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

快来打我* 2022-06-12 22:43 198阅读 0赞

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。

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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

@Override
    	public 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;
    	}

@Override
    	public 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

@Override
    	public 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。

[Image 1]: