1.1 Spring 测试环境搭建
Spring 模块概览，绿色是模块，Spring 中八大模块，彩色示意该模块蕴含的 jar 包（组件）。例如咱们想要用 IOC 容器，也就是绿色的 CoreContainer，咱们须要导入 Beans，Core,Context,SpEL（spring-expression）四个包。
Spring 模块概览
- Test：测试相干
- Core Container：IOC 容器
- AOP：面向切面编程
- Aspects：切面
- Instrumenttation：跟 JDK 关联，个别不必
- Messaging：音讯服务，个别不必
- Data Access/Integration：数据拜访与集成（JDBC 拜访，Transaction 事务，ORM 对象关系映射，OXM 和 XML 映射个别不必，JMS 为 Java 音讯服务 Java-message-service 个别不必）
- Web：Web 服务（WebSocket 网络通信协定，Servlet, Web，Portlet 个别不必）
最偷懒的形式，是间接导入 Spring-Framework。然而可能导入不必要的包，导致我的项目打包后比拟大
因为 Spring-Content 中的 ApplicationContent 是整个 IOC 的入口。咱们导入 Spring-context 包即可
<!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.2.3.RELEASE</version>
</dependency>咱们导入 spring-content 后，默认会导入该组件的依赖 jar，spring-content 底层的依赖能够看到，实际上咱们是导入了 Core Container 模块：
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
<version>5.2.3.RELEASE</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>5.2.3.RELEASE</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>5.2.3.RELEASE</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-expression</artifactId>
<version>5.2.3.RELEASE</version>
<scope>compile</scope>
</dependency>
</dependencies>新建 Spring 配置文件 spring.xml：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="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">
<!-- 注册一个对象，spring 回主动创立这个对象 -->
<!--
一个 bean 标签就示意一个对象
id: 这个对象的惟一标识
class: 注册对象的齐全限定名
-->
<bean id="hello" class="com.xiaodai.service.Hello">
<!-- 应用 property 标签给对象的属性赋值
name: 示意属性的名称
value：示意属性的值
-->
<property name="id" value="1"></property>
<property name="name" value="zhangsan"></property>
<property name="age" value="18"></property>
</bean>
</beans>编写测试类：
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 容器创立过程
从测试类的 new ClassPathXmlApplicationContext(“spring.xml”) 开始 debug，进入 ClassPathXmlApplicationContext，能够看到:
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {super(parent);
// 设置配置文件门路
setConfigLocations(configLocations);
if (refresh) {
// 外围步骤
refresh();}
}加载配置文件后，进入 refresh() 办法，该办法是容器初始化的外围步骤。该办法蕴含十三个办法：
@Override
public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
/**
* 筹备刷新，做一些最根本的筹备化工作
**/
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
/**
* 取得一个刷新的 bean 容器，本质就是获取工厂。* 加载 xml 等配置文件，用该文件产生的 BeanDefinition 来创立一个工厂
**/
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
/**
* 筹备 bean 工厂
**/
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// 后置加强，不便扩大
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 实例化并且执行 BeanFactoryPostProcessors
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 实例化并且注册所有的 BeanPostProcessor
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
// 国际化设置，个别用不到
initMessageSource();
// Initialize event multicaster for this context.
// 初始化应用程序的多波器和播送器
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 空办法，预留给子类做扩大
onRefresh();
// Check for listener beans and register them.
// 注册监听器
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// 工作中罕用，面试常问。实例化所有非懒加载的实例对象
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// 实现刷新
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() 蕴含的 13 个办法剖析
联合概览图一个一个办法剖析：
Bean 工厂实例化 Bean 概览图
办法 1：prepareRefresh() => 筹备工作
筹备刷新，做一些最根本的筹备化工作
protected void prepareRefresh() {
// Switch to active.
// 设置开始工夫
this.startupDate = System.currentTimeMillis();
// 敞开状态设置为 false
this.closed.set(false);
// 沉闷状态设置为 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.
