先看下启动 Spring 容器的一个例子:
public class App {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("classpath:application.xml");
// 从 context 中取出我们的 Bean
MessageService messageService = context.getBean(MessageService.class);
System.out.println(messageService.getMessage());
}
}
ClassPathXmlApplicationContext 的源码:
public class ClassPathXmlApplicationContext extends AbstractXmlApplicationContext {
// 将配置文件作为资源都存放到这个数组中
private Resource[] configResources;
// 如果已经有 ApplicationContext并需要配置成父子关系,那么调用这个构造方法
public ClassPathXmlApplicationContext(ApplicationContext parent) {
super(parent);
}
...
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
super(parent);
// 解析配置文件列表,放置到上面说的那个 configResources 数组中
setConfigLocations(configLocations);
if (refresh) {
refresh(); // 核心方法 调用AbstractApplicationContext.refresh()
}
}
...
}
// AbstractApplicationContext.java L509
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// 准备工作,记录下容器的启动时间、标记“已启动”状态、处理配置文件中的占位符
prepareRefresh();
// 这步比较关键,这步完成后,配置文件就会解析成一个个 Bean 定义,注册到 BeanFactory 中,这里的 Bean 还没有初始化,只是配置信息都提取出来了,
// 注册也只是将这些信息都保存到了注册中心(说到底核心是一个 beanName-> beanDefinition 的 map)
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 设置 BeanFactory 的类加载器,添加几个 BeanPostProcessor,手动注册几个特殊的 bean
// 这块待会会展开说
prepareBeanFactory(beanFactory);
try {
// 【这里需要知道 BeanFactoryPostProcessor 这个知识点,Bean 如果实现了此接口,那么在容器初始化以后,Spring 会负责调用里面的 postProcessBeanFactory 方法。】
// 这里是提供给子类的扩展点,到这里的时候,所有的 Bean 都加载、注册完成了,但是都还没有初始化
// 具体的子类可以在这步的时候添加一些特殊的BeanFactoryPostProcessor 的实现类或做点什么事
postProcessBeanFactory(beanFactory);
// 调用 BeanFactoryPostProcessor 各个实现类的 postProcessBeanFactory(factory) 方法
invokeBeanFactoryPostProcessors(beanFactory);
// 注册 BeanPostProcessor 的实现类,注意看和 BeanFactoryPostProcessor 的区别
// 此接口两个方法: postProcessBeforeInitialization 和 postProcessAfterInitialization
// 两个方法分别在 Bean 初始化之前和初始化之后得到执行。注意,到这里 Bean 还没初始化
registerBeanPostProcessors(beanFactory);
// 初始化当前 ApplicationContext 的 MessageSource(国际化相关信息),国际化这里就不展开说了
initMessageSource();
// 初始化当前 ApplicationContext 的事件广播器,这里也不展开了
initApplicationEventMulticaster();
// 从方法名就可以知道,典型的模板方法(钩子方法),
// 具体的子类可以在这里初始化一些特殊的 Bean(在初始化 singleton beans 之前)
onRefresh();
// 注册事件监听器,监听器需要实现 ApplicationListener 接口。这也不是我们的重点,过
registerListeners();
// 重点,重点,重点
// 初始化所有的 singleton beans
//(lazy-init 的除外)
finishBeanFactoryInitialization(beanFactory);
// 最后,广播事件,ApplicationContext 初始化完成
finishRefresh();
} catch (BeansException ex) {
// Destroy already created singletons to avoid dangling resources.
// 销毁已经初始化的 singleton 的 Beans,以免有些 bean 会一直占用资源
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// 把异常往外抛
throw ex;
}finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
接下来对refresh()方法进行分析:
1-0.prepareRefresh() 创建 Bean 容器前的准备工作
AbstractApplicationContext.java L557
protected void prepareRefresh() {
// 将 active 属性设置为 true,closed 属性设置为 false,它们都是 AtomicBoolean 类型
this.closed.set(false);
this.active.set(true);
// Initialize any placeholder property sources in the context environment
initPropertySources();
// 校验 xml 配置文件
getEnvironment().validateRequiredProperties();
this.earlyApplicationEvents = new LinkedHashSet<ApplicationEvent>();
}
1-1.obtainFreshBeanFactory() 创建 Bean 容器,加载并注册 Bean
// AbstractApplicationContext.java L613
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
// 关闭旧的 BeanFactory (如果有),创建新的 BeanFactory,加载 Bean 定义、注册 Bean 等等
refreshBeanFactory();
// 返回刚刚创建的 BeanFactory
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
refreshBeanFactory()是创建bean的入口,并将bean实例放到bean工厂的入口(beanName为key,bean实例为value放入beanFactory里的map中),在《【spring 源码】IOC 之bean实例的创建》里详细介绍这个方法的实现。
1-2 prepareBeanFactory(beanFactory) 准备bean容器
AbstractApplicationContext.java L627
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// 设置 BeanFactory 的类加载器,我们知道 BeanFactory 需要加载类,也就需要类加载器,这里设置为当前线程的上下文类加载器
beanFactory.setBeanClassLoader(getClassLoader());
//设置spring 的Spel表达式相关解析器,不是主流程,不做拓展
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
//设置PropertyEditorRegistrar,通过PropertyEditor将xml解析出来的bean属性(字符串)和相应的java类型做转换
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// 添加一个 BeanPostProcessor,这个 processor 比较简单,
// 实现了 Aware 接口的几个特殊的 beans 在初始化的时候,这个 processor 负责回调
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
// 下面几行的意思就是,如果某个 bean 依赖于以下几个接口的实现类,在自动装配的时候忽略它们,Spring 会通过其他方式来处理这些依赖。
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
/**
* 下面几行就是为特殊的几个 bean 赋值,如果有 bean 依赖了以下几个,会注入这边相应的值,
* 之前我们说过,"当前 ApplicationContext 持有一个 BeanFactory",这里解释了第一行
* ApplicationContext 继承了 ResourceLoader、ApplicationEventPublisher、MessageSource
* 所以对于这几个,可以赋值为 this,注意 this 是一个 ApplicationContext
*/
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// ,在 bean 实例化后,如果是 ApplicationListener 的子类,那么将其添加到 listener 列表中,可以理解成:注册事件监听器
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// 这里涉及到特殊的 bean:loadTimeWeaver,织入的一种方式,此处这不是我们的重点,忽略它
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()));
}
/**
* 从下面几行代码我们可以知道,Spring 往往很 "智能" 就是因为它会帮我们默认注册一些有用的 bean,
* 我们也可以选择覆盖
*/
//注册一个默认的environment的bean
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
//注册一个systemProperties的bean
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
//注册一个systemEnvironment的bean
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
}
至此,准备bean容器结束了,主要就是初始化bean工厂的一些环境、类加载器等
1-3 postProcessBeanFactory(beanFactory)
主要作用是:承接前文中的prepareBeanFactory()方法后,供子类在标准的基础上再添加自定义的属性性质,主要是注册BeanPostProcessors //AbstractRefreshableWebApplicationContext.java L159
/**
* Register request/session scopes, a {@link ServletContextAwareProcessor}, etc.
