《Spring源码深度解析郝佳第2版》ApplicationContext

往期博客：

《Spring源码深度解析郝佳第2版》容器的基本实现与XML文件的加载

《Spring源码深度解析郝佳第2版》XML标签的解析

《Spring源码深度解析郝佳第2版》bean的加载、循环依赖的解决

往期博客分析了BeanFactory接口以及他的默认实现类XmlBeanFactory

BeanFactory beanFactory = new XmlBeanFactory(new ClassPathResource("beanFactory.xml"));

接下来分析另外一个高级拓展接口ApplicationContext，以它加载xml文件为例分析

 // ClassPathXmlApplicationContext 继承 ApplicationContext
ApplicationContext context = new ClassPathXmlApplicationContext("sichaolong.xml");

入口ClassPathXmlApplicationContext

将配置文件路径数组保存到AbstractRefreshableApplicationContext的成员变量configLocations完成配置文件加载解析及容器核心功能，调用AbstractApplicationContetxt的refresh()

核心AbstractApplicationContetxt的refresh()的流程分析

// 准备刷新上下文环境this.prepareRefresh();// 初始化BeanFactory并进行xml文件读取ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();// 对BeanFactory的各种功能填充this.prepareBeanFactory(beanFactory);// 空实现，由子类覆盖重写拓展this.postProcessBeanFactory(beanFactory);// 激活各种BeanFactory处理器this.invokeBeanFactoryPostProcessors(beanFactory);// 注册拦截Bean创建的处理器，真正调用在getBean()时候this.registerBeanPostProcessors(beanFactory);// 为上下文初始化国际化处理this.initMessageSource();// 为上下文初始化应用消息广播器，放入applicationEventMulticast类型的bean中this.initApplicationEventMulticaster();// 留给子类初始化其他的beanthis.onRefresh();// 在注册bean中查找Listener bean,注册到8的应用上下文广播器this.registerListeners();// 初始化剩下的单实例 this.finishBeanFactoryInitialization(beanFactory);// 完成刷新过程，通知生命周期管理器lifecycleProcessor刷新过程this.finishRefresh();

SpringBoot的run()方法

// 启动类注解// run方法

一、入口ClassPathXmlApplicationContext

实例化ClassPathXmlApplicationContext传入xml配置文件的路径，可以传入多个路径

// 1. 将配置文件路径保存在AbstractRefreshableApplicationContext的成员变量configLocations

// 2. 对于数组路径的解析加载以及功能实现都在AbstractApplicationContext的refresh()中

// ClassPathXmlApplication 构造方法
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
        this(new String[]{configLocation}, true, (ApplicationContext)null);
    }
// 重载
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) throws BeansException {
		// 初始化父类容器
        super(parent);
        // 1. 解析传入的路径数组，调用reslovePath(),保存到成员变量AbstractRefreshableApplicationContext的configLocations
        this.setConfigLocations(configLocations);
        if (refresh) {
        	// 2. xml解析及容器功能实现,调用AbstractAplicationContext#refresh()
            this.refresh();
        }

    }

// 1. 解析传入的路径数组，调用reslovePath(),保存到成员变量AbstractRefreshableApplicationContext的configLocations

public void setConfigLocations(@Nullable String... locations) {
        if (locations != null) {
            Assert.noNullElements(locations, "Config locations must not be null");
            this.configLocations = new String[locations.length];

            for(int i = 0; i < locations.length; ++i) {
                this.configLocations[i] = this.resolvePath(locations[i]).trim();
            }
        } else {
            this.configLocations = null;
        }

    }

// 2. 功能实现AbstractAplicationContext#refresh()

 public void refresh() throws BeansException, IllegalStateException {
        synchronized(this.startupShutdownMonitor) {
        	// 1. 准备刷新上下文环境
            this.prepareRefresh();
            // 2. 初始化BeanFactory并进行xml文件读取
            ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
            // 3. 对BeanFactory的各种功能填充
            this.prepareBeanFactory(beanFactory);

            try {
            	// 4. 空实现，由子类覆盖重写拓展
                this.postProcessBeanFactory(beanFactory);
                // 5. 激活各种BeanFactory处理器
                this.invokeBeanFactoryPostProcessors(beanFactory);
                // 6. 注册拦截Bean创建的处理器，真正调用在getBean()时候
                this.registerBeanPostProcessors(beanFactory);
                // 7. 为上下文初始化国际化处理
                this.initMessageSource();
                // 8. 为上下文初始化应用消息广播器，放入applicationEventMulticast类型的bean中
                this.initApplicationEventMulticaster();
                // 9. 留给子类初始化其他的bean
                this.onRefresh();
                // 10. 在注册bean中查找Listener bean,注册到8的应用上下文广播器
                this.registerListeners();
                // 11. 初始化剩下的单实例
                this.finishBeanFactoryInitialization(beanFactory);
                // 12. 完成刷新过程，通知生命周期管理器lifecycleProcessor刷新过程
                this.finishRefresh();
            } catch (BeansException var9) {
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
                }

                this.destroyBeans();
                this.cancelRefresh(var9);
                throw var9;
            } finally {
                this.resetCommonCaches();
            }

        }
    }

二、核心AbstractApplicationContetxt的refresh()的流程分析 // 1. 准备刷新上下文环境 this.prepareRefresh();

