Spring源码分析（一）IOC容器的创建-XMLBeanFactory篇

在spring4.0中加载配置文件的类发生了变化，spring不在支持使用XmlBeanFactory  创建factory加载配置文件。而是采用了ClassPathXmlApplicationContext创建factory

具体查看下面代码

spring4.0之前可以采用下面这种方式

privatestatic XmlBeanFactory beanFactory;

privatefinal static  Object lock=new Object();

publicstatic void init(){

    XmlBeanFactory factory1 = newXmlBeanFactory(new InputStreamResource(

    BeansFactory.class.getResourceAsStream("application.factory.xml")));

    beanFactory=factory1;

}

spring4.0之后的采用这种新版的加载方式：

privatestatic BeanFactory beanFactory ;

privatefinal static  Object lock=new Object();

publicstatic void init(){

beanFactory= new ClassPathXmlApplicationContext("application.factory.xml");

 

设计理念：Spring将所有的东西都当成是Resource。外界只传递Resource对象就可了

Spring通过beanFactory来加载配置、管理对象

XmlBeanFactory[Spring3.1之前使用，后面被标记为Deprecated]（用xml来定义IOC容器中的bean）: 通过使用模板模式来得到对IOC 容器的抽象- AbstractBeanFactory,DefaultListableBeanFactory 这些抽象类为其提供模板服务。

通过resource 接口来抽象bean定义数据，对Xml定义文件的解析通过委托给XmlBeanDefinitionReader来完成。

使用方法：

XMLBeanFactory factoty= new XmlBeanFactory(new ClassPathResource(“beans.xml”));

factory.getBean(“person”);

读取xml文件，解析文件，将元素中的东西封装为对象。被spring管理

 

演示IOC容器的创建过程（不使用XMLBeanFactory的时候）： 

ClassPathResourceres = new ClassPathResource("beans.xml");   // 创建IOC配置文件的抽象资源

DefaultListableBeanFactoryfactory = new DefaultListableBeanFactory();  // 创建一个BeanFactory

XmlBeanDefinitionReaderreader = new XmlBeanDefinitionReader(factory);  //把读取配置信息的BeanDefinitionReader,这里是XmlBeanDefinitionReader配置给BeanFactory

reader.loadBeanDefinitions(res);   //从定义好的资源位置读入配置信息，具体的解析过程由XmlBeanDefinitionReader来完成

 

Spring加载资源并装配对象的过程：

1.    定义好spring的配置文件

2.    通过Resource对象将spring的配置文件进行抽象，抽象成一个Resource对象

3.    定义好bean工厂

4.    定义好XMLBeanDefinitionReader对象，并将工厂作为参数传递进去供后续回调使用

5.    通过XMLBeanDefinitionReader对象读取之前抽象出的Resource对象（包含了xml文件解析过程）

6.    本质上，xml文件的解析是由XmlBeanDefinitionReader对象交由BeanDefinitionParserDelegate委托来完成，实际上这里使用了委托模式。

7.    IOC、容器创建完毕，可以通过容器获得所有对象的信息。

 

1定义好spring的配置文件beans.xml

2通过Resource对象将spring的配置文件进行抽象，抽象成一个Resource对象【new ClassPathResource(“beans.xml”】

3定义好bean工厂XmlBeanFactory

4XmlBeanFactory内部维护了一个XMLBeanDefinitionReader对象，在XmlBeanFactory构造的时候，将XmlBeanFactory对象注入保存为BeanDefinitionRegistry（XmlBeanDefinitionReader中）。

5通过XMLBeanDefinitionReader对象调用loadBeanDefinitions读取之前抽象出的Resource对象（包含了xml文件解析过程）

6xml文件的解析是由XmlBeanDefinitionReader对象交由BeanDefinitionParserDelegate委托来完成，使用了委托模式。

XmlBeanDefinitionReader内部维护了一个DocumentLoader还有ThreadLocal等。

loadBeanDefinitions方法将先从ThreadLocal中获取资源容器set。如果没有则创建一个四空间大小的。然后set进去。如果有了，就把当前的资源文件add到这个set容器中。将这个资源文件转为字节流（如果编码了会进行转码），然后调用doLoadBeanDefinitions方法进行加载配置。

doLoadBeanDefinitions方法将先调用doLoadDocument对传入的资源字节流进行转换为Document。最后调用registerBeanDefinitions进行注册，返回注册的bean的数量。

doLoadDocument方法是使用DefaultDocumentLoader的loadDocument方法，最终返回一个Document

registerBeanDefinitions则是使用DefaultNamespaceHandlerResolver进行解析Document，调用其registerBeanDefinitions进行注入。

