一文搞定 Spring Bean 的創(chuàng)建全過程！

1.1 Spring測試環(huán)境搭建

Spring模塊概覽，綠色是模塊，Spring中八大模塊，黑色表示該模塊包含的jar包（組件）。例如我們想要用IOC容器，也就是綠色的CoreContainer，我們需要導(dǎo)入Beans，Core,Context,SpEL（spring-expression）四個包。

Spring模塊概覽

• Test：測試相關(guān)
• Core Container：IOC容器
• AOP：面向切面編程
• Aspects：切面
• Instrumenttation：跟JDK關(guān)聯(lián)，一般不用
• Messaging：消息服務(wù)，一般不用
• Data Access/Integration：數(shù)據(jù)訪問與集成（JDBC訪問，Transaction事務(wù)，ORM對象關(guān)系映射，OXM和XML映射一般不用，JMS為Java消息服務(wù)Java-message-service一般不用）
• Web：Web服務(wù)（WebSocket網(wǎng)絡(luò)通信協(xié)議，Servlet, Web，Portlet一般不用）

最偷懶的方式，是直接導(dǎo)入Spring-Framework。但是可能導(dǎo)入不必要的包，導(dǎo)致項目打包后比較大

由于Spring-Content中的ApplicationContent是整個IOC的入口。我們導(dǎo)入Spring-context包即可

????org.springframework
????spring-context
????5.2.3.RELEASE

我們導(dǎo)入spring-content后，默認會導(dǎo)入該組件的依賴jar，spring-content底層的依賴可以看到，實際上我們是導(dǎo)入了Core Container模塊：

??
????
??????org.springframework
??????spring-aop
??????5.2.3.RELEASE
??????compile
????
????
??????org.springframework
??????spring-beans
??????5.2.3.RELEASE
??????compile
????
????
??????org.springframework
??????spring-core
??????5.2.3.RELEASE
??????compile
????
????
??????org.springframework
??????spring-expression
??????5.2.3.RELEASE
??????compile
????
??

新建Spring配置文件spring.xml：

"1.0"?encoding="UTF-8"?>
"http://www.springframework.org/schema/beans"
???????xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
???????xsi:schemaLocation="http://www.springframework.org/schema/beans?http://www.springframework.org/schema/beans/spring-beans.xsd">

????
????
????"hello"?class="com.xiaodai.service.Hello">
????????
????????"id"?value="1">
????????"name"?value="zhangsan">
????????"age"?value="18">
????

編寫測試類：

import?com.xiaodai.service.Hello;
import?org.springframework.context.ApplicationContext;
import?org.springframework.context.support.ClassPathXmlApplicationContext;

public?class?Test?{

????public?static?void?main(String[]?args)?{
????????ApplicationContext?applicationContext?=?new?ClassPathXmlApplicationContext("spring.xml");
????????Hello?hello?=?applicationContext.getBean("hello",?Hello.class);
????????System.out.println(hello.getName());

????}

}

1.2 Debug容器創(chuàng)建過程

從測試類的new ClassPathXmlApplicationContext("spring.xml")開始debug，進入ClassPathXmlApplicationContext，可以看到:

?public?ClassPathXmlApplicationContext(
???String[]?configLocations,?boolean?refresh,?@Nullable?ApplicationContext?parent)
???throws?BeansException?{

??super(parent);
??//?設(shè)置配置文件路徑
??setConfigLocations(configLocations);
??if?(refresh)?{
??????????//?核心步驟
???refresh();
??}
?}

加載配置文件后，進入refresh()方法，該方法是容器初始化的核心步驟。該方法包含十三個方法：

????????@Override
?public?void?refresh()?throws?BeansException,?IllegalStateException?{
??synchronized?(this.startupShutdownMonitor)?{
???//?Prepare?this?context?for?refreshing.
???/**?
????*?準備刷新，做一些最基本的準備化工作
???**/
???prepareRefresh();

???//?Tell?the?subclass?to?refresh?the?internal?bean?factory.
???/**?
????*?獲得一個刷新的bean容器，實質(zhì)就是獲取工廠。
????*?加載xml等配置文件，用該文件產(chǎn)生的BeanDefinition來創(chuàng)建一個工廠
???**/
???ConfigurableListableBeanFactory?beanFactory?=?obtainFreshBeanFactory();