主要是初始化前的准备工作，如对系统属性和环境变量的准备验证，留了两个模板空实现，需要我们自己写XxxApplicationContext继承ApplicationContext接口重写方法使用

// AbstractApplicationContext
 protected void prepareRefresh() {
 		// 开始时间
        this.startupDate = System.currentTimeMillis();
        this.closed.set(false);
        this.active.set(true);
        if (this.logger.isDebugEnabled()) {
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("Refreshing " + this);
            } else {
                this.logger.debug("Refreshing " + this.getDisplayName());
            }
        }
		// 空实现，留给子类实现
        this.initPropertySources();
        // 空实现，验证需要的属性文件都以否放入环境中，可以重写自定义规则，如getEnvironment().setRequiredProperties("xiaosi")
        this.getEnvironment().validateRequiredProperties();
        if (this.earlyApplicationListeners == null) {
            this.earlyApplicationListeners = new linkedHashSet(this.applicationListeners);
        } else {
            this.applicationListeners.clear();
            this.applicationListeners.addAll(this.earlyApplicationListeners);
        }

        this.earlyApplicationEvents = new linkedHashSet();
    }

// 2. 初始化BeanFactory并进行xml文件读取ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();

// AbstractApplicationContext
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        this.refreshBeanFactory();
        return this.getBeanFactory();
    }
// 委托 AbstractRefreshableApplicationContext
 protected final void refreshBeanFactory() throws BeansException {
        if (this.hasBeanFactory()) {
            this.destroyBeans();
            this.closeBeanFactory();
        }

        try {
        	// 2.1 创建 DefaultListableBeanFactory 
            DefaultListableBeanFactory beanFactory = this.createBeanFactory();
            // 序列化id
            beanFactory.setSerializationId(this.getId());
            // 2.2 定制beanFactory，设置属性包括是否允许覆盖同名不同定义对象，是否允许循环依赖
            // 在书中说这里设置@Autowired、@Qualifier注解解析器QualifierAnnotationAutowireCondiateResolver，但是我看的SpringBoot 2.3.7版本已经无此设置
            this.customizeBeanFactory(beanFactory);
            // 2.3 加载BeanDefinitions，初始化DoucmentLoader读取解析xml
            this.loadBeanDefinitions(beanFactory);
            // 2.4 使用全局变量记录BeanFactory实例
            this.beanFactory = beanFactory;
        } catch (IOException var2) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + this.getDisplayName(), var2);
        }
    }

// 2.2 AbstractRefreshableApplicationContext#customizeBeanFactory()
// 依旧是模板方法留给子类覆盖设置这两个属性
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
        if (this.allowBeanDefinitionOverriding != null) {
            beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
        }

        if (this.allowCircularReferences != null) {
            beanFactory.setAllowCircularReferences(this.allowCircularReferences);
        }

    }

// 对2.2的补充，SpringBoot 2.3.7版本下直接使用的是SimpleAutowirdCandiateResolver解析@Autowired、@Qualifier，具体实现类是QualifierAnnotationAutowireCondiateResolver，即默认采用autowireByType方式注入

// 2.3 委托AbstractXmlApplication初始化XmlBeanDefinitionReader老loadBeanDefinitions()，解析configLocations下保存的xml数组路径，初始化DoucmentLoader读取。经过此步，XmlBeanDefinitionReader解析出来的BeanDefinitionHolder已经保存到DefaultListableBeanFactory。此时ApplicationContext已经拿到了BeanFactory的所有解析的好配置

// AbstractXmlApplication初始化XmlBeanDefinitionReader 
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
        beanDefinitionReader.setEnvironment(this.getEnvironment());
        beanDefinitionReader.setResourceLoader(this);
        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
        // 初始化beanDefinitionReader
        this.initBeanDefinitionReader(beanDefinitionReader);
        // 解析AbstractRefreshableApplicationContext成员变量configLocations，也就是xml配置文件路径数组
        this.loadBeanDefinitions(beanDefinitionReader);
    }
// AbstractXmlApplication使用XmlBeanDefinitionReader 解析xml
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        Resource[] configResources = this.getConfigResources();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }

        String[] configLocations = this.getConfigLocations();
        if (configLocations != null) {
        	// 解析，接着就是到AbstractBeanDefinitionReader，reader就是之前BeanFactory的那一套XmlBeanDefinitionReader
            reader.loadBeanDefinitions(configLocations);
        }

    }

// 3. 对BeanFactory的各种功能填充this.prepareBeanFactory(beanFactory);

上面已经完成BeanFactory配置文件解析和保存，此步开始就是ApplicationContext拓展功能的实现

// AbsractApplicationContext对DefaultListableBeanFactory进行功能拓展
// DefaultListableBeanFactory 继承 ConfigurableListableBeanFactory 
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		// 3.1 设置类加载器
        beanFactory.setBeanClassLoader(this.getClassLoader());
        // 3.2 增加支持#{bean.xxx}形式取值，即SpEL表达式
        
        //在bean初始化之后的属性填充，会调用AbstractAutowireCapableBeanFactory了的applyPropertyValues函数来完成功能
        // 就在这个函数中会构造BeanDefinitionValueResolver类型的valueRsolver来进行属性取值
        // 一般会通过AbstractBeanFactory的evaluateBeanDefinitionString方法完成SpEL的解析
		// 总结：就是在bean的依赖填充、属性填充的时候会用到应用语言解析器
        beanFactory.setBeanexpressionResolver(new StandardBeanexpressionResolver(beanFactory.getBeanClassLoader()));
        
