Spring bean的初始化源码分析-XML解析
XML解析部分，XML解析最终会将XML中配置的bean或者标签需要扫描的bean，都准备好，生成beanDefinition，用于后续的bean实例化
XmlBeanFactory bf = new XmlBeanFactory(new ClassPathResource("/spring-code-test.xml"));
DefaultListableBeanFactory 类是 spring bean 加载的核心类， XMLBeanFactory继承，实际是在里面封装了另一个类XmlBeanDefinitionReader， 这个类用于解析xml。本节主要讲这个类如何解析XML的。
public class XmlBeanFactory extends DefaultListableBeanFactory {
private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);
public XmlBeanFactory(Resource resource) throws BeansException {
this(resource, null);
}
public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) {
super(parentBeanFactory);
this.reader.loadBeanDefinitions(resource);
}
}
实际XML的加载过程封装在 XmlBeanDefinitionReader.loadBeanDefinitions 方法里了，实际过程是
1. 先对 输入的 文件进行 Resource 封装， new ClassPathResource("/spring-code-test.xml"), Resource对象传入XmlBeanDefinitionReader
2. XmlBeanDefinitionReader
2.1 对输入对象进行encoding封装
2.2 获取XML的验证模式，同时确认解析标签使用的XSD文档和对应标签解析的jar路径）
2.3 加载XML文件，得到对应的Document对象
// XmlBeanDefinitionReader
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
......
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());
}
......
}
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) {
try {
// XML 生成 document对象，doLoadDocument 内部会确认 XSD文档和解析标签所使用的jar包
Document doc = doLoadDocument(inputSource, resource);
return registerBeanDefinitions(doc, resource);
}
}
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
// 实际负责加载的document的类是 DefaultBeanDefinitionDocumentReader
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
DefaultBeanDefinitionDocumentReader 类做的事情就是根据 document ，进行element解析
// DefaultBeanDefinitionDocumentReader 类
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
// 获取root节点，进行解析
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}
/**
* Parse the elements at the root level in the document:
* "import", "alias", "bean".
* @param root the DOM root element of the document
*/
// 解析具体实现方法
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)) {
// 解析默认标签
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
// 解析默认标签，bean标签相关
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
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));
}
}