*/
@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
//注册ServletContextAwareProcessor
beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
beanFactory.ignoreDependencyInterface(ServletContextAware.class);
beanFactory.ignoreDependencyInterface(ServletConfigAware.class);
//注册web环境,包括request、session、golableSession、application
WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
//注册servletContext、contextParamters、contextAttributes、servletConfig单例bean
WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
}
1-4 invokeBeanFactoryPostProcessors(beanFactory)
主要是实例化和调用所有已注册的BeanFactoryPostProcessors的postProcessBeanFactory(factory) 方法 //AbstractApplicationContext.java L686
/**
* Instantiate and invoke all registered BeanFactoryPostProcessor beans,
* respecting explicit order if given.
* <p>Must be called before singleton instantiation.
*/
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
//通过一个委托类来处理实例化调用
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()));
}
}
1-4-0 invokeBeanFactoryPostProcessors(beanFactory,beanFactoryPostProcessors)
//PostProcessorRegistrationDelegate.java L52
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// 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> registryProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();
//遍历BeanFactoryPostProcessors
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
//BeanDefinitionRegistryPostProcessor这个类很重要,spring集成mybatis时会用到它。后面会有篇文章专门介绍它的作用
//BeanDefinitionRegistryPostProcessor允许在正常的BeanFactoryPostProcessor检测开始之前注册更多的自定义bean。经常用来自定义注解
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// Separate between BeanDefinitionRegistryPostProcessors that implement
// PriorityOrdered, Ordered, and the rest.
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, 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 (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
beanFactory.clearMetadataCache();
}
我们来总结一下,到目前为止,应该说 BeanFactory 已经创建完成,并且所有的实现了 BeanFactoryPostProcessor 接口的 Bean 都已经初始化并且其中的 postProcessBeanFactory(factory) 方法已经得到执行了。所有实现了 BeanPostProcessor 接口的 Bean 也都完成了初始化。
1-5 finishBeanFactoryInitialization(beanFactory)
初始化所有的 singleton beans
/**
* Finish the initialization of this context's bean factory,
* initializing all remaining singleton beans.
*/
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// 首先,初始化名字为 conversionService 的 Bean
// 注意了,初始化的动作包装在 beanFactory.getBean(...) 中
//conversionService这个类相信用过的人不会陌生,它用来将前端传过来的参数和后端的 controller 方法上的参数进行绑定的时候用。像前端传过来的字符串、整数要转换为后端的 String、Integer 很容易,但是如果 controller 方法需要的是一个枚举值,或者是 Date 这些非基础类型(含基础类型包装类)值的时候,我们就可以考虑采用 ConversionService 来进行转换
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
//beanFactory.getBean(),是bean真正初始化过程的关键入口
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.
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(new StringValueResolver() {
@Override
public String resolveStringValue(String strVal) {
return getEnvironment().resolvePlaceholders(strVal);
}
});
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// 开始初始化剩下的
beanFactory.preInstantiateSingletons();
}
从上面最后一行往里看,我们又回到 DefaultListableBeanFactory#preInstantiateSingletons了 //DefaultListableBeanFactory.java L728
public void preInstantiateSingletons() throws BeansException {
...
List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
for (String beanName : beanNames) {
//合并父bean中的配置
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
// FactoryBean 的话,在 beanName 前面加上 ‘&’ 符号。再调用 getBean
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
// 判断当前 FactoryBean 是否是 SmartFactoryBean 的实现,此处忽略,直接跳过
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
@Override
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
// 对于普通的 Bean,只要调用 getBean(beanName) 这个方法就可以进行初始化了
getBean(beanName);
}
}
}
// 到这里说明所有的非懒加载的 singleton beans 已经完成了初始化
// 如果我们定义的 bean 是实现了 SmartInitializingSingleton 接口的,那么在这里得到回调,忽略
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
smartSingleton.afterSingletonsInstantiated();
return null;
}
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
上面代码里多次出现getBean() 方法,这个方法我们经常用来从 BeanFactory 中获取一个 Bean,而初始化的过程也封装到了这个方法里,详见 【spring 源码】IOC 之 bean实例初始化。
(未完,待续)