在看源码之前,我们先明白一个问题
为什么要看Spring源码?
1.解决在使用Spring框架时,出现的一些莫名其妙的问题。
2.体会框架作者的设计思路,理解用到的设计模式。
3.是砸门程序员必须迈过的坎,面试经常问。
分析的入口就是ClassPathXmlApplicationContext有个构造方法
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
//逻辑就在这个方法里面
refresh();
}
}
如果是注解上下文对象AnnotationConfigApplicationContext,最终也是走的refresh方法,只是多了一步注册注解bean。
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
this();
register(annotatedClasses);
refresh();
}
接下来,就是重量级的方法了AbstractApplicationContext -> refresh()方法
// 完成IoC容器的创建及初始化工作
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// 1: 刷新预处理逻辑
prepareRefresh();
//重点步骤
// 2.1 创建IoC容器(DefaultListableBeanFactory)
// 2.2 加载解析XML文件(最终存储到Document对象中)
// 2.3读取Document对象,并完成BeanDefinition的加载和注册工作
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 3: 对beanFactory设置一些公共属性
prepareBeanFactory(beanFactory);
try {
// 4: 钩子函数,空实现
postProcessBeanFactory(beanFactory);
// 5: 调用BeanFactoryPostProcessor后置处理器对BeanDefinition处理(实现了BeanFactoryPostProcessor接口的类)
invokeBeanFactoryPostProcessors(beanFactory);
// 6: 注册BeanPostProcessor后置处理器(实现了BeanPostProcessor接口的类)
registerBeanPostProcessors(beanFactory);
// 7: 初始化一些消息源(比如处理国际化的i18n等消息源,其实就是往beanFactory中注册bean)
initMessageSource();
// 8: 初始化事件广播器(往beanFactory中注册bean)
initApplicationEventMulticaster();
// 9: 初始化一些特殊的bean(ThemeSource 在某些情况下没有找到bean,会采用这里注册的bean)
onRefresh();
// 10: 注册监听器(实现了ApplicationListener接口)
registerListeners();
//重点步骤
// 11: 实例化剩余的单例bean(非懒加载方式)
// 注意事项:Bean的IoC、DI和AOP都是发生在此步骤
finishBeanFactoryInitialization(beanFactory);
// 12:容器初始化完成,加上一些生命周期逻辑,发布完成事件
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
//如果bean实现了DisposableBean,会调用
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();
}
}
}
整个刷新步骤有12大步,下面主要分析第2,11两个重要步骤的源码。其它步骤大家可以自行脑补。
下面就来看上诉第二步:ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();创建ioc容器,完成beanDefinition的加载和注册
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
// 主要是通过该方法完成IoC容器的刷新
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
先看refreshBeanFactory()方法
@Override
protected final void refreshBeanFactory() throws BeansException {
// 如果之前有IoC容器,则销毁
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
// 创建IoC容器,也就是DefaultListableBeanFactory
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
// 设置工厂属性:是否允许BeanDefinition覆盖和是否允许循环依赖
customizeBeanFactory(beanFactory);
// 加载bean定义,当前类这个方法是个abstract方法
//下面看这个方法
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
由AbstractXmlApplicationContext -> 实现方法 loadBeanDefinitions()
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// 创建一个BeanDefinition阅读器,用于读取和加载beanDefinition
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
//设置reader的validate
initBeanDefinitionReader(beanDefinitionReader);
// 委托给beanDefinitionReader去加载BeanDefinition
//下面看这个方法
loadBeanDefinitions(beanDefinitionReader);
}
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
// 获取资源的定位
//获取的是ClassPathXmlApplicationContext类的 configResources属性值
Resource[] configResources = getConfigResources();
if (configResources != null) {
// XML B调用其父类AbstractBeanDefinitionReader读取定位的资源
reader.loadBeanDefinitions(configResources);
}
// 如果子类中获取的资源定位为空,则获取FileSystemXmlApplicationContext构造方法中setConfigLocations方法设置的资源
String[] configLocations = getConfigLocations();
if (configLocations != null) {
// XML 调用其父类AbstractBeanDefinitionReader读取定位的资源
reader.loadBeanDefinitions(configLocations);
}
}
下面继续看reader.loadBeanDefinitions(configLocations)方法
调用的是AbstractBeanDefinitionReader -> loadBeanDefinitions方法
@Override
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
Assert.notNull(locations, "Location array must not be null");
int count = 0;
for (String location : locations) {
//继续看这个方法
count += loadBeanDefinitions(location);
}
return count;
}
@Override
public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
return loadBeanDefinitions(location, null);
}
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
}
if (resourceLoader instanceof ResourcePatternResolver) {
try {
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
//继续看这个方法
int count = loadBeanDefinitions(resources);
if (actualResources != null) {
Collections.addAll(actualResources, resources);
}
if (logger.isTraceEnabled()) {
logger.trace("Loaded " + count + " bean definitions from location pattern [" + location + "]");
}
return count;
}
