Spring IOC源码之(2)obtainFreshBeanFactory
obtainFreshBeanFactory作为refresh中重要方法之一，主要承担了创建容器，解析配置文件、注解类中的bean信息，并注册进容器等相关工作。此时的bean是一个还未初始化的实例，接下来就一步步去了解Spring源码
在prepareRefresh中分析了容器在创建之前所做的一些准备工作。接下来就开始进入容器及bean创建的源码中，在分析之前，将上一篇的贯穿始终的整体分析图(往后都取名为分析图)拷贝过来，方便后续源码分析能随时了解整体结构的演变
跟随源码来到AbstractRefreshableApplicationContext中
// 和GenericApplicationContext不同是，每次的刷新都会创建一个新的容器实例，后者自始而终都是同一个容器
@Override
protected final void refreshBeanFactory() throws BeansException {
// 每次刷新前，都会改变上一个容器的标识位，并清除里面的Bean
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory();
// 给容器起一个全局唯一的标识
beanFactory.setSerializationId(getId());
// 定制是否相同的Bean是否进行覆盖，以及是否支持循环引用
customizeBeanFactory(beanFactory);
// 父类定义了加载动作，真正的实现会落到具体的子类中去完成
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}进入到AbstractXmlApplicationContext源码中。没研源码之前，网上或者听同事说Spring是一个分工明确，耦合性比较低，扩展性高的框架，研究了之后发现Spring对这几点做到了极致
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// 定义了从XML读取bean定义信息类
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));
// 同时也留给子类对reader进行定制化处理
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}对上述中提到的Reader，发现bean定义信息来源不同，其对应的reader也不同，同时上下文也会对应着不同，此时我重新修改下分析图。
接下来容器会将配置文件通过ResouceLoader转换为Resource，并转换为Document，直奔主题。Spring源码挨个分析的话，那就不用吃饭了，看着就会饱。
// DefaultBeanDefinitionDocumentReader源码
protected void doRegisterBeanDefinitions(Element root) {
// 当beans中嵌套beans，当前的方法会被递归调用，delegate引用的是上一次的值
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
// beans指定profile属性和spring.profiles.active相对应
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.isInfoEnabled()) {
logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
// 钩子方法
preProcessXml(root);
// 重点方法
parseBeanDefinitions(root, this.delegate);
// 钩子方法
postProcessXml(root);
// 调用结束前会将delegate恢复到上一轮的初始值，模拟出一个委托堆栈
this.delegate = parent;
}根据节点的不同去解析不同的元素
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)) {
// 解析默认的标签beans、bean、import、alias
parseDefaultElement(ele, delegate);
}
else {
// 解析上面之外的标签
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}我们先以
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
// 解析import标签
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
// alias
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
// bean
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
// beans，嵌套，递归调用
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// 最终丢给DefaultListableBeanFactory去进行注册
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
// 获取id和name(也就是bean的别名)
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List aliases = new ArrayList();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
// 如果bean没有给id，则以name(别名)中的第一个作为bean的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) {
checkNameUniqueness(beanName, aliases, ele);
}
// 将配置文件中的bean转换为BeanDefinition，并设置相应的属性值
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
beanName = this.readerContext.generateBeanName(beanDefinition);
// Register an alias for the plain bean class name, if still possible,
// if the generator returned the class name plus a suffix.
// This is expected for Spring 1.2/2.0 backwards compatibility.
String beanClassName = beanDefinition.getBeanClassName();
if (beanClassName != null &&
beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
aliases.add(beanClassName);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Neither XML 'id' nor 'name' specified - " +
"using generated bean name [" + beanName + "]");
}
}
catch (Exception ex) {
error(ex.getMessage(), ele);
return null;
}
}
String[] aliasesArray = StringUtils.toStringArray(aliases);
// 包装为BeanDefinitionHolder
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
} DefaultListableBeanFactory注册Bean到容器中
@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;
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
// 如果存在相同名字的bean，默认是可以覆盖老的bean
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
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 + "]");
}
}
// bean的名字相同，BeanDefinition不同就先记录一个日志
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 + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List updatedDefinitions = new ArrayList(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set updatedSingletons = new LinkedHashSet(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// beanDefinitionMap是用于存放BeanDefinition
this.beanDefinitionMap.put(beanName, beanDefinition);
// beanDefinitionNames用于存放bean的名字
this.beanDefinitionNames.add(beanName);
// 用于存放手动注册的bean
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
} 只是简单的介绍下整体流程，其实该分支还是挺复杂。整个Spring就像一个大树，根和枝众多，难以逐一分析透彻，倒不如按照一个主线理解其大致脉络即可。如下我总结的大致脉络图。
小弟不才，如有错误，望指正！！！