springboot系列之启动流程

Springboot简介

springboot封装了Spring组件，基于约定优于配置。提升了开发效率，本文主要讲解springboot框架的启动过程。

启动流程分析

1、首先，我们看一下启动类SpringApplication,它是位于org.springframework.boot包下面的。项目启动类源码

@SpringBootApplication
public class Application {

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

}

这里用到了SpringBootApplication注解，然后在main方法中启动boot应用。

2、我们接下来看看SpringBootApplication注解的源码

@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 {
    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return the classes to exclude
     */
    @AliasFor(annotation = EnableAutoConfiguration.class)
    Class<!--?-->[] exclude() default {};
    /**
     * Exclude specific auto-configuration class names such that they will never be
     * applied.
     * @return the class names to exclude
     * @since 1.3.0
     */
    @AliasFor(annotation = EnableAutoConfiguration.class)
    String[] excludeName() default {};
    /**
     * Base packages to scan for annotated components. Use {@link #scanBasePackageClasses}
     * for a type-safe alternative to String-based package names.
     * @return base packages to scan
     * @since 1.3.0
     */
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
    String[] scanBasePackages() default {};
    /**
     * Type-safe alternative to {@link #scanBasePackages} for specifying the packages to
     * scan for annotated components. The package of each class specified will be scanned.
     * <p>
     * Consider creating a special no-op marker class or interface in each package that
     * serves no purpose other than being referenced by this attribute.
     * @return base packages to scan
     * @since 1.3.0
     */
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
    Class<!--?-->[] scanBasePackageClasses() default {};
}

它是位于org.springframework.boot.autoconfigure包下面的。我们可以看到它依赖了几个重要的注解SpringBootConfiguration、EnableAutoConfiguration、ComponentScan这三个注解。其中EnableAutoConfiguration就是springboot自动配置用到的类，在接下来我们将会重点介绍。

3、我们在看SpringApplication运行的run方法

    /**
     * Static helper that can be used to run a {@link SpringApplication} from the
     * specified sources using default settings and user supplied arguments.
     * @param primarySources the primary sources to load
     * @param args the application arguments (usually passed from a Java main method)
     * @return the running {@link ApplicationContext}
     */
    public static ConfigurableApplicationContext run(Class<!--?-->[] primarySources, String[] args) {
        return new SpringApplication(primarySources).run(args);
    }

首先，创建SpringApplication应用对象，然后调用run方法传入启动参数

    public SpringApplication(ResourceLoader resourceLoader, Class<!--?-->... primarySources) {
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet&lt;&gt;(Arrays.asList(primarySources));
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = deduceMainApplicationClass();
    }


    this.webApplicationType = WebApplicationType.deduceFromClasspath();
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = deduceMainApplicationClass();

这是创建对象的方法，先校验启动类，然后调用deduceFromClasspath方法推断一个应用类型（是否是web项目）初始化工厂类，设置Spring监听器（观察者模式）。

4、创建好对象后，我们接着看run方法

/**
     * Run the Spring application, creating and refreshing a new
     * {@link ApplicationContext}.
     * @param args the application arguments (usually passed from a Java main method)
     * @return a running {@link ApplicationContext}
     */
    public ConfigurableApplicationContext run(String... args) {
        //开启系统启动时间监听        
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        //创建一场报告集合
        Collection<springbootexceptionreporter> exceptionReporters = new ArrayList&lt;&gt;();
        //配置检测无显示器也可以启动
        configureHeadlessProperty();
        //获取运行监听器，获取事件发布监听
        SpringApplicationRunListeners listeners = getRunListeners(args);
        //启动监听器
        listeners.starting();
        try {
            //通过启动参数构建应用参数
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //创建上线文环境
            ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
            //配置忽略的bean信息
            configureIgnoreBeanInfo(environment);
            //打印boot启动logo
            Banner printedBanner = printBanner(environment);
            //创建上线文（容器）
            context = createApplicationContext();
            //获取异常集合
            exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, context);
            //准备上下文
            prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            //刷新上下文（重点）
            refreshContext(context);
            //刷新之后
            afterRefresh(context, applicationArguments);
            //关闭系统时间监听
            stopWatch.stop();
            //打印日志
            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;
    }

