spring源码-2.1.解析xml准备

忘是亡心i 2024-04-17 06:01 27阅读 0赞

这一节我们来看一下obtainFreshBeanFactory都做了什么，这个方法主要就是创建了BeanFactory：

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        //创建BeanFactory
    	refreshBeanFactory();
    	//返回BeanFactory
    	return getBeanFactory();
    }

进入refreshBeanFactory（AbstractRefreshableApplicationContext.refreshBeanFactory()）：

protected final void refreshBeanFactory() throws BeansException {
        //如果已经有beanFactory，那么先清除
    	if (hasBeanFactory()) {
    		destroyBeans();
    		closeBeanFactory();
    	}
    	try {
    	    //创建beanFactory，这里就是new了一个DefaultListableBeanFactory
    		DefaultListableBeanFactory beanFactory = createBeanFactory();
    		//给beanFactory设置SerializationId
    		beanFactory.setSerializationId(getId());
    		/**
    		* 这个方法中做了两件事：
    		* 1.如果ApplicationContext中的allowBeanDefinitionOverriding值(允许beanDefinition覆盖)不为null，则赋值给beanFactory
    		* 2.如果ApplicationContext中的allowCircularReferences值(允许循环依赖)不为null，则赋值给beanFactory
    		* 注意：这两个值在创建beanFactory的时候，默认都是true
    		*/
    		customizeBeanFactory(beanFactory);
    		//解析xml，load文件中bean的定义
    		loadBeanDefinitions(beanFactory);
    		synchronized (this.beanFactoryMonitor) {
    		    //将初始化好的beanFactory赋值给applicationContext中的beanFactory
    			this.beanFactory = beanFactory;
    		}
    	}
    	catch (IOException ex) {
    		throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
    	}
    }

不难看出，核心代码为loadBeanDefinitions(beanFactory)：

protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
    	//通过beanFactory创建一个XmlBeanDefinitionReader
    	//主要是将XmlBeanDefinitionReader的BeanDefinitionRegistry设置成beanFactory
    	XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
    
    	//给reader对象设置environment
    	beanDefinitionReader.setEnvironment(this.getEnvironment());
    	//将自身（AbstractXmlApplicationContext）作为ResourceLoader，解析xml时要用到
    	beanDefinitionReader.setResourceLoader(this);
    	//设置EntityResolver
    	beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
    
    	//设置两个参数,validationMode和namespaceAware
    	initBeanDefinitionReader(beanDefinitionReader);
    	//准备读取解析xml
    	loadBeanDefinitions(beanDefinitionReader);
    }

进入loadBeanDefinitions(beanDefinitionReader):

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        //获取配置文件的path，如果之前没有设置，那么为null
    	Resource[] configResources = getConfigResources();
    	if (configResources != null) {
    		reader.loadBeanDefinitions(configResources);
    	}
    	//在refresh之前设置的配置文件的path
    	String[] configLocations = getConfigLocations();
    	if (configLocations != null) {
    	    //准备解析读取xml
    		reader.loadBeanDefinitions(configLocations);
    	}
    }

继续进入reader.loadBeanDefinitions(configLocations):

public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
    	Assert.notNull(locations, "Location array must not be null");
    	int count = 0;
    	for (String location : locations) {
    		count += loadBeanDefinitions(location);
    	}
    	return count;
    }

这里就是做了一个校验，并做了计数，继续进入loadBeanDefinitions(location):

//这里的参数actualResources为null
    public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
        //获取resourceLoader对象，就是之前set的applicationContext对象
    	ResourceLoader resourceLoader = getResourceLoader();
    	if (resourceLoader == null) {
    		throw new BeanDefinitionStoreException(
    				"Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
    	}
    	if (resourceLoader instanceof ResourcePatternResolver) {
    		try {
    		    //将配置文件抽象成resource对象
    			Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
    			//解析resource对象
    			int count = loadBeanDefinitions(resources);
    			if (actualResources != null) {
    				Collections.addAll(actualResources, resources);
    			}
    			if (logger.isTraceEnabled()) {
    				logger.trace("Loaded " + count + " bean definitions from location pattern [" + location + "]");
    			}
    			return count;
    		}
    		catch (IOException ex) {
    			throw new BeanDefinitionStoreException(
    					"Could not resolve bean definition resource pattern [" + location + "]", ex);
    		}
    	}
    	else {
    		……和if中的逻辑一样
    	}
    }