        // 3.3 增加PropertyEditor工具方便对bean的属性管理，
        // 如在xml中配置String类型的日期，解析到Bean的Date类型属性可能会报错
        // 解决办法就是自己定义一个PropertyEditor工具，创建XxxPropertyEditor继承PropertyEditorSupport重写setAsText实现自定义规则，然后放到容器中
        
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, this.getEnvironment()));
        
        // 3.4 添加BeanPostProcessor处理器
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        
		// 3.5 忽略几个自动装配的接口,因为实现了XxxAware接口可以自动获取Xxx，不需要自动注入装配
		// 实现了XxxAware的bean在初始化前、实例化后会调用postProcessBeforeInitialization()完成需要的属性装配
		// 详情看3.4添加的BeanPostProcessor处理器
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
        
        // 3.6 设置几个自动装配的规则
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
        
        // 3.7 增加对AspestJ的支持，静态AOP
        if (beanFactory.containsBean("loadTimeWeaver")) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
		// 3.8 添加默认的系统环境Bean，当我们的bean需要下列bean的时候可以直接拿到
        if (!beanFactory.containsLocalBean("environment")) {
            beanFactory.registerSingleton("environment", this.getEnvironment());
        }

        if (!beanFactory.containsLocalBean("systemProperties")) {
            beanFactory.registerSingleton("systemProperties", this.getEnvironment().getSystemProperties());
        }

        if (!beanFactory.containsLocalBean("systemEnvironment")) {
            beanFactory.registerSingleton("systemEnvironment", this.getEnvironment().getSystemEnvironment());
        }

    }

// 3.4 添加BeanPostProcessor处理器

在bean实例化前后会调用BeanPostProcessor的postProcessBeforeInitialization()和postProcessAfterInitialization()，后置处理默认为空

主要是前置处理，主要做的工作是对那些实现了XxxAware的bean在初始化后、实例化前会获得对应的资源，因此下面会忽略几个XxxAware的自动装配

// ApplicationContextAwareProcessor实现BeanPostProcessor
// 实例化前处理

 @Nullable
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (!(bean instanceof EnvironmentAware) && !(bean instanceof EmbeddedValueResolverAware) && !(bean instanceof ResourceLoaderAware) && !(bean instanceof ApplicationEventPublisherAware) && !(bean instanceof MessageSourceAware) && !(bean instanceof ApplicationContextAware)) {
            return bean;
        } else {
            AccessControlContext acc = null;
            if (System.getSecurityManager() != null) {
                acc = this.applicationContext.getBeanFactory().getAccessControlContext();
            }

            if (acc != null) {
                AccessController.doPrivileged(() -> {
                	// 调用
                    this.invokeAwareInterfaces(bean);
                    return null;
                }, acc);
            } else {
            	// 调用
                this.invokeAwareInterfaces(bean);
            }

            return bean;
        }
    }

	// 实现了这些Aware的接口的bean在初始化后、实例化前可以获取一些资源
    private void invokeAwareInterfaces(Object bean) {
        if (bean instanceof EnvironmentAware) {
            ((EnvironmentAware)bean).setEnvironment(this.applicationContext.getEnvironment());
        }

        if (bean instanceof EmbeddedValueResolverAware) {
            ((EmbeddedValueResolverAware)bean).setEmbeddedValueResolver(this.embeddedValueResolver);
        }

        if (bean instanceof ResourceLoaderAware) {
            ((ResourceLoaderAware)bean).setResourceLoader(this.applicationContext);
        }

        if (bean instanceof ApplicationEventPublisherAware) {
            ((ApplicationEventPublisherAware)bean).setApplicationEventPublisher(this.applicationContext);
        }

        if (bean instanceof MessageSourceAware) {
            ((MessageSourceAware)bean).setMessageSource(this.applicationContext);
        }

        if (bean instanceof ApplicationContextAware) {
            ((ApplicationContextAware)bean).setApplicationContext(this.applicationContext);
        }

    }

// 4. 空实现，由子类覆盖重写拓展this.postProcessBeanFactory(beanFactory);

4.1 作用

BeanFactoryPostProcessor和BeanPostProcessor类似，允许beanFactory容器在实例化任何其他bean的时候对bean统一的增强或修改，允许多个实现了Ordered接口的PostProcessBeanFactory来依次处理，他的范围是容器级的，不能跨容器，如果对bean的处理，最好还是使
用BeanPostPrecessor。

4.2 加载Properties文件的原理

具体应用就是PropertyPlaceholderConfigurer，他支持在xml配置文件使用 ${myPropertoes.msg}来从myProperties.properties文件取值。依靠在xml中配置PropertyPlaceholderConfigurer类型的bean，并在标签指定myProperties.properties文件的地址。原理就是PropertyPlaceholderConfigurer实现了BeanFactoryPostProcessor接口，在容器启动读取所有bean配置文件之后、bean初始化之前，会执行postPrecessBeanFactory()方法，该方法内会依次执行mergeProperties()、convertProperties()、processProperties()这三个方法读取properties内容到beanFactory

// 5. 激活各种BeanFactory处理器 this.invokeBeanFactoryPostProcessors(beanFactory);

