Spring驱动式开发

BigHong123

已于 2022-11-20 13:54:39 修改

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文章标签： spring java 后端

于 2022-02-03 18:11:47 首次发布

本文链接：https://blog.youkuaiyun.com/qq_23412557/article/details/122777383

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可参考

Spring注解驱动开发（五）_越努力越幸运的博客-优快云博客_spring注解驱动开发

bean的初始化方法

通过配置类 @Bean(initMethod = "initMethod",destroyMethod ="destroyMethod")
通过实现 InitializingBean,DisposableBean 实现对应的 afterPropertiesSet（）和 destroy() 方法
通过 @PostConstruct 注解

@Configuration
@ComponentScan("com.zhy.testinit.bean")
public class InitConfig {

    @Bean(initMethod = "initMethod",destroyMethod ="destroyMethod")
    public Cat cat(){
        return new Cat();
    }
}

@Component
public class Cat implements InitializingBean,DisposableBean {
	
	public Cat(){
		System.out.println("cat constructor...");
	}

	@PostConstruct
	public void postConstruct(){
		System.out.println("postConstruct");
	}

	@Override
	public void destroy() throws Exception {
		// TODO Auto-generated method stub
		System.out.println("cat...destroy...");
	}

	@Override
	public void afterPropertiesSet() throws Exception {
		// TODO Auto-generated method stub
		System.out.println("cat...afterPropertiesSet...");
	}

	public void initMethod(){
		System.out.println("intMethod");
	}

	public void destroyMethod(){
		System.out.println("destroyMethod");
	}
}

输出结果：

cat constructor...
postConstruct
cat...afterPropertiesSet...
intMethod

@Import注解的使用

/**
 * 给容器中注册组件；
 * 1）、包扫描+组件标注注解（@Controller/@Service/@Repository/@Component）[自己写的类]
 * 2）、@Bean[导入的第三方包里面的组件]
 * 3）、@Import[快速给容器中导入一个组件]
 *        1）、@Import(要导入到容器中的组件)；容器中就会自动注册这个组件，id默认是全类名
 *        2）、ImportSelector:返回需要导入的组件的全类名数组；
 *        3）、ImportBeanDefinitionRegistrar:手动注册bean到容器中
 * 4）、使用Spring提供的 FactoryBean（工厂Bean）;
 *        1）、默认获取到的是工厂bean调用getObject创建的对象
 *        2）、要获取工厂Bean本身，我们需要给id前面加一个&
 *           &colorFactoryBean
 */

@Configuration
@Import({Color.class, Red.class, MyImportSelector.class, MyImportBeanDefinitionRegistrar.class})
//@Import导入组件，id默认是组件的全类名
public class ImportConfig {

}

//自定义逻辑返回需要导入的组件
public class MyImportSelector implements ImportSelector {

	//返回值，就是到导入到容器中的组件全类名
	//AnnotationMetadata:当前标注@Import注解的类的所有注解信息
	@Override
	public String[] selectImports(AnnotationMetadata importingClassMetadata) {
		// TODO Auto-generated method stub
		//importingClassMetadata
		//方法不要返回null值
		return new String[]{"com.zhy.testinit.bean.Blue","com.zhy.testinit.bean.Yellow"};
	}

}

public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {

	/**
	 * AnnotationMetadata：当前类的注解信息
	 * BeanDefinitionRegistry:BeanDefinition注册类；
	 * 		把所有需要添加到容器中的bean；调用
	 * 		BeanDefinitionRegistry.registerBeanDefinition手工注册进来
	 */
	@Override
	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		
		boolean definition = registry.containsBeanDefinition("com.zhy.testinit.bean.Red");
		boolean definition2 = registry.containsBeanDefinition("com.zhy.testinit.bean.Blue");
		if(definition && definition2){
			//指定Bean定义信息；（Bean的类型，Bean。。。）
			RootBeanDefinition beanDefinition = new RootBeanDefinition(RainBow.class);
			//注册一个Bean，指定bean名
			registry.registerBeanDefinition("rainBow", beanDefinition);
		}
	}

