文章目录
本文概述
上文 如何初始化上下文、解析资源路径 主要介绍了super(parent)和setConfigLocations(configLocations) 两个方法，接下来将主要介绍容器初始化refresh函数中prepareRefresh()，obtainFreshBeanFactory()方法。
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
源码
refresh()
refresh方法负责完成了整个容器的初始化，下有很多方法，我们逐步跟进。
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//保证同一时刻只有一个线程在初始化
// 为refresh做准备:设置启动时间，设置active标记，验证require的标记的属性是否可解析
prepareRefresh();
// 对上下文的底层bean工厂执行一次实际的刷新，关闭之前的bean工厂(如果有的话)，并为上下文生命周期的下一阶段初始化一个新bean工厂
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 准备上下文的bean工厂
prepareBeanFactory(beanFactory);
try {
// 允许在子类的上下文中预处理bean工厂
postProcessBeanFactory(beanFactory);
// 执行在上下文中按照bean注册的工厂
invokeBeanFactoryPostProcessors(beanFactory);
// 注册拦截bean创建的bean处理器。
registerBeanPostProcessors(beanFactory);
// 初始化消息源
initMessageSource();
// 初始化事件多播
initApplicationEventMulticaster();
// 在子类上下文中初始化特殊的bean
onRefresh();
// 检查、注册监听bean
registerListeners();
// 实例化其他非懒加载的singletons.
finishBeanFactoryInitialization(beanFactory);
// 发布对应的事件
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// 删除已经创建的singletons
destroyBeans();
// 重置'active'标记.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// 重置普通缓存
resetCommonCaches();
}
}
}
prepareRefresh()
为refresh做准备:设置启动时间，设置active标记，验证require的标记的属性是否可解析，初始化。
protected void prepareRefresh() {
// 设置开始时间，改状态
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());
}
}
// 子类实现，空方法
initPropertySources();
// 检查所有必须的属性是否可解析
getEnvironment().validateRequiredProperties();
// 存储预刷新的应用监视器
if (this.earlyApplicationListeners == null) {
this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
}
else {
// 恢复本地应用监视器到预刷新状态
this.applicationListeners.clear();
this.applicationListeners.addAll(this.earlyApplicationListeners);
}
// 用于收集之前的应用事件，一旦多播准备好就发布
this.earlyApplicationEvents = new LinkedHashSet<>();
}
obtainFreshBeanFactory()
对上下文的底层bean工厂执行一次实际的刷新，关闭之前的bean工厂(如果有的话)，并为上下文生命周期的下一阶段初始化一个新bean工厂。
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory(); //加载配置
return getBeanFactory(); //返回类的bean工厂
}
refreshBeanFactory（）
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
destroyBeans(); // 模板方法，删除上下文管理的所有bean,默认实现销毁此上下文中所有缓存的单例对象
closeBeanFactory();//把SerializationId置空
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory(); //创建DefaultListableBeanFactory，父工厂为null
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory); //设置BeanFactory是否允许：bean定义覆盖、循环依赖，默认均为null
loadBeanDefinitions(beanFactory); //为给定的BeanFactory创建一个新的XmlBeanDefinitionReader,初始化，读取beanDefinitions。
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
loadBeanDefinitions(beanFactory);
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
XmlBeanDefinitionReader初始化
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
initBeanDefinitionReader(beanDefinitionReader); //留给子类提供定制的beanDefinitionReader初始化方式
loadBeanDefinitions(beanDefinitionReader); //加载BeanDefinition
}
可以看到，loadBeanDefinitions方法会从两个地方中加载数据。
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources(); //获取指向xml文件的Resource数组
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations(); //获取指向xml文件中指出的资源数组,也包含了location patterns，比如["spring-config.xml"]
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations); //通过字符串解析出Resource，然后再加载beanDefinition
}
}
两种方法非常接近，只是reader.loadBeanDefinitions(configLocations);步骤中多了从String[]获取到Resource[]的步骤，最终都会到loadBeanDefinitions(Resource… resources)中。
@Override
public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
Assert.notNull(resources, "Resource array must not be null");
int count = 0;
for (Resource resource : resources) {
count += loadBeanDefinitions(resource); //从Resource中加载BeanDefinition
}
return count;
}
继续跟进
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(); //获取当下正在被加载的Resource
if (currentResources == null) {
currentResources = new HashSet<>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
//检查是否有循环加载的问题
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());
}
return doLoadBeanDefinitions(inputSource, encodedResource.getResource()); //继续往下看
