1、XMLBeanFcatory

BeanFactory bf = new XmlBeanFactory(new ClassPathResource("beanFactory.xml"));

public class XmlBeanFactory extends DefaultListableBeanFactory {

   //核心程式碼,XmlBeanFactory中使用了自定義的XmlBeanDefinitionReader讀取XML檔案
   XmlBeanDefinitionReader reader = new  XmlBeanDefinitionReader(this);

   public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory){
      //讀取XML配置檔案的核心程式碼
      this.reader.loadBeanDefinitions(resource);
   }
}
 

2、配置檔案封裝

載入資原始檔可以使用Spring提供的類，如

Resource resource = new ClassPathResource("beanFactory.xml");

//getInputStream是在InputStreamResource中定義的唯一方法,它也是Spring對資源封裝的最上層介面
InputStream inputStream = resource.getInputStream();

public interface InputStreamSource {

   InputStream getInputStream() throws IOException;
}

public interface Resource extends InputStreamSource {

   boolean exists();

   boolean isReadable();

   boolean isOpen();

   URL getURL() throws IOException;

   URI getURI() throws IOException;

   File getFile() throws IOException;

   long contentLength() throws IOException;

   long lastModified() throws IOException;

   Resource createRelative(String relativePath) throws IOException;

   String getFilename();

   String getDescription();
}
 

3、載入資原始檔

當使用new ClassPathResource將資原始檔封裝為Resource之後，就可以使用XmlBeanDefinitionReader來讀取配置檔案。

BeanFactory bf = new XmlBeanFactory(new ClassPathResource("beanFactory.xml"));

public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory){
   this.reader.loadBeanDefinitions(resource);
}

public int loadBeanDefinitions(Resource resource){
   //EncodedResource主要用於對資原始檔的編碼處理的
   return loadBeanDefinitions(new EncodedResource(resource));
}

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
   //通過Set來記錄已經載入的資源,它是放在ThreadLocal中
   Set<EncodedResource> currentResources = resourcesCurrentlyBeingLoaded.get();
   if (currentResources == null) {
      currentResources = new HashSet<EncodedResource>(4);
      //放入ThreadLocal中
      this.resourcesCurrentlyBeingLoaded.set(currentResources);
   }
   if (!currentResources.add(encodedResource)) {
      throw new BeanDefinitionStoreException();
   }

   try {
      //獲取檔案輸入流,上面已經分析過
      InputStream inputStream = encodedResource.getResource().getInputStream();
      try {
         InputSource inputSource = new InputSource(inputStream);
         if (encodedResource.getEncoding() != null) {
            inputSource.setEncoding(encodedResource.getEncoding());
         }
         //真正進入讀取的邏輯核心部分,此處傳入的inputSource是org.xml.sax.InputResource,用於sax解析
         return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
   }
}

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource){
   try {
      //步驟1,獲取XML檔案的驗證模式,Spring用來校驗驗證模式的方法就是判斷是否包含DOCTYPE,如果包含就是DTD,否則就是XSD  
      int validationMode = getValidationModeForResource(resource);

      //步驟2,載入XML檔案,並得到對應的Document
      Document doc = this.documentLoader.loadDocument(
                              inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
      
      //步驟3,根據返回的Document註冊Bean資訊
      return registerBeanDefinitions(doc, resource);
   }
}

//步驟2
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
      ErrorHandler errorHandler, int validationMode, boolean namespaceAware){
   //SAX解析XML文件,返回Document物件
   DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
  
   DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
   return builder.parse(inputSource);
}

//步驟3
public int registerBeanDefinitions(Document doc, Resource resource) {
   BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
   //設定環境變數
   documentReader.setEnvironment(this.getEnvironment());
   //記錄之前BeanDefinition中定義的Bean的數量
   int countBefore = getRegistry().getBeanDefinitionCount();

   documentReader.registerBeanDefinitions(doc, createReaderContext(resource));

   //返回本次載入的BeanDefinition個數
   return getRegistry().getBeanDefinitionCount() - countBefore;
}
 

4、開始解析

documentReader.registerBeanDefinitions(doc, createReaderContext(resource));

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext){
   this.readerContext = readerContext;
   //讀取的根元素,debug時顯示為[beans: null]
   Element root = doc.getDocumentElement();
   doRegisterBeanDefinitions(root);
}

protected void doRegisterBeanDefinitions(Element root) {

   //處理profile元素,profile標籤可以用於配置生產環境、開發環境等
   String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
   if (StringUtils.hasText(profileSpec)) {
      Assert.state(this.environment != null, "Environment must set for evaluating profiles");
      String[] specifiedProfiles
	          = StringUtils.tokenizeToStringArray(profileSpec, 
	                                              BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
      if (!this.environment.acceptsProfiles(specifiedProfiles)) {
         return;
      }
   }

   //專門處理解析的代理
   BeanDefinitionParserDelegate parent = this.delegate;
   this.delegate = createDelegate(this.readerContext, root, parent);
   
   //此處的兩個方法為空實現,面向繼承設計,這是模板方法模式,子類可以繼承並在解析前做一些處理
   preProcessXml(root);

   parseBeanDefinitions(root, this.delegate);

   postProcessXml(root);

   this.delegate = parent;
}


protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
   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)) {
               //解析預設標籤,如bean
               parseDefaultElement(ele, delegate);
            }
            else {
               //解析自定義標籤,如<aop:aspectj-autoproxy/>
	       delegate.parseCustomElement(ele);
            }
         }
      }
   }
   else {
      delegate.parseCustomElement(ro