spring 解析配置文件BeanDefinition

1：ResourceLoader 加载配置文件 默认实现ResourcePatternResolver

2：XmlBeanDefinitionReader  读取配置文件封装BeanDefinition

3：BeanDefinitionRegistry 注册BeanBeanDefinition 默认实现是DefaultListableBeanFactory

解析配置文件默认由XmlWebApplicationContext 的loadBeanDefinitions方法

  protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws IOException {
        // Create a new XmlBeanDefinitionReader for the given BeanFactory.
        XmlBeanDefinitionReader beanDefinitionReader = XBeanHelper.createBeanDefinitionReader(this, beanFactory, xmlPreprocessors);

        // Configure the bean definition reader with this context's
        // resource loading environment.
        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);
    }

 4：DefaultBeanDefinitionDocumentReader在解析元素标签时会先判断是否是spring默认标签还是客户自定的，如果是自定义需要用客户的命名解析器。

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);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}

 5：在解析标签时，会根据不同标签进行解析

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {

// import 标签
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            importBeanDefinitionResource(ele);
        }

//alias 标签
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            processAliasRegistration(ele);
        }

//bean 标签
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            processBeanDefinition(ele, delegate);
        }
    }

 6：最终BeanDefinition 存入Map里

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException {

		Assert.hasText(beanName, "Bean name must not be empty");
		Assert.notNull(beanDefinition, "BeanDefinition must not be null");

		if (beanDefinition instanceof AbstractBeanDefinition) {
			try {
				((AbstractBeanDefinition) beanDefinition).validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}

		synchronized (this.beanDefinitionMap) {
			Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
			if (oldBeanDefinition != null) {
				if (!this.allowBeanDefinitionOverriding) {
					throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
							"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
							"': There is already [" + oldBeanDefinition + "] bound.");
				}
				else {
					if (this.logger.isInfoEnabled()) {
						this.logger.info("Overriding bean definition for bean '" + beanName +
								"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
					}
				}
			}
			else {
				this.beanDefinitionNames.add(beanName);
				this.frozenBeanDefinitionNames = null;
			}
			this.beanDefinitionMap.put(beanName, beanDefinition);

			resetBeanDefinition(beanName);
		}
	}