Spring源码之XmlBeanDefinitionReader与Resource

一、DefaultListableBeanFactory类，

里面有一个成员变量beanDefinitionMap，Bean定义对象的Map， BeanDefinition就对应XML的属性配置

/** Map of bean definition objects, keyed by bean name */
	private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>();

　　

二、上一篇讲到加载，读取xml的步骤。 

1、ClassPathResource resource = new ClassPathSource("beans.xml");

2、DefaultListableBeanFactory factory = new DefaultListableBeanFactory();  //创建DefaultListableBeanFactory对象

3、XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory); //创建XmlBeanDefinitionReader 对象

4、reader.loadBeanDefinitions(resource);  //加载bean的定义，bean来自资源文件。

 

如何定位资源，解析资源? 

下面进行具体分析：

1、ClassPathResource resource = new ClassPathSource("beans.xml");

首先进入ClassPathResource，进入构造函数

进入第二个构造函数

Assert翻译为中文为“断言”, 就是断定某一个实际的值就是自己预期想要得到的，如果不一样就抛出异常。

Assert.notNull(path, "Path must not be null");

如果path为空，就抛出异常

4、reader.loadBeanDefinitions(resource);

进入loadBeanDefinitions方法

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

　　

然后进入

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

	/**
	 * Load bean definitions from the specified XML file.
	 * @param encodedResource the resource descriptor for the XML file,
	 * allowing to specify an encoding to use for parsing the file
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 */
	public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
		Assert.notNull(encodedResource, "EncodedResource must not be null");
		if (logger.isInfoEnabled()) {
			logger.info("Loading XML bean definitions from " + encodedResource.getResource());
		}

		Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
		if (currentResources == null) {
			currentResources = new HashSet<EncodedResource>(4);
			this.resourcesCurrentlyBeingLoaded.set(currentResources);
		}
		if (!currentResources.add(encodedResource)) {
			throw new BeanDefinitionStoreException(
					"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
		}
		try {
			InputStream inputStream = encodedResource.getResource().getInputStream();
			try {
				InputSource inputSource = new InputSource(inputStream);
				if (encodedResource.getEncoding() != null) {
					inputSource.setEncoding(encodedResource.getEncoding());
				}
				return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
			}
			finally {
				inputStream.close();
			}
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"IOException parsing XML document from " + encodedResource.getResource(), ex);
		}
		finally {
			currentResources.remove(encodedResource);
			if (currentResources.isEmpty()) {
				this.resourcesCurrentlyBeingLoaded.remove();
			}
		}
	}

　　然后进入 doLoadBeanDefinitions(inputSource, encodedResource.getResource()); 方法。

loadDocument用来加载生成Document对象，代表xml文档对应的Document对象。

	protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
		try {
			int validationMode = getValidationModeForResource(resource);
			Document doc = this.documentLoader.loadDocument(
					inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
			return registerBeanDefinitions(doc, resource);
		}
		catch (BeanDefinitionStoreException ex) {
			throw ex;
		}
		catch (SAXParseException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
		}
		catch (SAXException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"XML document from " + resource + " is invalid", ex);
		}
		catch (ParserConfigurationException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Parser configuration exception parsing XML from " + resource, ex);
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"IOException parsing XML document from " + resource, ex);
		}
		catch (Throwable ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Unexpected exception parsing XML document from " + resource, ex);
		}
	}

　loadDocument的方法如下：

    public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
            ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {

        DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
        if (logger.isDebugEnabled()) {
            logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
        }
        DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
        return builder.parse(inputSource);
    }

registerBeanDefinitions方法

/**
	 * Register the bean definitions contained in the given DOM document.
	 * Called by <code>loadBeanDefinitions</code>.
	 * <p>Creates a new instance of the parser class and invokes
	 * <code>registerBeanDefinitions</code> 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 {
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		documentReader.setEnvironment(this.getEnvironment());
		int countBefore = getRegistry().getBeanDefinitionCount();
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

　　

　查看BeanDefinitionDocumentReader，

里面有一个BeanDefinitionParserDelegate，真正实现xml解析就是这个类，类中定义了常量对应的xml属性

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

doRegisterBeanDefinitions(root);