原创文章，转发请标注https://www.cnblogs.com/boycelee/p/12595884.html
目录
分析例子
启动类
Application，使用的是ClassPathXmlApplicationContext来加载xml文件
/**
* @author jianw.li
* @date 2020/3/16 11:53 PM
* @Description: TODO
*/
public class MyApplication {
private static final String CONFIG_LOCATION = "classpath:application_context.xml";
private static final String BEAN_NAME = "hello";
public static void main(String[] args) {
ApplicationContext ac = new ClassPathXmlApplicationContext(CONFIG_LOCATION);
Hello hello = (Hello) ac.getBean(BEAN_NAME);
hello.sayHello();
}
}
Bean
/**
* @author jianw.li
* @date 2020/3/16 11:53 PM
* @Description: TODO
*/
public class Hello {
public void sayHello() {
System.out.println("Hello World");
}
}
配置文件
在resources下建立名为classpath:application_context.xml的配置文件，并配置好Bean
<?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="hello" class="com.boyce.bean.Hello"></bean>
</beans>
总体结构
ClassPathXmlApplicationContext继承体系如下：
IoC总体结构图如下：
源码分析
BeanFactory获取
ClassPathXmlApplicationContext
//构造函数，创建ClassPathXmlApplicationContext，其中configLocation为Bean所在的文件路径
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
//null
super(parent);
//设置配置路径至ApplicationContext中
setConfigLocations(configLocations);
if (refresh) {
//核心方法，refresh会将旧的ApplicaionContext销毁
refresh();
}
}
AbstractApplicationContext
refresh
核心方法，refresh销毁旧ApplicationContext，生成新的ApplicationContext
@Override
public void refresh() throws BeansException, IllegalStateException {
//加锁.没有明确对象，只是想让一段代码同步，可以创建Object startupShutdownMonitor = new Object()
synchronized (this.startupShutdownMonitor) {
// 为context刷新准备.设置启动时间，设置激活状态等
prepareRefresh();
// 告知子类刷新内部bean factory.
// 获取BeanFactory,默认实现DefaultListableBeanFactory
// 加载BeanDefinition,并注册至BeanDefinitionRegistry
// （核心）
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// 进行BeanFactory的预准备工作，对BeanFactory进行信息设置
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// BeanFactory准备工作
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 实例化实现BeanFactoryPostProcessor接口的Bean,并调用接口方法
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 注册BeanPostProcessors（Bean的后置处理器），创建Bean的前后等执行
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
// 初始化MessageSource组件，国际化相关功能
initMessageSource();
// Initialize event multicaster for this context.
// 初始化事件派发器
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 子类重写，在容器刷新时可以自定义逻辑；如创建Tomcat、Jetty等Web服务器
onRefresh();
// Check for listener beans and register them.
// 注册应用的监听器（注册实现ApplicationListener接口的监听器bean）
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// 初始化所有非懒加载单例bean
// 属性填充
// 初始化方法的调用（例如afterPropertiesSet、init-method方法）
// 调用BeanPostProcessor（后置处理器）对实例bean进行后置处理
// （核心）
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
//广播初始化完成
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();
}
}
}
obtainFreshBeanFactory
告知子类刷新内部bean factory.
