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);
- }
- }
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;
- }