}

输出:

com.zhy.testinit.bean.Color
com.zhy.testinit.bean.Red
com.zhy.testinit.bean.Blue
com.zhy.testinit.bean.Yellow
colorFactoryBean
rainBow

BeanPostProcessor

public interface BeanPostProcessor {

    //初始化前
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}
    //初始化后
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}
}

public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
	//构造方法执行前
    @Nullable
	default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
		return null;
	}
    //构造方法执行后
	default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
		return true;
	}

	@Nullable
	default PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
			throws BeansException {

		return null;
	}

	@Deprecated
	@Nullable
	default PropertyValues postProcessPropertyValues(
			PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {

		return pvs;
	}

}

public interface SmartInstantiationAwareBeanPostProcessor extends InstantiationAwareBeanPostProcessor {

	@Nullable
	default Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException {
		return null;
	}

	@Nullable
	default Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName)
			throws BeansException {

		return null;
	}
    //获取早期对象
	default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
		return bean;
	}

}

public interface MergedBeanDefinitionPostProcessor extends BeanPostProcessor {

	void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName);

	default void resetBeanDefinition(String beanName) {
	}

}

调用时机

输出结果：

MyInstantiationAwareBeanPostProcessor---postProcessBeforeInstantiation
cat constructor...
MyInstantiationAwareBeanPostProcessor---postProcessAfterInstantiation
postProcessBeforeInitialization...cat=>com.zhy.testinit.beanprocess.Cat@5939a379
postConstruct
cat...afterPropertiesSet...
postProcessAfterInitialization...cat=>com.zhy.testinit.beanprocess.Cat@5939a379

@Override
	protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
			throws BeanCreationException {

		if (logger.isTraceEnabled()) {
			logger.trace("Creating instance of bean '" + beanName + "'");
		}
		RootBeanDefinition mbdToUse = mbd;

		// Make sure bean class is actually resolved at this point, and
		// clone the bean definition in case of a dynamically resolved Class
		// which cannot be stored in the shared merged bean definition.
		Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
		if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
			mbdToUse = new RootBeanDefinition(mbd);
			mbdToUse.setBeanClass(resolvedClass);
		}

		// Prepare method overrides.
		try {
			mbdToUse.prepareMethodOverrides();
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
					beanName, "Validation of method overrides failed", ex);
		}

		try {
            // 执行方法postProcessBeforeInstantiation 和 postProcessAfterInstantiation
            // 但是在此处不一定执行到 postProcessAfterInstantiation
			// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
			Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
			if (bean != null) {
				return bean;
			}
		}
		catch (Throwable ex) {
			throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
					"BeanPostProcessor before instantiation of bean failed", ex);
		}

		try {
			Object beanInstance = doCreateBean(beanName, mbdToUse, args);
			if (logger.isTraceEnabled()) {
				logger.trace("Finished creating instance of bean '" + beanName + "'");
			}
			return beanInstance;
		}
		catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
			// A previously detected exception with proper bean creation context already,
			// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
			throw ex;
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
		}
	}

@Nullable
	protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
		Object bean = null;
		if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
			// Make sure bean class is actually resolved at this point.
			if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
				Class<?> targetType = determineTargetType(beanName, mbd);
				if (targetType != null) {
                    //执行构造前函数
					bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
                   //如果返回的bean不空，执行构造后函数
					if (bean != null) {
						bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
					}
				}
			}
			mbd.beforeInstantiationResolved = (bean != null);
		}
		return bean;
	}

@Nullable
	protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
		for (BeanPostProcessor bp : getBeanPostProcessors()) {
			if (bp instanceof InstantiationAwareBeanPostProcessor) {
				InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
				Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
				if (result != null) {
					return result;
				}
			}
		}
		return null;
	}

@Override
	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			Object current = processor.postProcessAfterInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}