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 count = loadBeanDefinitions(resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isTraceEnabled()) {
logger.trace("Loaded " + count + " bean definitions from location [" + location + "]");
}
return count;
}
}
@Override
public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
Assert.notNull(resources, "Resource array must not be null");
int count = 0;
for (Resource resource : resources) {
//继续跟
count += loadBeanDefinitions(resource);
}
return count;
}
这里调用的是XmlBeanDefinitionReader - >loadBeanDefinitions
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
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 {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//继续进这个方法
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();
}
}
}
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//将resource转化为了Document对象
Document doc = doLoadDocument(inputSource, resource);
//终于看到注册bean的方法了,进去
int count = registerBeanDefinitions(doc, resource);
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}//删除了后面的catch
}
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//创建documentReader
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//记录之前bean数量
int countBefore = getRegistry().getBeanDefinitionCount();
//进去看看
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
//用现在的 - 之前的 = 本次加载的bean数量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
上面的documentReader.registerBeanDefinitions()方法
进入到了DefaultBeanDefinitionDocumentReader -> registerBeanDefinitions 方法
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
doRegisterBeanDefinitions(doc.getDocumentElement());
}
@SuppressWarnings("deprecation") // for Environment.acceptsProfiles(String...)
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.
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
// We cannot use Profiles.of(...) since profile expressions are not supported
// in XML config. See SPR-12458 for details.
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
//钩子方法 空实现
preProcessXml(root);
//继续看这个方法
parseBeanDefinitions(root, this.delegate);
//钩子方法 空实现
postProcessXml(root);
this.delegate = parent;
}
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)) {//解析默认标签
//下面看这个方法
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {//解析自定义标签
delegate.parseCustomElement(root);
}
}
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {//import
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {//alias
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {//bean
//下面解析bean标签
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {//beans
// recurse
doRegisterBeanDefinitions(ele);
}
}
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//解析出来了beanName beanDefinition alias等
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// 看这个 注册方法
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
调用的是BeanDefinitionReaderUtils.registerBeanDefinition()方法
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// 取出beanName和对应的beanDefinition注册
String beanName = definitionHolder.getBeanName();
//继续看这个方法
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
//注册beanName 和对应的别名
registry.registerAlias(beanName, alias);
}
}
}
registry.registerBeanDefinition()方法
调用的是DefaultListableBeanFactory -> registerBeanDefinition方法
@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();
}
}
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {//已经存在beanDefinition,不允许覆盖bean就报错
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
//中间删除了一下不重要的源码
//到这,表示bean已经存在了,直接覆盖
//private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256); 其实就是个
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {//判断是否有bean正在创建
// Cannot modify startup-time collection elements anymore (for stable iteration)
//这个时候不能修改集合元素
//这个地址加锁,应该是为了下面的list扩容吧
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
//不是很明白为什么注册bean,就创建一个list,然后复制到新的list
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
//private volatile List<String> beanDefinitionNames = new ArrayList<>(256);
this.beanDefinitionNames = updatedDefinitions;
//里面用Set去重了
removeManualSingletonName(beanName);
}
}
else {//没有创建的就直接put
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
//重置beanDefinition
resetBeanDefinition(beanName);
}
}
到这,第2步的主要流程算是走完了。
主要流程就是:加载配置文件,解析bean,加载bean,生成BeanDefinition对象,存放到了DefaultListableBeanFactory的beanDefinitionsMap<beanname,beanDefinition>中。