Spring應用上下文生命周期

2021 年 2 月 14 日
筆記
spring

Spring應用上下文生命周期整體分成四個階段

ConfigurableApplicationContext#refresh，載入或者刷新持久化配置
ConfigurableApplicationContext#start，啟動應用上下文
ConfigurableApplicationContext#stop，停止應用上下文
ConfigurableApplicationContext#close，關閉應用上下文，釋放鎖定資源

實際上refresh執行完成後Spring應用上下文從廣義上來說已經啟動了，start回調用LifeCycleProcessors的start方法，可以理解refresh處理Spring應用上下文啟動需要的東西，start相當於是一個擴展，close和stop是和refresh和close類似的逆向操作。

因此Spring應用上下文生命周期重頭戲是refresh和close兩個方法對應的實現。

refresh-刷新應用上下文

整個refresh階段程式碼如下所示:

從程式碼可以看出，refresh整體分為以下幾個階段:

準備刷新階段: prepareRefresh
BeanFactory創建階段: obtainFreshBeanFactory
BeanFactory準備階段: prepareBeanFactory
BeanFactory後置處理階段: postProcessBeanFactory、invokeBeanFactoryPostProcessors
BeanFactory註冊BeanPostProcessor階段: registerBeanPostProcessors
初始化內建Bean: initMessageSource、initApplicationEventMulticaster
Spring應用上下文刷新階段: onRefresh
Spring事件監聽器註冊階段: registerListener
BeanFactory初始化完成階段: finishBeanFactoryInitialization
Spring應用上下文刷新完成階段: finishRefresh

準備刷新階段

prepareRefresh方法注釋如下所示，可以看出，這個方法主要做了三件事來準備上下文刷新:

設置啟動時間
設置激活標
執行任何初始化屬性來源

    protected void prepareRefresh() {
        //設置啟動時間、激活標
        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());
            }
        }

        //初始化屬性源，擴展用
        initPropertySources();

        //校驗必要屬性
        getEnvironment().validateRequiredProperties();

        //創建存儲早期applicationListeners容器
        if (this.earlyApplicationListeners == null) {
            this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
        }
        else {
            this.applicationListeners.clear();
            this.applicationListeners.addAll(this.earlyApplicationListeners);
        }

        //創建存儲早期applicationEvents容器，存儲早期Spring Application事件，用於後面applicationEventMulticaster發布事件用
        this.earlyApplicationEvents = new LinkedHashSet<>();
    }

BeanFactory創建階段

在AbstractRefreshableApplicationContext的refreshBeanFactory實現里，會對這個應用上下文的底層BeanFactory做一個刷新，如果之前有BeanFactory，會先停止，再初始化一個新的BeanFactory

    protected final void refreshBeanFactory() throws BeansException {
　　　　 //如果有BeanFactory，先關掉這個BeanFactory　　
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {
　　　　　　  //創建新的BeanFactory
            DefaultListableBeanFactory beanFactory = createBeanFactory();
　　　　　　  //設置BeanFactory的id
            beanFactory.setSerializationId(getId());
　　　　　　  //設置是否允許BeanDefinition覆蓋、是否允許循環依賴
            customizeBeanFactory(beanFactory);
　　　　　　  //載入BeanDefinition
            loadBeanDefinitions(beanFactory);
　　　　　　  //設置新的BeanFactory為當前應用上下文IoC容器
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

BeanFactory準備階段

配置容器上下文特徵，例如上下文的ClassLoader和後置處理器。

    protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        //設置容器使用的類載入器: ClassLoader，默認是執行緒上下文類設置的載入器
        beanFactory.setBeanClassLoader(getClassLoader());
　　　　 //設置Bean表達式處理器，指定bean definition中的表達是值的解析策略
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
　　　　 //添加PropertyEditorRegistrar實現，存儲ResourceLoader和PropertyResolver
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

        //添加BeanPostProcessor實現，用於處理ApplicationContext的Aware回調
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
　　　　 //忽略指定介面作為依賴注入介面
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

        //註冊ResolvableDependency，這部分可以被依賴注入但不能被依賴查找
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);

        //註冊ApplicationListener探測器，如果一個Bean實現了ApplicationListener介面會被當作ApplicationListener註冊到Publisher
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

        //註冊動態織入後置處理器
        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()));
        }

        //註冊環境Bean單例對象
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
            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());
        }
    }

BeanFactory後置處理階段

postProcessBeanFactory和invokeBeanFactoryPostProcessors都是Spring提供的擴展方式。

postProcessBeanFactory在AbstractApplicationContext里沒有實際實現，postProcessBeanFactory注釋如下:

可以看出這時Spring應用上下文內部BeanFactory已經標準初始化完成，這時所有Bean的BeanDefinition已經被載入進來，但是還沒有被實例化，這時允許繼承類註冊特殊的BeanPostProcessors等內容。

invokeBeanFactoryPostProcessors方法注釋如下:

這個方法會實例化並且執行所有被註冊的BeanFactoryPostProcessor的Bean，如果給定顯示順序，按顯示順序執行，invokeBeanFactoryPostProcessors程式碼如下:

    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
　　　　 //處理BeanFactoryPostProcessors，這裡細節挺多的，要按一定順序執行BeanDefinitionRegistryPostProcessor#postProcessBeanDefinitionRegistry和BeanFactoryPostProcessor#postProcessBeanFactory
        PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

        //添加LoadTimeWeaverAwareProcessor
        if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
    }

