前言-阅读源码有利于陶冶情操，本文承接前文Spring源码情操陶冶-AbstractApplicationContext
约束：
- 本文指定
contextClass为默认的XmlWebApplicationContext- 从属
AbstractApplicationContext#refresh方法
AbstractApplicationContext#obtainFreshBeanFactory
该方法主要完成创建Bean工厂，涉及到解析spring文件，代码清单如下
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//更新bean工厂，其会销毁已存在的bean内容并重新创建
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
由以上代码所见，关键方法指向子类AbstractRefreshableApplicationContext#refreshBeanFactory,代码清单如下
protected final void refreshBeanFactory() throws BeansException {
//存在已有bean工厂则销毁
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
//创建默认的用List接口存放bean的工厂
DefaultListableBeanFactory beanFactory = createBeanFactory();
//这里同contextId
beanFactory.setSerializationId(getId());
//配置allowBeanDefinitionOverriding和allowCircularReferences属性，这里均不设置
customizeBeanFactory(beanFactory);
//调用子类的加载bean定义方法，这里会调用XmlWebApplicationContext子类的复写方法
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
XmlWebApplicationContext#loadBeanDefinitions
加载bean预方法，代码清单如下
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
//环境为StardEvironment对象
beanDefinitionReader.setEnvironment(getEnvironment());
//资源加载器为XmlWebApplicationContext
beanDefinitionReader.setResourceLoader(this);
//实体分解器为ResourceEntityResolver对象，主要用于javax.xml.parse解析xml所用
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
//此处为空方法
initBeanDefinitionReader(beanDefinitionReader);
//真切的开始加载bean
loadBeanDefinitions(beanDefinitionReader);
}
紧接着查看真实的加载bean方法XmlWebApplicationContext#loadBeanDefinitions(XmlBeanDefinitionReader reader)，代码清单如下
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
//获取spring配置文件的位置列表
String[] configLocations = getConfigLocations();
if (configLocations != null) {
for (String configLocation : configLocations) {
//读取加载
reader.loadBeanDefinitions(configLocation);
}
}
}
AbstractBeanDefinitionReader#loadBeanDefinitions
真实的加载bean内容可追溯到XmlBeanDefinitionReader的父类AbstractBeanDefinitionReader#loadBeanDefinitions(String location, Set<Resource> actualResources)方法，代码清单如下
//此处的actualResources参数传过来为null
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
//此处的ResourceLoader为XmlWebApplicationContext
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
}
//XmlWebApplicationContext符合此条件
if (resourceLoader instanceof ResourcePatternResolver) {
// Resource pattern matching available.
try {
//调用的是AbstractApplicationContext的getResources方法，追溯一下调用的其实是PathMatchingResourcePatternResolver.getResources方法，其会搜寻指定目录符合条件的文件集合
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
//加载某个spring bean文件
int loadCount = loadBeanDefinitions(resources);
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;
}
}
略过一些代码调用，直接看XmlBeanDefinitionReader#registerBeanDefinitions(Document doc,Resource resource)注册bean定义方法，代码清单如下
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
documentReader.setEnvironment(this.getEnvironment());
//此处的getRegistry()方法返回的实例为DefaultListableBeanFactory类型
int countBefore = getRegistry().getBeanDefinitionCount();
//调用DefaultBeanDefinitionDocumentReader.registerBeanDefinitions方法
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
DefaultBeanDefinitionDocumentReader#registerBeanDefinitions
代码清单如下
//解析bean定义
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
//此处的root节点一般为<beans>节点
Element root = doc.getDocumentElement();
//具体解析的方法
doRegisterBeanDefinitions(root);
}
解析bean具体方法DefaultBeanDefinitionDocumentReader#doRegisterBeanDefinitions，代码清单如下
protected void doRegisterBeanDefinitions(Element root) {
//此处针对<beans>的节点属性profile进行的操作
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
Assert.state(this.environment != null, "Environment must be set for evaluating profiles");
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!this.environment.acceptsProfiles(specifiedProfiles)) {
return;
}
}
// 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;
//读取<beans>标签中的default-*属性
this.delegate = createDelegate(this.readerContext, root, parent);
//预处理bean xml配置文件中的自定义标签，默认是为空的
preProcessXml(root);
//解析bean xml配置文件
parseBeanDefinitions(root, this.delegate);
//处理bean xml配置文件中的自定义标签，默认是为空的
postProcessXml(root);
this.delegate = parent;
}
从上述的注释可知，我们只需关注DefaultBeanDefinitionDocumentReader#parseBeanDefinitions对bean xml文件的解析，鉴于其重要性，将于下一章节详细解读
下节预告
Spring源码情操陶冶-DefaultBeanDefinitionDocumentReader#parseBeanDefinitions