SpringBoot启动过程原理（转）

1.1 Springboot启动：

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

从上面代码看，调用了SpringApplication的静态方法run。这个run方法会构造一个SpringApplication的实例，然后再调用这里实例的run方法就表示启动SpringBoot。具体对象处理流程看下边时序图：

概述：

构造SpringApplication的实例（时序图步骤1-2）
调用SpringApplication.run()方法（时序图步骤3）
构造SpringApplicationRunListeners 实例（时序图步骤3.1.1）
发布ApplicationStartedEvent事件（时序图步骤3.1.2）
SpringApplicationRunListeners 实例准备环境信息（时序图步骤3.1.3）
创建ApplicationContext对象（时序图步骤3.1.4）
ApplicationContext实例准备环境信息（时序图步骤3.1.5）
刷新的上下文（时序图步骤3.1.6）
注：文章按照该顺序讲解【1.2 启动加载过程分析】

时序图：

1.2 启动加载过程分析

1.2.1 构造SpringApplication的实例（时序图步骤1-2）

代码

public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
    // 步骤1
    return new SpringApplication(sources).run(args);
}
public SpringApplication(Object... sources) {
    // 步骤1.1
    initialize(sources);
}
@SuppressWarnings({ "unchecked", "rawtypes" })
private void initialize(Object[] sources) {
    if (sources != null && sources.length > 0) {
        this.sources.addAll(Arrays.asList(sources));
    }
    this.webEnvironment = deduceWebEnvironment();
    //加载META-INF/spring.factories路径ApplicationContextInitializer.class
    getSpringFactoriesInstances(
            ApplicationContextInitializer.class));
    setListeners((Collection) 
    //加载META-INF/spring.factories路径ApplicationListener.class
    getSpringFactoriesInstances(ApplicationListener.class));
    this.mainApplicationClass = deduceMainApplicationClass();
}

1.2.2 步骤3.1.1:

代码

private SpringApplicationRunListeners getRunListeners(String[] args) {
        Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
        // (1)
        return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
                SpringApplicationRunListener.class, types, this, args));
    }

分析
(1). 通过ClassLoader.getResources加载META-INF/spring.factories路径下的
文件信息，从中找key为SpringApplicationRunListener对应类，并实例化。

1.2.3 步骤3.1.2：

代码

public void starting() {
    for (SpringApplicationRunListener listener : this.listeners) {
        listener.starting();
    }
}
@Override
@SuppressWarnings("deprecation")
public void starting() {
    this.initialMulticaster.multicastEvent(new ApplicationStartedEvent(this.application, this.args));
}

分析
发布ApplicationStartedEvent事件。

1.2.4 步骤3.1.3：

代码

private ConfigurableEnvironment prepareEnvironment(
        SpringApplicationRunListeners listeners,
        ApplicationArguments applicationArguments) {
    // Create and configure the environment
    // ⑴. 得到环境对象ConfigurableEnvironment，没有则创建一个StandardServletEnvironment
    ConfigurableEnvironment environment = getOrCreateEnvironment();
    // ⑵. 配置环境信息（激活环境，通过从系统环境变量里取）
    configureEnvironment(environment, applicationArguments.getSourceArgs());
    // ⑶. 发布ApplicationEnvironmentPreparedEvent事件，加载配置文件，具体请看（ConfigFileApplicationListener）。
    listeners.environmentPrepared(environment);
    if (isWebEnvironment(environment) && !this.webEnvironment) {
        environment = convertToStandardEnvironment(environment);
    }
    return environment;
}

protected void configureEnvironment(ConfigurableEnvironment environment,String[] args) {
    configurePropertySources(environment, args);
    // 配置ConfigurableEnvironment中的激活属性
    configureProfiles(environment, args);
}
protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
    environment.getActiveProfiles(); // ensure they are initialized
    // additionalProfiles是项目启动时在main中SpringApplication.setAdditionalProfiles("")配置的
    Set<String> profiles = new LinkedHashSet<>(this.additionalProfiles);
    // 获取环境变量中设置的spring.profiles.active属性
    profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
    // 赋值 activeProfiles
    environment.setActiveProfiles(StringUtils.toStringArray(profiles));
}

分析
⑴. 得到环境对象ConfigurableEnvironment，没有则创建一个StandardServletEnvironment
⑵. 配置激活环境信息，通过从系统环境变量里取或启动时通过SpringApplication.setAdditionalProfiles("")添加进来的
⑶. 发布ApplicationEnvironmentPreparedEvent事件，加载Spring配置文件信息，例如application.properties等。具体请看Spring Boot 属性文件（三）

