XmlBeanFactory源码分析

ゝ一世哀愁。 2022-08-24 11:51 175阅读 0赞

public class XmlBeanFactory extends DefaultListableBeanFactory {
    
    	private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);
    
    
    	/**
    	 * Create a new XmlBeanFactory with the given resource,
    	 * which must be parsable using DOM.
    	 * @param resource XML resource to load bean definitions from
    	 * @throws BeansException in case of loading or parsing errors
    	 */
    	public XmlBeanFactory(Resource resource) throws BeansException {
    		this(resource, null);
    	}
    
    	/**
    	 * Create a new XmlBeanFactory with the given input stream,
    	 * which must be parsable using DOM.
    	 * @param resource XML resource to load bean definitions from
    	 * @param parentBeanFactory parent bean factory
    	 * @throws BeansException in case of loading or parsing errors
    	 */
    	public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
    		super(parentBeanFactory);
    		this.reader.loadBeanDefinitions(resource);
    	}
    
    }

这个类的代码很简单，一个成员对象加两个构造函数，从这里我们可以看出，最重要的地方在于最后一个构造函数：

public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
    		super(parentBeanFactory);
    		this.reader.loadBeanDefinitions(resource);
    	}

第一句就是将父亲工厂交给父类的构造函数，实际上最后也就是把父工厂保存到类的parentBeanFactory成员对象中，这个对象是在AbstractBeanFactory抽象类中定义的，而这个父工厂也会一直传递到该抽象类进行保存。第二句就是整个类中最重要的地方了，顾名思义，它的目的是通过XmlBeanDefinitionReader这个XML的Reader从资源resource中（也就是你的配置文件）读取bean的定义。接下来我们打开XmlBeanDefinitionReader的loadBeanDefinitions方法，我们可看到在这个方法里代码就一行，调用了一个同名不同参的方法，而参数是EncodedResource的一个实例，这个类实际上是Resource的一个包装类，用来保存资源的Encode的，那接下来我们再看被调用的loadBeanDefinitions方法，这个方法里最主要的部分就是：

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();
    			}
    		}
    	}

InputSource inputSource = new InputSource(inputStream);
                   if (encodedResource.getEncoding() != null) {
                       inputSource.setEncoding(encodedResource.getEncoding());
                   }
           return doLoadBeanDefinitions(inputSource, encodedResource.getResource());

这里的目的是将资源包装成一个InputSource，连同Resource作为参数传递到doLoadBeanDefinitions方法

int validationMode = getValidationModeForResource(resource);
    			Document doc = this.documentLoader.loadDocument(
    					inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
    			return registerBeanDefinitions(doc, resource);

这个方法的目的一目了然，就是为了将资源解释成为Document对象，然后调用registerBeanDefinitions方法，这里不做详细解释，不了解的话请去看看关于JAXP的介绍。接下来我们打开registerBeanDefinitions方法：

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
    		// Read document based on new BeanDefinitionDocumentReader SPI.
    		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    		int countBefore = getRegistry().getBeanDefinitionCount();
    		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    		return getRegistry().getBeanDefinitionCount() - countBefore;
    	}