进入到loadBeanDefinitions(resources):

public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
    	Assert.notNull(resources, "Resource array must not be null");
    	int count = 0;
    	for (Resource resource : resources) {
    		count += loadBeanDefinitions(resource);
    	}
    	return count;
    }

继续进入loadBeanDefinitions(resource):

//在进入之前会先将resource对象封装成EncodedResource
    public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
        //去看看有没有正在被本线程load的resource，如果没有，则将参数中的resource添加进去
    	Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
    	if (currentResources == null) {
    		currentResources = new HashSet<>(4);
    		this.resourcesCurrentlyBeingLoaded.set(currentResources);
    	}
    	if (!currentResources.add(encodedResource)) {
    		throw new BeanDefinitionStoreException(
    				"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
    	}
    	try {
    	    //将xml文件抽象成的resource对象转换成输入流
    		InputStream inputStream = encodedResource.getResource().getInputStream();
    		try {
    			InputSource inputSource = new InputSource(inputStream);
    			if (encodedResource.getEncoding() != null) {
    				inputSource.setEncoding(encodedResource.getEncoding());
    			}
    			//解析xml,加载beanDefinitions
    			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();
    		}
    	}
    }

继续进入doLoadBeanDefinitions(inputSource, encodedResource.getResource())：

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
    			throws BeanDefinitionStoreException {
    
    	try {
    	    //将resource再抽象成document对象
    		Document doc = doLoadDocument(inputSource, resource);
    		//解析document对象为beanDefinition，并register
    		int count = registerBeanDefinitions(doc, resource);
    		if (logger.isDebugEnabled()) {
    			logger.debug("Loaded " + count + " bean definitions from " + resource);
    		}
    		return count;
    	}
    	catch ……
    }

继续进入registerBeanDefinitions(doc, resource)：

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        //初始化一个DocumentReader对象
    	BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    	int countBefore = getRegistry().getBeanDefinitionCount();
    	//将解析出来的beanDefinitions注册到这个documentReader对象上
    	documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    	return getRegistry().getBeanDefinitionCount() - countBefore;
    }

继续进入documentReader.registerBeanDefinitions(doc, createReaderContext(resource)):

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        //设置一下在上一步中初始化出来的readerContext
    	this.readerContext = readerContext;
    	//注册beanDefinitions
    	doRegisterBeanDefinitions(doc.getDocumentElement());
    }

继续进入doRegisterBeanDefinitions(doc.getDocumentElement()):

protected void doRegisterBeanDefinitions(Element root) {
    	BeanDefinitionParserDelegate parent = this.delegate;
    	//创建delegate对象，如果root标签中设置了默认的属性，也会一并设置到default属性中
    	this.delegate = createDelegate(getReaderContext(), root, parent);
        //如果是root级标签，则校验其profile属性，如果在对应的环境不需要加载，那么直接跳过
        //例如设置profile="!dev",那么在dev环境中不加载该配置
    	if (this.delegate.isDefaultNamespace(root)) {
    		String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
    		if (StringUtils.hasText(profileSpec)) {
    			String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
    					profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
    			if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
    				if (logger.isDebugEnabled()) {
    					logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
    							"] not matching: " + getReaderContext().getResource());
    				}
    				return;
    			}
    		}
    	}
        //空方法，可有用户自定义实现
    	preProcessXml(root);
    	//解析出beanDefinitions
    	parseBeanDefinitions(root, this.delegate);
    	//空方法，可有用户自定义实现
    	postProcessXml(root);
    	this.delegate = parent;
    }

继续进入parseBeanDefinitions(root, this.delegate):

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        //这里首先判断root元素的nameSpace是不是默认的
        //判断依据为是否为：http://www.springframework.org/schema/beans
    	if (delegate.isDefaultNamespace(root)) {
    	    /**
    	    * 获取所有的子标签，判断是否为默认名称空间
    	    * 如果是，则进行默认标签解析
    	    * 如果不是，则进行自定义标签解析
    	    */
    		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)) {
    				    //解析默认标签
    					parseDefaultElement(ele, delegate);
    				}
    				else {
    				    //解析自定义标签
    					delegate.parseCustomElement(ele);
    				}
    			}
    		}
    	}
    	else {
    	    //如果不是默认的，那么进行自定义标签解析
    		delegate.parseCustomElement(root);
    	}
    }

这边会对每一个子标签进行解析，分为默认标签解析（import,bean等标签）和自定义标签的解析，下一节详细看一下默认标签的解析。