核心方法，初始化BeanFactory、加载Bean、注册Bean
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//刷新Bean工厂，关闭并销毁旧BeanFacroty
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
refreshBeanFactory
关闭并销毁旧BeanFactory，创建与初始化新BeanFactory。为什么是DefaultListableBeanFactory？
@Override
protected final void refreshBeanFactory() throws BeansException {
// 判断是否已有BeanFactory
if (hasBeanFactory()) {
// 如果已有，则销毁beans且关闭BeanFactory
destroyBeans();
closeBeanFactory();
}
try {
//初始化DefaultListableBeanFactory，为什么选择实例化DefaultListableBeanFactory？而不是其他的Bean工厂
DefaultListableBeanFactory beanFactory = createBeanFactory();
//Bean工厂序列化设置id
beanFactory.setSerializationId(getId());
//定制Bean工厂,设置不允许覆盖Bean,不允许循环依赖等
customizeBeanFactory(beanFactory);
//加载BeanDefinitions
loadBeanDefinitions(beanFactory);
//此处synchronized块与#hasBeanFactory中的synchronized块存在关联，此处锁住之后hasBeanFactory中的synchronized块将等待
//避免beanFactory未销毁或未关闭的情况
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
customizeBeanFactory
定制BeanFactory。设置Bean覆盖、循环依赖等。什么是循环依赖？
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
if (this.allowBeanDefinitionOverriding != null) {
//默认值为false不允许对Bean进行覆盖
beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
if (this.allowCircularReferences != null) {
//默认值为false,不允许循环依赖
beanFactory.setAllowCircularReferences(this.allowCircularReferences);
}
}
BeanFactory获取时序图
BeanDefinition加载注册
AbstractXmlApplicationContext
loadBeanDefinitions
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
// 为BeanFactory创建XmlBeanDefinitionReader对象，用于解析xml对象
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
// 为beanDefinitionReader设置环境信息
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
// 允许子类自定义初始化阅读器
initBeanDefinitionReader(beanDefinitionReader);
//加载BeanDefinition
loadBeanDefinitions(beanDefinitionReader);
}
loadBeanDefinitions
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources();
if (configResources != null) {
//加载资源对象，最终还是会回到这种方式去加载bean.
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
//加载资源路径吗
reader.loadBeanDefinitions(configLocations);
}
}
AbstractBeanDefinitionReader
loadBeanDefinitions
@Override
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
Assert.notNull(locations, "Location array must not be null");
int counter = 0;
//循环配置文件路径
for (String location : locations) {
counter += loadBeanDefinitions(location);
}
return counter;
}
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
}
if (resourceLoader instanceof ResourcePatternResolver) {
// Resource pattern matching available.
try {
// 将xml转为Resource,所以上面的两种资源加载方式，最终都会回到Resource为参数的加载方式
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
// 加载资源配置中的BeanDeinition对象，并返回数量
int loadCount = loadBeanDefinitions(resources);
if (actualResources != null) {
for (Resource resource : resources) {
actualResources.add(resource);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
}
return loadCount;
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"Could not resolve bean definition resource pattern [" + location + "]", ex);
}
}
else {
// Can only load single resources by absolute URL.
Resource resource = resourceLoader.getResource(location);
int loadCount = loadBeanDefinitions(resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
}
}
@Override
public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
// 就算是入参为location的loadBeanDefinitions，最终也会回到入参为resource的loadBeanDefinitions中
Assert.notNull(resources, "Resource array must not be null");
int counter = 0;
for (Resource resource : resources) {
counter += loadBeanDefinitions(resource);
}
return counter;
}
XmlBeanDefinitionReader
loadBeanDefinitions
从详细的XML文件中加载Bean
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isInfoEnabled()) {
logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}
//用于存储编译过的Reource
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
// 将xml文件流封装为InputSource对象
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
// 执行加载BeanDefinitions
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
inputStream.close();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
doLoadBeanDefinitions
从xml文件中加载bean，将xml转为Document并注册Bean
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
// 将xml转为Document
Document doc = doLoadDocument(inputSource, resource);
// 解析document对象,封装BeanDefinition对象并注册Bean
return registerBeanDefinitions(doc, resource);
}
...
}
registerBeanDefinitions
计算从当前配置文件中加载bean的数量
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// 获取已注册的BeanDefinition的数量
int countBefore = getRegistry().getBeanDefinitionCount();
// 注册BeanDefinition
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
// 计算新注册BeanDefinition的数量并返回
return getRegistry().getBeanDefinitionCount() - countBefore;
}
DefaultBeanDefinitionDocumentReader
registerBeanDefinitions
从“spring-beans” xsd中解析bean。什么是xsd？XML结构定义 （ XML Schemas Definition）
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
// 执行注册BeanDefinitions
doRegisterBeanDefinitions(root);
}
doRegisterBeanDefinitions
从根节点开始注册每一个Bean
/**
* Register each bean definition within the given root {@code <beans/>} element.