DefaultNamespaceHandlerResolver 的registerBeanDefinitions方法中先是获取了xml的根元素，然后根据根元素调用doRegisterBeanDefinitions方法去逐个获取元素。

doRegisterBeanDefinitions方法委托了BeanDefinitionParserDelegate类进行解析。调用了parseBeanDefinitions方法来解析元素。【委托模式可以实现业务的解耦】

parseBeanDefinitions方法中，循环进行遍历，调用parseDefaultElement进行比对，如果是对应的配置，如bean，则调用相应的方法，比方说bean的就调用了processBeanDefinition方法

processBeanDefinition方法中最终调用了BeanDefinitionReaderUtils.registerBeanDefinition。这里会最终调用到BeanDefinitionRegistry，也就是当前的XmlBeanFactory的registerBeanDefinition方法，这个方法主要就是put元素进到内部维护的map中（在XmlBeanFactory的父类中实现，也就是DefaultListableBeanFactory中实现。同理，这里实现了其他的注册，都是以map的方式进行维护的）

7委托得到的结果（bean等），通过调用XmlBeanFactory的父类DefaultListableBeanFactory的registerBeanDefinition方法，put到map中进行维护。IOC、容器创建完毕，可以通过容器获得所有对象的信息

@Deprecated
@SuppressWarnings({"serial", "all"})
public class XmlBeanFactory extends DefaultListableBeanFactory {
//定义了一个默认使用的bean定义读取器 ，完成对xml的读取
   private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this); 
   public XmlBeanFactory(Resource resource) throws BeansException {
      this(resource, null);
   }
//在初始化函数中使用读取器来对资源进行读取，得到bean定义信息
   public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
      super(parentBeanFactory);
      this.reader.loadBeanDefinitions(resource);  // 调用了xmlBeanDefinitionReafer进行加载配置资源
   }
}

读取器读取资源和注册bean定义信息的整个过程，基本上是和上下文的处理是一样的，

从这里可看到上下文和XmlBeanFactory这两种IOC容器的区别:

BeanFactory往往不具备对资源定义的能力，

而上下文可自己完成资源定义，从这个角度上看上下文更好用一些。 

DefaultListableBeanFactory：

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
      implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
// 这里将把bean注入到map中。【不管如何，最后都是要put进去的】
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
      throws BeanDefinitionStoreException {
   if (beanDefinition instanceof AbstractBeanDefinition) {
      try {
         ((AbstractBeanDefinition) beanDefinition).validate();
      }catch (BeanDefinitionValidationException ex) {
       throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Va ";
      }
   }
   BeanDefinition oldBeanDefinition;
   oldBeanDefinition = this.beanDefinitionMap.get(beanName);
   if (oldBeanDefinition != null) {
      if (!isAllowBeanDefinitionOverriding()) {
 throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannd.");
      }
      this.beanDefinitionMap.put(beanName, beanDefinition);
   }
   else {
      if (hasBeanCreationStarted()) {
         // Cannot modify startup-time collection elements anymore (for stable iteration)
         synchronized (this.beanDefinitionMap) {
            this.beanDefinitionMap.put(beanName, beanDefinition);
           List updatedDefinitions = new ArrayList(this.beanDefinitionNames.size() + 1);
            updatedDefinitions.addAll(this.beanDefinitionNames);
            updatedDefinitions.add(beanName);
            this.beanDefinitionNames = updatedDefinitions;
            if (this.manualSingletonNames.contains(beanName)) {
               Set updatedSingletons = new LinkedHashSet(this.manualSingletonNames);
               updatedSingletons.remove(beanName);
               this.manualSingletonNames = updatedSingletons;
            }
         }
      }
      else {
         // Still in startup registration phase
         this.beanDefinitionMap.put(beanName, beanDefinition);
         this.beanDefinitionNames.add(beanName);
         this.manualSingletonNames.remove(beanName);
      }
      this.frozenBeanDefinitionNames = null;
   }
   if (oldBeanDefinition != null || containsSingleton(beanName)) {
      resetBeanDefinition(beanName);
   }
}

