说明
本文从源码的角度分析Spring中Bean的加载过程，本文使用的Spring版本为4.3.25.RELEASE
测试代码
测试代码如下，根据这段简单的测试代码，一步步跟踪Spring中Bean的生命周期。
@Test
public void testSingleConfigLocation() {
ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("/org/springframework/context/support/simpleContext.xml");
Assert.assertTrue(ctx.containsBean("someMessageSource"));
ctx.close();
}
一行行的分析上面这段代码
1、首先看ClassPathXmlApplicationContext容器加载。
ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("/org/springframework/context/support/simpleContext.xml");
2、参考ClassPathXmlApplicationContext的UML图。 附上ClassPathXmlApplicationContext的UML图，以便于理解接口之间的关系。
3、跟踪代码到下面这个构造方法的实现
/**
* Create a new ClassPathXmlApplicationContext, loading the definitions
* from the given XML file and automatically refreshing the context.
* @param configLocation resource location
* @throws BeansException if context creation failed
*/
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
/**
* Create a new ClassPathXmlApplicationContext with the given parent,
* loading the definitions from the given XML files.
* @param configLocations array of resource locations
* @param refresh whether to automatically refresh the context,
* loading all bean definitions and creating all singletons.
* Alternatively, call refresh manually after further configuring the context.
* @param parent the parent context
* @throws BeansException if context creation failed
* @see #refresh()
*/
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
这个构造方法就是整个Bean加载过程的核心内容，根据上面的介绍，我们可以了解到
- ClassPathXmlApplicationContext 通过父类的的构造方法创建了上下文
- 从配置文件的定义中加载了所有的bean，并且默认创建都是singletons
- 在配置完上下文之后进一步调用refresh方法
4、最主要的就是这个refresh方法了，下面分析一下这个refresh方法
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// 1、Prepare this context for refreshing.
prepareRefresh();
// 2、Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 3、Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// 4、Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// 5、Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// 6、Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// 7、Initialize message source for this context.
initMessageSource();
// 8、Initialize event multicaster for this context.
initApplicationEventMulticaster();
// 9、Initialize other special beans in specific context subclasses.
onRefresh();
// 10、Check for listener beans and register them.
registerListeners();
// 11、Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// 12、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 {
//13、 Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
这个fresh方法中包含了13个步，那就把这13一步一步的分析。
4.1、prepareRefresh()
这个方法意思是为刷新准备一个上下文，那进入这个方法，看它提供了什么？
/**
* Prepare this context for refreshing, setting its startup date and
* active flag as well as performing any initialization of property sources.
*/
protected void prepareRefresh() {
// 记一个开始时间
this.startupDate = System.currentTimeMillis();
this.closed.set(false);
this.active.set(true);
if (logger.isInfoEnabled()) {
logger.info("Refreshing " + this);
}
// 初始化占位符属性，此处是空方法，以供子类继承扩展
initPropertySources();
// 验证标记为所需的所有属性都是可解析的
// see ConfigurablePropertyResolver#setRequiredProperties
getEnvironment().validateRequiredProperties();
// 这里是收集前期的应用事件
// to be published once the multicaster is available...
this.earlyApplicationEvents = new LinkedHashSet<ApplicationEvent>();
}
4.2、ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()
这个方法主要是告诉子类刷新bean工厂，这个类的代码如下：
/**
* 子类刷新内部工厂，如果子类覆盖refreshBeanFactory方法
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
这里的refreshBeanFactory是在AbstractRefreshableApplicationContext里实现的，这里附一下DefaultListableBeanFactory的UML图
这里就不贴代码了，这个obtainFreshBeanFactory的目的如下：
1.如果之前存在beanfactory则销毁
2.创建一个DefaultListableBeanFactory类型的beanfactory
3.加载DefaultListableBeanFactory
4.3、prepareBeanFactory(beanFactory);
在上下文中准备bean工厂
/**
* Configure the factory's standard context characteristics,
* such as the context's ClassLoader and post-processors.
