【Spring源码分析】非懒加载的单例Bean初始化前后的一些操作
2024-03-22 12:22:48
前言
之前两篇文章【Spring源码分析】非懒加载的单例Bean初始化过程（上篇）和【Spring源码分析】非懒加载的单例Bean初始化过程（下篇）比较详细地分析了非懒加载的单例Bean的初始化过程，整个流程始于AbstractApplicationContext的refresh()方法：
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) {
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
}
}
之前重点分析的是finishBeanFactoryInitialization方法，这个方法完成了所有非懒加载的单例Bean的初始化。今天我回头重看了一下refresh()方法，发现前面有一些方法还是忽略了没有去特别在意，其实他们都是Spring整个启动流程中的重要组成部分，下面就来分析一下finishBeanFactoryInitialization方法前面的一些方法。
obtainFreshBeanFactory方法之前已经详细分析过了，就从prepareBeanFactory方法开始。
PrepareBeanFactory方法
看一下PrepareBeanFactory方法的实现：
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver());
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));
// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
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.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, 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.containsBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
Map systemProperties;
try {
systemProperties = System.getProperties();
}
catch (AccessControlException ex) {
systemProperties = new ReadOnlySystemAttributesMap() {
@Override
protected String getSystemAttribute(String propertyName) {
try {
return System.getProperty(propertyName);
}
catch (AccessControlException ex) {
if (logger.isInfoEnabled()) {
logger.info("Not allowed to obtain system property [" + propertyName + "]: " +
ex.getMessage());
}
return null;
}
}
};
}
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, systemProperties);
}
if (!beanFactory.containsBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
Map<String,String> systemEnvironment;
try {
systemEnvironment = System.getenv();
}
catch (AccessControlException ex) {
systemEnvironment = new ReadOnlySystemAttributesMap() {
@Override
protected String getSystemAttribute(String variableName) {
try {
return System.getenv(variableName);
}
catch (AccessControlException ex) {
if (logger.isInfoEnabled()) {
logger.info("Not allowed to obtain system environment variable [" + variableName + "]: " +
ex.getMessage());
}
return null;
}
}
};
}
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, systemEnvironment);
}
}
首先是第3行，配置当前上下文ClassLoader
接着是第4行，这是一个表达是语言处理器，可以使用#{bean.xxx}的方式来调用相关属性值
接着是第5行，这是一个属性编辑器，具体没怎么用过
接着是第8行，第8行增加了一个ApplicationContextAwareProcessor用于上下文回调，它是BeanPostProcessor的实现类，跟一下这个接口的两个方法postProcessBeforeInitialization和postProcessAfterInitialization即可知道这个方法的作用是：
- 如果Bean是EmbeddedValueResolverAware接口的实现类，则调用setEmbeddedValueResolver方法，传入当前BeanFactory
- 如果Bean是ResourceLoaderAware接口的实现类，则调用setResourceLoader方法，传入当前上下文ApplicationContext
- 如果Bean是ApplicationEventPublisherAware的实现类，则调用setApplicationEventPublisher方法，传入当前上下文ApplicationContext
- 如果Bean是MessageSourceAware的实现类，则调用setMessageSource方法，传入当前上下文ApplicationContext
- 如果Bean是ApplicationContextAware的实现类，则调用setApplicationContext方法，传入当前上下文ApplicationContext
接着是第9行~第12行，意思是Bean如果是这些接口的实现类，则不会被自动装配，自动装配见【Spring9】Autowire（自动装配）机制
接着是第16行~第19行，意思是修正依赖，这里是一些自动装配的特殊规则，比如是BeanFactory接口的实现类，则修正为当前BeanFactory
接着是第22行~第26行，意思是如果自定义的Bean中有定义过一个名为"loadTimeWeaver"的Bean，则会添加一个LoadTimeWeaverAwareProcessor
最后是第29行~第77行，意思是如果自定义的Bean中没有名为"systemProperties"和"systemEnvironment"的Bean，则注册两个Bena，Key为"systemProperties"和"systemEnvironment"，Value为Map，这两个Bean就是一些系统配置和系统环境信息，具体可以写这么一段代码测试一下：