}
finally {
inputStream.close();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource); //加载完资源，再把它从正在加载资源set中去掉
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
然后执行下面这段代码，首先把文件资源读入Document类中
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
Document doc = doLoadDocument(inputSource, resource); //把xml文件解析为Document类，暂不深入
int count = registerBeanDefinitions(doc, resource); //从Document类中解析出bean，并统计bean的个数。
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
catch (各种各样的Exception ex) {
throw ex;
}
}
registerBeanDefinitions(doc, resource)
继续跟进
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
doRegisterBeanDefinitions(doc.getDocumentElement());
}
在doRegisterBeanDefinitions这个方法中，任何嵌套的<beans>元素都会导致递归。为了正确地传播和保存beans 的默认属性，跟踪当前父委托（可为空）。创建新的子委托并且有父委托的引用用于回退，然后最终将this.delegate重置回它原来的(父)引用。这个行为模拟了一个委托堆栈，而实际上并不需要一个委托
protected void doRegisterBeanDefinitions(Element root) {
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
//获取 <beans ... profile="***" /> 中的 profile参数与当前环境是否匹配，如果不匹配则不再进行解析
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);
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;
}
}
}
//默认实现为空，留给子类扩展
preProcessXml(root);
//解析BeanDefinitions
parseBeanDefinitions(root, this.delegate);
//默认实现为空，留给子类扩展
postProcessXml(root);
this.delegate = parent;
}
解析部分
// 在root级别（"import", "alias", "bean"）解析:
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)) {
//检查namespace
parseDefaultElement(ele, delegate); //解析<import> <alias> <bean> <beans>
}
else {
delegate.parseCustomElement(ele); //解析其他标签
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
parseDefaultElement(ele, delegate)
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>
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
//<beans>
doRegisterBeanDefinitions(ele);
}
}
先看对<import>的处理: 解析路径中的占位符，从给的资源路径中加载BeanDefinitions。
protected void importBeanDefinitionResource(Element ele) {
String location = ele.getAttribute(RESOURCE_ATTRIBUTE); //获取资源路径
if (!StringUtils.hasText(location)) {
//检查是否为空
getReaderContext().error("Resource location must not be empty", ele);
return;
}
location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location); //解析下路径中的占位符
Set<Resource> actualResources = new LinkedHashSet<>(4);
boolean absoluteLocation = false;
try {
absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute();
}
catch (URISyntaxException ex) {
}
if (absoluteLocation) {
//如果是绝对路径，直接通过loadBeanDefinitions方法载入BeanDefinition
try {
int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
if (logger.isTraceEnabled()) {
logger.trace("Imported " + importCount + " bean definitions from URL location [" + location + "]");
}
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error(
"Failed to import bean definitions from URL location [" + location + "]", ele, ex);
}
}
else {
// 如果是相对路径，要先创建Resource ，然后读取BeanDefinition
try {
int importCount;
Resource relativeResource = getReaderContext().getResource().createRelative(location);
if (relativeResource.exists()) {
importCount = getReaderContext().getReader().loadBeanDefinitions(relativeResource);
actualResources.add(relativeResource);
}
else {
String baseLocation = getReaderContext().getResource().getURL().toString();
importCount = getReaderContext().getReader().loadBeanDefinitions(
StringUtils.applyRelativePath(baseLocation, location), actualResources);
}
if (logger.isTraceEnabled()) {
logger.trace("Imported " + importCount + " bean definitions from relative location [" + location + "]");
}
}
catch (IOException ex) {
getReaderContext().error("Failed to resolve current resource location", ele, ex);
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error(
"Failed to import bean definitions from relative location [" + location + "]", ele, ex);
}
}
Resource[] actResArray = actualResources.toArray(new Resource[0]);
getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele)); //触发导入处理事件
}
对<alias>的处理
protected void processAliasRegistration(Element ele) {