在上面说明了BeanFactoryPostProcessor的用处，接下来需要知道这些处理器是怎么被激活的。

// AbstarctApplicationContext
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		// 委托PostProcessorRegistrationDelegate的静态方法
        PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, this.getBeanFactoryPostProcessors());
        if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean("loadTimeWeaver")) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }

    }

// 委托PostProcessorRegistrationDelegate的静态方法进行BeanFactoryPostProcessor的激活，主要是两类

激活BeanDefinitionRegistry激活普通的BeanFactoryPostProcessor

public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List beanFactoryPostProcessors) {
		// 存放的BeanFactoryPostProcessor集合
        Set processedBeans = new HashSet();
        ArrayList regularPostProcessors;
        ArrayList registryProcessors;
        int var9;
        ArrayList currentRegistryProcessors;
        String[] postProcessorNames;
        // 1. 第一类 BeanDefinitionRegistry
        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry)beanFactory;
            // 存放第二类常规硬编码的BeanFactoryPostProcessors
            regularPostProcessors = new ArrayList();
            // 存放第一类硬编码BeanDefinitionRegistry
            registryProcessors = new ArrayList();
            
            // 遍历全部
            Iterator var6 = beanFactoryPostProcessors.iterator();

            while(var6.hasNext()) {
                BeanFactoryPostProcessor postProcessor = (BeanFactoryPostProcessor)var6.next();
                // 第一类注册及添加硬编码registryProcessors 集合
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor)postProcessor;
                    
                    registryProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryProcessors.add(registryProcessor);
                } else {
                	// 第二类添加硬编码regularPostProcessors 集合
                    regularPostProcessors.add(postProcessor);
                }
            }
			
            currentRegistryProcessors = new ArrayList();
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            String[] var16 = postProcessorNames;
            var9 = postProcessorNames.length;

            int var10;
            String ppName;
            for(var10 = 0; var10 < var9; ++var10) {
                ppName = var16[var10];
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }

            sortPostProcessors(currentRegistryProcessors, beanFactory);
            registryProcessors.addAll(currentRegistryProcessors);
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            var16 = postProcessorNames;
            var9 = postProcessorNames.length;

            for(var10 = 0; var10 < var9; ++var10) {
                ppName = var16[var10];
                if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
			
			// 第二类，普通的BeanFactoryPostProcessor
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            registryProcessors.addAll(currentRegistryProcessors);
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();
            boolean reiterate = true;

            while(reiterate) {
                reiterate = false;
                postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                String[] var19 = postProcessorNames;
                var10 = postProcessorNames.length;

                for(int var26 = 0; var26 < var10; ++var26) {
                    String ppName = var19[var26];
                    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();
            }

            invokeBeanFactoryPostProcessors((Collection)registryProcessors, (ConfigurableListableBeanFactory)beanFactory);
            invokeBeanFactoryPostProcessors((Collection)regularPostProcessors, (ConfigurableListableBeanFactory)beanFactory);
        } else {
            invokeBeanFactoryPostProcessors((Collection)beanFactoryPostProcessors, (ConfigurableListableBeanFactory)beanFactory);
        }

        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
        regularPostProcessors = new ArrayList();
        registryProcessors = new ArrayList();
        currentRegistryProcessors = new ArrayList();
        postProcessorNames = postProcessorNames;
        int var20 = postProcessorNames.length;

        String ppName;
        for(var9 = 0; var9 < var20; ++var9) {
            ppName = postProcessorNames[var9];
            if (!processedBeans.contains(ppName)) {
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    regularPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
                } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    registryProcessors.add(ppName);
                } else {
                    currentRegistryProcessors.add(ppName);
                }
            }
        }

        sortPostProcessors(regularPostProcessors, beanFactory);
        invokeBeanFactoryPostProcessors((Collection)regularPostProcessors, (ConfigurableListableBeanFactory)beanFactory);
        List orderedPostProcessors = new ArrayList(registryProcessors.size());
        Iterator var21 = registryProcessors.iterator();

        while(var21.hasNext()) {
            String postProcessorName = (String)var21.next();
            orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }

        sortPostProcessors(orderedPostProcessors, beanFactory);
        invokeBeanFactoryPostProcessors((Collection)orderedPostProcessors, (ConfigurableListableBeanFactory)beanFactory);
        List nonOrderedPostProcessors = new ArrayList(currentRegistryProcessors.size());
        Iterator var24 = currentRegistryProcessors.iterator();

        while(var24.hasNext()) {
            ppName = (String)var24.next();
            nonOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
        }

        invokeBeanFactoryPostProcessors((Collection)nonOrderedPostProcessors, (ConfigurableListableBeanFactory)beanFactory);
        beanFactory.clearmetadataCache();
    }

// 6. 注册拦截Bean创建的处理器，真正调用在getBean()时候this.registerBeanPostProcessors(beanFactory);

此步注册BeanPostProcessors，真正进行bean初始化之前会调用

在beanFactory等容器的时候因为没有实现后处理器的自动注册，因此需要用户手动注册才能使用，但是在ApplicationContext中，已经自动注册了如InstationAwareBeanPostProcessor，所以我们在xml中配置了实现了InstationAwareBeanPostProcessor的bean并重写了postProcessBeforeInstation等方法之后，就会对bean初始化、实例化前后进行处理。