我们只看几个重要的方法，首先看createApplicationContext()创建上下文（容器）方法

    /**
     * Strategy method used to create the {@link ApplicationContext}. By default this
     * method will respect any explicitly set application context or application context
     * class before falling back to a suitable default.
     * @return the application context (not yet refreshed)
     * @see #setApplicationContextClass(Class)
     */
    protected ConfigurableApplicationContext createApplicationContext() {
        //获取启动类
        Class<!--?--> contextClass = this.applicationContextClass;
        //推断上下文类型，默认web类型，
        if (contextClass == null) {
            try {
                switch (this.webApplicationType) {
                case SERVLET:
                    contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
                    break;
                //flux类型上下文
                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);
            }
        }
        //实例化上下文，容器
        return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
    }

我们在看，prepareContext(context, environment, listeners, applicationArguments, printedBanner);准备上下文方法

    private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
            SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
        //设置上下文环境        
        context.setEnvironment(environment);
        //处理应用上下文
        postProcessApplicationContext(context);
        //应用初始化类
        applyInitializers(context);
        //监听器准备上下文
        listeners.contextPrepared(context);
        if (this.logStartupInfo) {
            logStartupInfo(context.getParent() == null);
            logStartupProfileInfo(context);
        }
        // Add boot specific singleton beans
        //创建bean工厂
        ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        //注册应用参数bean                        
        beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
        if (printedBanner != null) {
            beanFactory.registerSingleton("springBootBanner", printedBanner);
        }
        if (beanFactory instanceof DefaultListableBeanFactory) {
            ((DefaultListableBeanFactory) beanFactory)
                    .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
        }
        // Load the sources
        Set<object> sources = getAllSources();
        Assert.notEmpty(sources, "Sources must not be empty");
        load(context, sources.toArray(new Object[0]));
        listeners.contextLoaded(context);
    }

在看、重要的refreshContext(context);刷新上下文方法重点

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

点进去refresh(context);方法进入

    /**
     * Refresh the underlying {@link ApplicationContext}.
     * @param applicationContext the application context to refresh
     */
    protected void refresh(ApplicationContext applicationContext) {
        Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
        ((AbstractApplicationContext) applicationContext).refresh();
    }

类型转换为AbstractApplicationContext，继续看refresh方法

@Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            //准备刷新
            prepareRefresh();
            // 刷新子类工厂
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
            // 准备beanFactory
            prepareBeanFactory(beanFactory);
            try {
                // 处理bean工厂
                postProcessBeanFactory(beanFactory);
                // 调用bean共产处理器重点
            invokeBeanFactoryPostProcessors(beanFactory);
                // 注册bean工厂处理器
            registerBeanPostProcessors(beanFactory);
                // 初始化消息类
                initMessageSource();
                // 初始化应用事件广播
                initApplicationEventMulticaster();
                // 正在刷新的
                onRefresh();
                // 发布事件监听器
                registerListeners();
                // 完成bean工厂注册
            finishBeanFactoryInitialization(beanFactory);
                // 完成事件刷新
                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();
            }
        }
    }

我们在看prepareRefresh准备刷新方法

/**
     * Prepare this context for refreshing, setting its startup date and
     * active flag as well as performing any initialization of property sources.
     */
    protected void prepareRefresh() {
        // 启动应用开关
        this.startupDate = System.currentTimeMillis();
        this.closed.set(false);
        //设置启动状态
        this.active.set(true);
        if (logger.isDebugEnabled()) {
            if (logger.isTraceEnabled()) {
                logger.trace("Refreshing " + this);
            }
            else {
                logger.debug("Refreshing " + getDisplayName());
            }
        }

