这是我参与8月更文挑战的第23天，活动详情查看：8月更文挑战
前言
前面两篇文章介绍了一下Spring IOC的概念和一些核心组件，这两天又重新看了下《Spring源码深度解析》，《Spring实战》和《Spring揭秘》三本书，说到Spring大家可能很熟悉，作为后端研发基本都是用的Spring框架。说到Spring源码我们一般都想到什么呢？IOC， Spring bean生命周期，aop, Spring 生命周期中各种扩展点。Spring使用门槛不高，但是入门的门槛是极高的，不了解源码，面对各种中间件，开源代码里面的问题就很难入手了。
对于源码不太了解的新手建议可以看看《Spring揭秘》这本书。
Spring的IoC容器在实现控制反转和依赖注入的过程中,可以划分为两个阶段，
- 容器启动阶段
- Bean实例化阶段
Spring 源码分析系列
1. 容器启动过程分析
例子
// 定义接口
public interface MessageService {
String send();
}
// 定义实现类
public class MessageServiceImpl implements MessageService {
@Override
public String send() {
return "say hi";
}
}
定义MessageBean.xml文件
<?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">
<bean id="messageService" class="com.br.spring.demo.impl.MessageServiceImpl"/>
</beans>
APP应用
public class App {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("classpath:MessageBean.xml");
System.out.println("context start success");
// 从 context 中取出我们的 Bean，控制反转将创建对象操作交给Spring 不需要自己在new对象
MessageService messageService = context.getBean(MessageService.class);
// 这句将输出: say hi
System.out.println(messageService.send());
}
}
输出结果
1.1 入口ClassPathXmlApplicationContext构造函数
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
super(parent);
// 根据提供的路径，处理成配置文件
setConfigLocations(configLocations);
if (refresh) {
// 核心方法
refresh();
}
}
1.2 获取资源加载器 (AbstractApplicationContext)
public abstract class AbstractApplicationContext extends DefaultResourceLoader
implements ConfigurableApplicationContext {
static {
// Eagerly load the ContextClosedEvent class to avoid weird classloader issues
// on application shutdown in WebLogic 8.1. (Reported by Dustin Woods.)
ContextClosedEvent.class.getName();
}
public AbstractApplicationContext(@Nullable ApplicationContext parent) {
this();
setParent(parent);
}
public AbstractApplicationContext() {
// 获取一个Spring reource的加载器
this.resourcePatternResolver = getResourcePatternResolver();
}
// ....
}
Spring资源加载器 AbstractApplicationContext#getResourcePatternResolver
protected ResourcePatternResolver getResourcePatternResolver() {
return new PathMatchingResourcePatternResolver(this);
}
public PathMatchingResourcePatternResolver(ResourceLoader resourceLoader) {
Assert.notNull(resourceLoader, "ResourceLoader must not be null");
this.resourceLoader = resourceLoader;
}
1.3 解析配置路径 AbstractRefreshableConfigApplicationContext
获取到资源加载器后， 再调用父类 AbstractRefreshableConfigApplicationContext 的 setConfigLocations() 方法设定位配置文件的路径信息。
// 处理单个资源文件
public void setConfigLocation(String location) {
setConfigLocations(StringUtils.tokenizeToStringArray(location, CONFIG_LOCATION_DELIMITERS));
}
// 处理多个资源文件
public void setConfigLocations(@Nullable String... locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
1.4 开始启动流程 AbstractApplicationContext#refresh()
Spring IOC容器对bean的装载是从refresh方法开始的，refresh()是一个模板方法，规定了IOC 容器的启动流程， 当然也定义了一些钩子函数，交给子类去实现。
refresh()方法主要为 IOC 容器 Bean 的生命周期管理提供条件，整个 refresh() 中 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory() 这句以后代码的都是注册容器的信息源和生命周期事件，我们前面说的载入就是从这句代码开始启动。Spring IOC 容器载入 Bean 配置信息是从其子类容器的 refreshBeanFactory() 方法启动。
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
// 1. 准备工作，记录容器启动时间，标记已启动状态
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
// 2.告诉子类启动refreshBeanFactory()方法，Bean定义资源文件的载入从子类的refreshBeanFactory()方法启动
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// 3.为BeanFactory配置处理器，例如类加载器、事件处理器等
prepareBeanFactory(beanFactory);
try {
// 4. 前置处理器
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 5.调用所有注册的BeanFactoryPostProcessor的Bean
invokeBeanFactoryPostProcessors(beanFactory);
// 6. 为BeanFactory注册BeanPost事件处理器， BeanPostProcessor是Bean后置处理器，用于监听容器触发的事件
registerBeanPostProcessors(beanFactory);
//7.初始化信息源，和国际化相关.
initMessageSource();
// Initialize event multicaster for this context.
