * annotation.
	 * 看到所有的bean都以导入的方式被加载进去
	 */
	private void collectImports(SourceClass sourceClass, Set<SourceClass> imports, Set<SourceClass> visited)
			throws IOException {

		if (visited.add(sourceClass)) {
			for (SourceClass annotation : sourceClass.getAnnotations()) {
				String annName = annotation.getMetadata().getClassName();
				if (!annName.equals(Import.class.getName())) {
					collectImports(annotation, imports, visited);
				}
			}
			imports.addAll(sourceClass.getAnnotationAttributes(Import.class.getName(), "value"));
		}
	}
12、继续回到ConfigurationClassParser中的parse方法中的最后一行,继续跟进该方法：
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this.deferredImportSelectorHandler.process()
-------------
public void process() {
			List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors;
			this.deferredImportSelectors = null;
			try {
				if (deferredImports != null) {
					DeferredImportSelectorGroupingHandler handler = new DeferredImportSelectorGroupingHandler();
					deferredImports.sort(DEFERRED_IMPORT_COMPARATOR);
					deferredImports.forEach(handler::register);
					handler.processGroupImports();
				}
			}
			finally {
				this.deferredImportSelectors = new ArrayList<>();
			}
		}
---------------
  public void processGroupImports() {
			for (DeferredImportSelectorGrouping grouping : this.groupings.values()) {
				grouping.getImports().forEach(entry -> {
					ConfigurationClass configurationClass = this.configurationClasses.get(
							entry.getMetadata());
					try {
						processImports(configurationClass, asSourceClass(configurationClass),
								asSourceClasses(entry.getImportClassName()), false);
					}
					catch (BeanDefinitionStoreException ex) {
						throw ex;
					}
					catch (Throwable ex) {
						throw new BeanDefinitionStoreException(
								"Failed to process import candidates for configuration class [" +
										configurationClass.getMetadata().getClassName() + "]", ex);
					}
				});
			}
		}
------------
    /**
		 * Return the imports defined by the group.
		 * @return each import with its associated configuration class
		 */
		public Iterable<Group.Entry> getImports() {
			for (DeferredImportSelectorHolder deferredImport : this.deferredImports) {
				this.group.process(deferredImport.getConfigurationClass().getMetadata(),
						deferredImport.getImportSelector());
			}
			return this.group.selectImports();
		}
	}
------------
    public DeferredImportSelector getImportSelector() {
			return this.importSelector;
		}
------------
    @Override
		public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {
			Assert.state(deferredImportSelector instanceof AutoConfigurationImportSelector,
					() -> String.format("Only %s implementations are supported, got %s",
							AutoConfigurationImportSelector.class.getSimpleName(),
							deferredImportSelector.getClass().getName()));
			AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)
					.getAutoConfigurationEntry(getAutoConfigurationMetadata(), annotationMetadata);
			this.autoConfigurationEntries.add(autoConfigurationEntry);
			for (String importClassName : autoConfigurationEntry.getConfigurations()) {
				this.entries.putIfAbsent(importClassName, annotationMetadata);
			}
		}

运行原理

1、启动器

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

​ springboot-boot-starter:就是springboot的场景启动器。springboot将所有的功能场景都抽取出来，做成一个个的starter，只需要在项目中引入这些starter即可，所有相关的依赖都会导入进来，根据公司业务需求决定导入什么启动器即可。

2、主程序

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package com.oi;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
//SpringBootApplication注解用来标注一个主程序类，说明是一个springboot应用
@SpringBootApplication
public class StudyApplication {

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

查看@SpringBootApplication

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/*
@ComponentScan:自动扫描并加载符合条件的组件或者bean，将这个bean定义加载到IOC容器中

@SpringBootConfiguration:标注在某个类上，表示这是一个springboot的配置类。

@EnableAutoConfiguration:开启自动配置功能,之前在使用springboot的时候，springboot可以自动帮我们完成配置功能，@EnableAutoConfiguration告诉springboot开启自动配置功能，这样自动配置才能生效
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {}
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/*
可以看到SpringBootConfiguration使用了Configuration注解来标注
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {}
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/*
可以看到Configuration也是容器中的一个组件
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {}
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/*
@AutoConfigurationPackage:自动配置包

@Import(AutoConfigurationImportSelector.class)：导入哪些组件的选择器，它将所有需要导入的组件以全类名的方式返回，这些组件就会被添加到容器中，它会给容器中导入非常多的自动配置类，就是给容器中导入这个场景需要的所有组件，并配置好这些组件
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {}
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/*
给容器导入一个组件，导入的组件由AutoConfigurationPackages.Registrar.class将主配置类（@SpringBootApplication标注的类）的所在包及包下面所有子包里面的所有组件扫描到spring容器
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {}
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/*
在AutoConfigurationImportSelector类中有如下方法，可以看到

*/
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;
	}
/*

此时返回的就是启动自动导入配置文件的注解类
*/
protected Class<?> getSpringFactoriesLoaderFactoryClass() {
		return EnableAutoConfiguration.class;
	}

//进入SpringFactoriesLoader类中
/*
看到会读取对应的配置文件，位置在META-INF/spring.factories中

*/
public final class SpringFactoriesLoader {

	/**
	 * The location to look for factories.
	 * <p>Can be present in multiple JAR files.
	 */
public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";}