        // 初始化属性类
        initPropertySources();
        // 校验属性
        // see ConfigurablePropertyResolver#setRequiredProperties
        getEnvironment().validateRequiredProperties();
        // Store pre-refresh ApplicationListeners...
        if (this.earlyApplicationListeners == null) {
            this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
        }
        else {
            // Reset local application listeners to pre-refresh state.
            this.applicationListeners.clear();
            this.applicationListeners.addAll(this.earlyApplicationListeners);
        }

        // Allow for the collection of early ApplicationEvents,
        // to be published once the multicaster is available...
        this.earlyApplicationEvents = new LinkedHashSet<>();
    }

在看prepareBeanFactory准备配置工厂方法

/**
     * Configure the factory's standard context characteristics,
     * such as the context's ClassLoader and post-processors.
     * @param beanFactory the BeanFactory to configure
     */
    protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // 设置类加载器
        beanFactory.setBeanClassLoader(getClassLoader());
        //设置bean表达式处理
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        //设置属性编辑器注册
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

        // 配置bean处理器，后置处理
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

        // BeanFactory interface not registered as resolvable type in a plain factory.
        // MessageSource registered (and found for autowiring) as a bean.
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);

        // 添加事件监听处理器
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

        // Detect a LoadTimeWeaver and prepare for weaving, if found.
        if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            // Set a temporary ClassLoader for type matching.
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }

        // Register default environment beans.
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
    //注册环境bean        beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
        }
    }

在看postProcessBeanFactory(beanFactory);处理工厂类（子类）

在ServletWebServerApplicationContext类中实现了这个方法
    @Override
    protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        beanFactory.addBeanPostProcessor(new WebApplicationContextServletContextAwareProcessor(this));
        beanFactory.ignoreDependencyInterface(ServletContextAware.class);
        registerWebApplicationScopes();
    }

在看invokeBeanFactoryPostProcessors(beanFactory);调用bean工厂处理器方法

    /**
     * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
     * respecting explicit order if given.
     * <p>Must be called before singleton instantiation.
     */
    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
//处理工厂类代表    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 &amp;&amp; beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
    }

点进去看看

public static void invokeBeanFactoryPostProcessors(
            ConfigurableListableBeanFactory beanFactory, List<beanfactorypostprocessor> beanFactoryPostProcessors) {

        // Invoke BeanDefinitionRegistryPostProcessors first, if any.
        Set<string> processedBeans = new HashSet&lt;&gt;();

        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            List<beanfactorypostprocessor> regularPostProcessors = new ArrayList&lt;&gt;();
            List<beandefinitionregistrypostprocessor> registryProcessors = new ArrayList&lt;&gt;();

            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&lt;&gt;();

            // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            for (String ppName : postProcessorNames) {
                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();

            // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            for (String ppName : postProcessorNames) {
                if (!processedBeans.contains(ppName) &amp;&amp; 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.
            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.
            invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
            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&lt;&gt;();
        List<string> orderedPostProcessorNames = new ArrayList&lt;&gt;();
        List<string> nonOrderedPostProcessorNames = new ArrayList&lt;&gt;();
        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&lt;&gt;();
        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&lt;&gt;();
        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();
    }

点进去invokeBeanFactoryPostProcessors方法

    /**
     * Invoke the given BeanFactoryPostProcessor beans.
     */
    private static void invokeBeanFactoryPostProcessors(
            Collection<!--? extends BeanFactoryPostProcessor--> postProcessors, ConfigurableListableBeanFactory beanFactory) {

        for (BeanFactoryPostProcessor postProcessor : postProcessors) {
            postProcessor.postProcessBeanFactory(beanFactory);
        }
    }

点击postProcessBeanFactory(beanFactory);找到实现类

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        int factoryId = System.identityHashCode(beanFactory);
        if (this.factoriesPostProcessed.contains(factoryId)) {
            throw new IllegalStateException(
                    "postProcessBeanFactory already called on this post-processor against " + beanFactory);
        }
        this.factoriesPostProcessed.add(factoryId);
        if (!this.registriesPostProcessed.contains(factoryId)) {
            // BeanDefinitionRegistryPostProcessor hook apparently not supported...
            // Simply call processConfigurationClasses lazily at this point then.
            processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);
        }

        enhanceConfigurationClasses(beanFactory);
        beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
    }