public class TestSpring {
@SuppressWarnings("unchecked")
@Test
public void testSpring() {
ApplicationContext ac = new ClassPathXmlApplicationContext("spring/spring.xml");
Map<String, String> systemPropertiesBean = (Map<String, String>)ac.getBean("systemProperties");
for (Map.Entry<String, String> entry : systemPropertiesBean.entrySet()) {
System.out.println(entry.getKey() + "--->" + entry.getValue());
}
System.out.println("==============================华丽的分隔符==============================");
Map<String, String> systemEnvironmentBean = (Map<String, String>)ac.getBean("systemEnvironment");
for (Map.Entry<String, String> entry : systemEnvironmentBean.entrySet()) {
System.out.println(entry.getKey() + "--->" + entry.getValue());
}
}
}
涉及个人信息，运行结果我就不贴了，大家可以自己试试，至此整个PrepareBeanFactory方法的细节已经分析完毕了。
invokeBeanFactoryPostProcessors方法
这个是整个Spring流程中非常重要的一部分，是Spring留给用户的一个非常有用的扩展点，BeanPostProcessor接口针对的是每个Bean初始化前后做的操作而BeanFactoryPostProcessor接口针对的是所有Bean实例化前的操作，注意用词，初始化只是实例化的一部分，表示的是调用Bean的初始化方法，BeanFactoryPostProcessor接口方法调用时机是任意一个自定义的Bean被反射生成出来前。
OK，看一下源码：
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<String>();
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
new LinkedList<BeanDefinitionRegistryPostProcessor>();
for (BeanFactoryPostProcessor postProcessor : getBeanFactoryPostProcessors()) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryPostProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
registryPostProcessors.add(registryPostProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
Map<String, BeanDefinitionRegistryPostProcessor> beanMap =
beanFactory.getBeansOfType(BeanDefinitionRegistryPostProcessor.class, true, false);
List<BeanDefinitionRegistryPostProcessor> registryPostProcessorBeans =
new ArrayList<BeanDefinitionRegistryPostProcessor>(beanMap.values());
OrderComparator.sort(registryPostProcessorBeans);
for (BeanDefinitionRegistryPostProcessor postProcessor : registryPostProcessorBeans) {
postProcessor.postProcessBeanDefinitionRegistry(registry);
}
invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(registryPostProcessorBeans, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
processedBeans.addAll(beanMap.keySet());
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(getBeanFactoryPostProcessors(), beanFactory);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
List<String> orderedPostProcessorNames = new ArrayList<String>();
List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
else if (isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
OrderComparator.sort(priorityOrderedPostProcessors);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
OrderComparator.sort(orderedPostProcessors);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
}
我们可以自己实现BeanFactoryPostProcessor接口并实现postProcessBeanFactory方法，在所有Bean加载的流程开始前，会调用一次postProcessBeanFactory方法。分析一下这段代码，首先我们使用的是DefaultListableBeanFactory，它是BeanDefinitionRegistry的子类，因此进入第4行的判断。
整个判断获取的是当前有的BeanFactoryPostProcessor并调用postProcessBeanFactory，这些BeanFactoryPostProcessor是前置通过AbstractApplicationContext的addBeanFactoryPostProcessor方法添加的而不是配置文件里面配置的BeanFactoryPostProcessor的实现Bean，因此这个判断没有任何可执行的BeanFactoryPostProcessor。