* 从根节点开始注册每一个Bean
*/
protected void doRegisterBeanDefinitions(Element root) {
// Any nested <beans> elements will cause recursion in this method. In
// order to propagate and preserve <beans> default-* attributes correctly,
// keep track of the current (parent) delegate, which may be null. Create
// the new (child) delegate with a reference to the parent for fallback purposes,
// then ultimately reset this.delegate back to its original (parent) reference.
// this behavior emulates a stack of delegates without actually necessitating one.
//可以通过spring.profiles.active设定当前环境激活的profile,例如配置prod,可以通过@ActiveProfiles配置
// 解析bean定义
// 委托模式
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
//获取元素中profile属性，可以通过xml或@Profile设置当前bean所属的profile
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
//不能做profile属性则直接跳过
if (StringUtils.hasText(profileSpec)) {
//配置多profile
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
//元素中的profile是否是环境指定的profiles之一
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isInfoEnabled()) {
logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
//不在当前环境指定的profile中则return
return;
}
}
}
preProcessXml(root);
// 解析元素
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
parseBeanDefinitions
从文档根节点开始解析元素，import、alias、bean等
/**
* Parse the elements at the root level in the document:
* "import", "alias", "bean".
* @param root the DOM root element of the document
*/
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
if (delegate.isDefaultNamespace(root)) {
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element) node;
if (delegate.isDefaultNamespace(ele)) {
//解析default namespace下的元素（例如：<import>、<alias>、<beans>、<bean>）
parseDefaultElement(ele, delegate);
}
else {
//解析Custom元素（例如：<mvc>、<context>、<aop>），自定义标签
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
parseDefaultElement
解析default namespace下的元素（例如：
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
//解析bean元素为BeanDefinition
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
processBeanDefinition
获取bean元素解析并注册
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
* 获取bean元素解析并注册
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//解析bean元素成BeanDefinition,并将BeanDefinition封装成BeanDefinitionHolder对象
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
//注册装饰的实例,完成BeanDefinition注册
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
//发送注册事件
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
BeanDefinitionReaderUtils
registerBeanDefinition
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
DefaultListableBeanFactory
registerBeanDefinition
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
//beanDefinitionMap放置所有注册的Bean
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
//如果bean名已存在
if (oldBeanDefinition != null) {
//不允许覆盖bean
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
//通过比较BeanRole.判断谁覆盖谁
else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
//新bean覆盖旧bean
else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
//将bean放置beanDefinitionMap中
this.beanDefinitionMap.put(beanName, beanDefinition);
}
//beanName没有与beanDefinitionMap中的重复
else {
//非正常情况下，其他的Bean已经初始化，如果已经有bean初始化，则使用者已经在进行业务操作，无法保证对beanDefinitionMap、beanDefinitionNames、manualSingletonNames进行操作的一些列动作的线程安全，所以需要加锁。参考：https://blog.csdn.net/qq_41907991/article/details/97614337
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
//bean放置beanDefinitionMap中
this.beanDefinitionMap.put(beanName, beanDefinition);
//记录bean名称
this.beanDefinitionNames.add(beanName);
//bean不需要手动注册
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
BeanDefinition加载注册流程图
总结
至此已经完成了IoC容器的初始化。将xml文件中的bean元素解析为Bean，将Bean注册至注册中心，并发送注册事件。DefaultListableBeanFactory建立Bean配置信息，这些信息都存放在BeanDefinitionMap中，由IoC容器来维护。
最后，懂得不多，做得很少。文章肯定又不少错误，如大家发现麻烦及时指出，为了避免误导更多人，我也会及时学习并修改！
引用参考
[1]《Spring技术内幕》