AbstractBeanDefinitionReader

public abstract class AbstractBeanDefinitionReader implements EnvironmentCapable, BeanDefinitionReader {
protected final Log logger = LogFactory.getLog(getClass());
private final BeanDefinitionRegistry registry;  // 这里保存了XmlBeanFactory
private ResourceLoader resourceLoader;
private ClassLoader beanClassLoader;
private Environment environment;
private BeanNameGenerator beanNameGenerator = new DefaultBeanNameGenerator();
protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {
   this.registry = registry; 
   if (this.registry instanceof ResourceLoader) {
      this.resourceLoader = (ResourceLoader) this.registry;
   }
   else {
      this.resourceLoader = new PathMatchingResourcePatternResolver();
   }
   // Inherit Environment if possible
   if (this.registry instanceof EnvironmentCapable) {
      this.environment = ((EnvironmentCapable) this.registry).getEnvironment();
   }
   else {
      this.environment = new StandardEnvironment();
   }
}

XmlBeanDefinitionReader

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {
。。。
   private static final Constants constants = new Constants(XmlBeanDefinitionReader.class);
   private int validationMode = VALIDATION_AUTO;
   private boolean namespaceAware = false;
   private Class documentReaderClass = DefaultBeanDefinitionDocumentReader.class;
   private ProblemReporter problemReporter = new FailFastProblemReporter();
   private ReaderEventListener eventListener = new EmptyReaderEventListener();
   private SourceExtractor sourceExtractor = new NullSourceExtractor();
   private NamespaceHandlerResolver namespaceHandlerResolver;
   private DocumentLoader documentLoader = new DefaultDocumentLoader();
   private EntityResolver entityResolver;
   private ErrorHandler errorHandler = new SimpleSaxErrorHandler(logger);
   private final XmlValidationModeDetector validationModeDetector = new XmlValidationModeDetector();
   private final ThreadLocal> resourcesCurrentlyBeingLoaded =new NamedThreadLocal>("XML bean definition resources currently being loaded");
   public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
      super(registry);  // 将XmlBeanFactory进行保存
   }
…….
   protected EntityResolver getEntityResolver() {
      if (this.entityResolver == null) {
         ResourceLoader resourceLoader = getResourceLoader();
         if (resourceLoader != null) {
            this.entityResolver = new ResourceEntityResolver(resourceLoader);
         } else {
            this.entityResolver = new DelegatingEntityResolver(getBeanClassLoader());
         }
      }
      return this.entityResolver;
   }
   @Override
   public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
      return loadBeanDefinitions(new EncodedResource(resource));  // 包装了一下
   }
// 返回发现bean的个数
  public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
      Set currentResources = this.resourcesCurrentlyBeingLoaded.get(); //尝试获取
      if (currentResources == null) {   // 如果没有，是刚初始化，就进行初始化
         currentResources = new HashSet(4); // 默认空间大小为4
         this.resourcesCurrentlyBeingLoaded.set(currentResources);  
      }
      if (!currentResources.add(encodedResource)) {  // 添加当前的资源文件到Set容器中
         throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");
      }
      try { // 获得配置文件的输入流(将配置资源文件转换为流)
         InputStream inputStream = encodedResource.getResource().getInputStream(); 
         try {
            InputSource inputSource = new InputSource(inputStream); // 包装了这个流，为Source
            if (encodedResource.getEncoding() != null) {   // 是否编码。编码了就进行解码
               inputSource.setEncoding(encodedResource.getEncoding());
            }
            return doLoadBeanDefinitions(inputSource, encodedResource.getResource()); // 这里加载这个配置
         } finally {
            inputStream.close();
         }
      } catch (IOException ex) {。。。。
      }
      finally {
         currentResources.remove(encodedResource); //
         if (currentResources.isEmpty()) {   // 如果为空，则从ThreadLocal中移除
            this.resourcesCurrentlyBeingLoaded.remove();
         }
      }
   }
   public int loadBeanDefinitions(InputSource inputSource) throws BeanDefinitionStoreException {
      return loadBeanDefinitions(inputSource, "resource loaded through SAX InputSource");
   }
   public int loadBeanDefinitions(InputSource inputSource, String resourceDescription) throws BeanDefinitionStoreException {
      return doLoadBeanDefinitions(inputSource, new DescriptiveResource(resourceDescription));
   }
//实际完成对xml进行载入的方法
   protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException {
      try {      // Document代表xml文档对象
         Document doc = doLoadDocument(inputSource, resource); // 总之这里会返回一个Document
         return registerBeanDefinitions(doc, resource);  // 将返回的Document注册
      } catch (BeanDefinitionStoreException ex) {
         throw ex; …. 
      catch (Throwable ex) {
         throw new BeanDefinitionStoreException(resource.getDescription(),"Unexpected om ");
      }
   }
// 加载xml文件，返回Document。使用DefaultDocumentLoader的loadDocument方法，返回一个Document
   protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
      return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
            getValidationModeForResource(resource), isNamespaceAware());
   }
//使用DefaultNamespaceHandlerResolver 进行解析Document
   public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
      BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// 用代理对象
      int countBefore = getRegistry().getBeanDefinitionCount();  // 获取父类的BeanDefinitionRegistry（这里也就是IOC容器XmlBeanFactory），然后调用getBeanDefinitionCount方法。获得注册之前的数量
      documentReader.registerBeanDefinitions(doc, createReaderContext(resource));// 这里进行了解析和注入，DefaultBeanDefinitionDocumentReader中实现
      return getRegistry().getBeanDefinitionCount() - countBefore;  // 这里返回了数量
   }
   protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
  return BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
   }
   public XmlReaderContext createReaderContext(Resource resource) {
      return new XmlReaderContext(resource, this.problemReporter, this.eventListener, this.sourceExtractor, this, getNamespaceHandlerResolver());
   }
   public NamespaceHandlerResolver getNamespaceHandlerResolver() {  // 单例模式获取
      if (this.namespaceHandlerResolver == null) {
         this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
      }
      return this.namespaceHandlerResolver;
   }
   protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
      return new DefaultNamespaceHandlerResolver(getResourceLoader().getClassLoader());
   }
}