接着40行~41行这两行，获取的是beanDefinitionMap中的Bean，即用户自定义的Bean。
接着第45行~61行，这里分出了三个List，表示开发者可以自定义BeanFactoryPostProcessor的调用顺序，具体为调用顺序为：
- 如果BeanFactoryPostProcessor实现了PriorityOrdered接口（PriorityOrdered接口是Ordered的子接口，没有自己的接口方法定义，只是做一个标记，表示调用优先级高于Ordered接口的子接口），是优先级最高的调用，调用顺序是按照接口方法getOrder()的实现，对返回的int值从小到大进行排序，进行调用
- 如果BeanFactoryPostProcessor实现了Ordered接口，是优先级次高的调用，将在所有实现PriorityOrdered接口的BeanFactoryPostProcessor调用完毕之后，依据getOrder()的实现对返回的int值从小到大排序，进行调用
- 不实现Ordered接口的BeanFactoryPostProcessor在上面的BeanFactoryPostProcessor调用全部完毕之后进行调用，调用顺序就是Bean定义的顺序
最后的第63行~第80行就是按照上面的规则依次先将BeanFactoryPostProcessor接口对应的实现类实例化出来并调用postProcessBeanFactory方法。
registerBeanPostProcessors方法
接下来看看registerBeanPostProcessors方法，顾名思义，就是注册自定义的BeanPostProcessor接口。看一下代码实现：
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
// Register BeanPostProcessorChecker that logs an info message when
// a bean is created during BeanPostProcessor instantiation, i.e. when
// a bean is not eligible for getting processed by all BeanPostProcessors.
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
// Separate between BeanPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
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 (isTypeMatch(ppName, PriorityOrdered.class)) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
else if (isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, register the BeanPostProcessors that implement PriorityOrdered.
OrderComparator.sort(priorityOrderedPostProcessors);
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);
}
}
OrderComparator.sort(orderedPostProcessors);
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.
OrderComparator.sort(internalPostProcessors);
registerBeanPostProcessors(beanFactory, internalPostProcessors);
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector());
}
整体代码思路和invokeBeanFactoryPostProcessors方法类似，但是这里不会调用BeanPostProcessor接口的方法，而是把每一个BeanPostProcessor接口实现类实例化出来并按照顺序放入一个List中，到时候按顺序进行调用。
具体代码思路可以参考invokeBeanFactoryPostProcessors，这里就根据代码总结一下BeanPostProcessor接口的调用顺序：
- 优先调用PriorityOrdered接口的子接口，调用顺序依照接口方法getOrder的返回值从小到大排序
- 其次调用Ordered接口的子接口，调用顺序依照接口方法getOrder的返回值从小到大排序
- 接着按照BeanPostProcessor实现类在配置文件中定义的顺序进行调用
- 最后调用MergedBeanDefinitionPostProcessor接口的实现Bean，同样按照在配置文件中定义的顺序进行调用
initMessageSource方法
initMessageSource方法用于初始化MessageSource，MessageSource是Spring定义的用于实现访问国际化的接口，看一下源码：
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 + "]");
}
}
}
这个if...else...判断比较好理解：
- 如果自定义了名为"messageSource"的Bean，那么直接实例化Bean，该Bean必须是MessageSource接口的实现Bean，顺便该Bean如果是HierarchicalMessageSource接口的实现类，强转为HierarchicalMessageSource接口，并设置一下parentMessageSource
- 如果没有自定义名为"messageSource"的Bean，那么会默认注册一个DelegatingMessageSource并加入
initApplicationEventMulticaster方法
initApplicationEventMulticaster方法是用于初始化上下文事件广播器的，看一下源码：
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 + "]");
}
}
}
和initMessageSource方法一样，这个if...else...判断也比较好理解：
- 如果自定义了名为"applicationEventMulticaster"的Bean，就实例化自定义的Bean，但自定义的Bean必须是ApplicationEventMulticaster接口的实现类
- 如果没有自定义名为"ApplicationEventMulticaster"的Bean，那么就注册一个类型为SimpleApplicationEventMulticaster的Bean
整个Spring的广播器是观察者模式的经典应用场景之一，这个之后有时间会分析Spring广播器的源码。
onRefresh方法
接下来简单说说onRefresh方法，AbstractApplicationContext中这个方法没有什么定义：
/**
* Template method which can be overridden to add context-specific refresh work.