步骤3.1.4：
分析
创建ApplicationContext对象 ，本文启动的是SERVLET所以会创建AnnotationConfigServletWebServerApplicationContext对象

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);
}

public AnnotationConfigServletWebServerApplicationContext() {
        this.reader = new AnnotatedBeanDefinitionReader(this);
        this.scanner = new ClassPathBeanDefinitionScanner(this);
}

会创建AnnotatedBeanDefinitionReader对象检测是否需要将一下对象放到Spring上下文中

// 用户配置Configuration注解，实现了BeanDefinitionRegistryPostProcessor接口，在容器刷新时，处理后置工厂处理器用来扫描Spring，注册Bean
ConfigurationClassPostProcessor
// 用于配置Autowired注解，实现了MergedBeanDefinitionPostProcessor接口
AutowiredAnnotationBeanPostProcessor
// 用于配置Required注解，实现了MergedBeanDefinitionPostProcessor接口
RequiredAnnotationBeanPostProcessor
// 用于配置JSR-250注解，实现了InstantiationAwareBeanPostProcessor接口
CommonAnnotationBeanPostProcessor
// 用于配置JPA注解
PersistenceAnnotationBeanPostProcessor
// 用于配置EventListener注解，实现了SmartInitializingSingleton接口
EventListenerMethodProcessor
// EventListener工厂
DefaultEventListenerFactory

步骤3.1.5：

代码

private void prepareContext(ConfigurableApplicationContext context,
            ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments, Banner printedBanner) {
    // ⑴.对ApplicationContext设置环境变量；
    context.setEnvironment(environment);
    // ⑵.配置属性ResourceLoader和ClassLoader属性；
    postProcessApplicationContext(context);
    // ⑶.循环初始化继承ApplicationContextInitializer接口的类
    applyInitializers(context);
    listeners.contextPrepared(context);
    if (this.logStartupInfo) {
        logStartupInfo(context.getParent() == null);
        logStartupProfileInfo(context);
    }

    // Add boot specific singleton beans
    context.getBeanFactory().registerSingleton("springApplicationArguments",
            applicationArguments);
    if (printedBanner != null) {
        context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
    }

    // Load the sources
    Set<Object> sources = getSources();
    Assert.notEmpty(sources, "Sources must not be empty");
    load(context, sources.toArray(new Object[sources.size()]));
    listeners.contextLoaded(context);
}

@Override
public void setEnvironment(ConfigurableEnvironment environment) {
    super.setEnvironment(environment);
    this.reader.setEnvironment(environment);
    this.scanner.setEnvironment(environment);
}

分析：
⑴.对ApplicationContext设置环境变量；
⑵.配置属性ResourceLoader和ClassLoader属性；
⑶.调用步骤1查询出来ApplicationContextInitializer子类，循环调用initialize()方法。

@SuppressWarnings({ "rawtypes", "unchecked" })
    protected void applyInitializers(ConfigurableApplicationContext context) {
        for (ApplicationContextInitializer initializer : getInitializers()) {
            Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(
                    initializer.getClass(), ApplicationContextInitializer.class);
            Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
            initializer.initialize(context);
        }
    }

⑷.发布ApplicationPreparedEvent事件。

步骤3.1.6

代码：

@Override
public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // ⑴.准备刷新的上下文环境
        prepareRefresh();
        
        // ⑵.初始化BeanFactory
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
        
        // ⑶.对BeanFactory进行各种功能填充
        prepareBeanFactory(beanFactory);

        try {
            // ⑷.子类覆盖方法做额外的处理
            postProcessBeanFactory(beanFactory);

            // ⑸.激活各种BeanFactory处理器
            invokeBeanFactoryPostProcessors(beanFactory);

            // ⑹.注册拦截Bean创建的Bean处理，这里只是注册，真正调用是再拿去Bean的时候
            registerBeanPostProcessors(beanFactory);

            // ⑺.为上下文初始化Message源，即不同语言的消息体，国际化处理
            initMessageSource();

            // ⑻.初始化应用消息广播器，并放到applicationEventMulticaster bean中
            initApplicationEventMulticaster();

            // ⑼.留给子类来初始化其他bean
            onRefresh();

            // ⑽.在所有注册的bean中查找Listener bean，注册到消息广播中
            registerListeners();

            // ⑾.初始化剩下的单实例（非惰性）
            finishBeanFactoryInitialization(beanFactory);

            // ⑿.完成刷新过程，通知生命周期处理器lifecycleProcessor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();
        }
    }
}