DefaultNamespaceHandlerResolver：

public class DefaultBeanDefinitionDocumentReader implements BeanDefinitionDocumentReader {
   public static final String BEAN_ELEMENT = BeanDefinitionParserDelegate.BEAN_ELEMENT;
   public static final String NESTED_BEANS_ELEMENT = "beans";
   public static final String ALIAS_ELEMENT = "alias";
   public static final String NAME_ATTRIBUTE = "name";
   public static final String ALIAS_ATTRIBUTE = "alias";
   public static final String IMPORT_ELEMENT = "import";
   public static final String RESOURCE_ATTRIBUTE = "resource";
   public static final String PROFILE_ATTRIBUTE = "profile";
   protected final Log logger = LogFactory.getLog(getClass());
   private XmlReaderContext readerContext;
   private BeanDefinitionParserDelegate delegate; 
   @Override
   public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
      this.readerContext = readerContext; 
      Element root = doc.getDocumentElement();// 获得xml文档的根元素
      doRegisterBeanDefinitions(root);
   }
   protected final XmlReaderContext getReaderContext() {
      return this.readerContext;
   }
   protected Object extractSource(Element ele) {
      return getReaderContext().extractSource(ele);
   }
// 获取元素
   protected void doRegisterBeanDefinitions(Element root) {
      BeanDefinitionParserDelegate parent = this.delegate;
// 创建了代理类（本质，xml文件解析是由代理进行）
      this.delegate = createDelegate(getReaderContext(), root, parent);
      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;
            }
         }
      }
// 模板装饰模式
      preProcessXml(root);  // 本类中为空实现，供子类复写实现
      parseBeanDefinitions(root, this.delegate);   // 解析元素
      postProcessXml(root);  // 本类中为空实现
      this.delegate = parent;
   }
   protected BeanDefinitionParserDelegate createDelegate(XmlReaderContext readerContext, Element root, BeanDefinitionParserDelegate parentDelegate) {
      BeanDefinitionParserDelegate delegate = new BeanDefinitionParserDelegate(readerContext);
      delegate.initDefaults(root, parentDelegate);
      return delegate;
   }
// 这里解析了元素
   protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
      if (delegate.isDefaultNamespace(root)) {
         NodeList nl = root.getChildNodes();
         for (int i = 0; i < nl.getLength(); i++) {  // 根据元素的数量一个一个解析出元素
            Node node = nl.item(i);
            if (node instanceof Element) {
               Element ele = (Element) node;
               if (delegate.isDefaultNamespace(ele)) {
                  parseDefaultElement(ele, delegate);  // 这里对元素进行解析，同名就解析出来
               } else {
                  delegate.parseCustomElement(ele);
               }
            }
         }
      } else {
         delegate.parseCustomElement(root);
      }
   }
   private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
      if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {//import
         importBeanDefinitionResource(ele);
      }  else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {//alias
         processAliasRegistration(ele);
      }  else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {//bean
         processBeanDefinition(ele, delegate);
      }  else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) { //nested
         doRegisterBeanDefinitions(ele);
      }
   }
   protected void importBeanDefinitionResource(Element ele) {
      String location = ele.getAttribute(RESOURCE_ATTRIBUTE);
      if (!StringUtils.hasText(location)) {
         getReaderContext().error("Resource location must not be empty", ele);
         return;