// AbstractApplicationContext
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		// 委托PostProcessorRegistrationDelegate的静态方法
        PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
    }

// 配置的BeanPostProcessor可以分为四类

实现了PriorityOrdered的BeanPostProcessor实现了Ordered的BeanPostProcessor所有无序的BeanPostProcessor所有MergerdBeanDefinitionPostProcessor，并排除重复注册

// // 委托PostProcessorRegistrationDelegate的静态方法进行BeanPostProcessor处理器的注册
public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new PostProcessorRegistrationDelegate.BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
        // 实现了PriorityOrdered的BeanPostProcessor
        List priorityOrderedPostProcessors = new ArrayList();
        List internalPostProcessors = new ArrayList();
        
        // 实现了Ordered的BeanPostProcessor
        List orderedPostProcessorNames = new ArrayList();
        
        // 所有无序的BeanPostProcessor
        List nonOrderedPostProcessorNames = new ArrayList();
        String[] var8 = postProcessorNames;
        int var9 = postProcessorNames.length;

        String ppName;
        BeanPostProcessor pp;
        for(int var10 = 0; var10 < var9; ++var10) {
            ppName = var8[var10];
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            } else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }
		// 第一类，排序注册
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, (List)priorityOrderedPostProcessors);

        List orderedPostProcessors = new ArrayList(orderedPostProcessorNames.size());
        Iterator var14 = orderedPostProcessorNames.iterator();
        while(var14.hasNext()) {
            String ppName = (String)var14.next();
            BeanPostProcessor pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
            orderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        
		// 第二类，排序注册
        sortPostProcessors(orderedPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, (List)orderedPostProcessors);
        List nonOrderedPostProcessors = new ArrayList(nonOrderedPostProcessorNames.size());
        Iterator var17 = nonOrderedPostProcessorNames.iterator();

        while(var17.hasNext()) {
            ppName = (String)var17.next();
            pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
		// 第三类，排序注册
        registerBeanPostProcessors(beanFactory, (List)nonOrderedPostProcessors);
        sortPostProcessors(internalPostProcessors, beanFactory);
        // 第四类，注册
        registerBeanPostProcessors(beanFactory, (List)internalPostProcessors);
		
		// 添加ApplicationListener探测器
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }
// 注册
private static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, List postProcessors) {
        Iterator var2 = postProcessors.iterator();

        while(var2.hasNext()) {
            BeanPostProcessor postProcessor = (BeanPostProcessor)var2.next();
            // 委托AbstarctApplicationContext
            beanFactory.addBeanPostProcessor(postProcessor);
        }

    }
// 委托AbstarctApplicationContext
public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
        Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
        // 防止重复
        this.beanPostProcessors.remove(beanPostProcessor);
        if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
            this.hasInstantiationAwareBeanPostProcessors = true;
        }

        if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
            this.hasDestructionAwareBeanPostProcessors = true;
        }

        this.beanPostProcessors.add(beanPostProcessor);
    }

// 7. 为上下文初始化国际化处理this.initMessageSource(); // 8. 为上下文初始化应用消息广播器，放入applicationEventMulticast类型的bean中this.initApplicationEventMulticaster();

先看看事件监听的用法，需要定义

实现ApplicationEvent定义监听事件实现ApplicationListener定义监听器，重写onApplicationEvent方法根据形参ApplicationEvent处理事件添加配置文件，将时间监听器通过xml放到容器测试，创建事件实例，使用ApplicationContext实例调用publishEvent()事件

类似观察者模式，可以在比较关心的事件发生之后及时的处理

// AbstractApplicationContext
protected void initApplicationEventMulticaster() {
        ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
        // 判断本地有无自定义的事件广播器，有就使用自定义的
        if (beanFactory.containsLocalBean("applicationEventMulticaster")) {
            this.applicationEventMulticaster = (ApplicationEventMulticaster)beanFactory.getBean("applicationEventMulticaster", ApplicationEventMulticaster.class);
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
            }
        } else {
        	// 使用默认的事件广播器 SimpleApplicationEventMulticaster
            this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
            beanFactory.registerSingleton("applicationEventMulticaster", this.applicationEventMulticaster);
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("No 'applicationEventMulticaster' bean, using [" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
            }
        }

    }
// SimpleApplicationEventMulticaster的multicastEvent

// 当发生Spring事件，SimpleApplicationEventMulticaster会调用multicastEvent广播事件
public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType) {
        ResolvableType type = eventType != null ? eventType : this.resolveDefaultEventType(event);
        Executor executor = this.getTaskExecutor();
        Iterator var5 = this.getApplicationListeners(event, type).iterator();

        while(var5.hasNext()) {
            ApplicationListener listener = (ApplicationListener)var5.next();
            if (executor != null) {
                executor.execute(() -> {
                	// 唤醒listeners
                    this.invokeListener(listener, event);
                });
            } else {
                this.invokeListener(listener, event);
            }
        }

    }

// 9. 留给子类初始化其他的bean模板this.onRefresh();

主要实现类有

// 10. 在注册bean中查找Listener bean,注册到8的应用上下文广播器this.registerListeners();