分析：

⑴.准备刷新的上下文环境
⑵.初始化BeanFactory
⑶.对BeanFactory进行各种功能填充
⑷.子类覆盖方法做额外的处理，这里会调用子类AnnotationConfigServletWebServerApplicationContext注入
⑸.激活各种BeanFactory处理器
⑹.注册拦截Bean创建的Bean处理，这里只是注册，真正调用是再拿去Bean的时候
⑺.为上下文初始化Message源，即不同语言的消息体，国际化处理
⑻.初始化事件派发器，并放到applicationEventMulticaster bean中
⑼.留给子类来初始化其他bean
⑽.在所有注册的bean中查找Listener bean，注册到事件派发器中
⑾.初始化剩下的单实例（非惰性）
⑿.完成刷新过程，通知生命周期处理器lifecycleProcessor刷新过程，同时发出ContextRefreshEvent通知别人

⑷.子类覆盖方法做额外的处理

@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    super.postProcessBeanFactory(beanFactory);
    if (this.basePackages != null && this.basePackages.length > 0) {
        this.scanner.scan(this.basePackages);
    }
    if (!this.annotatedClasses.isEmpty()) {
        this.reader.register(ClassUtils.toClassArray(this.annotatedClasses));
    }
}

@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    // 添加后置处理器，在创建Tomcat时会利用这个后置处理器来初始化Tomcat Server类
    beanFactory.addBeanPostProcessor(
            new WebApplicationContextServletContextAwareProcessor(this));
    beanFactory.ignoreDependencyInterface(ServletContextAware.class);
    registerWebApplicationScopes();
}

添加后置处理器，在创建Tomcat时会利用这个后置处理器来初始化Tomcat Server类

⑸.激活各种BeanFactory处理器
主要利用**步骤3.1.4：**创建AnnotatedBeanDefinitionReader对象往Spring容器中注入的ConfigurationClassPostProcessor来处理组件的注入

具体请看容器刷新，

⑺.为上下文初始化Message源，即不同语言的消息体，国际化处理

protected void initMessageSource() {
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
        this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
        // Make MessageSource aware of parent MessageSource.
        if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
            HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
            if (hms.getParentMessageSource() == null) {
                // Only set parent context as parent MessageSource if no parent MessageSource
                // registered already.
                hms.setParentMessageSource(getInternalParentMessageSource());
            }
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Using MessageSource [" + this.messageSource + "]");
        }
    }
    else {
    // 
        // Use empty MessageSource to be able to accept getMessage calls.
        DelegatingMessageSource dms = new DelegatingMessageSource();
        dms.setParentMessageSource(getInternalParentMessageSource());
        this.messageSource = dms;
        beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
        if (logger.isDebugEnabled()) {
            logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
                    "': using default [" + this.messageSource + "]");
        }
    }
}

如果容器中没有则创建一个DelegatingMessageSource国际化，并将它注册到Spring容器中

⑻.初始化事件派发器，并放到applicationEventMulticaster bean中

protected void initApplicationEventMulticaster() {
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
        this.applicationEventMulticaster =
                beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
        if (logger.isDebugEnabled()) {
            logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
        }
    }
    else {
        this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
        beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
        if (logger.isDebugEnabled()) {
            logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
                    APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
                    "': using default [" + this.applicationEventMulticaster + "]");
        }
    }
}

如果容器中没有则创建一个SimpleApplicationEventMulticaster事件派发器，并将它注册到Spring容器中

⑼.留给子类来初始化其他bean
主要目的是初始化Tomcat等内置服务器

SpingBoot启动过程二

⑽.在所有注册的bean中查找Listener bean，注册到事件派发器中

protected void registerListeners() {
        // Register statically specified listeners first.
        for (ApplicationListener<?> listener : getApplicationListeners()) {
            getApplicationEventMulticaster().addApplicationListener(listener);
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let post-processors apply to them!
        // 从容器中获取所有的事件监听器，添加到事件派发器
        String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
        for (String listenerBeanName : listenerBeanNames) {
            getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
        }

        // Publish early application events now that we finally have a multicaster...
        // 如果早期有些事件，则在此将其派发出去
        Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
        this.earlyApplicationEvents = null;
        if (earlyEventsToProcess != null) {
            for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
                getApplicationEventMulticaster().multicastEvent(earlyEvent);
            }
        }
    }

