springIOC源码解析(五)

现在咱们来看一下ApplicationContext是怎么初始化容器的

ApplicationContext ctx = new ClassPathXmlApplicationContext("springioc.xml");Engine engine2 = (Engine)ctx.getBean("engine");System.out.println(engine2.getBrandName());Car car2 = (Car)ctx.getBean("car");car2.introduce();

进入ClassPathXmlApplicationContext的构造函数会发现最终进入了如下的重载构造函数,其中refresh()方法就是容器初始化的入口

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)            throws BeansException {        super(parent);        setConfigLocations(configLocations);        if (refresh) {            refresh();        }    }

refresh()方法如下

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) {                if (logger.isWarnEnabled()) {                    logger.warn("Exception encountered during context initialization - " +                            "cancelling refresh attempt: " + ex);                }                // Destroy already created singletons to avoid dangling resources.                destroyBeans();                // Reset 'active' flag.                cancelRefresh(ex);                // Propagate exception to caller.                throw ex;            }            finally {                // Reset common introspection caches in Spring's core, since we                // might not ever need metadata for singleton beans anymore...                resetCommonCaches();            }        }    }

这里定义了IOC容器初始化的过程,使用了模板模式,首先咱们看第二行创建BeanFactory的过程

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

refreshBeanFactory()方法在AbstractRefreshableApplicationContext中实现,咱们接着进去看看

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);        }    }

分析一下这里的逻辑:首先判断一下BeanFactory是否存在,如果存在则把已有的BeanFactory销毁掉(因为传入的refresh为true,即要重新加载);然后会创建一个用DefaultListableBeanFactory实现的BeanFactory;再然后通过loadBeanDefinitions()方法载入bean信息

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这里是不是就和BeanFactory初始化容器很像了:在初始化BeanFactory之后载入bean

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咱们接着看看如何载入bean,这里中间经过好几个跳转,最终实现如下

public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {        ResourceLoader resourceLoader = getResourceLoader();        if (resourceLoader == null) {            throw new BeanDefinitionStoreException(                    "Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");        }        if (resourceLoader instanceof ResourcePatternResolver) {            // Resource pattern matching available.            try {                Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);                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);            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()方法会跳到如下方法中

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.remove();            }        }    }

咱们再看try块中的doLoadBeanDefinitions()方法

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);        }    }

这里的逻辑很好理解,把Resource转成Document接口,这是解析XML的方式之一,解析XML之后进行bean注册
registerBeanDefinitions()方法经过跳转之后会进入如下方法

protected void doRegisterBeanDefinitions(Element root) {        // Any nested <beans> elements will cause recursion in this method. In        // order to propagate and preserve <beans> default-* attributes correctly,        // keep track of the current (parent) delegate, which may be null. Create        // the new (child) delegate with a reference to the parent for fallback purposes,        // then ultimately reset this.delegate back to its original (parent) reference.        // this behavior emulates a stack of delegates without actually necessitating one.        BeanDefinitionParserDelegate parent = this.delegate;        this.delegate = createDelegate(getReaderContext(), root, parent);        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.isInfoEnabled()) {                        logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +                                "] not matching: " + getReaderContext().getResource());                    }                    return;                }            }        }        preProcessXml(root);        parseBeanDefinitions(root, this.delegate);        postProcessXml(root);        this.delegate = parent;    }

这些代码很眼熟有没有?没错,这就是BeanFactory加载bean的方法.所以接下来如何管理bean我就不继续往下看了,想了解的同学可以看看我前面的博客

OK,咱们回到容器初始化模板的地方,再说一个比较重要的方法finishBeanFactoryInitialization(),这个方法作用是什么呢?预知后事如何,且看下回分解