@SuppressWarnings("deprecation")  // for postProcessPropertyValues
	protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
		if (bw == null) {
			if (mbd.hasPropertyValues()) {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
			}
			else {
				// Skip property population phase for null instance.
				return;
			}
		}
        //调用构造函数后 处理
		// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
		// state of the bean before properties are set. This can be used, for example,
		// to support styles of field injection.
		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
						return;
					}
				}
			}
		}

		PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);

		int resolvedAutowireMode = mbd.getResolvedAutowireMode();
		if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
			// Add property values based on autowire by name if applicable.
			if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
				autowireByName(beanName, mbd, bw, newPvs);
			}
			// Add property values based on autowire by type if applicable.
			if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
				autowireByType(beanName, mbd, bw, newPvs);
			}
			pvs = newPvs;
		}

		boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
		boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);

		PropertyDescriptor[] filteredPds = null;
		if (hasInstAwareBpps) {
			if (pvs == null) {
				pvs = mbd.getPropertyValues();
			}
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
					if (pvsToUse == null) {
						if (filteredPds == null) {
							filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
						}
						pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvsToUse == null) {
							return;
						}
					}
					pvs = pvsToUse;
				}
			}
		}
		if (needsDepCheck) {
			if (filteredPds == null) {
				filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
			}
			checkDependencies(beanName, mbd, filteredPds, pvs);
		}

		if (pvs != null) {
			applyPropertyValues(beanName, mbd, bw, pvs);
		}
	}

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				invokeAwareMethods(beanName, bean);
				return null;
			}, getAccessControlContext());
		}
		else {
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
        //初始化前
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}
       //初始化
		try {
			invokeInitMethods(beanName, wrappedBean, mbd);
		}
		catch (Throwable ex) {
			throw new BeanCreationException(
					(mbd != null ? mbd.getResourceDescription() : null),
					beanName, "Invocation of init method failed", ex);
		}
        //初始化后
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}

		return wrappedBean;
	}

AutowiredAnnotationBeanPostProcessor（@Autowire依赖注入）

AnnotationAwareAspectJAutoProxyCreator（AOP实现）

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AspectJAutoProxyRegistrar.class)
public @interface EnableAspectJAutoProxy {

}

class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar {

	@Override
	public void registerBeanDefinitions(
			AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
         //注册AnnotationAwareAspectJAutoProxyCreator
		AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);

		AnnotationAttributes enableAspectJAutoProxy =
				AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
		if (enableAspectJAutoProxy != null) {
			if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) {
				AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
			}
			if (enableAspectJAutoProxy.getBoolean("exposeProxy")) {
				AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
			}
		}
	}

}

 @Nullable
    public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, @Nullable Object source) {
        return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
    }

InfrastructureAdvisorAutoProxyCreator（事务管理实现）

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {

}

public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {

	@Override
	protected String[] selectImports(AdviceMode adviceMode) {
		switch (adviceMode) {
			case PROXY:
				return new String[] {AutoProxyRegistrar.class.getName(),
						ProxyTransactionManagementConfiguration.class.getName()};
			case ASPECTJ:
				return new String[] {determineTransactionAspectClass()};
			default:
				return null;
		}
	}
}

public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {

	private final Log logger = LogFactory.getLog(getClass());

	@Override
	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		boolean candidateFound = false;
		Set<String> annTypes = importingClassMetadata.getAnnotationTypes();
		for (String annType : annTypes) {
			AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);
			if (candidate == null) {
				continue;
			}
			Object mode = candidate.get("mode");
			Object proxyTargetClass = candidate.get("proxyTargetClass");
			if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&
					Boolean.class == proxyTargetClass.getClass()) {
				candidateFound = true;
				if (mode == AdviceMode.PROXY) {
                    //这里注册postProcess
					AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
					if ((Boolean) proxyTargetClass) {
						AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
						return;
					}
				}
			}
		}
		if (!candidateFound && logger.isInfoEnabled()) {
			String name = getClass().getSimpleName();
			logger.info(String.format("%s was imported but no annotations were found " +
					"having both 'mode' and 'proxyTargetClass' attributes of type " +
					"AdviceMode and boolean respectively. This means that auto proxy " +
					"creator registration and configuration may not have occurred as " +
					"intended, and components may not be proxied as expected. Check to " +
					"ensure that %s has been @Import'ed on the same class where these " +
					"annotations are declared; otherwise remove the import of %s " +
					"altogether.", name, name, name));
		}
	}