⑾.初始化剩下的单实例（非惰性）

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
            beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
        beanFactory.setConversionService(
                beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    }
    if (!beanFactory.hasEmbeddedValueResolver()) {
        beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    }
    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
        getBean(weaverAwareName);
    }
    beanFactory.setTempClassLoader(null);
    beanFactory.freezeConfiguration();

    // 实例化单实例bean
    beanFactory.preInstantiateSingletons();
}

@Override
public void preInstantiateSingletons() throws BeansException {
    if (logger.isDebugEnabled()) {
        logger.debug("Pre-instantiating singletons in " + this);
    }
    
    // 获取容器中所有的Bean，实例化
    List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
    for (String beanName : beanNames) {
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        // 如果不是抽象，是单实例，并且不是懒加载
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
        // 没有实现FactoryBean接口的Bean
            if (isFactoryBean(beanName)) {
                Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
                if (bean instanceof FactoryBean) {
                    final FactoryBean<?> factory = (FactoryBean<?>) bean;
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
                                        ((SmartFactoryBean<?>) factory)::isEagerInit,
                                getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
            }
            else {
                getBean(beanName);
            }
        }
    }

    // Trigger post-initialization callback for all applicable beans...
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {
            final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                    smartSingleton.afterSingletonsInstantiated();
                    return null;
                }, getAccessControlContext());
            }
            else {
                smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

首先判断Bean不是抽象，是单实例，不是懒加载，再判断Bean没有实现FactoryBean，则调用getBean()方法创建Bean

1 getBean方法创建Bean

@Override
public Object getBean(String name) throws BeansException {
    return doGetBean(name, null, null, false);
}

@SuppressWarnings("unchecked")
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
        @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {

    final String beanName = transformedBeanName(name);
    Object bean;

    // Eagerly check singleton cache for manually registered singletons.
    Object sharedInstance = getSingleton(beanName);
    if (sharedInstance != null && args == null) {
        if (logger.isDebugEnabled()) {
            if (isSingletonCurrentlyInCreation(beanName)) {
                logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
                        "' that is not fully initialized yet - a consequence of a circular reference");
            }
            else {
                logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
            }
        }
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    }    else {    
        ........省略
        // 如果实现了dependsOn则现将dependsOn创建出来
        String[] dependsOn = mbd.getDependsOn();
        if (dependsOn != null) {
            for (String dep : dependsOn) {
                if (isDependent(beanName, dep)) {
                    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                            "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
                }
                registerDependentBean(dep, beanName);
                try {
                    getBean(dep);
                }
                catch (NoSuchBeanDefinitionException ex) {
                    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                            "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
                }
            }
        }
        // 单实例Bean创建
        if (mbd.isSingleton()) {
            sharedInstance = getSingleton(beanName, () -> {
                try {
                    return createBean(beanName, mbd, args);
                }
                catch (BeansException ex) {
                    destroySingleton(beanName);
                    throw ex;
                }
            });
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
        }
    }
}

1.1 createBean

@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
        throws BeanCreationException {
....省略

    try {
    // 处理InstantiationAwareBeanPostProcessor类型的后置处理器
        Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
        if (bean != null) {
            return bean;
        }
    }
    catch (Throwable ex) {
    }

    try {
    // 创建Bean
        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }
    catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
    }
    catch (Throwable ex) {
    }
}

会先调用resolveBeforeInstantiation，判断当前后置处理器是否是InstantiationAwareBeanPostProcessor，如果是，则提前执行applyBeanPostProcessorsBeforeInstantiation，如果applyBeanPostProcessorsBeforeInstantiation方法返回的结果不是null，则执行applyBeanPostProcessorsAfterInitialization方法，如果最终结果不是null则直接返回不是则进行doCreateBean方法

protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
    Object bean = null;
    if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
        // Make sure bean class is actually resolved at this point.
        if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            Class<?> targetType = determineTargetType(beanName, mbd);
            if (targetType != null) {
            bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
                if (bean != null) {
                    bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
                }
            }
        }
        mbd.beforeInstantiationResolved = (bean != null);
    }
    return bean;
}

1.1.1 doCreateBean方法

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)throws BeanCreationException {
    BeanWrapper instanceWrapper = null;
    ....省略
    // 创建bean实例
    final Object bean = instanceWrapper.getWrappedInstance();
    ....省略
        
    synchronized (mbd.postProcessingLock) {
        if (!mbd.postProcessed) {
            try {
               // 触发后置处理器MergedBeanDefinitionPostProcessor
                applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
            }
            catch (Throwable ex) {
                throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                        "Post-processing of merged bean definition failed", ex);
            }
            mbd.postProcessed = true;
        }
    }
        ....省略
 