// AbstractApplicationContext

protected void registerListeners() {
        Iterator var1 = this.getApplicationListeners().iterator();
		// 硬编码监听器注册
        while(var1.hasNext()) {
            ApplicationListener listener = (ApplicationListener)var1.next();
            this.getApplicationEventMulticaster().addApplicationListener(listener);
        }
		// 通过配置文件配置的监听器注册
        String[] listenerBeanNames = this.getBeanNamesForType(ApplicationListener.class, true, false);
        String[] var7 = listenerBeanNames;
        int var3 = listenerBeanNames.length;

        for(int var4 = 0; var4 < var3; ++var4) {
            String listenerBeanName = var7[var4];
            this.getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
        }

        Set earlyEventsToProcess = this.earlyApplicationEvents;
        this.earlyApplicationEvents = null;
        if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
            Iterator var9 = earlyEventsToProcess.iterator();

            while(var9.hasNext()) {
                ApplicationEvent earlyEvent = (ApplicationEvent)var9.next();
                this.getApplicationEventMulticaster().multicastEvent(earlyEvent);
            }
        }

    }

// 11. 初始化剩下的单实例this.finishBeanFactoryInitialization(beanFactory);

完成BeanFactory的初始化工作，其中包括

ConversionService的设置：自定义XxxConvert实现Convert 接口，重写convert方法，返回newType。然后注册ConvertService类型的bean设置MyConvert。然后测试，创建DefultConversionService实例，addService(new MyConvert())，然后调用convert方法返回需要的newType配置冻结：synchronized锁住beanDefinitionMap初始化非延迟加载单例bean：ApplicationContext实现的默认行为是在启动的时候将所有的单例bean提前委托DefaultListabelBeanFactory进行实例化，意味着bean的实例化和容器的初始化为一个过程，通常这是一个好事，因为在配置bean过程中的错误会被立即发现。

// AbstractApplicationContext

// ConversionService的设置，类似之前自定义转换器从String转为Date的方式
// 在Spring还有另外一种方式，也就是使用Convert
 protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        if (beanFactory.containsBean("conversionService") && beanFactory.isTypeMatch("conversionService", ConversionService.class)) {
            beanFactory.setConversionService((ConversionService)beanFactory.getBean("conversionService", ConversionService.class));
        }

        if (!beanFactory.hasEmbeddedValueResolver()) {
            beanFactory.addEmbeddedValueResolver((strVal) -> {
                return this.getEnvironment().resolvePlaceholders(strVal);
            });
        }
		// AspectJ 静态AOP配置
        String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
        String[] var3 = weaverAwareNames;
        int var4 = weaverAwareNames.length;

        for(int var5 = 0; var5 < var4; ++var5) {
            String weaverAwareName = var3[var5];
            this.getBean(weaverAwareName);
        }

        beanFactory.setTempClassLoader((ClassLoader)null);
       	// 冻结所有的bean定义，说明注册的bean定义将不被修改或任何一步的改变
        beanFactory.freezeConfiguration();
        // 初始化剩下的单实例（非惰性）
        beanFactory.preInstantiateSingletons();
    }

// DefaultListableBeanFactory

public void preInstantiateSingletons() throws BeansException {
        if (this.logger.isTraceEnabled()) {
            this.logger.trace("Pre-instantiating singletons in " + this);
        }

        List beanNames = new ArrayList(this.beanDefinitionNames);
        Iterator var2 = beanNames.iterator();

        while(true) {
            String beanName;
            Object bean;
            do {
                while(true) {
                    RootBeanDefinition bd;
                    do {
                        do {
                            do {
                                if (!var2.hasNext()) {
                                    var2 = beanNames.iterator();

                                    while(var2.hasNext()) {
                                        beanName = (String)var2.next();
                                        Object singletonInstance = this.getSingleton(beanName);
                                        if (singletonInstance instanceof SmartInitializingSingleton) {
                                            SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton)singletonInstance;
                                            if (System.getSecurityManager() != null) {
                                                AccessController.doPrivileged(() -> {
                                                    smartSingleton.afterSingletonsInstantiated();
                                                    return null;
                                                }, this.getAccessControlContext());
                                            } else {
                                                smartSingleton.afterSingletonsInstantiated();
                                            }
                                        }
                                    }

                                    return;
                                }

                                beanName = (String)var2.next();
                                bd = this.getMergedLocalBeanDefinition(beanName);
                            } while(bd.isAbstract());
                        } while(!bd.isSingleton());
                    } while(bd.isLazyInit());

                    if (this.isFactoryBean(beanName)) {
                        bean = this.getBean("&" + beanName);
                        break;
                    }

                    this.getBean(beanName);
                }
            } while(!(bean instanceof FactoryBean));

            FactoryBean factory = (FactoryBean)bean;
            boolean isEagerInit;
            if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                SmartFactoryBean var10000 = (SmartFactoryBean)factory;
                ((SmartFactoryBean)factory).getClass();
                isEagerInit = (Boolean)AccessController.doPrivileged(var10000::isEagerInit, this.getAccessControlContext());
            } else {
                isEagerInit = factory instanceof SmartFactoryBean && ((SmartFactoryBean)factory).isEagerInit();
            }

            if (isEagerInit) {
                this.getBean(beanName);
            }
        }
    }

// 12. 完成刷新过程，通知生命周期管理器lifecycleProcessor刷新过程this.finishRefresh();