???//?Prepare?the?bean?factory?for?use?in?this?context.
???/**
????*?準備bean工廠
???**/
???prepareBeanFactory(beanFactory);

???try?{
????//?Allows?post-processing?of?the?bean?factory?in?context?subclasses.
????//?后置增強，方便擴展
????postProcessBeanFactory(beanFactory);

????//?Invoke?factory?processors?registered?as?beans?in?the?context.
????//?實例化并且執(zhí)行BeanFactoryPostProcessors
????invokeBeanFactoryPostProcessors(beanFactory);

????//?Register?bean?processors?that?intercept?bean?creation.
????//?實例化并且注冊所有的BeanPostProcessor
????registerBeanPostProcessors(beanFactory);

????//?Initialize?message?source?for?this?context.
????//?國際化設(shè)置，一般用不到
????initMessageSource();

????//?Initialize?event?multicaster?for?this?context.
????//?初始化應(yīng)用程序的多波器和廣播器
????initApplicationEventMulticaster();

????//?Initialize?other?special?beans?in?specific?context?subclasses.
????//?空方法，預(yù)留給子類做擴展
????onRefresh();

????//?Check?for?listener?beans?and?register?them.
????//?注冊監(jiān)聽器
????registerListeners();

????//?Instantiate?all?remaining?(non-lazy-init)?singletons.
????//?工作中常用，面試常問。實例化所有非懶加載的實例對象
????finishBeanFactoryInitialization(beanFactory);

????//?Last?step:?publish?corresponding?event.
????//?完成刷新
????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();
???}
??}
?}

1.3 AbstractApplicationContext的refresh()包含的13個方法分析

結(jié)合概覽圖一個一個方法分析：

Bean工廠實例化Bean概覽圖

方法1：prepareRefresh() => 準備工作

準備刷新，做一些最基本的準備化工作

?protected?void?prepareRefresh()?{
??//?Switch?to?active.
??//?設(shè)置開始時間
??this.startupDate?=?System.currentTimeMillis();
??//?關(guān)閉狀態(tài)設(shè)置為false
??this.closed.set(false);
??//?活躍狀態(tài)設(shè)置為true
??this.active.set(true);

????????//?打印日志
??if?(logger.isDebugEnabled())?{
???if?(logger.isTraceEnabled())?{
????logger.trace("Refreshing?"?+?this);
???}
???else?{
????logger.debug("Refreshing?"?+?getDisplayName());
???}
??}

??//?Initialize?any?placeholder?property?sources?in?the?context?environment.
??//?初始化屬性資源
??initPropertySources();

??//?Validate?that?all?properties?marked?as?required?are?resolvable:
??//?see?ConfigurablePropertyResolver#setRequiredProperties
??//?獲取環(huán)境信息，驗證屬性信息
??getEnvironment().validateRequiredProperties();

??//?Store?pre-refresh
??//?存儲預(yù)刷新的一些應(yīng)用信息的監(jiān)聽器
??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...
??//?創(chuàng)建一些監(jiān)聽器事件的集合
??this.earlyApplicationEvents?=?new?LinkedHashSet<>();
?}

總結(jié)：1.設(shè)置啟動事件 2.設(shè)置關(guān)閉活躍的狀態(tài) 3.獲取環(huán)境對象并設(shè)置屬性值 4.設(shè)置監(jiān)聽器以及需要發(fā)布事件的集合。Spring的核心思想，總結(jié)得非常好！推薦看下。

重要的點：

• 獲取環(huán)境信息，驗證屬性信息，getEnvironment().validateRequiredProperties();
• 存儲預(yù)刷新的一些應(yīng)用信息的監(jiān)聽器，在Spring中是空實現(xiàn)，但是SpringBoot中，是有具體的值的

方法2：obtainFreshBeanFactory() => 獲得一個刷新的bean容器

獲得一個刷新的bean容器，實質(zhì)就是獲取工廠。創(chuàng)建容器對象DefaultListableBeanFactory;加載xml配置文件的屬性到當前的工廠中，最重要的就是BeanDefinition