    Object exposedObject = bean;
    try {
        // 为bean属性赋值
        populateBean(beanName, mbd, instanceWrapper);
        exposedObject = initializeBean(beanName, exposedObject, mbd);
    }
}

创建Bean，触发后置处理器MergedBeanDefinitionPostProcessor，执行postProcessMergedBeanDefinition方法

1.1.1.1populateBean方法

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
    if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
        for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof InstantiationAwareBeanPostProcessor) {
                InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                    // 执行后置处理器InstantiationAwareBeanPostProcessor的postProcessAfterInstantiation方法
                if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
                    continueWithPropertyPopulation = false;
                    break;
                }
            }
        }
    }
        ....省略
        if (hasInstAwareBpps || needsDepCheck) {
        if (pvs == null) {
            pvs = mbd.getPropertyValues();
        }
        PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
        if (hasInstAwareBpps) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof InstantiationAwareBeanPostProcessor) {
                // 执行后置处理器InstantiationAwareBeanPostProcessor的postProcessPropertyValues方法
                    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                    pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                    if (pvs == null) {
                        return;
                    }
                }
            }
        }
        if (needsDepCheck) {
            checkDependencies(beanName, mbd, filteredPds, pvs);
        }
    }
    ....省略
// 为属性赋值
    if (pvs != null) {
        applyPropertyValues(beanName, mbd, bw, pvs);
    }
}

1.1.1.2 initializeBean方法

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
    if (System.getSecurityManager() != null) {
        AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
            invokeAwareMethods(beanName, bean);
            return null;
        }, getAccessControlContext());
    }
    else {
    // 处理Aware接口
        invokeAwareMethods(beanName, bean);
    }

    Object wrappedBean = bean;
    if (mbd == null || !mbd.isSynthetic()) {
    // 后置处理器触发postProcessBeforeInitialization方法
        wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
    }

    try {
    // 执行初始化方法
        invokeInitMethods(beanName, wrappedBean, mbd);
    }
    catch (Throwable ex) {
        throw new BeanCreationException(
                (mbd != null ? mbd.getResourceDescription() : null),
                beanName, "Invocation of init method failed", ex);
    }
    if (mbd == null || !mbd.isSynthetic()) {
        // 后置处理器触发postProcessAfterInitialization方法
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    }

    return wrappedBean;
}

其它：

SpringBoot_run()启动流程
SpringApplication实例初始化：
a)、根据classpath里面是否存在特征类（org.springframework.web.context.ConfigurableWebApplicationCobtext）来决定创建为web应用使用ApplicationContext类型，还是标准Standalone应用使用的ApplicationContext类型。
b)、使用SpringFactoriesLoader在classpath中查找并加载所有可用的ApplicationContextInitiazier
c)、使用SpringFactoriesLoader在classpath中查找并加载所有可用的ApplicationListener
d)、推断并main方法的定义类

SpringApplication实例初始化完成，遍历SpringFactoriesLoader可以找到并加载的SpringApplicationRunListnner，调用他们的start()方法。

创建并配置当前SpringBoot应用将要使用的Envrioment（包括配置要使用的PropertySource以及Profile）

遍历调用所有SpringApplicationRunListener的environmentPrepared()的方法——即通知【run监听器SpringBoot应用的使用环境已经搭建完成】

创建对应类型的ApplicationContext，根据条件决定是否添加ShutdownHook，决定是否使用自定义的BeanNameGenerator、ResourceLoader。将之前准备好的Enviroment设置给创建好的ApplicationContext使用

完成创建ApplicationContext，通过SpringFactoriesLoader查找并加载classpath中所有可用的ApplicationContextInitializer的Initialize（）方法来对ApplicationContext进行进一步的处理

遍历所有的SpringApplicationRunListenner的contextPrepared（）方法，通知【run监听器】ApplicationContext已经准备好了。

将之前通过@EnableAutoConfiguration获取的所有配置以及其他形式的IOC容器配置加载到已经准备完毕的ApplicationContext

遍历所有的SpringApplicationRunListener的contextLoaded（）方法，通知【run监听器和ApplicationContext装填完毕】

调用ApplicationContext的refresh（）——完成填充IOC容器

查找当前ApplicationContext中是否注册有CommandLineRunner，如果有，则遍历执行它们。

遍历执行SpringApplicationRunListener的finished（）。
——启动完毕
————————————————

原文链接：https://blog.csdn.net/hackerHL/article/details/78270780

原文链接：https://blog.csdn.net/u010811939/article/details/80592461