}

 @Nullable
    public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, @Nullable Object source) {
        return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
    }

ApplicationContextAware（常用来获取applicationContext对象）

public interface ApplicationContextAware extends Aware {

	void setApplicationContext(ApplicationContext applicationContext) throws BeansException;

}

class ApplicationContextAwareProcessor implements BeanPostProcessor {

	private final ConfigurableApplicationContext applicationContext;

	private final StringValueResolver embeddedValueResolver;


	/**
	 * Create a new ApplicationContextAwareProcessor for the given context.
	 */
	public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {
		this.applicationContext = applicationContext;
		this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory());
	}


	@Override
	@Nullable
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
				bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
				bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){
			return bean;
		}

		AccessControlContext acc = null;

		if (System.getSecurityManager() != null) {
			acc = this.applicationContext.getBeanFactory().getAccessControlContext();
		}

		if (acc != null) {
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				invokeAwareInterfaces(bean);
				return null;
			}, acc);
		}
		else {
			invokeAwareInterfaces(bean);
		}

		return bean;
	}

	private void invokeAwareInterfaces(Object bean) {
		if (bean instanceof EnvironmentAware) {
			((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
		}
		if (bean instanceof EmbeddedValueResolverAware) {
			((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
		}
		if (bean instanceof ResourceLoaderAware) {
			((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
		}
		if (bean instanceof ApplicationEventPublisherAware) {
			((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
		}
		if (bean instanceof MessageSourceAware) {
			((MessageSourceAware) bean).setMessageSource(this.applicationContext);
		}
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}

}

BeanFactoryPostProcessor

public interface BeanFactoryPostProcessor {

	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

	void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;

}

例：

@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		System.out.println("MyBeanFactoryPostProcessor...postProcessBeanFactory...");
		int count = beanFactory.getBeanDefinitionCount();
		String[] names = beanFactory.getBeanDefinitionNames();
		System.out.println("当前BeanFactory中有"+count+" 个Bean");
		System.out.println(Arrays.asList(names));
	}

}

@Component
public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor{

	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		// TODO Auto-generated method stub
		System.out.println("MyBeanDefinitionRegistryPostProcessor...bean的数量："+beanFactory.getBeanDefinitionCount());
	}

	//BeanDefinitionRegistry Bean定义信息的保存中心，以后BeanFactory就是按照BeanDefinitionRegistry里面保存的每一个bean定义信息创建bean实例；
	@Override
	public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
		// TODO Auto-generated method stub
		System.out.println("postProcessBeanDefinitionRegistry...bean的数量："+registry.getBeanDefinitionCount());
		//RootBeanDefinition beanDefinition = new RootBeanDefinition(Blue.class);
		AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Blue.class).getBeanDefinition();
		registry.registerBeanDefinition("hello", beanDefinition);
	}

}

输出结果：

MyBeanDefinitionRegistryPostProcessor...postProcessBeanDefinitionRegistry...bean的数量：18
MyBeanDefinitionRegistryPostProcessor...postProcessBeanFactory..bean的数量：19
MyBeanFactoryPostProcessor...postProcessBeanFactory...
当前BeanFactory中有19 个Bean

先执行 BeanDefinitionRegistryPostProcessor中的postProcessBeanDefinitionRegistry
再执行BeanDefinitionRegistryPostProcessor中的postProcessBeanFactory
再执行BeanFactoryPostProcessor中的postProcessBeanFactory