//进入loadFactoryNames方法中
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);
		}
	}

springboot在启动的时候从类路径下的META-INF/spring.factories中获取EnableAutoConfiguration指定的值，将这些值作为自动配置类导入容器，自动配置类就生效，帮我们进行自动配置的工作：spring.factories文件位于springboot-autoconfigure.jar包中。

所以真正实现是从classpath中搜寻所有的META-INF/spring.factories配置文件，并将其中对应org.springframework.boot.autoconfigure.包下的配置项通过反射实例化为对应标注了@Configuration的JavaConfig形式的IOC容器配置类，然后将这些都汇总称为一个实例并加载到IOC容器中。

自动配置

springboot配置文件的装配过程

1、springboot在启动的时候会加载主配置类，开启了@EnableAutoConfiguration。

2、@EnableAutoConfiguration的作用：

  • 利用AutoConfigurationImportSelector给容器导入一些组件。
  • 查看selectImports方法的内容，返回一个AutoConfigurationEntry
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AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(autoConfigurationMetadata,
      annotationMetadata);
------
List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
------
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;
	}
  • 可以看到SpringFactoriesLoader.loadFactoryNames，继续看又调用了loadSpringFactories方法，获取META-INF/spring.factories资源文件
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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);
		}
	}

总结：将类路径下 META-INF/spring.factories 里面配置的所有EnableAutoConfiguration的值加入到了容器中；每一个xxxAutoConfiguration类都是容器中的一个组件，最后都加入到容器中，用来做自动配置，每一个自动配置类都可以进行自动配置功能

使用HttpEncodingAutoConfiguration来解释自动装配原理

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/*
表名这是一个配置类，
*/
@Configuration(proxyBeanMethods = false)
/*
启动指定类的ConfigurationProperties功能,进入HttpProperties查看，将配置文件中对应的值和HttpProperties绑定起来，并把HttpProperties加入到ioc容器中
*/
@EnableConfigurationProperties(HttpProperties.class)
/*
spring底层@Confitional注解，根据不同的条件判断，如果满足指定的条件，整个配置类里面的配置就会生效
此时表示判断当前应用是否是web应用，如果是，那么配置类生效
*/
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
/*
判断当前项目由没有这个类CharacterEncodingFilter，springmvc中进行乱码解决的过滤器
*/
@ConditionalOnClass(CharacterEncodingFilter.class)
/*
判断配置文件中是否存在某个配置：spring.http.encoding.enabled
如果不存在，判断也是成立的，
即使我们配置文件中不配置spring.http.encoding.enabled=true，也是默认生效的
*/
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {

    //和springboot的配置文件映射
	private final HttpProperties.Encoding properties;

    //只有一个有参构造器的情况下，参数的值就会从容器中拿
	public HttpEncodingAutoConfiguration(HttpProperties properties) {
		this.properties = properties.getEncoding();
	}

    //给容器中添加一个组件，这个组件的某些值需要从properties中获取
	@Bean
	@ConditionalOnMissingBean//判断容器中是否有此组件
	public CharacterEncodingFilter characterEncodingFilter() {
		CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
		filter.setEncoding(this.properties.getCharset().name());
		filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));
		filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));
		return filter;
	}

	@Bean
	public LocaleCharsetMappingsCustomizer localeCharsetMappingsCustomizer() {
		return new LocaleCharsetMappingsCustomizer(this.properties);
	}

	private static class LocaleCharsetMappingsCustomizer
			implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory>, Ordered {

		private final HttpProperties.Encoding properties;

		LocaleCharsetMappingsCustomizer(HttpProperties.Encoding properties) {
			this.properties = properties;
		}

		@Override
		public void customize(ConfigurableServletWebServerFactory factory) {
			if (this.properties.getMapping() != null) {
				factory.setLocaleCharsetMappings(this.properties.getMapping());
			}
		}

		@Override
		public int getOrder() {
			return 0;
		}
	}
}

根据当前不同的条件判断，决定这个配置类是否生效！

总结：

​ 1、springboot启动会加载大量的自动配置类

​ 2、查看需要的功能有没有在springboot默认写好的自动配置类中华

​ 3、查看这个自动配置类到底配置了哪些组件

​ 4、给容器中自动配置类添加组件的时候，会从properties类中获取属性

@Conditional：自动配置类在一定条件下才能生效

@Conditional扩展注解 作用
@ConditionalOnJava 系统的java版本是否符合要求
@ConditionalOnBean 容器中存在指定Bean
@ConditionalOnMissingBean 容器中不存在指定Bean
@ConditionalOnExpression 满足SpEL表达式
@ConditionalOnClass 系统中有指定的类
@ConditionalOnMissingClass 系统中没有指定的类
@ConditionalOnSingleCandidate 容器中只有一个指定的Bean，或者是首选Bean
@ConditionalOnProperty 系统中指定的属性是否有指定的值
@ConditionalOnResource 类路径下是否存在指定资源文件
@ConditionOnWebApplication 当前是web环境
@ConditionalOnNotWebApplication 当前不是web环境
@ConditionalOnJndi JNDI存在指定项