/**
* Create a new XmlBeanFactory with the given input stream,
* which must be parsable using DOM.
* @param resource XML resource to load bean definitions from
* @param parentBeanFactory parent bean factory
* @throws BeansException in case of loading or parsing errors
*/
public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
super(parentBeanFactory);
this.reader.loadBeanDefinitions(resource);
}
整个处理过程：
1）封装资源文件
当进入XmlBeanDefinitionReader后首先对参数Resource使用EncodeResource类进行封装
2）获取输入流
从Resource中获取对应的InputSteam并构造InputSource
3）通过构造的InputSource实例和Resource实例继续调用doLoadBeanDefinitions.
loadBeanDefinition的实现：
/**
* Load bean definitions from the specified XML file.
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
new EncodeResource(resource)实现：
private EncodedResource(Resource resource, String encoding, Charset charset) {
super();
Assert.notNull(resource, "Resource must not be null");
this.resource = resource;
this.encoding = encoding;
this.charset = charset;
}
/**
* Open a {@code java.io.Reader} for the specified resource, using the specified
* {@link #getCharset() Charset} or {@linkplain #getEncoding() encoding}
* (if any).
* @throws IOException if opening the Reader failed
* @see #requiresReader()
* @see #getInputStream()
*/
public Reader getReader() throws IOException {
if (this.charset != null) {
return new InputStreamReader(this.resource.getInputStream(), this.charset);
}
else if (this.encoding != null) {
return new InputStreamReader(this.resource.getInputStream(), this.encoding);
}
else {
return new InputStreamReader(this.resource.getInputStream());
}
}
真正的数据准备阶段：
/**
* Load bean definitions from the specified XML file.
* @param encodedResource the resource descriptor for the XML file,
* allowing to specify an encoding to use for parsing the file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isInfoEnabled()) {
logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}
//通过属性值来记录已经加载的资源
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<EncodedResource>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
//从encodeResource中获取已经封装的Resource对象并再次从Resource中获取其中的inputStream
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
//InputResource这个类不来自与Spring 全类路径是org.xml.sax.InputSource
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//真正的逻辑核心部分
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();
}
}
}
首先对传入的resource参数做封装，目的是考虑到Resource可能存在的编码要求的情况，其次，通过SAX读取XML文件的方式来准备InputSource对象，最后将准备的数据通过参数传入真正的核心处理部分doLoadBeanDefinitions(inputSource,encodeResource.getResource()).
/**
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #doLoadDocument
* @see #registerBeanDefinitions
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//加载XML文件，并得到对应的Document
Document doc = doLoadDocument(inputSource, resource);
//根据返回的Document注册Bean信息
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);
}
}
获取XML的验证模式
DTD和XSD区别
DTD即文档类型定义，是一种XML约束模式语言，是XML文件的验证机制，属于XML文件组成的一部分。DTD是一种保证XML文档格式正确的有效方法，可以通过比较XML和DTD文件来看文档是否符合规范，元素和标签使用是否正确。一个DTD文档包含：元素的定义规则，元素间关系的定义规则，元素可使用的属性，可使用的实体或符号规则。
要使用DTD验证模式的时候需要在XML文件的头部声明，以下是在Spring中使用DTD声明方式的代码：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//Spring//DTD BEAN 2.0//EN" "http://www.Springframework.org/dtd/Spring-beans-2.0.dtd">
获取Document
/**
* Load the {@link Document} at the supplied {@link InputSource} using the standard JAXP-configured
* XML parser.
*/
@Override
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception { DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
if (logger.isDebugEnabled()) {
logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
}
DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
return builder.parse(inputSource);
}
首先创建DocumentBuilderFactory，再通过DocumentBuilderFactory创建DocumentBuilder,进而解析inputSource来返回Document对象。
在上述方法中涉及一个参数EntityResolver何为EntityResolver?如果SAX应用程序需要实现自定义处理外部实体，则必须实现此接口并使用setEntityResolver方法向SAX驱动器注册一个实例，也就是说，对于解析一个XML，SAX首先读取该XML文档的声明，根据声明去寻找相应的DTD定义，以便对文档进行一个严重。默认的寻找规则，即通过网络来下载相应的DTD声明，并进行认证。
EntityResolver的作用是项目本身就可以提供一个如何寻找DTD声明的方法，即由程序来实现寻找DTD声明的过程，比如我们将DTD文件放到项目中某处，在实现时直接将此文档读取并返回给SAX即可。
解析及注册BeanDefinitions
当把文件转换为Document后，接下来的提取及注册Bean就是我们的重头戏，当程序已经拥有XML文档文件的Document实例对象时，就会被引入如下的方法：
/**
* Register the bean definitions contained in the given DOM document.
* Called by {@code loadBeanDefinitions}.
* <p>Creates a new instance of the parser class and invokes
* {@code registerBeanDefinitions} on it.
* @param doc the DOM document
* @param resource the resource descriptor (for context information)
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of parsing errors
* @see #loadBeanDefinitions
* @see #setDocumentReaderClass
* @see BeanDefinitionDocumentReader#registerBeanDefinitions
*/
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//使用DefaultBeanDefinitionDocumentReader实例化BeanDefinitionDocumentReader
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//记录统计前BeanDefinition的加载个数
int countBefore = getRegistry().getBeanDefinitionCount();
//加载及注册bean
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
//记录本次加载的BeanDefinition个数
return getRegistry().getBeanDefinitionCount() - countBefore;
}
/**
* Register each bean definition within the given root {@code <beans/>} element.
*/
protected void doRegisterBeanDefinitions(Element root) {
// 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;
this.delegate = createDelegate(getReaderContext(), root, parent); if (this.delegate.isDefaultNamespace(root)) {
//处理profile属性
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;
}
}
}
//解析前处理，留给子类实现
preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
//解析后处理，留给子类实现
postProcessXml(root); this.delegate = parent;
}
preProcessXml和postProcessXml两个方法是空的，这是模板方法模式，在面向对象设计方法中常说：一个雷要么面向集成的设计，要么就用final修饰，这两个方法正是为子类设计的，如果继承自DefaultBeanDefinitionDocumentReader的子类需要在Bean解析前后做一些处理的话，那么只需要重写这两个方法就可以了。
解析并注册BeanDefinition:
/**
* Parse the elements at the root level in the document:
* "import", "alias", "bean".
* @param root the DOM root element of the document
*/
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//对beans的处理
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)) {
//对bean的处理
parseDefaultElement(ele, delegate);
}
else {
//对bean的处理
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
在Spring的XML配置里面有两大类Bean声明，一个是默认的，如：
<bean id="test" class="com.slp.Test"/>
另一类就是自定义的，如：
<tx:annotation-driven/>
这两种方式的读取及解析差别是非常大的，如果采用Spring默认的配置，Spring当然知道该如何做，但是如果是自定义的，那么久需要用户实现一些接口及配置了。对于根节点或者子节点如果是默认命名空间的话则采用parseDefaultElement方法进行解析，否则使用delegate.parseCutomElement方法对自定义命名空间进行解析。而判断是否默认命名空间还是自定义命名空间的方法其实是使用node.getNamespaceURI()获取命名空间，并与Spring的命名空间进行对比，如果一致则是默认，否则是自定义。