Spring源码分析之IOC2

本篇将介绍下ApplicationContext上下文方式的得到bean的源码
上篇用到一个列子

ApplicationContext ac=new ClassPathXmlApplicationContext("beans.xml");

就从ClassPathXmlApplicationContext入手吧
找到它的构造函数

public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
		this(new String[] {configLocation}, true, null);
	}

调用的是上面的这个
里面又调用另一个构造函数

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
			throws BeansException {

		super(parent);
		setConfigLocations(configLocations);
		if (refresh) {
			refresh();
		}
	}

看到setConfigLocations(configLocations);这个方法，在跟进去咯

public void setConfigLocations(String[] locations) {
		if (locations != null) {
			Assert.noNullElements(locations, "Config locations must not be null");
			this.configLocations = new String[locations.length];
			for (int i = 0; i < locations.length; i++) {
				this.configLocations[i] = resolvePath(locations[i]).trim();
			}
		}
		else {
			this.configLocations = null;
		}
	}

这里面的关键点是

this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
				this.configLocations[i] = resolvePath(locations[i]).trim();
			}

这里面有个属性configLocations其定义如下

private String[] configLocations;

，就是个数组来存放路径的，
在上面关键代码第一行初始化，然后for语句段就是解析路径的。resolvePath方法就不跟进咯，OK，在回到上上面的构造函数里，解释了setConfigLocations方法，在往下走咯。就来到

if (refresh) {
			refresh();
		}
	}

由于传进来的refresh参数是true,所以refresh()方法就会执行咯。好吧，上refresh这牛X的方法

public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// Check for listener beans and register them.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}

			catch (BeansException ex) {
				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}
		}
	}

这方法的东西好丰富哦，就各点来击破咯
first 这 synchronized (this.startupShutdownMonitor) 都懂得啥下面first的方法是prepareRefresh();这方法可以忽略咯，就是setting its startup date，
second 就是ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
这里调用的是父类AbstractRefreshableApplicationContext的方法obtainFreshBeanFactory()；
源码如下

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}

这里面又有别的方法调用咯，第一个方法实现

protected final void refreshBeanFactory() throws BeansException {
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
			customizeBeanFactory(beanFactory);
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}

这里面又调用了createBeanFactory(),看方法就明白意思了啥，就是创建BeanFactory.

protected DefaultListableBeanFactory createBeanFactory() {
		return new DefaultListableBeanFactory(getInternalParentBeanFactory());
	}

在回到refreshBeanFactory()方法中，接下来就是调用loadBeanDefinitions(beanFactory)，看意思就是加载beanDefinition了，这个方法是在AbstractRefreshableConfigApplicationContext的子类AbstractXmlApplicationContext实现的

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

		// 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);
	}

这里面创建了一个XmlBeanDefinitionReader 对象，这玩意就是来读取基于XML bean定义的
。而beanDefinitionReader.setResourceLoader(this);这句咯是为reader配置resourceLoader,因为DefaultResourceLoader是父类，所以this可以直接被使用。initBeanDefinitionReader(beanDefinitionReader);是初始化，而loadBeanDefinitions(beanDefinitionReader);类容多了

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			reader.loadBeanDefinitions(configLocations);
		}
	}

这里面的有两种方式加载bean咯，一个是Resouce，一个是String，来看下reader.loadBeanDefinitions(configResources);的实现

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

这里面又调用了 loadBeanDefinitions()这方式的实现是在XmlBeanDefinitionReader中，

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.set(null);
			}
		}
	}

这代码的主要意思是，的到xml文件，并得到IO的InputSource.在返回时有句doLoadBeanDefinitions(inputSource, encodedResource.getResource());这发放的源码

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {
		try {
			int validationMode = getValidationModeForResource(resource);
			Document doc = this.documentLoader.loadDocument(
					inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
			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);
		}
	}

这方法就是加载bean定义在制定的XML文件。主要代码是

Document doc = this.documentLoader.loadDocument(
					inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());

documentLoader的实例 private DocumentLoader documentLoader = new DefaultDocumentLoader();它主要是取得XML文件Document对象。这里就不在详述了，时间有限咯。 
  在取得Document对象后，就要开始注册咯registerBeanDefinitions(doc, resource);就由这方法搞定咯

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;
	}