Bean工廠實例繼承關(guān)系圖

AbstractRefreshableApplicationContext:

????//?只要進到這個方法，那么我們創(chuàng)建的一定是一個新的工廠
?@Override
?protected?final?void?refreshBeanFactory()?throws?BeansException?{
??if?(hasBeanFactory())?{
??????//?如果存在先銷毀，后關(guān)閉
???destroyBeans();
???closeBeanFactory();
??}
??try?{
??????//?創(chuàng)建bean工廠，這里使用的就是DefaultListableBeanFactory。此時創(chuàng)建的工廠里面的屬性值都是默認值
???DefaultListableBeanFactory?beanFactory?=?createBeanFactory();
???//?序列化id
???beanFactory.setSerializationId(getId());
???//?設(shè)置一些屬性值
???customizeBeanFactory(beanFactory);
???//?加載bean的定義屬性值。該方法有很多重載，非常復(fù)雜，核心是do操作
???//?完成配置文件或者配置類文件的加載
???loadBeanDefinitions(beanFactory);
???synchronized?(this.beanFactoryMonitor)?{
????this.beanFactory?=?beanFactory;
???}
??}
??catch?(IOException?ex)?{
???throw?new?ApplicationContextException("I/O?error?parsing?bean?definition?source?for?"?+?getDisplayName(),?ex);
??}
?}

方法3：prepareBeanFactory(beanFactory) => 準備（初始化）Bean工廠

為方法2拿到的工廠，設(shè)置某些具體的值

?protected?void?prepareBeanFactory(ConfigurableListableBeanFactory?beanFactory)?{
??//?Tell?the?internal?bean?factory?to?use?the?context's?class?loader?etc.
??//?為bean工廠設(shè)置類加載器
??beanFactory.setBeanClassLoader(getClassLoader());
??//?設(shè)置SPEL解析器
??beanFactory.setBeanExpressionResolver(new?StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
??beanFactory.addPropertyEditorRegistrar(new?ResourceEditorRegistrar(this,?getEnvironment()));

??//?Configure?the?bean?factory?with?context?callbacks.
??//?添加一個BeanPostProcessor
??beanFactory.addBeanPostProcessor(new?ApplicationContextAwareProcessor(this));
??//?忽略對應(yīng)接口的實現(xiàn)
??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.
????????//?注冊一些依賴
??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添加一個BeanPostProcessor增強器
??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.
??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());
??}
?}

方法4：postProcessBeanFactory(beanFactory) => 后置增強Bean(擴展實現(xiàn))

空方法，方便擴展

方法5：invokeBeanFactoryPostProcessors(beanFactory) => 執(zhí)行BFPP

實例化并且執(zhí)行BeanFactoryPostProcessors

?/**
??*?Instantiate?and?invoke?all?registered?BeanFactoryPostProcessor?beans,
??*?respecting?explicit?order?if?given.
??*?
Must?be?called?before?singleton?instantiation.
??*?單例對象之前一定調(diào)用，因為單例bean創(chuàng)建后就只有一份
??*/
?protected?void?invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory?beanFactory)?{
??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?&&?beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME))?{
???beanFactory.addBeanPostProcessor(new?LoadTimeWeaverAwareProcessor(beanFactory));
???beanFactory.setTempClassLoader(new?ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
??}
?}

方法6：registerBeanPostProcessors(beanFactory) => 注冊BPP

實例化并且注冊所有的BeanPostProcessor。實例化Bean之前的準備工作

?/**
??*?Instantiate?and?register?all?BeanPostProcessor?beans,
??*?respecting?explicit?order?if?given.
??*?
Must?be?called?before?any?instantiation?of?application?beans.
??*/
?protected?void?registerBeanPostProcessors(ConfigurableListableBeanFactory?beanFactory)?{
??PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory,?this);
?}