// 初始化属性资源
initPropertySources();
// Validate that all properties marked as required are resolvable:
// see ConfigurablePropertyResolver#setRequiredProperties
// 获取环境信息，验证属性信息
getEnvironment().validateRequiredProperties();
// Store pre-refresh
// 存储预刷新的一些利用信息的监听器
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...
// 创立一些监听器事件的汇合
this.earlyApplicationEvents = new LinkedHashSet<>();}总结：1. 设置启动事件 2. 设置敞开沉闷的状态 3. 获取环境对象并设置属性值 4. 设置监听器以及须要公布事件的汇合
重要的点：
- 获取环境信息，验证属性信息，getEnvironment().validateRequiredProperties();
- 存储预刷新的一些利用信息的监听器，在 Spring 中是空实现，然而 SpringBoot 中，是有具体的值的
办法 2：obtainFreshBeanFactory() => 取得一个刷新的 bean 容器
取得一个刷新的 bean 容器，本质就是获取工厂。创立容器对象 DefaultListableBeanFactory; 加载 xml 配置文件的属性到以后的工厂中，最重要的就是 BeanDefinition
Bean 工厂实例继承关系图
AbstractRefreshableApplicationContext:
// 只有进到这个办法，那么咱们创立的肯定是一个新的工厂
@Override
protected final void refreshBeanFactory() throws BeansException {if (hasBeanFactory()) {
// 如果存在先销毁，后敞开
destroyBeans();
closeBeanFactory();}
try {
// 创立 bean 工厂，这里应用的就是 DefaultListableBeanFactory。此时创立的工厂外面的属性值都是默认值
DefaultListableBeanFactory beanFactory = createBeanFactory();
// 序列化 id
beanFactory.setSerializationId(getId());
// 设置一些属性值
customizeBeanFactory(beanFactory);
// 加载 bean 的定义属性值。该办法有很多重载，非常复杂，外围是 do 操作
// 实现配置文件或者配置类文件的加载
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {this.beanFactory = beanFactory;}
}
catch (IOException ex) {throw new ApplicationContextException("I/O error parsing bean definition source for" + getDisplayName(), ex);
}
}办法 3：prepareBeanFactory(beanFactory) => 筹备（初始化）Bean 工厂
为办法 2 拿到的工厂，设置某些具体的值
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
// 为 bean 工厂设置类加载器
beanFactory.setBeanClassLoader(getClassLoader());
// 设置 SPEL 解析器
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
// 增加一个 BeanPostProcessor
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
// 疏忽对应接口的实现
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.
// 注册一些依赖
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 增加一个 BeanPostProcessor 增强器
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());
}
}办法 4：postProcessBeanFactory(beanFactory) => 后置加强 Bean(扩大实现)
空办法，不便扩大
办法 5：invokeBeanFactoryPostProcessors(beanFactory) => 执行 BFPP
实例化并且执行 BeanFactoryPostProcessors
/**
* Instantiate and invoke all registered BeanFactoryPostProcessor beans,
* respecting explicit order if given.
* <p>Must be called before singleton instantiation.
* 单例对象之前肯定调用，因为单例 bean 创立后就只有一份
*/
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()));
}
}办法 6：registerBeanPostProcessors(beanFactory) => 注册 BPP
实例化并且注册所有的 BeanPostProcessor。实例化 Bean 之前的筹备工作
/**
* Instantiate and register all BeanPostProcessor beans,
* respecting explicit order if given.
* <p>Must be called before any instantiation of application beans.
*/
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}办法 7：initMessageSource() => 国际化设置
办法 8：initApplicationEventMulticaster() => 初始化应用程序的多波器和播送器
也属于筹备工作
办法 9：onRefresh() => 预留给子类做扩大
空办法
办法 10：registerListeners() => 注册监听器
也属于筹备工作
/**
* 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<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
this.earlyApplicationEvents = null;
if (earlyEventsToProcess != null) {for (ApplicationEvent earlyEvent : earlyEventsToProcess) {getApplicationEventMulticaster().multicastEvent(earlyEvent);
}
}
}办法 11：finishBeanFactoryInitialization(beanFactory) => 实例化所有单例对象
面试常问，工作罕用。过程比较复杂
/**
* 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.
