Spring5源码解析3-refresh方法初探

接上回分析完register(annotatedClasses);后，现在来看一下refresh();方法。

// new AnnotationConfigApplicationContext(AppConfig.class); 源码
public AnnotationConfigApplicationContext(Class... annotatedClasses) {
    //调用默认无参构造器,里面有一大堆初始化逻辑
    this();

    //把传入的Class进行注册,Class既可以有@Configuration注解,也可以没有@Configuration注解
    //怎么注册? 委托给了 org.springframework.context.annotation.AnnotatedBeanDefinitionReader.register 方法进行注册
    // 传入Class 生成  BeanDefinition , 然后通过 注册到 BeanDefinitionRegistry
    register(annotatedClasses);

    //刷新容器上下文
    refresh();
}

refresh方法

点开refresh();方法，里面调用了超级多的方法，我们一个个来看。

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        //准备上下文,设置其启动日期和活动标志,执行属性源的初始化
        prepareRefresh();
    
        // Tell the subclass to refresh the internal bean factory.
        //调用子类 refreshBeanFactory()方法
        //获取 BeanFactory 实例 DefaultListableBeanFactory , DefaultListableBeanFactory 实现了 ConfigurableListableBeanFactory 接口
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    
        // Prepare the bean factory for use in this context.
        //配置 beanFactory 上下文
        //1.添加 ApplicationContextAwareProcessor 和 ApplicationListenerDetector
        //2.忽略部分类型的自动装配
        //3.注册特殊的依赖类型，并使用相应的autowired值
        //4.注册默认的environment beans
        //5.设置environment beans
        prepareBeanFactory(beanFactory);
    
        try {
            // Allows post-processing of the bean factory in context subclasses.
            //留给子类去扩展的一个方法
            postProcessBeanFactory(beanFactory);
    
            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);
    
            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);
    
            // Initialize message source for this context.
            initMessageSource();
    
            // Initialize event multicaster for this context.
            initApplicationEventMulticaster();
    
            // Initialize other special beans in specific context subclasses.
            onRefresh();
    
            // Check for listener beans and register them.
            registerListeners();
    
            // Instantiate all remaining (non-lazy-init) singletons.
            finishBeanFactoryInitialization(beanFactory);
    
            // Last step: publish corresponding event.
            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();
        }
    }
}

prepareRefresh();

prepareRefresh();做的事情比较简单：准备上下文，设置其启动日期和活动标志，执行属性源的初始化。

protected void prepareRefresh() {
    // Switch to active.
    this.startupDate = System.currentTimeMillis();
    this.closed.set(false);
    this.active.set(true);

    if (logger.isDebugEnabled()) {
        if (logger.isTraceEnabled()) {
            logger.trace("Refreshing " + this);
        } else {
            logger.debug("Refreshing " + getDisplayName());
        }
    }

    // Initialize any placeholder property sources in the context environment.
    //这是一个空方法,AnnotationConfigApplicationContext 并没有 Override 改方法
    initPropertySources();

    // Validate that all properties marked as required are resolvable:
    // see ConfigurablePropertyResolver#setRequiredProperties
    getEnvironment().validateRequiredProperties();

    // Store pre-refresh ApplicationListeners...
    if (this.earlyApplicationListeners == null) {
        //默认情况下,earlyApplicationListeners 为 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<>();
}

obtainFreshBeanFactory();

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    refreshBeanFactory();
    return getBeanFactory();
}

refreshBeanFactory(); 是一个抽象方法，它有两个具体是实现：

AnnotationConfigApplicationContext 继承 GenericApplicationContext，所以很显然此处执行的应该是GenericApplicationContext类中的方法。GenericApplicationContext的refreshBeanFactory()源码如下：

//GenericApplicationContext#refreshBeanFactory 源码
@Override
protected final void refreshBeanFactory() throws IllegalStateException {
    if (!this.refreshed.compareAndSet(false, true)) {
        throw new IllegalStateException(
                "GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
    }
    this.beanFactory.setSerializationId(getId());
}

obtainFreshBeanFactory();方法最后调用 getBeanFactory();方法，并且返回ConfigurableListableBeanFactory对象。

getBeanFactory();，顾名思义就是获取BeanFactory，Spring中使用的是 DefaultListableBeanFactory，该类也同时实现了ConfigurableListableBeanFactory接口。

prepareBeanFactory(beanFactory);

prepareBeanFactory(beanFactory);源码比较简单：

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    // Tell the internal bean factory to use the context's class loader etc.
    beanFactory.setBeanClassLoader(getClassLoader());
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

    // Configure the bean factory with context callbacks.
    //增加 BeanPostProcessor 实例 ApplicationContextAwareProcessor
    //ApplicationContextAwareProcessor 主要作用是对  Aware接口的支持,如果实现了相应的 Aware接口，则注入对应的资源
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

    //默认情况下，只忽略BeanFactoryAware接口,现在新增忽略如下类型的自动装配
    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.

    //注册自动装配规则,如果发现依赖特殊类型，就使用该指定值注入
    beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
    beanFactory.registerResolvableDependency(ResourceLoader.class, this);
    beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
    beanFactory.registerResolvableDependency(ApplicationContext.class, this);

    // Register early post-processor for detecting inner beans as ApplicationListeners.
    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.
    //注册默认的environment beans.
    if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
        // Environment
        beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
    }
    if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
        // System Properties
        beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
    }
    if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
        // System Environment
        beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
    }
}

ApplicationContextAwareProcessor

prepareBeanFactory(beanFactory);方法中往beanFactory中添加了一个ApplicationContextAwareProcessor对象：beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));。

ApplicationContextAwareProcessor类实现了BeanPostProcessor接口，其中主要是 Override 了postProcessBeforeInitialization方法，其作用主要是用来对 Aware系列接口的支持，发现Bean实现了Aware系列接口，就调用其相应的方法，具体为哪些Aware接口，请查看源码：

//ApplicationContextAwareProcessor#postProcessBeforeInitialization 源码
public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
    AccessControlContext acc = null;

    if (System.getSecurityManager() != null &&
            (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
                    bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
                    bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
        acc = this.applicationContext.getBeanFactory().getAccessControlContext();
    }

    if (acc != null) {
        AccessController.doPrivileged((PrivilegedAction