// 8.初始化容器事件传播器
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 9.调用子类的某些特殊Bean初始化方法
onRefresh();
// Check for listener beans and register them.
// 10.为事件传播器注册事件监听器.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// 11.初始化所有剩余的单例Bean
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// 12.初始化容器的生命周期事件处理器，并发布容器的生命周期事件
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.
// 13.销毁已创建的Bean
destroyBeans();
// Reset 'active' flag.
// 14.取消refresh操作，重置容器的同步标识。
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...
// 15.重设公共缓存
resetCommonCaches();
}
}
}
1.4.1 prepareRefresh
protected void prepareRefresh() {
// Switch to active. 设置启动时间，启动标识
this.startupDate = System.currentTimeMillis();
this.closed.set(false);
this.active.set(true);
if (logger.isDebugEnabled()) {
if (logger.isTraceEnabled()) {
logger.trace("Refreshing " + this);
}
else {
logger.debug("Refreshing " + getDisplayName());
}
}
// Initialize any placeholder property sources in the context environment.
initPropertySources();
// Validate that all properties marked as required are resolvable:
// see ConfigurablePropertyResolver#setRequiredProperties
getEnvironment().validateRequiredProperties();
// Store pre-refresh 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...
this.earlyApplicationEvents = new LinkedHashSet<>();
}
1.4.2. obtainFreshBeanFactory
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
return getBeanFactory();
}
AbstractRefreshableApplicationContext#refreshBeanFactory 创建容器
@Override
protected final void refreshBeanFactory() throws BeansException {
// 如果已经有容器，销毁容器中的bean，关闭容器
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
// 创建IOC容器
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
// 自定义IOC容器，如设置启动参数，开启注解的自动装配等
customizeBeanFactory(beanFactory);
// 装载Bean的定义
// 委派模式，在当前类中只定义了抽象的loadBeanDefinitions方法，具体的实现调用子类容器 loadBeanDefinitions(beanFactory);
loadBeanDefinitions(beanFactory);
this.beanFactory = beanFactory;
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
AbstractXmlApplicationContext#loadBeanDefinitions(beanFactory)
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// 创建XmlBeanDefinitionReader
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// 为Bean读取器设置Spring资源加载器
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// 当Bean读取器读取Bean定义的Xml资源文件时，启用Xml的校验机制
initBeanDefinitionReader(beanDefinitionReader);
// Bean读取器真正实现加载的方法
loadBeanDefinitions(beanDefinitionReader);
}
initBeanDefinitionReader
protected void initBeanDefinitionReader(XmlBeanDefinitionReader reader) {
reader.setValidating(this.validating);
}
loadBeanDefinitions
// Xml Bean读取器加载Bean定义资源
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
// 获取Bean定义资源的定位
Resource[] configResources = getConfigResources();
if (configResources != null) {
// Xml Bean读取器调用其父类AbstractBeanDefinitionReader读取定位的Bean定义资源
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
// Xml Bean读取器调用其父类AbstractBeanDefinitionReader读取定位的Bean定义资源
reader.loadBeanDefinitions(configLocations);
}
}
1.4.3 prepareBeanFactory(beanFactory)
这个方法不难理解，定了一堆处理器，比如类加载器，事件处理器等等。
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.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
// ....
}
1.4.4 postProcessBeanFactory(beanFactory) 前置处理器
spring中并没有具体去实现postProcessBeanFactory方法，是提供给想要实现BeanPostProcessor的三方框架使用的。
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
}
1.4.5 invokeBeanFactoryPostProcessors
为BeanFactory注册BeanPost事件处理器， BeanPostProcessor是Bean后置处理器，用于监听容器触发的事件，核心方法后面还会详细去介绍
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
1.4.6 registerBeanPostProcessors(beanFactory)
为BeanFactory注册BeanPost事件处理器， BeanPostProcessor是Bean后置处理器，用于监听容器触发的事件.
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}
1.4.7 initMessageSource
初始化信息源，和国际化相关.
1.4.8 initApplicationEventMulticaster
初始化容器事件传播器.
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.isTraceEnabled()) {
logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
}
}
else {
this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
if (logger.isTraceEnabled()) {
logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
"[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
}
}
}
1.4.9 onRefresh()
调用子类的某些特殊Bean初始化方法, 主要和web相关
1.4.10 registerListeners
为事件传播器注册事件监听器.
protected void registerListeners() {
//手动注册的监听器绑定到广播器
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);
}
// 先发布早期的监听器
Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
this.earlyApplicationEvents = null;
if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
getApplicationEventMulticaster().multicastEvent(earlyEvent);
}
}
}
1.4.11 finishBeanFactoryInitialization
初始化所有剩余的单例Bean
1.4.12 finishRefresh
初始化容器的生命周期事件处理器，并发布容器的生命周期事件
2. Bean实例化阶段
参考
《Spring源码深度解析》
《Spring实战》
《Spring揭秘》