/**
* 把类型转化操作，设置到以后的 beanFactory 外面去
**/
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.
/**
* 判断以后的 beanFactory 有没有内置的值处理器
**/
if (!beanFactory.hasEmbeddedValueResolver()) {beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
/**
* 织入 Aware
**/
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
// 设置类加载器
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
/**
* 解冻：某些 bean 不须要进行批改操作了，放入
**/
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
/**
* 实例化所有非懒加载的实例对象 (重要)
**/
beanFactory.preInstantiateSingletons();}实例化所有非懒加载的实例对象办法：
@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.
/**
* 拿到所有注册 bean 的名称
**/
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
// 循环去创立咱们须要的单例对象
for (String beanName : beanNames) {
// 拿到 bean 的定义信息，就是咱们在 xml 配置文件外面指定的一些属性
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
// 是否是形象的，是否是单例的，是否是懒加载的
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
// 判断以后类是否实现了 factoryBean 接口。个别没实现，间接进入上面的 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<Boolean>)
((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {getBean(beanName);
}
}
}
else {
// 通过 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<Object>) () -> {smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {smartSingleton.afterSingletonsInstantiated();
}
}
}
}重要办法：
- getMergedLocalBeanDefinition
/**
* Return a merged RootBeanDefinition, traversing the parent bean definition
* if the specified bean corresponds to a child bean definition.
* @param beanName the name of the bean to retrieve the merged definition for
* @return a (potentially merged) RootBeanDefinition for the given bean
* @throws NoSuchBeanDefinitionException if there is no bean with the given name
* @throws BeanDefinitionStoreException in case of an invalid bean definition
*/
// 返回一个合并好的 RootBeanDefinition。整合子类和父类
protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
// Quick check on the concurrent map first, with minimal locking.
RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);
if (mbd != null && !mbd.stale) {return mbd;}
return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
}- getBean() => doGetBean()
/**
* Return an instance, which may be shared or independent, of the specified bean.
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @param typeCheckOnly whether the instance is obtained for a type check,
* not for actual use
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
@SuppressWarnings("unchecked")
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
// 获取 beanName
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
// 单例查看，如果一级，二级，三级缓存中存在该 Bean, 间接获取到了
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {if (logger.isTraceEnabled()) {if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean'" + beanName +
"'that is not fully initialized yet - a consequence of a circular reference");
}
else {logger.trace("Returning cached instance of singleton bean'" + beanName + "'");
}
}
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
// 如果是单例对象的话，尝试解决循环依赖问题
if (isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
// 获取父类容器
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {return ((AbstractBeanFactory) parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {return (T) parentBeanFactory.getBean(nameToLookup);
}
}
// 标记位。如果不是类型查看，示意要创立 bean, 此处在汇合中做一个记录
if (!typeCheckOnly) {markBeanAsCreated(beanName);
}
try {
// 获取 beanDefinition
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
// 检测 beanDefinition
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
// 查看以后的 bean 是否有其余依赖的 bean
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
// 如果有依赖的 bean, 咱们要先递归解决其余依赖的 bean
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);
}
}
}
// Create bean instance.
// 是否是单例的
if (mbd.isSingleton()) {sharedInstance = getSingleton(beanName, () -> {
try {return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {throw new IllegalStateException("No Scope registered for scope name'" + scopeName + "'");
}
try {Object scopedInstance = scope.get(beanName, () -> {beforePrototypeCreation(beanName);
try {return createBean(beanName, mbd, args);
}
finally {afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope'" + scopeName + "'is not active for the current thread; consider" +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && !requiredType.isInstance(bean)) {
try {T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean'" + name + "'to required type'" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}- getSingleton
/**
* Return the (raw) singleton object registered under the given name,
* creating and registering a new one if none registered yet.
* @param beanName the name of the bean
* @param singletonFactory the ObjectFactory to lazily create the singleton
* with, if necessary
* @return the registered singleton object
*/
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while singletons of this factory are in destruction" +
"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
}
if (logger.isDebugEnabled()) {logger.debug("Creating shared instance of singleton bean'" + beanName + "'");
}
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {this.suppressedExceptions = new LinkedHashSet<>();
}
try {
// 实际上就是调用了 CreateBean
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {throw ex;}
}
catch (BeanCreationException ex) {if (recordSuppressedExceptions) {for (Exception suppressedException : this.suppressedExceptions) {ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {if (recordSuppressedExceptions) {this.suppressedExceptions = null;}
afterSingletonCreation(beanName);
}
if (newSingleton) {addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}- doCreateBean => 通过上办法的 singletonObject = singletonFactory.getObject(); 进入的
/**
* Actually create the specified bean. Pre-creation processing has already happened
* at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
* <p>Differentiates between default bean instantiation, use of a
* factory method, and autowiring a constructor.
* @param beanName the name of the bean
* @param mbd the merged bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a new instance of the bean
* @throws BeanCreationException if the bean could not be created
* @see #instantiateBean
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
*/
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
/**
* 外围的创立实例化 Bean 的过程
**/
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {mbd.resolvedTargetType = beanType;}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {if (!mbd.postProcessed) {
try {applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
/**
* 解决循环依赖。应用三级缓存
**/
if (earlySingletonExposure) {if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean'" + beanName +
"'to allow for resolving potential circular references");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
/**
* 填充属性，上文的实例化只是默认属性值。填充属性是初始化的第一步，第二步是执行 init 办法
**/
populateBean(beanName, mbd, instanceWrapper);
/**
* 执行 init 办法
**/
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {throw (BeanCreationException) ex;
}
else {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}
if (earlySingletonExposure) {Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {if (exposedObject == bean) {exposedObject = earlySingletonReference;}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name'" + beanName + "'has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been" +
"wrapped. This means that said other beans do not use the final version of the" +
"bean. This is often the result of over-eager type matching - consider using" +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
/**
* 须要销毁的时候，销毁的钩子函数
**/
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}面试题：为甚么循环依赖的解决要应用三级缓存？
- createBeanInstance => 外围的创立和实例化 bean 的过程，由 doCreateBean 调用
大量的反射呈现在该办法中，用来创建对象
/**
* Create a new instance for the specified bean, using an appropriate instantiation strategy:
* factory method, constructor autowiring, or simple instantiation.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a BeanWrapper for the new instance
* @see #obtainFromSupplier
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
* @see #instantiateBean
*/
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
Class<?> beanClass = resolveBeanClass(mbd, beanName);
if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
}
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {return obtainFromSupplier(instanceSupplier, beanName);
}
if (mbd.getFactoryMethodName() != null) {return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {synchronized (mbd.constructorArgumentLock) {if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {if (autowireNecessary) {return autowireConstructor(beanName, mbd, null, null);
}
else {return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
// 结构器
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
ctors = mbd.getPreferredConstructors();
if (ctors != null) {return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
/**
* 默认无参结构
**/
return instantiateBean(beanName, mbd);
}- instantiateBean(beanName, mbd) => 默认无参结构
/**
* Instantiate the given bean using its default constructor.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @return a BeanWrapper for the new instance
*/
protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
try {
Object beanInstance;
final BeanFactory parent = this;
if (System.getSecurityManager() != null) {beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
// 实例化只会分配内存空间，设置默认值
getInstantiationStrategy().instantiate(mbd, beanName, parent),
getAccessControlContext());
}
else {beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
}
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}- instantiate
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// Don't override the class with CGLIB if no overrides.
if (!bd.hasMethodOverrides()) {
Constructor<?> constructorToUse;
synchronized (bd.constructorArgumentLock) {constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
if (constructorToUse == null) {final Class<?> clazz = bd.getBeanClass();
if (clazz.isInterface()) {throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {if (System.getSecurityManager() != null) {
constructorToUse = AccessController.doPrivileged((PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
}
else {constructorToUse = clazz.getDeclaredConstructor();
}
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
return BeanUtils.instantiateClass(constructorToUse);
}
else {
// Must generate CGLIB subclass.
return instantiateWithMethodInjection(bd, beanName, owner);
}
}- BeanUtils.instantiateClass => 通过结构器反射创立 bean
/**
* Convenience method to instantiate a class using the given constructor.
