2.菜鸟总结spring源码——获取Document

1.上一篇文档大概回顾了Resource resource = new ClassPathResource("beanFactoryTest.xml")的加载机制；

   本次回顾从BeanFactory factory = new XmlBeanFactory(resource);这句话开始；
   public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
super(parentBeanFactory);
this.reader.loadBeanDefinitions(resource);
   }
   其中reader就是XmlBeanDefinitionReader类的对象；
   首先从构造方法看起：EncodeResource实际就是对流做了一层封装；



   


我们再次整理一下数据准备阶段的逻辑，首先对传入的resource参数进行封装，目的是考虑可能存在的编码要求的情况，其次是通过SAX读取XML文件的方式来准备InputSource对象，最后把准备的数据传入核心处理部分doLoadBeanDefinitions(inputSource, encodedResource.getResource());

下面进入doLoadBeanDefinitions（）方法：protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
Document doc = doLoadDocument(inputSource, resource);
return registerBeanDefinitions(doc, resource);
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (SAXParseException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
}
catch (SAXException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"XML document from " + resource + " is invalid", ex);
}
catch (ParserConfigurationException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Parser configuration exception parsing XML from " + resource, ex);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"IOException parsing XML document from " + resource, ex);
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Unexpected exception parsing XML document from " + resource, ex);
}
}这个方法除去异常，其实只做了三件事：
（1）：获取对XML文件的验证模式  ；（2）：加载XML文件，并得到对应的Document；（3）根据Document注册Bean信息；

下面进入doLoadDocument方法：


这个doLoadDocument方法关注两个点：getValidationModeForResource（）方法：此方法就是获取资源的验证模式DTD和XSD两个模式，还有一个时genEntityResolver（）方法

下面进入这个方法：getValidationModeForResource（）

protected int getValidationModeForResource(Resource resource) {
//如果手动指定了验证模式就用手工指定的验证模式；
int validationModeToUse = getValidationMode();
if (validationModeToUse != VALIDATION_AUTO) {
return validationModeToUse;
}
//如果未指定则使用自动检测；
int detectedMode = detectValidationMode(resource);
if (detectedMode != VALIDATION_AUTO) {
return detectedMode;
}
// Hmm, we didn't get a clear indication... Let's assume XSD,
// since apparently no DTD declaration has been found up until
// detection stopped (before finding the document's root tag).
return VALIDATION_XSD;
}

下面进入

genEntityResolver（）：protected EntityResolver getEntityResolver() {
if (this.entityResolver == null) {
// Determine default EntityResolver to use.
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader != null) {
this.entityResolver = new ResourceEntityResolver(resourceLoader);
}else {
this.entityResolver = new DelegatingEntityResolver(getBeanClassLoader());
}
}
return this.entityResolver;
}那么EntityResolver到底是做什么用的呢；验证文件默认加载方式是通过URL进行网络下载获取的，这样会造成延迟，用户体验也不好，一般的做法都是将验证文件放置在自己的工程里，那么怎么才能将这个URL转化为自己的工程里面呢？以加载DTD文件为例来看看spring中是如何实现的，

@Override
@Nullable
public InputSource resolveEntity(String publicId, @Nullable String systemId) throws IOException {
if (logger.isTraceEnabled()) {
logger.trace("Trying to resolve XML entity with public ID [" + publicId +
"] and system ID [" + systemId + "]");
}
if (systemId != null && systemId.endsWith(DTD_EXTENSION)) {
int lastPathSeparator = systemId.lastIndexOf("/");
int dtdNameStart = systemId.indexOf(DTD_NAME, lastPathSeparator);
if (dtdNameStart != -1) {
//spring-beans + .dtd
String dtdFile = DTD_NAME + DTD_EXTENSION;
if (logger.isTraceEnabled()) {
logger.trace("Trying to locate [" + dtdFile + "] in Spring jar onclas
4000
spath");
}
try {
//此构造方法传入getClass（）    文件名需要和此类在同一个包中；
// Resource resource = new ClassPathResource("文件名")   以classpath为基础的
Resource resource = new ClassPathResource(dtdFile, getClass());
InputSource source = new InputSource(resource.getInputStream());
source.setPublicId(publicId);
source.setSystemId(systemId);
if (logger.isDebugEnabled()) {
logger.debug("Found beans DTD [" + systemId + "] in classpath: " + dtdFile);
}
return source;
}
catch (IOException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Could not resolve beans DTD [" + systemId + "]: not found in classpath", ex);
}
}

}
}
// Use the default behavior -> download from website or wherever.
return null;
}

下面就进入构造document了：步骤为
1.DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

2.DocumentBuilder builder = factory.newDocumentBuilder();

3.builder.parse(inputSource);

下面为详细代码--- 获取factory：



     第二步为：获取DocumentBuilder



   第三步为：用builder构造document



至此已经获取document文档。