在Spring中提供了Liftcycle接口，主要用于生命周期相关，Liftcycle包含strart、stop方法

// AbstractApplicationContext
protected void finishRefresh() {
        this.clearResourceCaches();
        // 1. 在ApplicationContext启动或者停止的时候会通过ListcycleProcessor对所有声明的bean周期做状态更新，需要先初始化它
        this.initLifecycleProcessor();
        // 2. 启动所有实现了Listcycle接口的bean
        this.getLifecycleProcessor().onRefresh();
        // 3. 发布启动成功的事件
        this.publishEvent((ApplicationEvent)(new ContextRefreshedEvent(this)));
        LiveBeansView.registerApplicationContext(this);
    }

// 1. 在ApplicationContext启动或者停止的时候会通过ListcycleProcessor对所有声明的bean周期做状态更新，需要先初始化它
protected void initLifecycleProcessor() {
        ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
        if (beanFactory.containsLocalBean("lifecycleProcessor")) {
            this.lifecycleProcessor = (LifecycleProcessor)beanFactory.getBean("lifecycleProcessor", LifecycleProcessor.class);
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("Using LifecycleProcessor [" + this.lifecycleProcessor + "]");
            }
        } else {
            DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
            defaultProcessor.setBeanFactory(beanFactory);
            this.lifecycleProcessor = defaultProcessor;
            beanFactory.registerSingleton("lifecycleProcessor", this.lifecycleProcessor);
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("No 'lifecycleProcessor' bean, using [" + this.lifecycleProcessor.getClass().getSimpleName() + "]");
            }
        }

    }
 // 2. 启动所有实现了Listcycle接口的bean
 // DefaultLifecycleProcessor 
 public void onRefresh() {
        this.startBeans(true);
        this.running = true;
    }
 private void startBeans(boolean autoStartupOnly) {
        Map lifecycleBeans = this.getLifecycleBeans();
        Map phases = new HashMap();
        
        lifecycleBeans.forEach((beanName, bean) -> {
            if (!autoStartuponly || bean instanceof SmartLifecycle && ((SmartLifecycle)bean).isAutoStartup()) {
                int phase = this.getPhase(bean);
                DefaultLifecycleProcessor.LifecycleGroup group = (DefaultLifecycleProcessor.LifecycleGroup)phases.get(phase);
                if (group == null) {
                    group = new DefaultLifecycleProcessor.LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
                    phases.put(phase, group);
                }

                group.add(beanName, bean);
            }

        });
        if (!phases.isEmpty()) {
            List keys = new ArrayList(phases.keySet());
            Collections.sort(keys);
            Iterator var5 = keys.iterator();

            while(var5.hasNext()) {
                Integer key = (Integer)var5.next();
                // 启动
                ((DefaultLifecycleProcessor.LifecycleGroup)phases.get(key)).start();
            }
        }

    }

三、SpringBoot的run()方法

启动类

// 1. 启动类注解
@SpringBootApplication
public class StudySpringApplication {

    public static void main(String[] args) {
    	// 2. run()方法
        SpringApplication.run(StudySpringApplication.class, args);
    }

}

// 1. 启动类注解


package org.springframework.boot.autoconfigure;


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@documented
@Inherited

@SpringBootConfiguration // 配置类
@EnableAutoConfiguration // 自动装配
// 包扫描
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) }) 
public @interface SpringBootApplication {

	
	@AliasFor(annotation = EnableAutoConfiguration.class)
	Class[] exclude() default {};

	
	@AliasFor(annotation = EnableAutoConfiguration.class)
	String[] excludeName() default {};

	
	@AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
	String[] scanbasePackages() default {};

	
	@AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
	Class[] scanbasePackageClasses() default {};


	@AliasFor(annotation = ComponentScan.class, attribute = "nameGenerator")
	Class nameGenerator() default BeanNameGenerator.class;

	
	@AliasFor(annotation = Configuration.class)
	boolean proxyBeanMethods() default true;

}

// 2. run方法

// 入口

 public static ConfigurableApplicationContext run(Class primarySource, String... args) {
 		//primarySource为 StudySpringApplication.class
        return run(new Class[]{primarySource}, args);
    }
// 重载
public static ConfigurableApplicationContext run(Class[] primarySources, String[] args) {
        return (new SpringApplication(primarySources)).run(args);
    }

// 构造函数
public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) {
        this.sources = new linkedHashSet();
        // 图标模式
        this.bannerMode = Mode.CONSOLE;
        this.logStartupInfo = true;
        this.addCommandLineProperties = true;
        // 转换器
        this.addConversionService = true;
        this.headless = true;
        this.registerShutdownHook = true;
        this.additionalProfiles = new HashSet();
        this.isCustomEnvironment = false;
        this.lazyInitialization = false;
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new linkedHashSet(Arrays.asList(primarySources));
        // web容器类型
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
        this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = this.deduceMainApplicationClass();
    }
// web容器类型，根据ClassPath判断,设置成员变量webApplicationType 
static WebApplicationType deduceFromClasspath() {
        if (ClassUtils.isPresent("org.springframework.web.reactive.DispatcherHandler", (ClassLoader)null) && !ClassUtils.isPresent("org.springframework.web.servlet.DispatcherServlet", (ClassLoader)null) && !ClassUtils.isPresent("org.glassfish.jersey.servlet.ServletContainer", (ClassLoader)null)) {
            return REACTIVE;
        } else {
            String[] var0 = SERVLET_INDICATOR_CLASSES;
            int var1 = var0.length;

            for(int var2 = 0; var2 < var1; ++var2) {
                String className = var0[var2];
                if (!ClassUtils.isPresent(className, (ClassLoader)null)) {
                    return NONE;
                }
            }

            return SERVLET;
        }
    }

// 重载

public ConfigurableApplicationContext run(String... args) {
		// 1. 计时器
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        // 2. 容器
        ConfigurableApplicationContext context = null;
        Collection exceptionReporters = new ArrayList();
        this.configureHeadlessProperty();
        SpringApplicationRunListeners listeners = this.getRunListeners(args);
        listeners.starting();

