本节会揭晓：
获得 Bean 工厂的大致步骤
根据前面的文章，回顾一下 obtainFreshBeanFactory() 的来源：
跟 ClassPathXmlApplicationContext 构造函数里的 refresh() 方法，
refresh() 方法实现在其父类 AbstractApplicationContext 里，其中有一行：
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
这是我们 refresh() 里第一个重要的方法，它的作用是：
- 创建 BeanFactory 对象
- xml 解析
- 把解析出来的 xml 标签封装成 BeanDefinition 对象
下面涉及的几个类的结构图：
跟 refreshBeanFactory()：
@Override
protected final void refreshBeanFactory() throws BeansException {
//如果BeanFactory不为空，则清除 BeanFactory 和里面的实例
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
//创建 beanFactory 实例工厂，以后就是从这个工厂里拿到实例（bean）
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
//设置是否可以循环依赖 allowCircularReferences
//是否允许使用相同名称重新注册不同的bean实现.
customizeBeanFactory(beanFactory);
//重点
//解析xml，并把xml中的标签封装成BeanDefinition对象
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
跟 loadBeanDefinitions(beanFactory)：
AbstractXmlApplicationContext 里，实现了这个方法：
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
//创建xml的解析器，以后的工作主要交给它来做
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(this.getEnvironment());
//这里传一个this进去，因为ApplicationContext是实现了ResourceLoader接口的
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.
initBeanDefinitionReader(beanDefinitionReader);
//主要看这个方法 重要程度 5
loadBeanDefinitions(beanDefinitionReader);
}
跟 loadBeanDefinitions(beanDefinitionReader)：
跟 loadBeanDefinitions(configLocations)：
类 AbstractBeanDefinitionReader
跟 loadBeanDefinitions(location)：
跟 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) {
// Resource pattern matching available.
try {
//把字符串类型的xml文件路径，形如：classpath*:user/**/*-context.xml,转换成Resource对象类型，
//其实就是用流的方式加载配置文件，然后封装成Resource对象，不重要，可以不看
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
//主要看这个方法. 重要程度:5
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;
}
}
跟 loadBeanDefinitions(resources)：
跟 loadBeanDefinitions(resource)：
跟 loadBeanDefinitions：
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 {
//获取Resource对象中的xml文件流对象
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
//InputSource是jdk中的sax xml文件解析对象
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//主要看这个方法，,重要程度：5
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();
}
}
}
跟 doLoadBeanDefinitions：
跟 registerBeanDefinitions：
跟 registerBeanDefinitions：
类 BeanDefinitionDocumentReader
跟 registerBeanDefinitions：
类 DefaultBeanDefinitionDocumentReader
跟 doRegisterBeanDefinitions：
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);
//主要看这个方法，标签具体解析过程
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
跟 parseBeanDefinitions：
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)) {
//默认标签解析，见1.1.2
parseDefaultElement(ele, delegate);
}
else {
//自定义标签解析，见1.1.3
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
