Spring 4.x （五、BeanFactory 源码分析）

以你之姓@ 2022-05-10 04:22 204阅读 0赞

我们在之前的[文章][Link 1]简单的介绍了BeanFactory，现在看下源码。

## 启动 ##

我们看下之前的代码

ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
    // 获取xml文件。生成Resource
    Resource res = resolver.getResource("classpath:resource/spring-config.xml");
    // 创建DefaultListableBeanFactory对象
    DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
    XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
    // 初始化BeanFactory
    reader.loadBeanDefinitions(res);

### Resource —— getResource ###

这里实现的是：PathMatchingResourcePatternResolver类的getResource

/**
    	* Return the ResourceLoader that this pattern resolver works with.
    	 */
    	public ResourceLoader getResourceLoader() {
    		return this.resourceLoader;
    	}
    	@Override
    	public Resource getResource(String location) {
    		return getResourceLoader().getResource(location);
    	}

### new DefaultListableBeanFactory(); ###

/**
    	 * Create a new DefaultListableBeanFactory.
    	 */
    	public DefaultListableBeanFactory() {
    		super();
    	}
    	/**
    	 * Create a new AbstractAutowireCapableBeanFactory.
    	 */
    	public AbstractAutowireCapableBeanFactory() {
    		super();
    		ignoreDependencyInterface(BeanNameAware.class);
    		ignoreDependencyInterface(BeanFactoryAware.class);
    		ignoreDependencyInterface(BeanClassLoaderAware.class);
    	}
    	/**
    	 * Create a new AbstractBeanFactory.
    	 */
    	public AbstractBeanFactory() {
    	}

我们可以看到不仅仅是创建了一个DefaultListableBeanFactory对象，同时还创建了：AbstractAutowireCapableBeanFactory，AbstractBeanFactory两个对象。

### new XmlBeanDefinitionReader(factory); ###

/**
    	 * Create new XmlBeanDefinitionReader for the given bean factory.
    	 * @param registry the BeanFactory to load bean definitions into,
    	 * in the form of a BeanDefinitionRegistry
    	 */
    	public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
    		super(registry);
    	}
    	// 父类
    	protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {
    		Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
    		this.registry = registry;
    
    		// Determine ResourceLoader to use.
    		if (this.registry instanceof ResourceLoader) {
    			this.resourceLoader = (ResourceLoader) this.registry;
    		}
    		else {
    			this.resourceLoader = new PathMatchingResourcePatternResolver();
    		}
    
    		// Inherit Environment if possible
    		if (this.registry instanceof EnvironmentCapable) {
    			this.environment = ((EnvironmentCapable) this.registry).getEnvironment();
    		}
    		else {
    			this.environment = new StandardEnvironment();
    		}
    	}

### loadBeanDefinitions ###

/**
    	 * Load bean definitions from the specified XML file.
    	 * @param resource the resource descriptor for the XML file
    	 * @return the number of bean definitions found
    	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
    	 */
    	@Override
    	public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
    		return loadBeanDefinitions(new EncodedResource(resource));
    	}

下面是重载的方法

/**
 	 * 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();
 			}
 		}
 	}

其实可以看成两部分代码  
第一部分：

// 如果资源文件不是空的话，
 		Assert.notNull(encodedResource, "EncodedResource must not be null");
 		// 判断是否启用了信息日志记录
 		if (logger.isInfoEnabled()) {
 			logger.info("Loading XML bean definitions from " + encodedResource.getResource());
 		}
 		// 将资源设置为当前Resource
 		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!");
 		}

第二部分：

try {
    		// 将Resource还原为InputStream流。
    			InputStream inputStream = encodedResource.getResource().getInputStream();
    			try {
    			// 再将InputStream流转换为InputSource — 对XML实体的一个单个输入源
    				InputSource inputSource = new InputSource(inputStream);
    				if (encodedResource.getEncoding() != null) {
    					inputSource.setEncoding(encodedResource.getEncoding());
    				}
    				// 核心方法：doLoadBeanDefinitions。
    				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();
    			}
    		}

### doLoadBeanDefinitions ###

/**
    	 * Actually load bean definitions from the specified XML file.
    	 * 实际上从指定的XML文件加载bean定义。
    	 * @param inputSource the SAX InputSource to read from
    	 * @param resource the resource descriptor for the XML file
    	 * @return the number of bean definitions found
    	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
    	 * @see #doLoadDocument
    	 * @see #registerBeanDefinitions
    	 */
    	protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
    			throws BeanDefinitionStoreException {
    		try {
    			Document doc = doLoadDocument(inputSource, resource);
    			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);
    		}
    	}

其中核心代码为：

// 将资源文件转成Document对象
    			Document doc = doLoadDocument(inputSource, resource);
    			// 将Document对象注册成为Bean。
    			return registerBeanDefinitions(doc, resource);

看下Document对象：

### Document ###

我们看下Document接口介绍

package org.w3c.dom;
 
 /**
 * The <code>Document</code> interface represents the entire HTML or XML
 * document. Conceptually, it is the root of the document tree, and provides
 * the primary access to the document's data.
 * 
 * 翻译：
 * Document接口代表全部的 HTML 或者 XML文件。
 * 概念上，他是整个文件树的根，同时给文件的数据提供最主要的入口。
 */

同时要确定一点，Document接口是W3C的，并不是Spring的。

看下registerBeanDefinitions方法：

### registerBeanDefinitions ###

/**
 	 * Register the bean definitions contained in the given DOM document.
 	 * 注册包含在给定DOM文档中的bean定义。
 	 * Called by {@code loadBeanDefinitions}.
 	 * Creates a new instance of the parser class and invokes
 	 * 。。。
 	 * 返回发现bean定义的数目
 	 * @return the number of bean definitions found
 	 * 。。。
 	 */
 	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
 		// 获取BeanDefinitionDocumentReader对象
 		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
 		// 返回注册表中定义的bean的数目。
 		int countBefore = getRegistry().getBeanDefinitionCount();
 		// 更新BeanDefinitionDocumentReader对象
 		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
 		return getRegistry().getBeanDefinitionCount() - countBefore;
 	}

两个主要的方法：`createBeanDefinitionDocumentReader`和`registerBeanDefinitions`  
createBeanDefinitionDocumentReader

/**
 	 * Create the {@link BeanDefinitionDocumentReader} to use for actually
 	 * reading bean definitions from an XML document.
 	 * The default implementation instantiates the specified "documentReaderClass".
 	 * @see #setDocumentReaderClass
 	 * 翻译：
 	 * 创建BeanDefinitionDocumentReader，用于实际读取XML文档中的bean定义。
 	 * 默认实现实例化指定的“DopeCudieCrar类”。
 	 */
 	protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
 		return BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
 	}

registerBeanDefinitions

/**
 	 * This implementation parses bean definitions according to the "spring-beans" XSD
 	 * (or DTD, historically).
 	 * Opens a DOM Document; then initializes the default settings
 	 * specified at the {@code <beans/>} level; then parses the contained bean definitions.
 	 * 翻译：
 	 * 此实现根据“Spring Bean”XSD（或DTD，历史上）解析bean定义。
 	 * 打开DOM文档；然后初始化在该级别指定的默认设置；然后解析包含的bean定义。
 	 */
 	@Override
 	public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
 		this.readerContext = readerContext;
 		logger.debug("Loading bean definitions");
 		Element root = doc.getDocumentElement();
 		doRegisterBeanDefinitions(root);
 	}

[Link 1]: https://blog.csdn.net/java_yes/article/details/81505865