* @param beanFactory the BeanFactory to configure
*/
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// 设置类加载器：存在则直接设置/不存在则新建一个默认类加载器
beanFactory.setBeanClassLoader(getClassLoader());
// 设置EL表达式解析器（Bean初始化完成后填充属性时会用到）
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
//设置属性注册解析器PropertyEditor
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
//将当前的ApplicationContext对象交给ApplicationContextAwareProcessor类来处理，从而在Aware接口实现类中的注入applicationContext
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
//设置忽略自动装配的接口
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
// 注册可以解析的自动装配
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// Register early post-processor for detecting inner beans as ApplicationListeners.
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// 如果当前BeanFactory包含loadTimeWeaver Bean，
//说明存在类加载期织入AspectJ，则把当前BeanFactory交给类加载期BeanPostProcessor
//实现类LoadTimeWeaverAwareProcessor来处理，从而实现类加载期织入AspectJ的目的。
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()));
}
//注册当前容器环境environment组件Bean.
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
//注册系统配置的systemProperties组件Bean
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
//注册系统环境systemEnvironment组件Bean
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
}
4.4、 postProcessBeanFactory(beanFactory)
调用上下文中注册为bean的工厂处理器。
/**
* 在标准出书画之后修改应用程序上下文的bean factory
* 所有bean定义都将被加载，但是还没有bean被实例化。
* 这允许在特定的ApplicationContext实现中注册特殊的beanpstprocessors等。
*/
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
}
4.5、invokeBeanFactoryPostProcessors(beanFactory)
/**
* 如果有顺序就按照顺序实例化所有注册的BeanFactoryPostProcessor
*
*/
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
// 如果当前BeanFactory包含loadTimeWeaver Bean，
//说明存在类加载期织入AspectJ，则把当前BeanFactory交给类加载期BeanPostProcessor
//实现类LoadTimeWeaverAwareProcessor来处理，从而实现类加载期织入AspectJ的目的。
if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
4.6、 registerBeanPostProcessors(beanFactory)
注册拦截bean创建的bean处理器。
/**
* 实例化并注册所有beanPostProcessorbean，如果给定显式顺序，则遵循显式顺序。
*/
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}
PostProcessorRegistrationDelegate.registerBeanPostProcessors的实现如下
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
// 注册BeanPostProcessorChecker，在BeanPostProcessor实例化期间创建bean时记录信息消息
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
//区分BeanPostProcessors是实现了PriorityOrdered、Ordered、其他
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
List<String> orderedPostProcessorNames = new ArrayList<String>();
List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, register the BeanPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// Next, register the BeanPostProcessors that implement Ordered.
List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
for (String ppName : orderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
orderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
sortPostProcessors(orderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
// Now, register all regular BeanPostProcessors.
List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
for (String ppName : nonOrderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
nonOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
// Finally, re-register all internal BeanPostProcessors.
sortPostProcessors(internalPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, internalPostProcessors);
//重新注册后处理器，以便将内部bean检测为应用程序侦听器，并将其移动到处理器链的末端（用于获取代理等）
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
4.7、initMessageSource();
初始化此上下文的消息源。
/**
* Initialize the MessageSource.
* Use parent's if none defined in this context.
*/
protected void initMessageSource() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
// Make MessageSource aware of parent MessageSource.
if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
if (hms.getParentMessageSource() == null) {
// Only set parent context as parent MessageSource if no parent MessageSource
// registered already.
hms.setParentMessageSource(getInternalParentMessageSource());
}
}
if (logger.isDebugEnabled()) {
logger.debug("Using MessageSource [" + this.messageSource + "]");
}
}
else {
// Use empty MessageSource to be able to accept getMessage calls.
