分析源码是一件很枯燥的事件。
spring boot的源码最后还是落到refresh()，spring这里来。故，分析spring 源码。
spring 版本 4.3.11。
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("classpath:application.xml");
System.out.println("context 启动成功");
MessageService messageService = context.getBean(MessageService.class);
System.out.println(messageService.getMessage());
}
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {configLocation}, true, null);
}
// new ClassPathXmlApplicationContext可以传入多个配置文件，可以控制是否
// 启动刷新spring容器，以及父子ApplicationContext对象
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
// 保存配置文件路径
setConfigLocations(configLocations);
if (refresh) {
// 刷新spring容器，重点操作
refresh();
}
}
public void setConfigLocations(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++) {
// resolvePath对传入的配置文件路径，进行一下占位符替换等操作，比如传入
// ${class:application}会把class替换为windows环境变量的class变量。
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
启动spring容器，为什么叫refresh，因为如果已经启动了spring容器，则会销毁，重新启动一个。
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// 标记了激活、关闭状态，验证了下参数
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) {
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();
}
}
}
protected void prepareRefresh() {
this.startupDate = System.currentTimeMillis();
// 标记一下激活、关闭状态
this.closed.set(false);
this.active.set(true);
if (logger.isInfoEnabled()) {
logger.info("Refreshing " + this);
}
// 给子类实现的,什么都没做
initPropertySources();
// 校验一下属性是否齐全，ConfigurablePropertyResolver.setRequiredProperties方法可以设置必须要哪些属性
// getEnvironment()返回StandardEnvironment对象，StandardEnvironment对象实现了ConfigurablePropertyResolver接口
// 这里之前并没有调用setRequiredProperties方法设置必须要的属性，所以属性校验肯定通过
getEnvironment().validateRequiredProperties();
// 早期application事件
this.earlyApplicationEvents = new LinkedHashSet<ApplicationEvent>();
}
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
protected final void refreshBeanFactory() throws BeansException {
// 如果之前已经初始化过spring容器，这里就销毁掉
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
// 创建BeanFactory，创建的beanFactory是DefaultListableBeanFactory
// DefaultListableBeanFactory是一个功能很强大的BeanFactory,它几乎实现了BeanFactory下的所有乱七八糟的子接口
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
// 设置beanFactory是否允许bean重写，以及bean循环依赖
// 默认都为null
// beanFactory重写是指，不同配置文件下同名bean会存在覆盖的情况
customizeBeanFactory(beanFactory);
// 加载BeanDefinitions，重点
// BeanDefinitions保存了bean相关的所有信息，bean解析的信息最后包装成beanDefinition
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
// 创建BeanFactory，创建的beanFactory是DefaultListableBeanFactory
protected DefaultListableBeanFactory createBeanFactory() {
return new
// getInternalParentBeanFactory返回的是父容器的BeanFactory，父容器没有，所以是null，
DefaultListableBeanFactory(getInternalParentBeanFactory());
}
// 设置beanFactory是否允许bean重写，以及bean循环依赖
// 默认都为null
// beanFactory重写是指，不同配置文件下同名bean会存在覆盖的情况
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
if (this.allowBeanDefinitionOverriding != null) { beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
if (this.allowCircularReferences != null) {beanFactory.setAllowCircularReferences(this.allowCircularReferences);
}
}
加载BeanDefinitions，重点
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// 用来解析配置文件的。
//维护了一个变量：this.resourceLoader = new PathMatchingResourcePatternResolver();
//PathMatchingResourcePatternResolver是解析类路径下的配置文件的
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
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.
// 让子类初始化的
initBeanDefinitionReader(beanDefinitionReader);
// 加载BeanDefinitions，重点
loadBeanDefinitions(beanDefinitionReader);
}
加载BeanDefinitions
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources();
// 只有字符串类型的resouce配置文件，没有resouce对象的resouce配置文件
// 不会进入这里
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
// 用前面创建的XmlBeanDefinitionReader解析配置文件
reader.loadBeanDefinitions(configLocations);
}
}
// 解析配置文件，返回解析的配置文件数
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
Assert.notNull(locations, "Location array must not be null");
int counter = 0;
for (String location : locations) {
counter += loadBeanDefinitions(location);
}
return counter;
}
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
// resourceLoader 就是ClassPathApplicationContext
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
}
// ClassPathApplicationContext实现了ResourcePatternResolver接口，进入这里
if (resourceLoader instanceof ResourcePatternResolver) {
// Resource pattern matching available.
