Spring通过在META-INF/spring.handlers中的属性进行配置文件解析

在Spring的入口函数refresh()之中进行的。  

AbstractApplicationContext
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();//获得一个新的beanFactory,并进行一些相关的load
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        refreshBeanFactory();//通知子类context刷新内部的BeanFactory
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
return beanFactory;
    }
AbstractRefreshableApplicationContext
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
            destroyBeans();//销毁当前context管理的所有bean
            closeBeanFactory();//关闭beanFactory
        }
try {//创建一个新的beanFactory(DefaultListableBeanFactory)
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            beanFactory.setSerializationId(getId());
            customizeBeanFactory(beanFactory);
            loadBeanDefinitions(beanFactory);//加载BeanDefinition
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
            }
        }
//...
    }
XmlWebApplicationContext
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
//创建一个新的XmlBeanDefinitionReader
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
        beanDefinitionReader.setEnvironment(this.getEnvironment());
        beanDefinitionReader.setResourceLoader(this);
        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
        initBeanDefinitionReader(beanDefinitionReader);
        loadBeanDefinitions(beanDefinitionReader);//接着加载BeanDefinition
    }
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
        String[] configLocations = getConfigLocations();//获得ServletConfig的配置文件位置
if (configLocations != null) {
for (String configLocation : configLocations) {
                reader.loadBeanDefinitions(configLocation);//根据位置加载BeanDefinition
            }
        }
    }
中间省略
XmlBeanDefinitionReader
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        documentReader.setEnvironment(this.getEnvironment());
int countBefore = getRegistry().getBeanDefinitionCount();
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));//创建一个ReaderContext,
//注册BeanDefinition
return getRegistry().getBeanDefinitionCount() - countBefore;
    }
protected XmlReaderContext createReaderContext(Resource resource) {
if (this.namespaceHandlerResolver == null) {//创建默认的名称控件处理器解析器
this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
        }//返回创建好的xmlReaderContext,将创建好的namespaceHandlerResolver传入
return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
this.sourceExtractor, this, this.namespaceHandlerResolver);
    }
protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {//对应的NamespaceHandlerResolver
return new DefaultNamespaceHandlerResolver(getResourceLoader().getClassLoader());
    }
public DefaultNamespaceHandlerResolver(ClassLoader classLoader) {
this(classLoader, DEFAULT_HANDLER_MAPPINGS_LOCATION);//这个位置就在META-INF/spring.handlers
    }
接着往下走注册BeanDefinitioni的过程
DefaultBeanDefinitionDocumentReader
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        Element root = doc.getDocumentElement();
        doRegisterBeanDefinitions(root);//注册beanDefinition 将root根节点传入
    }
protected void doRegisterBeanDefinitions(Element root) {
//....
this.delegate = createDelegate(this.readerContext, root, parent);//创建一个委托
        preProcessXml(root);
        parseBeanDefinitions(root, this.delegate);//处理
        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)) {
                        parseDefaultElement(ele, delegate);
                    }
else {
                        delegate.parseCustomElement(ele);//解析自定义的节点
                    }
                }
            }
        }
else {
            delegate.parseCustomElement(root);
        }
    }
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {//null
        String namespaceUri = getNamespaceURI(ele);//根据之前设置的解析器对这个uri进行解析，获得一个NamespaceHandler
//通过键值对的形式存在文件里面，在resolve里面对类名获取，然后实例化一个handler对象
                 NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
//....现在可以对配置文件进行解析了。
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
    }
DefaultNamespaceHandlerResolver
public NamespaceHandler resolve(String namespaceUri) {
        Map<String, Object> handlerMappings = getHandlerMappings();
        Object handlerOrClassName = handlerMappings.get(namespaceUri);//获取处理器的类名
if (handlerOrClassName == null) {
return null;
        }
else if (handlerOrClassName instanceof NamespaceHandler) {
return (NamespaceHandler) handlerOrClassName;
        }
else {
            String className = (String) handlerOrClassName;
try {//利用反射根据类名进行类的装载
                Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
"] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
                }//根据类进行实例化
                NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
                namespaceHandler.init();
                handlerMappings.put(namespaceUri, namespaceHandler);//缓存这个handler,下次其他的可以再次利用
return namespaceHandler;
            }
//....
        }
    }