DelegatingMessageSource dms = new DelegatingMessageSource();
dms.setParentMessageSource(getInternalParentMessageSource());
this.messageSource = dms;
beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
"': using default [" + this.messageSource + "]");
}
}
}
4.8、 initApplicationEventMulticaster();
为上下文初始化事件广播
/**
* 初始化应用容器事件，如果没有定义的话就用默认的SimpleApplicationEventMulticaster
*
*/
protected void initApplicationEventMulticaster() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
this.applicationEventMulticaster =
beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
if (logger.isDebugEnabled()) {
logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
}
}
else {
this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
"': using default [" + this.applicationEventMulticaster + "]");
}
}
}
附一下SimpleApplicationEventMulticaster的UML图
4.9、onRefresh()
初始化特定上下文子类中的其他特殊bean。
/**
* 这个是一个模板方法，为特殊的bean初始化用，在单例实例化之前
*
*/
protected void onRefresh() throws BeansException {
// For subclasses: do nothing by default.
}
4.10. registerListeners();
注册监听器
/**
* 添加实现了ApplicationListener的监听器
* 不会影响哪些没有注册成bean的侦听器
*/
protected void registerListeners() {
// Register statically specified listeners first.
for (ApplicationListener<?> listener : getApplicationListeners()) {
getApplicationEventMulticaster().addApplicationListener(listener);
}
// 不要在这里初始化FactoryBeans：我们需要保留所有常规bean
// 未初始化以允许后处理器应用于它们！
String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
for (String listenerBeanName : listenerBeanNames) {
getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
}
// 发布早期的应用程序event，这里使用就是观察者设计模式
Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
this.earlyApplicationEvents = null;
if (earlyEventsToProcess != null) {
for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
getApplicationEventMulticaster().multicastEvent(earlyEvent);
}
}
}
4.11、 finishBeanFactoryInitialization(beanFactory)
实例化所有剩余的（非延迟初始化）单例。
/**
* 完成上下文的初始化，初始化所有剩余的bean
*/
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
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));
}
//如果没有bean后处理器则注册一个默认的解析器EmbeddedValueResolver
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(new StringValueResolver() {
@Override
public String resolveStringValue(String strVal) {
return getEnvironment().resolvePlaceholders(strVal);
}
});
}
// 尽早初始化LoadTimeWeaverAware bean，以便尽早注册其转换器。
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// 停止使用临时类加载器进行类型匹配。
beanFactory.setTempClassLoader(null);
// 允许缓存所有bean定义元数据，不需要进一步更改。
beanFactory.freezeConfiguration();
// 实例化所有剩余的（非延迟初始化）单例
beanFactory.preInstantiateSingletons();
}
4.12、 finishRefresh()
最后一步：发布对应的事件。这一步bean加载就结束了，通知相应的监听器。
/**
* 完成容器上下文的刷新，执行onRefresh()方法并发布事件
* org.springframework.context.event.ContextRefreshedEvent
*/
protected void finishRefresh() {
// 初始化生命周期处理器
initLifecycleProcessor();
// 将增殖刷新到生命周期
getLifecycleProcessor().onRefresh();
// 发布最终的事件.
publishEvent(new ContextRefreshedEvent(this));
//参与MBean如果存在.
LiveBeansView.registerApplicationContext(this);
}
附bean生命周期DefaultLifecycleProcessor的UML
4.13、 resetCommonCaches();
在Spring的核心中重置常见的内省缓存，因为我们可能不再需要singleton bean的元数据了
/**
* Reset Spring's common core caches, in particular the {@link ReflectionUtils},
* {@link ResolvableType} and {@link CachedIntrospectionResults} caches.
* @since 4.2
* @see ReflectionUtils#clearCache()
* @see ResolvableType#clearCache()
* @see CachedIntrospectionResults#clearClassLoader(ClassLoader)
*/
protected void resetCommonCaches() {
ReflectionUtils.clearCache();
ResolvableType.clearCache();
CachedIntrospectionResults.clearClassLoader(getClassLoader());
}
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