        Collection exceptionReporters;
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            
            // 3.准备环境，根据webApplicationType 准备上下文环境
            // webApplicationType 是在构造函数时根据ClassPath下内容设置的
            ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
            this.configureIgnoreBeanInfo(environment);
            
            Banner printedBanner = this.printBanner(environment);
            
            // 4. 创建容器,根据webApplicationType给contextClass赋值，然后初始化对应上下文容器
            context = this.createApplicationContext();
            
            exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
            // 5. 准备容器相关
            this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            
            // 6. 刷新容器，这里委托ConfigurableApplicationContext接口的refesh(),
            // 真实调用的是AbstractApplicationContext.refresh(),也就是上面分析的部分
            this.refreshContext(context);
            
            this.afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
            }

            listeners.started(context);
            this.callRunners(context, applicationArguments);
        } catch (Throwable var10) {
            this.handleRunFailure(context, var10, exceptionReporters, listeners);
            throw new IllegalStateException(var10);
        }

        try {
            listeners.running(context);
            return context;
        } catch (Throwable var9) {
            this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
            throw new IllegalStateException(var9);
        }
    }

// 2.3 根据webApplicationType 准备环境prepareEnvironment()

// 准备环境，根据webApplicationType 准备上下文环境

// webApplicationType 是在构造函数时根据ClassPath下内容设置的，主要作用是判断是web服务还是一般的boot服务，来创建对用的上下文ApplicationContext

 private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
 
 		// 1. 获取ClassPath下的当前上下文环境，方法内部给根据成员变量webApplicationType赋值
 		// 有SERVLET、NONE、REACTIVE等，下面会对比是否添加web-starter的Debug
        ConfigurableEnvironment environment = this.getOrCreateEnvironment();
        
        this.configureEnvironment((ConfigurableEnvironment)environment, applicationArguments.getSourceArgs());
        ConfigurationPropertySources.attach((Environment)environment);
        listeners.environmentPrepared((ConfigurableEnvironment)environment);
        this.bindToSpringApplication((ConfigurableEnvironment)environment);
        if (!this.isCustomEnvironment) {
            environment = (new EnvironmentConverter(this.getClassLoader())).convertEnvironmentIfNecessary((ConfigurableEnvironment)environment, this.deduceEnvironmentClass());
        }

        ConfigurationPropertySources.attach((Environment)environment);
        return (ConfigurableEnvironment)environment;
    }

// 1. 调用方法根据 在构造函数执行的时候根据ClassPath设置了成员变量webApplicationType
private ConfigurableEnvironment getOrCreateEnvironment() {
        if (this.environment != null) {
            return this.environment;
        } else {
            switch(this.webApplicationType) {
            case SERVLET:
                return new StandardServletEnvironment();
            case REACTIVE:
                return new StandardReactiveWebEnvironment();
            default:
                return new StandardEnvironment();
            }
        }
    }

// Debug prepareEnvironment() ：pom依赖有web-starter，观察webApplicationType的值为枚举类值SERVLET

// Debug prepareEnvironment() ：pom依赖无web-starter，观察webApplicationType的值为枚举类值NONE

总结：

有web服务情况下上下文Environment为StandardServletEnvironment。无web服务的情况下上下文Environment为StandardEnvironment。 // 2.4. 创建容器context = this.createApplicationContext();

根据成员变量判断创建那种ApplicationContext，即根据Environmet的值先给成员变量contextClass赋值

然后return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);创建ApplicationContext上下文

private Class applicationContextClass;

protected ConfigurableApplicationContext createApplicationContext() {
        Class contextClass = this.applicationContextClass;
        if (contextClass == null) {
            try {
                switch(this.webApplicationType) {
                // 有web的默认上下文
                case SERVLET:
                    contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
                    break;
                case REACTIVE:
                    contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
                    break;
                 // 没有web的默认上下文
                default:
                    contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
                }
            } catch (ClassNotFoundException var3) {
                throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
            }
        }

        return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);
    }

// Debug createApplicationContext()：pom有web-starter，观察contextClass的值为AnnotationConfigServletWebServerApplicationContext

// Debug createApplicationContext()：pom无web-starter，观察contextClass的值为AnnotationConfigApplicationContext

总结：

有web服务情况下上下文Environment为StandardServletEnvironment。上下文为AnnotationConfigServletWebServerApplicationContext无web服务的情况下上下文Environment为StandardEnvironment。上下文为AnnotationConfigApplicationContext // 2.6. 刷新容器，这里委托ConfigurableApplicationContext接口的refesh(),真实调用的是AbstractApplicationContext.refresh(),也就是上面分析的部分this.refreshContext(context);

《Spring源码深度解析 郝佳 第2版》ApplicationContext

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《Spring源码深度解析郝佳第2版》ApplicationContext