方法7：initMessageSource() => 國際化設(shè)置

方法8：initApplicationEventMulticaster() => 初始化應(yīng)用程序的多波器和廣播器

也屬于準備工作

方法9：onRefresh() => 預(yù)留給子類做擴展

空方法

方法10：registerListeners() => 注冊監(jiān)聽器

也屬于準備工作

?/**
??*?Add?beans?that?implement?ApplicationListener?as?listeners.
??*?Doesn't?affect?other?listeners,?which?can?be?added?without?being?beans.
??*/
?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!
??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...
??Set?earlyEventsToProcess?=?this.earlyApplicationEvents;
??this.earlyApplicationEvents?=?null;
??if?(earlyEventsToProcess?!=?null)?{
???for?(ApplicationEvent?earlyEvent?:?earlyEventsToProcess)?{
????getApplicationEventMulticaster().multicastEvent(earlyEvent);
???}
??}
?}

方法11：finishBeanFactoryInitialization(beanFactory) => 實例化所有單例對象

面試常問，工作常用。過程比較復(fù)雜

?/**
??*?Finish?the?initialization?of?this?context's?bean?factory,
??*?initializing?all?remaining?singleton?beans.
??*/
?protected?void?finishBeanFactoryInitialization(ConfigurableListableBeanFactory?beanFactory)?{
??//?Initialize?conversion?service?for?this?context.
??/**
???*?把類型轉(zhuǎn)化操作，設(shè)置到當前的beanFactory里面去
??**/
??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));
??}

??//?Register?a?default?embedded?value?resolver?if?no?bean?post-processor
??//?(such?as?a?PropertyPlaceholderConfigurer?bean)?registered?any?before:
??//?at?this?point,?primarily?for?resolution?in?annotation?attribute?values.
??/**
???*?判斷當前的beanFactory有沒有內(nèi)置的值處理器
??**/
??if?(!beanFactory.hasEmbeddedValueResolver())?{
???beanFactory.addEmbeddedValueResolver(strVal?->?getEnvironment().resolvePlaceholders(strVal));
??}

??//?Initialize?LoadTimeWeaverAware?beans?early?to?allow?for?registering?their?transformers?early.
??/**
???*?織入Aware
??**/
??String[]?weaverAwareNames?=?beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class,?false,?false);
??for?(String?weaverAwareName?:?weaverAwareNames)?{
???getBean(weaverAwareName);
??}

??//?Stop?using?the?temporary?ClassLoader?for?type?matching.
??//?設(shè)置類加載器
??beanFactory.setTempClassLoader(null);

??//?Allow?for?caching?all?bean?definition?metadata,?not?expecting?further?changes.
??/**
???*?凍結(jié)：某些bean不需要進行修改操作了，放入
??**/
??beanFactory.freezeConfiguration();

??//?Instantiate?all?remaining?(non-lazy-init)?singletons.
??/**
???*?實例化所有非懶加載的實例對象(重要)
??**/
??beanFactory.preInstantiateSingletons();
?}

實例化所有非懶加載的實例對象方法：

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

??//?Iterate?over?a?copy?to?allow?for?init?methods?which?in?turn?register?new?bean?definitions.
??//?While?this?may?not?be?part?of?the?regular?factory?bootstrap,?it?does?otherwise?work?fine.
??/**
???*?拿到所有注冊bean的名稱
???**/
??List?beanNames?=?new?ArrayList<>(this.beanDefinitionNames);

??//?Trigger?initialization?of?all?non-lazy?singleton?beans...
??//?循環(huán)去創(chuàng)建我們需要的單例對象
??for?(String?beanName?:?beanNames)?{
??????//?拿到bean的定義信息，就是我們在xml配置文件里面指定的一些屬性
???RootBeanDefinition?bd?=?getMergedLocalBeanDefinition(beanName);
???//?是否是抽象的，是否是單例的，是否是懶加載的
???if?(!bd.isAbstract()?&&?bd.isSingleton()?&&?!bd.isLazyInit())?{
???????//?判斷當前類是否實現(xiàn)了factoryBean接口。一般沒實現(xiàn)，直接進入下面的getBean
????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)
???????????((SmartFactoryBean)?factory)::isEagerInit,
?????????getAccessControlContext());
??????}
??????else?{
???????isEagerInit?=?(factory?instanceof?SmartFactoryBean?&&
?????????((SmartFactoryBean)?factory).isEagerInit());
??????}
??????if?(isEagerInit)?{
???????getBean(beanName);
??????}
?????}
????}
????else?{
????????//?通過beanName。拿到bean
?????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