      }
      location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);
      Set actualResources = new LinkedHashSet(4); 
      boolean absoluteLocation = false;
      try {
         absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute();
      } catch (URISyntaxException ex) {
      }
      if (absoluteLocation) {
         try {
            int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources); 
         }  catch (BeanDefinitionStoreException ex) {
            getReaderContext().error("Failed to import bean definitions from URL location [" + location + "]", ele, ex);
         }
      }
      else {
         try {
            int importCount;
            Resource relativeResource = getReaderContext().getResource().createRelative(location);
            if (relativeResource.exists()) {
               importCount = getReaderContext().getReader().loadBeanDefinitions(relativeResource);
               actualResources.add(relativeResource);
            }  else {
               String baseLocation = getReaderContext().getResource().getURL().toString();
               importCount = getReaderContext().getReader().loadBeanDefinitions(
                     StringUtils.applyRelativePath(baseLocation, location), actualResources);
            }
         } catch (IOException ex) {
            getReaderContext().error("Failed to resolve current resource location", ele, ex);
         } catch (BeanDefinitionStoreException ex) {
            getReaderContext().error("Failed to import bean definitions from relative location [" + location + "]",ele, ex);
         }
      }
      Resource[] actResArray = actualResources.toArray(new Resource[actualResources.size()]);
      getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele));
   }
   protected void processAliasRegistration(Element ele) {
      String name = ele.getAttribute(NAME_ATTRIBUTE);
      String alias = ele.getAttribute(ALIAS_ATTRIBUTE);
      boolean valid = true;
      if (!StringUtils.hasText(name)) {
         getReaderContext().error("Name must not be empty", ele);
         valid = false;
      }
      if (!StringUtils.hasText(alias)) {
         getReaderContext().error("Alias must not be empty", ele);
         valid = false;
      }
      if (valid) {
         try {
            getReaderContext().getRegistry().registerAlias(name, alias);
         } catch (Exception ex) {
            getReaderContext().error("Failed to register alias '" + alias +"' for bean with name '" + name + "'", ele, ex);
         }
         getReaderContext().fireAliasRegistered(name, alias, extractSource(ele));
      }
   }
// 这里是解析bean的
   protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
      BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
      if (bdHolder != null) {
         bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
         try {
            BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());  // 这里会最终调用到BeanDefinitionRegistry，也就是当前的XmlBeanFactory的registerBeanDefinition方法，这个方法主要就是put元素进到内部维护的map中（在XmlBeanFactory的父类中实现，也就是DefaultListableBeanFactory中实现。同理，这里实现了其他的注册，都是以map的方式进行维护的）
         } catch (BeanDefinitionStoreException ex) {
            getReaderContext().error("Failed to register bean definition with name '" +bdHolder.getBeanName() + "'", ele, ex);
         }
         // Send registration event.
         getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
      }
   }
   protected void preProcessXml(Element root) { }
   protected void postProcessXml(Element root) {}
}