BeanFactory註冊BeanPostProcessor

registerBeanPostProcessors方法注釋如下:

這個方法的作用就是實例化並且註冊所有BeanPostProcessor的Bean，會按給定順序註冊。

這裡註冊的順序是:

先註冊實現PriorityOrdered的BeanPostProcessor的Bean
再註冊實現Ordered的BeanPostProcessor的Bean
然後註冊普通的BeanPostProcessor的Bean
後面註冊MergedBeanDefinitionPostProcess的Bean
最後註冊ApplicationListenerDetector的Bean

初始化內建Bean

初始化內建Bean會初始化兩個Bean: MessageSource和ApplicationEventMulticaster。

這兩個實現比較類似，都是判斷當前BeanFactory(不判斷父BeanFactory)是否包含對應Bean，如果不包含，就創建並且用registerSingleton方法註冊到BeanFactory。

Spring應用上下文刷新階段

onRefresh方法注釋如下所示:

onRefresh方法是個可以被子類覆蓋的模板方法，可以在實例化單例前初始化特殊的Bean。

Spring事件監聽器註冊階段

registerListeners方法注釋如下所示:

registerListeners方法會把實現ApplicationListener的Bean和非Bean對象註冊到ApplicationEventMulticaster。

registerListeners方法程式碼如下:

    protected void registerListeners() {
        //註冊非Bean的ApplicationListener實現類的對象
        for (ApplicationListener<?> listener : getApplicationListeners()) {
            getApplicationEventMulticaster().addApplicationListener(listener);
        }

        //註冊ApplicationListener實現類對應的Bean
        String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
        for (String listenerBeanName : listenerBeanNames) {
            getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
        }

        //發送早期ApplicationEvent事件
        Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
        this.earlyApplicationEvents = null;
        if (earlyEventsToProcess != null) {
            for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
                getApplicationEventMulticaster().multicastEvent(earlyEvent);
            }
        }
    }

BeanFactory初始化完成階段

finishBeanFactoryInitialization方法注釋如下所示:

這個方法會結束Spring應用上下文的BeanFactory的初始化，初始化所有剩餘的單例Bean。

finishBeanFactoryInitialization方法程式碼如下所示:

    protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        //如果BeanFactory有ConversionService對象，關聯到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));
        }

        //添加StringValueResolver對象
        if (!beanFactory.hasEmbeddedValueResolver()) {
            beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
        }

        //依賴查找LoadTimeWeaverAware的Bean
        String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
        for (String weaverAwareName : weaverAwareNames) {
            getBean(weaverAwareName);
        }

        //BeanFactory臨時ClassLoader置為null
        beanFactory.setTempClassLoader(null);

        //BeanFactory凍結配置
        beanFactory.freezeConfiguration();

        //實例化所有不是懶載入的單例對象
        beanFactory.preInstantiateSingletons();
    }

Spring應用上下文刷新完成階段

finishRefresh方法注釋如下所示:

finishRefresh方法結束Spring應用上下文刷新，調用LifecycleProcessor#onRefresh方法並且發送ContextRefreshedEvent。

finishRefresh方法程式碼如下所示:

    protected void finishRefresh() {
        //清除ResourceLoader快取
        clearResourceCaches();

        //初始化LifecycleProcessor對象
        initLifecycleProcessor();

        //調用LifecycleProcessor#onRefresh方法
        getLifecycleProcessor().onRefresh();

        //發布Spring應用上下文已刷新事件
        publishEvent(new ContextRefreshedEvent(this));

        //向MBeanServer託管Live Bean
        LiveBeansView.registerApplicationContext(this);
    }

start-啟動應用上下文

start方法程式碼如下所示:

    public void start() {
　　　　 //啟動LifecycleProcessor
        getLifecycleProcessor().start();
　　　　 //發布應用上下文啟動事件
        publishEvent(new ContextStartedEvent(this));
    }

stop-停止應用上下文

stop方法程式碼如下所示:

    public void stop() {
　　　　 //停止LifecycleProcessor
        getLifecycleProcessor().stop();
　　　　 //發布應用上下文停止事件
        publishEvent(new ContextStoppedEvent(this));
    }

close-關閉應用上下文

    protected void doClose() {
        //檢查激活標
        if (this.active.get() && this.closed.compareAndSet(false, true)) {
            if (logger.isDebugEnabled()) {
                logger.debug("Closing " + this);
            }
　　　　　　  //Live Bean註銷託管
            LiveBeansView.unregisterApplicationContext(this);

            try {
                //發布Spring應用上下文已關閉事件
                publishEvent(new ContextClosedEvent(this));
            }
            catch (Throwable ex) {
                logger.warn("Exception thrown from ApplicationListener handling ContextClosedEvent", ex);
            }

            //關閉LifecycleProcessor
            if (this.lifecycleProcessor != null) {
                try {
                    this.lifecycleProcessor.onClose();
                }
                catch (Throwable ex) {
                    logger.warn("Exception thrown from LifecycleProcessor on context close", ex);
                }
            }

            //銷毀Spring Bean
            destroyBeans();

            //關閉BeanFactory
            closeBeanFactory();

            //回調onClose
            onClose();

            //重置本地監聽者
            if (this.earlyApplicationListeners != null) {
                this.applicationListeners.clear();
                this.applicationListeners.addAll(this.earlyApplicationListeners);
            }

            //激活標設置為沒激活
            this.active.set(false);
        }
    }

Tags: spring