点击processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);方法找到

// Parse each @Configuration class
        ConfigurationClassParser parser = new ConfigurationClassParser(
                this.metadataReaderFactory, this.problemReporter, this.environment,
                this.resourceLoader, this.componentScanBeanNameGenerator, registry);

        Set<beandefinitionholder> candidates = new LinkedHashSet&lt;&gt;(configCandidates);
        Set<configurationclass> alreadyParsed = new HashSet&lt;&gt;(configCandidates.size());
        do {
            parser.parse(candidates);
            parser.validate();

            Set<configurationclass> configClasses = new LinkedHashSet&lt;&gt;(parser.getConfigurationClasses());
            configClasses.removeAll(alreadyParsed);

继续找parse方法,找到ConfigurationClassParser类这个方法，接着找

    @Nullable
    protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
            throws IOException {

// Process any @Import annotations processImports(configClass, sourceClass, getImports(sourceClass), true);

    // Process any @ImportResource annotations
    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](https://my.oschina.net/bean) methods
    Set<methodmetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
    for (MethodMetadata methodMetadata : beanMethods) {
        configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
    }

    // Process default methods on interfaces
    processInterfaces(configClass, sourceClass);

    // Process superclass, if any
    if (sourceClass.getMetadata().hasSuperClass()) {
        String superclass = sourceClass.getMetadata().getSuperClassName();
        if (superclass != null &amp;&amp; !superclass.startsWith("java") &amp;&amp;
                !this.knownSuperclasses.containsKey(superclass)) {
            this.knownSuperclasses.put(superclass, configClass);
            // Superclass found, return its annotation metadata and recurse
            return sourceClass.getSuperClass();
        }
    }

    // No superclass -&gt; processing is complete
    return null;


我们找到processImports的处理地方


this.importStack.push(configClass);
        try {
            for (SourceClass candidate : importCandidates) {
                if (candidate.isAssignable(ImportSelector.class)) {
                    // Candidate class is an ImportSelector -&gt; delegate to it to determine imports
                    Class<!--?--> candidateClass = candidate.loadClass();
                    ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);
                    ParserStrategyUtils.invokeAwareMethods(
                            selector, this.environment, this.resourceLoader, this.registry);
                    if (selector instanceof DeferredImportSelector) {
                        this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
                    }
                    else {
                        String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
                        Collection<sourceclass> importSourceClasses = asSourceClasses(importClassNames);
                        processImports(configClass, currentSourceClass, importSourceClasses, false);
                    }
                }
                else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
                    // Candidate class is an ImportBeanDefinitionRegistrar -&gt;
                    // delegate to it to register additional bean definitions
                    Class<!--?--> candidateClass = candidate.loadClass();
                    ImportBeanDefinitionRegistrar registrar =
                            BeanUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class);
                    ParserStrategyUtils.invokeAwareMethods(
                            registrar, this.environment, this.resourceLoader, this.registry);
                    configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
                }
                else {
                    // Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar -&gt;
                    // process it as an [@Configuration](https://my.oschina.net/pointdance) class
                    this.importStack.registerImport(
                            currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
                    processConfigurationClass(candidate.asConfigClass(configClass));
                }
            }
        }


ImportSelector接口处理的地方，自动配置外部bean的方法

接下来，看registerBeanPostProcessors(beanFactory);注册bean处理器工厂

然后，看onRefresh方法


[@Override](https://my.oschina.net/u/1162528)
protected void onRefresh() {
    super.onRefresh();
    try {
        createWebServer();
    }
    catch (Throwable ex) {
        throw new ApplicationContextException("Unable to start web server", ex);
    }
}


在这里创建web容器
完成刷新，应用启动完成，还有细节结下来在细说。

有问题，请留言！ 个人博客地址