* <p>Note that this method tries to set the constructor accessible if given a
* non-accessible (that is, non-public) constructor, and supports Kotlin classes
* with optional parameters and default values.
* @param ctor the constructor to instantiate
* @param args the constructor arguments to apply (use {@code null} for an unspecified
* parameter, Kotlin optional parameters and Java primitive types are supported)
* @return the new instance
* @throws BeanInstantiationException if the bean cannot be instantiated
* @see Constructor#newInstance
*/
public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {Assert.notNull(ctor, "Constructor must not be null");
try {ReflectionUtils.makeAccessible(ctor);
if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass())) {return KotlinDelegate.instantiateClass(ctor, args);
}
else {Class<?>[] parameterTypes = ctor.getParameterTypes();
Assert.isTrue(args.length <= parameterTypes.length, "Can't specify more arguments than constructor parameters");
Object[] argsWithDefaultValues = new Object[args.length];
for (int i = 0 ; i < args.length; i++) {if (args[i] == null) {Class<?> parameterType = parameterTypes[i];
argsWithDefaultValues[i] = (parameterType.isPrimitive() ? DEFAULT_TYPE_VALUES.get(parameterType) : null);
}
else {argsWithDefaultValues[i] = args[i];
}
}
return ctor.newInstance(argsWithDefaultValues);
}
}
catch (InstantiationException ex) {throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
}
catch (IllegalAccessException ex) {throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
}
catch (IllegalArgumentException ex) {throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
}
catch (InvocationTargetException ex) {throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
}
}办法 12：finishRefresh() => 实现刷新
/**
* Finish the refresh of this context, invoking the LifecycleProcessor's
* onRefresh() method and publishing the
* {@link org.springframework.context.event.ContextRefreshedEvent}.
*/
protected void finishRefresh() {// Clear context-level resource caches (such as ASM metadata from scanning).
//
clearResourceCaches();
// Initialize lifecycle processor for this context.
initLifecycleProcessor();
// Propagate refresh to lifecycle processor first.
getLifecycleProcessor().onRefresh();
// Publish the final event.
publishEvent(new ContextRefreshedEvent(this));
// Participate in LiveBeansView MBean, if active.
LiveBeansView.registerApplicationContext(this);
}办法 13：resetCommonCaches() => 缓存重置
/**
* Reset Spring's common reflection metadata caches, in particular the
* {@link ReflectionUtils}, {@link AnnotationUtils}, {@link ResolvableType}
* and {@link CachedIntrospectionResults} caches.
* @since 4.2
* @see ReflectionUtils#clearCache()
* @see AnnotationUtils#clearCache()
* @see ResolvableType#clearCache()
* @see CachedIntrospectionResults#clearClassLoader(ClassLoader)
*/
protected void resetCommonCaches() {ReflectionUtils.clearCache();
AnnotationUtils.clearCache();
ResolvableType.clearCache();
CachedIntrospectionResults.clearClassLoader(getClassLoader());
}最初回顾整个流程概览图：
Bean 工厂实例化 Bean 概览图
作者：x1aoda1
起源：www.cnblogs.com/darope/p/13917264.html
近期热文举荐：
1.600+ 道 Java 面试题及答案整顿 (2021 最新版)
2. 终于靠开源我的项目弄到 IntelliJ IDEA 激活码了，真香！
3. 阿里 Mock 工具正式开源，干掉市面上所有 Mock 工具！
4.Spring Cloud 2020.0.0 正式公布，全新颠覆性版本！
5.《Java 开发手册（嵩山版）》最新公布，速速下载！
感觉不错，别忘了顺手点赞 + 转发哦！