ApplicationListener

3、ApplicationListener：监听容器中发布的事件。事件驱动模型开发；
*    public interface ApplicationListener<E extends ApplicationEvent>
*     监听 ApplicationEvent 及其下面的子事件；
* 
*   步骤：
*     1）、写一个监听器（ApplicationListener实现类）来监听某个事件（ApplicationEvent及其子类）
*        @EventListener;
*        原理：使用EventListenerMethodProcessor处理器来解析方法上的@EventListener；
* 
*     2）、把监听器加入到容器；
*     3）、只要容器中有相关事件的发布，我们就能监听到这个事件；
*           ContextRefreshedEvent：容器刷新完成（所有bean都完全创建）会发布这个事件；
*           ContextClosedEvent：关闭容器会发布这个事件；
*     4）、发布一个事件：
*           applicationContext.publishEvent()；
*  
*  原理：
*      ContextRefreshedEvent、IOCTest_Ext$1[source=我发布的时间]、ContextClosedEvent；
*  1）、ContextRefreshedEvent事件：
*      1）、容器创建对象：refresh()；
*      2）、finishRefresh();容器刷新完成会发布ContextRefreshedEvent事件
*  2）、自己发布事件；
*  3）、容器关闭会发布ContextClosedEvent；
*  
*  【事件发布流程】：
*      3）、publishEvent(new ContextRefreshedEvent(this));
*            1）、获取事件的多播器（派发器）：getApplicationEventMulticaster()
*            2）、multicastEvent派发事件：
*            3）、获取到所有的ApplicationListener；
*               for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
*               1）、如果有Executor，可以支持使用Executor进行异步派发；
*                  Executor executor = getTaskExecutor();
*               2）、否则，同步的方式直接执行listener方法；invokeListener(listener, event);
*                拿到listener回调onApplicationEvent方法；
*  
*  【事件多播器（派发器）】
*      1）、容器创建对象：refresh();
*      2）、initApplicationEventMulticaster();初始化ApplicationEventMulticaster；
*         1）、先去容器中找有没有id=“applicationEventMulticaster”的组件；
*         2）、如果没有this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
*            并且加入到容器中，我们就可以在其他组件要派发事件，自动注入这个applicationEventMulticaster；
*  
*  【容器中有哪些监听器】
*      1）、容器创建对象：refresh();
*      2）、registerListeners();
*         从容器中拿到所有的监听器，把他们注册到applicationEventMulticaster中；
*         String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
*         //将listener注册到ApplicationEventMulticaster中
*         getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);

@Component
public class MyApplicationListener implements ApplicationListener<ApplicationEvent> {

	//当容器中发布此事件以后，方法触发
	@Override
	public void onApplicationEvent(ApplicationEvent event) {
		// TODO Auto-generated method stub
		System.out.println("收到事件："+event);
	}

}

@Service
public class ListenerAnnotation {
	
	@EventListener(classes={ApplicationEvent.class})
	public void listen(ApplicationEvent event){
		System.out.println("ListenerAnnotation。。监听到的事件："+event);
	}

}

public class MyEvent extends ApplicationEvent {
    /**
     * Create a new {@code ApplicationEvent}.
     *
     * @param source the object on which the event initially occurred or with
     *               which the event is associated (never {@code null})
     */
    public MyEvent(Object source) {
        super(source);
    }
}

AnnotationConfigApplicationContext rootAppContext = new AnnotationConfigApplicationContext(InitConfig.class);
        rootAppContext.publishEvent(new MyEvent(new Object()));

Spring初始化的主要流程

AnnotationConfigApplicationContext rootAppContext = new AnnotationConfigApplicationContext(InitConfig.class);

	public AnnotationConfigApplicationContext(Class<?>... componentClasses) {
		this();
		register(componentClasses);
		refresh();
	}

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

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

			try {
				// Allows post-processing of the bean factory in context subclasses.
				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();
			}
		}
	}