String name = ele.getAttribute(NAME_ATTRIBUTE);
String alias = ele.getAttribute(ALIAS_ATTRIBUTE);
boolean valid = true;
if (!StringUtils.hasText(name)) {
getReaderContext().error("Name must not be empty", ele);
valid = false;
}
if (!StringUtils.hasText(alias)) {
getReaderContext().error("Alias must not be empty", ele);
valid = false;
}
if (valid) {
try {
getReaderContext().getRegistry().registerAlias(name, alias); //注册别名
}
catch (Exception ex) {
getReaderContext().error("Failed to register alias '" + alias +
"' for bean with name '" + name + "'", ele, ex);
}
getReaderContext().fireAliasRegistered(name, alias, extractSource(ele)); //触发别名注册事件。
}
}
@Override
public void registerAlias(String name, String alias) {
Assert.hasText(name, "'name' must not be empty");
Assert.hasText(alias, "'alias' must not be empty");
synchronized (this.aliasMap) {
if (alias.equals(name)) {
//如果别名和名称一样，就忽略
this.aliasMap.remove(alias);
if (logger.isDebugEnabled()) {
logger.debug("Alias definition '" + alias + "' ignored since it points to same name");
}
}
else {
String registeredName = this.aliasMap.get(alias);
if (registeredName != null) {
if (registeredName.equals(name)) {
//已经存在且一样，不需要注册
return;
}
if (!allowAliasOverriding()) {
//存在且不一样，而且不允许别名覆盖，直接抛异常
throw new IllegalStateException("Cannot define alias '" + alias + "' for name '" +
name + "': It is already registered for name '" + registeredName + "'.");
}
if (logger.isDebugEnabled()) {
logger.debug("Overriding alias '" + alias + "' definition for registered name '" +
registeredName + "' with new target name '" + name + "'");
}
}
checkForAliasCircle(name, alias); //检查给定的名称是否以别名的形式指向另一个方向的给定别名，在前面捕获循环引用并抛出相应的IllegalStateException
this.aliasMap.put(alias, name); //把别名放进ConcurrentHashMap<String,String>中
if (logger.isTraceEnabled()) {
logger.trace("Alias definition '" + alias + "' registered for name '" + name + "'");
}
}
}
}
重点要看对<bean>的处理
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); //BeanDefinitionHolder中包含了beanDefinition、beanName、aliases三个属性。
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); //解析自定义属性
try {
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry()); //注册BeanDefinition，、继续跟进
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder)); //触发bean注册事件
}
}
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
String beanName = definitionHolder.getBeanName(); //注册名字
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);//注册别名
}
}
}
@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(); //验证BeanDefinition
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
//检查是否注册过，如果注册过是否可以重写
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isInfoEnabled()) {
logger.info("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
existingDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(existingDefinition)) {
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition); //放进ConcurrentHashMap<String,BeanDefinition>
}
else {
if (hasBeanCreationStarted()) {
//如果已经开始创建Bean，就要防止并发问题
synchronized (this.beanDefinitionMap) {
// 把bean
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions; //beanDefinitionNames （ArrayList）中新增name
removeManualSingletonName(beanName); //从手动注册单例名单中移除。
}
}
else {
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
对<beans>的处理
注册root element中所有的BeanDefinition，又回到了上文中doRegisterBeanDefinitions(doc.getDocumentElement());。
protected void doRegisterBeanDefinitions(Element root) {
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;
}
}
}
preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
getBeanFactory（）
到这里已经初始化了 Bean 容器，Bean的配置也相应的转换为了一个个BeanDefinition，然后注册所有的BeanDefinition到beanDefinitionMap中。getBeanFactory（）获取刚才初始化的beanFactory。
@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
synchronized (this.beanFactoryMonitor) {
if (this.beanFactory == null) {
throw new IllegalStateException("BeanFactory not initialized or already closed - " +
"call 'refresh' before accessing beans via the ApplicationContext");
}
return this.beanFactory;
}
}
因篇幅太长下文还在整理中。