转：Spring技术内幕——深入解析Spring架构与设计原理（二）IOC实现原理

这里使用 XmlBeanDefinitionReader来载入BeanDefinition到容器中，如以下代码清单所示：

Java代码 //这里是调用的入口。
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
//这里是载入XML形式的BeanDefinition的地方。
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());
}

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 recursive loading of " + encodedResource + " - check your import definitions!");
}
//这里得到XML文件，并得到IO的InputSource准备进行读取。
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.set(null);
}
}
}
//具体的读取过程可以在doLoadBeanDefinitions方法中找到：
//这是从特定的XML文件中实际载入BeanDefinition的地方
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
int validationMode = getValidationModeForResource(resource);
//这里取得XML文件的Document对象，这个解析过程是由 documentLoader完成的，这个documentLoader是DefaultDocumentLoader,在定义documentLoader的地方创建
Document doc = this.documentLoader.loadDocument(
inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
//这里启动的是对BeanDefinition解析的详细过程，这个解析会使用到Spring的Bean配置规则，是我们下面需要详细关注的地方。
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);
}
}
//这里是调用的入口。 public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException { return loadBeanDefinitions(new EncodedResource(resource)); } //这里是载入XML形式的BeanDefinition的地方。 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()); } 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 recursive loading of " + encodedResource + " - check your import definitions!"); } //这里得到XML文件，并得到IO的InputSource准备进行读取。 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.set(null); } } } //具体的读取过程可以在doLoadBeanDefinitions方法中找到： //这是从特定的XML文件中实际载入BeanDefinition的地方 protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { int validationMode = getValidationModeForResource(resource); //这里取得XML文件的Document对象，这个解析过程是由 documentLoader完成的，这个documentLoader是DefaultDocumentLoader,在定义documentLoader的地方创建 Document doc = this.documentLoader.loadDocument( inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware()); //这里启动的是对BeanDefinition解析的详细过程，这个解析会使用到Spring的Bean配置规则，是我们下面需要详细关注的地方。 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); } }
关于具体的Spring BeanDefinition的解析，是在BeanDefinitionParserDelegate中完成的。这个类里包含了各种Spring Bean定义规则的处理，感兴趣的同学可以仔细研究。我们举一个例子来分析这个处理过程，比如我们最熟悉的对Bean元素的处理是怎样完成的，也就是我们 在XML定义文件中出现的<bean></bean>这个最常见的元素信息是怎样被处理的。在这里，我们会看到那些熟悉的 BeanDefinition定义的处理，比如id、name、aliase等属性元素。把这些元素的值从XML文件相应的元素的属性中读取出来以后，会 被设置到生成的BeanDefinitionHolder中去。这些属性的解析还是比较简单的。对于其他元素配置的解析，比如各种Bean的属性配置，通 过一个较为复杂的解析过程，这个过程是由parseBeanDefinitionElement来完成的。解析完成以后，会把解析结果放到 BeanDefinition对象中并设置到BeanDefinitionHolder中去，如以下清单所示：

Java代码 public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
//这里取得在<bean>元素中定义的id、name和aliase属性的值
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

List<String> aliases = new ArrayList<String>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, BEAN_NAME_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}

String beanName = id;
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isDebugEnabled()) {
logger.debug("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}

if (containingBean == null) {
checkNameUniqueness(beanName, aliases, ele);
}

//这个方法会引发对bean元素的详细解析
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
beanName = this.readerContext.generateBeanName(beanDefinition);
// Register an alias for the plain bean class name, if still possible,
// if the generator returned the class name plus a suffix.
// This is expected for Spring 1.2/2.0 backwards compatibility.
String beanClassName = beanDefinition.getBeanClassName();
if (beanClassName != null &&
beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
aliases.add(beanClassName);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Neither XML 'id' nor 'name' specified - " +
"using generated bean name [" + beanName + "]");
}
}
catch (Exception ex) {
error(ex.getMessage(), ele);
return null;
}
}
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}

return null;
}
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) { //这里取得在<bean>元素中定义的id、name和aliase属性的值 String id = ele.getAttribute(ID_ATTRIBUTE); String nameAttr = ele.getAttribute(NAME_ATTRIBUTE); List<String> aliases = new ArrayList<String>(); if (StringUtils.hasLength(nameAttr)) { String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, BEAN_NAME_DELIMITERS); aliases.addAll(Arrays.asList(nameArr)); } String beanName = id; if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) { beanName = aliases.remove(0); if (logger.isDebugEnabled()) { logger.debug("No XML 'id' specified - using '" + beanName + "' as bean name and " + aliases + " as aliases"); } } if (containingBean == null) { checkNameUniqueness(beanName, aliases, ele); } //这个方法会引发对bean元素的详细解析 AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean); if (beanDefinition != null) { if (!StringUtils.hasText(beanName)) { try { if (containingBean != null) { beanName = BeanDefinitionReaderUtils.generateBeanName( beanDefinition, this.readerContext.getRegistry(), true); } else { beanName = this.readerContext.generateBeanName(beanDefinition); // Register an alias for the plain bean class name, if still possible, // if the generator returned the class name plus a suffix. // This is expected for Spring 1.2/2.0 backwards compatibility. String beanClassName = beanDefinition.getBeanClassName(); if (beanClassName != null && beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() && !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) { aliases.add(beanClassName); } } if (logger.isDebugEnabled()) { logger.debug("Neither XML 'id' nor 'name' specified - " + "using generated bean name [" + beanName + "]"); } } catch (Exception ex) { error(ex.getMessage(), ele); return null; } } String[] aliasesArray = StringUtils.toStringArray(aliases); return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray); } return null; }