try {
// 把指定路径的配置文件读取成Resouce对象，通过PathMatchingResourcePatternResolver对象
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
// 解析Resouce对象
int loadCount = loadBeanDefinitions(resources);
// actualResources 为空
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;
}
}
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
加载BeanDefinitions，重点
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());
}
// ThreadLocal对象保存EncodedResource集合
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<EncodedResource>(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());
}
// 加载BeanDefinitions，重点
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 {
// 把配置文件xml，解析成Document对象，解析过程忽略
// 注册BeanDefinition
Document doc = doLoadDocument(inputSource, resource);
return registerBeanDefinitions(doc, resource);
}
注册BeanDefinitions：将document对象，解析成Definition，并注册
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// 创建BeanDefinition document的解析对象
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// getRegistry返回的就是DefaultListableBeanFactory，前面设置进去的
// 注册前，获取BeanDefinitionRegistry已经注册了多个beanDefinition
// 注册的BeanDefinition其实就是把BeanDefinition保存在DefaultListableBeanFactory的一个map中:beanDefinitionMap。
// 所以统计数量直接统计这个map的size就可以
int countBefore = getRegistry().getBeanDefinitionCount();
// 分析注册BeanDefinition，重点
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
// 解析注册
doRegisterBeanDefinitions(root);
}
protected void doRegisterBeanDefinitions(Element root) {
// BeanDefinitionParserDelegate 解析委托类，也就是负责解析的
// 先把父解析委托类保存起来，解析完了在赋值回去，因为bean子元素还可能有bean
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
// 根节点是否是默认命名空间，xml有命名空间，比如aop、context都需要加命名空间
if (this.delegate.isDefaultNamespace(root)) {
// 元素有profile属性，环境标识，比如<bean profile='test'>
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
// 有profile属性，则判断当前active激活的环境是否是这个环境，不是则return忽略这个元素
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isInfoEnabled()) {
logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
// 钩子，跟子类实现的，解析前做一些事情
preProcessXml(root);
// 真正解析和注册，重点
parseBeanDefinitions(root, this.delegate);
// 钩子，跟子类实现的，解析后做一些事情
postProcessXml(root);
this.delegate = parent;
}
解析Element元素
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
// 是否是默认命名空间
if (delegate.isDefaultNamespace(root)) {
// 获取子元素
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
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
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)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
解析注册：
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// 解析元素，最后会解析车工BeanDefintion，并且封装成BeanDefinitionHolder，重点，看下文
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
// 装饰一下，不重要
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
// 把BeanDefinition注册到BeanFactory中去，其实也就是存到一个map中去，DefaultListableBeanFactory的beanDefinitionMap，前面说了，逻辑比较简单，不分析。
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
//发送注册完成事件
// XmlReaderContext的事件监听器ReaderEventListener，其实不会对这个事件进行任何处理，可以直接忽略.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
// 获取xml中bean的id和name
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List<String> aliases = new ArrayList<String>();
// 如果name是逗号分隔的多个name，则分开，并且添加到别名
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
// 如果没有指定id，则取别名中的第一个作为id
String beanName = id;
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isDebugEnabled()) {
logger.debug("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
if (containingBean == null) {
// 解析beanName是否唯一，不唯一则报错
checkNameUniqueness(beanName, aliases, ele);
}
// 解析BeanDefintion，重点，下文有详细解析。分析出bean的所有attribute和property等
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
// beanName不存在，则生成beanName，忽略
beanName = ...
String[] aliasesArray = StringUtils.toStringArray(aliases);
// BeanDefinition包装成BeanDefinitionHolder
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
// 解析class属性
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
try {
String parent = null;
// 解析parent属性
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
// 创建BeanDefinition
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
// 分析Bean的各个属性：singleton、scope、abstract、lazy-init、autowire、
// dependency-check、depends-on、autowire-candidate、primary、init-
// method、destroy-method、factory-method、factory-bean
// 并设置到BeanDefinntion中去保存
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
parseMetaElements(ele, bd);
// 分析look-up重写方，look-up方法，标记的方法，spring容器会cglib重写这个方法，根据这个方法的返回值，然后从容器中getbean返回。可以解决single对象依赖prototype对象，每次返回新的对象的问题。
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
// 分析replace-method替换方法。替换方法
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
// 分析<constructor>元素
parseConstructorArgElements(ele, bd);
parsePropertyElements(ele, bd);
parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
finally {
this.parseState.pop();
}
return null;
}
至此，spring容器applicationContext的子类的refresh方法，分析完了obtainFreshBeanFactory获取BeanFactory。
总结：
1、BeanFactory是DefaultListableBeanFactory类。
2、可以配置是否允许不同配置文件bean重写，是否允许bean循环依赖。
3、会根据profile，忽略没有active的profile的元素解析。
4、会分开处理解析默认命名空间和自定义命名空间。默认命名空间下的元素有：import，alias，beans，bean。
5、bean解析，最终会解析成BeanDefinition，会解析id, name, name可以指定多个，并且都会作为别名， id不存在则会取别名的第一个，会解析class，parent，singleton、scope、abstract、lazy-init、autowire、
// dependency-check、depends-on、autowire-candidate、primary、init-
// method、destroy-method、factory-method、factory-bean等元素。还有lookup、replace-method等。反正会把bean最终解析成BeanDefinition。
6、然后会把BeanDefinition注册进BeanFactory的map中，也就是保存到这个map中去。
接下来来就是把BeanDefinition初始化成bean对象了。
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