Spring源码学习--Spring配置文件解析BeanDefinitionReader（二）

Spring配置文件的解析是通过BeanDefinitionReader来实现的，其实了解BeanDefinitionReader实现的机制就会发现，其只是将ApplicationContext.xml配置文件解析成Document对象，真正对xml中元素解析的类是在BeanDefinitionDocumentReader的实现类中来完成的，接下来我们也会对它进行介绍。

对ApplicationContext.xml中开始解析的方法是loadBeanDefinitions

AbstractBeanDefinitionReader的loadBeanDefinitions中会对ApplicationContext.xml进行解析

@Overridepublic int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {Assert.notNull(locations, "Location array must not be null");int counter = 0;for (String location : locations) {counter += loadBeanDefinitions(location);}return counter;}

@Overridepublic int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {return loadBeanDefinitions(location, null);}

loadBeanDefinitions中会根据文件地址来进行解析操作：

public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {//判断资源地址类型if (resourceLoader instanceof ResourcePatternResolver) {// Resource pattern matching available.try {Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);//在子类的loadBeanDefinitions进行解析操作int loadCount = loadBeanDefinitions(resources);if (actualResources != null) {for (Resource resource : resources) {actualResources.add(resource);}}if (logger.isDebugEnabled()) {logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");}return loadCount;}catch (IOException ex) {throw new BeanDefinitionStoreException("Could not resolve bean definition resource pattern [" + location + "]", ex);}}else {// Can only load single resources by absolute URL.Resource resource = resourceLoader.getResource(location);//在子类的loadBeanDefinitions进行解析操作int loadCount = loadBeanDefinitions(resource);if (actualResources != null) {actualResources.add(resource);}if (logger.isDebugEnabled()) {logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");}return loadCount;}}

loadBeanDefinitions是在子类XmlBeanDefinitionReader中实现

@Overridepublic int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {return loadBeanDefinitions(new EncodedResource(resource));}

doLoadBeanDefinitions会将文件地址解析为数据流，然后解析数据流

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {..........try {//从xml文件中获取流InputStream inputStream = encodedResource.getResource().getInputStream();try {InputSource inputSource = new InputSource(inputStream);if (encodedResource.getEncoding() != null) {inputSource.setEncoding(encodedResource.getEncoding());}//解析文件流return doLoadBeanDefinitions(inputSource, encodedResource.getResource());}finally {inputStream.close();}}.......}

doLoadBeanDefinitions中会将文件流解析成Document对象

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)throws BeanDefinitionStoreException {try {Document doc = doLoadDocument(inputSource, resource);return registerBeanDefinitions(doc, resource);}.....}

registerBeanDefinitions中会创建BeanDefinitionDocumentReader来对Document进行解析，对Spring配置文件中的元素进行解析处理。

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {//创建Document解析处理器BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();int countBefore = getRegistry().getBeanDefinitionCount();//在BeanDefinitionDocumentReader中解析xml中配置的元素documentReader.registerBeanDefinitions(doc, createReaderContext(resource));return getRegistry().getBeanDefinitionCount() - countBefore;}

总结：简单来说BeanDefinitionReader所做的处理操作是将配置的ApplicationContext.xml解析成为Document对象，接下来会有BeanDefinitionDocumentReader来对Document进行解析。