2.1 doLoadBeanDefinitions(inputSource, encodedResource.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 {             //获取XML的验证方式，加载XML文件得到对应的Document            Document doc = doLoadDocument(inputSource, resource);            //根据返回的Dcoument注册Bean信息            return registerBeanDefinitions(doc, resource);        }        .........................................   }

2,2 Document doc = doLoadDocument(inputSource, resource);

/**     * Actually load the specified document using the configured DocumentLoader.     * @param inputSource the SAX InputSource to read from     * @param resource the resource descriptor for the XML file     * @return the DOM Document     * @throws Exception when thrown from the DocumentLoader     * @see #setDocumentLoader     * @see DocumentLoader#loadDocument     */    protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {        return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,                getValidationModeForResource(resource), isNamespaceAware());    }

2.2.3  getValidationModeForResource(resource) DTD或者XSD文件格式的读取

 

/**     * Gets the validation mode for the specified {
    @link Resource}. If no explicit     * validation mode has been configured then the validation mode is     * {
    @link #detectValidationMode detected}.     * 
Override this method if you would like full control over the validation     * mode, even when something other than {
    @link #VALIDATION_AUTO} was set.     */    protected int getValidationModeForResource(Resource resource) {        int validationModeToUse = getValidationMode();    // 如果手动指定了校验模式，则使用指定的校验模式        if (validationModeToUse != VALIDATION_AUTO) {            return validationModeToUse;        }// 如果手动没有指定校验模式，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;    }

 

自动检测的代码逻辑分析：

先定义一个变量 isDtdValidated 是否是DTD约束 默认是 false,然后一行行的读取xml资源文件，如果里面包含 DOCTYPE  字符串则是DTD约束，则上返回，停止自动检测。

 

int detectedMode = detectValidationMode(resource);public int detectValidationMode(InputStream inputStream) throws IOException {        // Peek into the file to look for DOCTYPE.        BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));        try {                        boolean isDtdValidated = false;            String content;            while ((content = reader.readLine()) != null) {                content = consumeCommentTokens(content);                // 如果读取的行是空行或者注释，则省略                if (this.inComment || !StringUtils.hasText(content)) {                    continue;                }                // 判断是否含有 DOCTYPE 标签                if (hasDoctype(content)) {                    isDtdValidated = true;                    break;                }                if (hasOpeningTag(content)) {                    // End of meaningful data...                    break;                }            }            return (isDtdValidated ? VALIDATION_DTD : VALIDATION_XSD);        }

 

2,2,4 getEntityResolver() 获取资源文件约束的声明

 

entityResolver接口有以下一个方法

 

public abstract InputSource resolveEntity (String publicId,                                               String systemId)        throws SAXException, IOException;}

 

他接受两个参数：publicId和systemId，并返回InputSource 对象

 

如果是XSD资源文件：
     
           
        
      将会读取到以下两个参数：publicId：nullsystemId：http://www.springframework.org/schema/beans/spring-beans-2.5.xsd如果是 DTD约束：
     
     
      ...............................
     将会读取到以下两个参数：publicId：-//mybatis.org//DTDsystemId:http://mybatis.org/dtd/mybatis-3-mapper.dtd通过getEntityResolver方法获取EntityResolver接口对象，DelegatingEntityResolver为EntityResolver的实现类。protected EntityResolver getEntityResolver() {        if (this.entityResolver == null) {            // Determine default EntityResolver to use.            ResourceLoader resourceLoader = getResourceLoader();            if (resourceLoader != null) {    如果资源加载器不为空，则使用ResourceEntityResolver对象进行文件约束的声明                this.entityResolver = new ResourceEntityResolver(resourceLoader);            }            else {                this.entityResolver = new DelegatingEntityResolver(getBeanClassLoader());            }        }        return this.entityResolver;    }

 

2.2.5 new ResourceEntityResolver(resourceLoader)

public DelegatingEntityResolver(ClassLoader classLoader) {        // 判断是否是DTD约束           this.dtdResolver = new BeansDtdResolver();       //  如果是XSD约束 在获取声明的默认路经是：      // META-INF/spring.schemas        this.schemaResolver = new PluggableSchemaResolver(classLoader);    }

 

2.3 解析并注册 BeanDefinitions

 

 将文件装换为Document以后,接下来的提取以及注册Bean就是我们的重头戏。

 

/**     * Register the bean definitions contained in the given DOM document.     * Called by {
    @code loadBeanDefinitions}.     * 
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 对象        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();// 记录统计前BeanDefinition的加载个数        int countBefore = getRegistry().getBeanDefinitionCount();// 加载以及注册Bean

 //  这里使用到了单一职责原则，将逻辑处理委托给单一的类进行处理，这个逻辑处理类就是 BeanDefinitionDocumentReader 对象

documentReader.registerBeanDefinitions(doc, createReaderContext(resource));// 统计本次加载Beanfinition的个数        return getRegistry().getBeanDefinitionCount() - countBefore;    }

 

继续深入registerBeanDefinitions方法：

 

/**     * This implementation parses bean definitions according to the "spring-beans" XSD     * (or DTD, historically).     * 
Opens a DOM Document; then initializes the default settings     * specified at the {
    @code 
      } level; then parses the contained bean definitions.     */    @Override    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {        this.readerContext = readerContext;        logger.debug("Loading bean definitions");        Element root = doc.getDocumentElement();        doRegisterBeanDefinitions(root);    }

 

继续深入doRegisterBeanDefinitions方法：doRegisterBeanDefinitions算开始真正解析XML文件了。

 

protected void doRegisterBeanDefinitions(Element root) {        // Any nested 
     
       elements will cause recursion in this method. In        // order to propagate and preserve 
      
        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);       // 处理profile 属性        if (this.delegate.isDefaultNamespace(root)) {            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)) {                    return;                }            }        }         // 空代码留给子类去实现 模板设计模式 继承 DefaultBeanDefinitionDocumentReader 的子类咋XML解析前做一些处理，可以实现此方法        preProcessXml(root);        // 解析除了 profile以外的属性        parseBeanDefinitions(root, this.delegate);        // 空代码留给子类去实现 模板设计模式 继承 DefaultBeanDefinitionDocumentReader 的子类咋XML解析后做一些处理，可以实现此方法                postProcessXml(root);        this.delegate = parent;    }
      
     

 

2.4 判断标签的解析方式

 

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {      // 对Bean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)) {                  // 默认标签解析    parseDefaultElement(ele, delegate);                    }                    else {                  // 自定义标签解析                        delegate.parseCustomElement(ele);                    }                }            }        }        else {          // 自定义标签解析            delegate.parseCustomElement(root);        }    }