* Called on initialization of special beans, before instantiation of singletons.
* <p>This implementation is empty.
* @throws BeansException in case of errors
* @see #refresh()
*/
protected void onRefresh() throws BeansException {
// For subclasses: do nothing by default.
}
看一下注释的意思：一个模板方法，重写它的作用是添加特殊上下文刷新的工作，在特殊Bean的初始化时、初始化之前被调用。在Spring中，AbstractRefreshableWebApplicationContext、GenericWebApplicationContext、StaticWebApplicationContext都实现了这个方法。
registerListeners方法
registerListeners方法顾名思义，用于注册监听器：
/**
* 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 lisName : listenerBeanNames) {
getApplicationEventMulticaster().addApplicationListenerBean(lisName);
}
}
这里先向applicationEventMulticaster中注册一些静态的、特定的监听器。
finishRefresh方法
最后一步，结束Spring上下文刷新：
/**
* Finish the refresh of this context, invoking the LifecycleProcessor's
* onRefresh() method and publishing the
* {@link org.springframework.context.event.ContextRefreshedEvent}.
*/
protected void finishRefresh() {
// Initialize lifecycle processor for this context.
initLifecycleProcessor(); // Propagate refresh to lifecycle processor first.
getLifecycleProcessor().onRefresh(); // Publish the final event.
publishEvent(new ContextRefreshedEvent(this));
}
这里面分了三步，第一步，初始化LifecycleProcessor接口：
protected void initLifecycleProcessor() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
this.lifecycleProcessor =
beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
if (logger.isDebugEnabled()) {
logger.debug("Using LifecycleProcessor [" + this.lifecycleProcessor + "]");
}
}
else {
DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
defaultProcessor.setBeanFactory(beanFactory);
this.lifecycleProcessor = defaultProcessor;
beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate LifecycleProcessor with name '" +
LIFECYCLE_PROCESSOR_BEAN_NAME +
"': using default [" + this.lifecycleProcessor + "]");
}
}
}
流程和initMessageSource方法、initApplicationEventMulticaster方法基本类似：
- 先找一下有没有自定义名为"lifecycleProcessor"的Bean，有的话就实例化出来，该Bean必须是LifecycleProcessor的实现类
- 没有自定义名为"lifecycleProcessor"的Bean，向Spring上下文中注册一个类型为DefaultLifecycleProcessor的LifecycleProcessor实现类
第二步，调用一下LifecycleProcessor的onRefresh方法。
第三步，由于之前已经初始化了：
public void publishEvent(ApplicationEvent event) {
Assert.notNull(event, "Event must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Publishing event in " + getDisplayName() + ": " + event);
}
getApplicationEventMulticaster().multicastEvent(event);
if (this.parent != null) {
this.parent.publishEvent(event);
}
}
后记
再看AbstractApplicationContext的refresh方法，从中读到了很多细节：
- Spring默认加载的两个Bean，systemProperties和systemEnvironment，分别用于获取环境信息、系统信息
- BeanFactoryPostProcessor接口用于在所有Bean实例化之前调用一次postProcessBeanFactory
- 可以通过实现PriorityOrder、Order接口控制BeanFactoryPostProcessor调用顺序
- 可以通过实现PriorityOrder、Order接口控制BeanPostProcessor调用顺序
- 默认的MessageSource，名为"messageSource"
- 默认的ApplicationEventMulticaster，名为"applicationEventMulticaster"
- 默认的LifecycleProcessor，名为"lifecycleProcessor"
除了这些，在整个refresh方法里还隐藏了许多细节，这里就不一一罗列了，多读源码，会帮助我们更好地使用Spring。
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