BeanDefinitionParserDelegate：Spring真正的解析代理类：

public class BeanDefinitionParserDelegate {
   public static final String BEANS_NAMESPACE_URI = "http://www.springframework.org/schema/beans";
   public static final String MULTI_VALUE_ATTRIBUTE_DELIMITERS = ",; ";
   public static final String TRUE_VALUE = "true";
   public static final String FALSE_VALUE = "false";
   public static final String DEFAULT_VALUE = "default";
   public static final String DESCRIPTION_ELEMENT = "description";
   public static final String AUTOWIRE_NO_VALUE = "no";
   public static final String AUTOWIRE_BY_NAME_VALUE = "byName";
   public static final String AUTOWIRE_BY_TYPE_VALUE = "byType";
   public static final String AUTOWIRE_CONSTRUCTOR_VALUE = "constructor";
   public static final String AUTOWIRE_AUTODETECT_VALUE = "autodetect";
   public static final String DEPENDENCY_CHECK_ALL_ATTRIBUTE_VALUE = "all";
   public static final String DEPENDENCY_CHECK_SIMPLE_ATTRIBUTE_VALUE = "simple";
   public static final String DEPENDENCY_CHECK_OBJECTS_ATTRIBUTE_VALUE = "objects";
   public static final String NAME_ATTRIBUTE = "name";
   public static final String BEAN_ELEMENT = "bean";
   public static final String META_ELEMENT = "meta";
   public static final String ID_ATTRIBUTE = "id";
   public static final String PARENT_ATTRIBUTE = "parent";
   public static final String CLASS_ATTRIBUTE = "class";
   public static final String ABSTRACT_ATTRIBUTE = "abstract";
   public static final String SCOPE_ATTRIBUTE = "scope";
   private static final String SINGLETON_ATTRIBUTE = "singleton";
   public static final String LAZY_INIT_ATTRIBUTE = "lazy-init";
   public static final String AUTOWIRE_ATTRIBUTE = "autowire";
   public static final String AUTOWIRE_CANDIDATE_ATTRIBUTE = "autowire-candidate";
   public static final String PRIMARY_ATTRIBUTE = "primary";
   public static final String DEPENDENCY_CHECK_ATTRIBUTE = "dependency-check";
   public static final String DEPENDS_ON_ATTRIBUTE = "depends-on";
   public static final String INIT_METHOD_ATTRIBUTE = "init-method";
   public static final String DESTROY_METHOD_ATTRIBUTE = "destroy-method";
   public static final String FACTORY_METHOD_ATTRIBUTE = "factory-method";
   public static final String FACTORY_BEAN_ATTRIBUTE = "factory-bean";
   public static final String CONSTRUCTOR_ARG_ELEMENT = "constructor-arg";
   public static final String INDEX_ATTRIBUTE = "index";
   public static final String TYPE_ATTRIBUTE = "type";
   public static final String VALUE_TYPE_ATTRIBUTE = "value-type";
   public static final String KEY_TYPE_ATTRIBUTE = "key-type";
   public static final String PROPERTY_ELEMENT = "property";
   public static final String REF_ATTRIBUTE = "ref";
   public static final String VALUE_ATTRIBUTE = "value";
   public static final String LOOKUP_METHOD_ELEMENT = "lookup-method";
   public static final String REPLACED_METHOD_ELEMENT = "replaced-method";
   public static final String REPLACER_ATTRIBUTE = "replacer";
   public static final String ARG_TYPE_ELEMENT = "arg-type";
   public static final String ARG_TYPE_MATCH_ATTRIBUTE = "match";
   public static final String REF_ELEMENT = "ref";
   public static final String IDREF_ELEMENT = "idref";
   public static final String BEAN_REF_ATTRIBUTE = "bean";
   public static final String LOCAL_REF_ATTRIBUTE = "local";
   public static final String PARENT_REF_ATTRIBUTE = "parent";
   public static final String VALUE_ELEMENT = "value";
   public static final String NULL_ELEMENT = "null";
   public static final String ARRAY_ELEMENT = "array";
   public static final String LIST_ELEMENT = "list";
   public static final String SET_ELEMENT = "set";
   public static final String MAP_ELEMENT = "map";
   public static final String ENTRY_ELEMENT = "entry";
   public static final String KEY_ELEMENT = "key";
   public static final String KEY_ATTRIBUTE = "key";
