接上篇【】 ，我们看到BeanDefinitionReader解决的是从资源文件（xml,propert）到BeanDefinition集合的过程。所以BeanDefinitionReader接口有两个实现版本。
BeanDefinitionReader的接口声明，ResourceLoader是spring中解决Resource加载的操作。四个loadBeanDefinitions就是重载解决单个或者多个资源文件的处理问题。
loadBeanDefinitions 是加载BeanDefinition接口的核心入口，AbstractBeanDefinitionReader中剩下了loadBeanDefinitions(Resource resource)这个方法给子类实现。
开始加载资源文件，这一步会将Resource构造为一个EncodedResource，添加了编码的相关控制信息。
//XmlBeanDefinitionReader.java
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
下一步需要去判断当前配置文件是否被循环加载。
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());
}
//没有明白为什么需要使用ThreadLoacal?
//private final ThreadLocal<Set<EncodedResource>> resourcesCurrentlyBeingLoaded = new NamedThreadLocal<Set<EncodedResource>>("XML bean definition resources currently being loaded");
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 {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
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();
}
}
}
真正执行加载操作的是doLoadBeanDefinitions方法。
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//获取xml的校验格式，dtd或者xsd的校验模式
int validationMode = getValidationModeForResource(resource);
//解析xml为dom，用了sax解析的
Document doc = this.documentLoader.loadDocument(
inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
//真正的主角来了
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);
}
}
spring解析xml文件为org.w3c.dom.Document使用了SAX的实现方法，除了SAX，常用的xml解析方法还有dom，dom4j，jdom等方法。
registerBeanDefinitions是正式注册BeanDefinition的地方，这里又引入了一个新的接口BeanDefinitionDocumentReader（定义如何解析dom为BeanDefinition）。
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//创建一个解析器
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//设置上下文环境
documentReader.setEnvironment(this.getEnvironment());
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
解析的实现为reader.registerBeanDefinitions方法。
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}
缓存readerContext，目的不清楚。直接parse
protected void doRegisterBeanDefinitions(Element root) {
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;
this.delegate = createHelper(this.readerContext, root, parent);
preProcessXml(root);
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
preProcessXml和postProcessXml方法暂时留空，目的为了需要增加新的实现版本时候方便扩展。
protected void preProcessXml(Element root) {
}
protected void postProcessXml(Element root) {
}
parseBeanDefinitions方法内将
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//判断解析的BeanDefinition是spring定义的还是自定义扩展的
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)) {
parseDefaultElement(ele, delegate);
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
对于spring定义的BeanDefinition的解析以beans , bean , import , alias开头的四种bean，其他标示开始认为是自定义bean。自定义bean的解析机制都要从NamespaceHandler接口出发。Spring-core和Spring-beans包内就提供了如下这些实现。
下面是BeanDefinitionParserDelegate类中具体处理自定义bean的代码，允许根据不同的nameSpaceUri查找当前应用下面定义的解析类
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(ele);
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
至此解析部分完成了。但是解析完成的BeanDefinition放到哪里了呢？看一个例子：
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.
//真正执行注册BeanDefinition的类
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));
}
}
这样解析加载注册BeanDefinition 的任务就结束了。