   public static final String KEY_REF_ATTRIBUTE = "key-ref";
   public static final String VALUE_REF_ATTRIBUTE = "value-ref";
   public static final String PROPS_ELEMENT = "props";
   public static final String PROP_ELEMENT = "prop";
   public static final String MERGE_ATTRIBUTE = "merge";
   public static final String QUALIFIER_ELEMENT = "qualifier";
   public static final String QUALIFIER_ATTRIBUTE_ELEMENT = "attribute";
   public static final String DEFAULT_LAZY_INIT_ATTRIBUTE = "default-lazy-init";
   public static final String DEFAULT_MERGE_ATTRIBUTE = "default-merge";
   public static final String DEFAULT_AUTOWIRE_ATTRIBUTE = "default-autowire";
   public static final String DEFAULT_DEPENDENCY_CHECK_ATTRIBUTE = "default-dependency-check";
   public static final String DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE = "default-autowire-candidates";
   public static final String DEFAULT_INIT_METHOD_ATTRIBUTE = "default-init-method";
   public static final String DEFAULT_DESTROY_METHOD_ATTRIBUTE = "default-destroy-method";
   protected final Log logger = LogFactory.getLog(getClass());
   private final XmlReaderContext readerContext;
   private final DocumentDefaultsDefinition defaults = new DocumentDefaultsDefinition();
   private final ParseState parseState = new ParseState();
   private final Set usedNames = new HashSet();
、。。。。。。以下是详细解析的方法
public void initDefaults(Element root) {
   initDefaults(root, null);
}
public void initDefaults(Element root, BeanDefinitionParserDelegate parent) {
   populateDefaults(this.defaults, (parent != null ? parent.defaults : null), root);
   this.readerContext.fireDefaultsRegistered(this.defaults);
}
protected void populateDefaults(DocumentDefaultsDefinition defaults, DocumentDefaultsDefinition parentDefaults, Element root) {
   String lazyInit = root.getAttribute(DEFAULT_LAZY_INIT_ATTRIBUTE);
   if (DEFAULT_VALUE.equals(lazyInit)) {
      lazyInit = (parentDefaults != null ? parentDefaults.getLazyInit() : FALSE_VALUE);
   }
   defaults.setLazyInit(lazyInit);
   String merge = root.getAttribute(DEFAULT_MERGE_ATTRIBUTE);
   if (DEFAULT_VALUE.equals(merge)) {
      merge = (parentDefaults != null ? parentDefaults.getMerge() : FALSE_VALUE);
   }
   defaults.setMerge(merge);
   String autowire = root.getAttribute(DEFAULT_AUTOWIRE_ATTRIBUTE);
   if (DEFAULT_VALUE.equals(autowire)) {
      autowire = (parentDefaults != null ? parentDefaults.getAutowire() : AUTOWIRE_NO_VALUE);
   }
   defaults.setAutowire(autowire); defaults.setDependencyCheck(root.getAttribute(DEFAULT_DEPENDENCY_CHECK_ATTRIBUTE));
   if (root.hasAttribute(DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE)) {
     defaults.setAutowireCandidates(root.getAttribute(DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE));
   }
   else if (parentDefaults != null) {
      defaults.setAutowireCandidates(parentDefaults.getAutowireCandidates());
   }
   if (root.hasAttribute(DEFAULT_INIT_METHOD_ATTRIBUTE)) {
      defaults.setInitMethod(root.getAttribute(DEFAULT_INIT_METHOD_ATTRIBUTE));
   }
   else if (parentDefaults != null) {
      defaults.setInitMethod(parentDefaults.getInitMethod());
   }
   if (root.hasAttribute(DEFAULT_DESTROY_METHOD_ATTRIBUTE)) {
      defaults.setDestroyMethod(root.getAttribute(DEFAULT_DESTROY_METHOD_ATTRIBUTE));
   }
   else if (parentDefaults != null) {
      defaults.setDestroyMethod(parentDefaults.getDestroyMethod());
   }
   defaults.setSource(this.readerContext.extractSource(root));
}
。。。。。

XMLBeanFactory的getBean是父类的方法。调用的是父类的：

 

大致过程：

1.    Spring的bean实际上是缓存在CurrentHashMap对象中

2.    在创建bean之前，首先需要将该bean的创建标识设定好，表示该bean已经或是即将被创建，为的是增加缓存的效率

3.    根据bean的scope属性来确定是singleton还是prototype等范围，然后创建相应的bean对象

4.    通过java反射来创建bean的实例，在创建之前首先检查访问修饰符，如果不是public，则调用setAccessible（true）来突破java的语法限制，使得可以通知如私有的构造方法来创建对象实例

5.    接下来，寻找bean的属性值，完成属性的注入

6.    将所创建出的singleton对象添加到缓存当中，供下次调用使用