spring IOC源码分析（ApplicationContext）

在上一篇文章中，我们以BeanFactory这条主线进行IOC的源码解析的，这里，将以ApplicationContext这条线进行分析。先看使用方法:

    @Test
    public void testApplicationContext(){
        //在启动容器时，解析注册beanDefinition,实例化bean（针对非延迟加载的bean），然后完成依赖注入，最后初始化bean(在容器启动完成后，完成了所有的这些操作)
        @SuppressWarnings("resource")
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-context.xml");
        StudentManager studentManager = (StudentManager) applicationContext.getBean("studentManager");
        studentManager.study();
    }

进入ClassPathXmlApplicationContext类

    public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
            throws BeansException {
        super(parent);
　　　　　//将资源文件存放到数组中
        setConfigLocations(configLocations);
        if (refresh) {
            refresh(); //进入该方法
        }
    }

进入refresh方法

    @Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            prepareRefresh();
　　　　　　　 //启动容器，完成BeanDefination的解析注册 进入该方法
            // 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();
                //实例化所有的非延迟加载的bean 进入该方法
                // 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();
            }
        }
    }

进入obtainFreshBeanFactory方法

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        //重启容器 进入该方法
        refreshBeanFactory();
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }

进入refreshBeanFactory方法

    @Override
    protected final void refreshBeanFactory() throws BeansException {
        //如果已存在容器，则销毁容器中所有的bean，然后关闭容器
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {
　　　　　　　 //生成容器　
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            beanFactory.setSerializationId(getId());
            customizeBeanFactory(beanFactory);
　　　　　　　 //解析加载BeanDefination　进入该方法
            loadBeanDefinitions(beanFactory);
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

进入loadBeanDefinitions方法

    @Override
    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        // Create a new XmlBeanDefinitionReader for the given BeanFactory.
        //XmlBeanDefinitionReader由名字可知，它的作用是读取xml文件，然后解析为BeanDefination       
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

// Configure the bean definition reader with this context's
        // resource loading environment.
        beanDefinitionReader.setEnvironment(this.getEnvironment());
        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);
        //进入该方法
        loadBeanDefinitions(beanDefinitionReader);
    }

进入loadBeanDefinations方法

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        Resource[] configResources = getConfigResources();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            //进入该方法，configLocations是之前存放资源文件的数组
            reader.loadBeanDefinitions(configLocations);
        }
    }

进入loadBeanDefinitions

    @Override
    public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
        Assert.notNull(locations, "Location array must not be null");
        int counter = 0;
        // 
        for (String location : locations) {
            //进入该方法 
            counter += loadBeanDefinitions(location); 
        }
        return counter;
    }

进入loadBeanDefinitions

    @Override
    public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
        return loadBeanDefinitions(location, null); //进入该方法
    }

进入loadBeanDefinitions方法

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 {
                //获取资源文件
                Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
                //进入该方法  
                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;
        }
    }

进入loadBeanDefinitins

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

 进入 loadBeanDefinitions

@Override
    public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
        return loadBeanDefinitions(new EncodedResource(resource)); //进入该方法
    }

进入loadBeanDefinitions方法

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());
                }
         　　　　 //进入该方法
                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();
            }
        }
    }

进入doLoadBeanDefinitions方法

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {
        try {
            //把resource文件转为document 
            Document doc = doLoadDocument(inputSource, resource);
            //进入该方法
            return registerBeanDefinitions(doc, resource);
        }
        catch (BeanDefinitionStoreException ex) {
            throw ex;
        }
        //以下catch到的各种异常就是在解析document时的报错信息，经常会遇到
        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);
        }
    }

进入registerBeanDefinitions方法

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        int countBefore = getRegistry().getBeanDefinitionCount();
        //进入该方法 
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }

进入registerBeanDefinitions方法

@Override
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        Element root = doc.getDocumentElement();
　　　　　//进入该方法
        doRegisterBeanDefinitions(root);
    }

进入doRegiseterBeanDefinitions方法

    /**
     * Register each bean definition within the given root {@code <beans/>} element.
     */
    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.
        //BeanDefinitionsParserDelegate用来解析BeanDefination的，进入该类可知，该类定义有解析beanDefination的各种方法
　　　　　BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = createDelegate(getReaderContext(), root, parent);
        //判断是否是默认的命名空间
        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); //进入该方法
        postProcessXml(root);

        this.delegate = parent;
    }

进入parseBeanDefinitions方法

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        if (delegate.isDefaultNamespace(root)) {
            //获取document的所有子节点，并对每个子节点逐一解析
　　　　　　　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)) {
                        //如果是默认的命名空间，用默认的解析方法解析beanDefinition  进入该方法
　　　　　　　　　　　　　　//默认的命名空间是 http://www.springframework.org/schema/beans　　
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        //如果不是默认的命名空间，使用自定义的解析方法解析beanDefinition  进入该方法
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

进入方法 parseDefaultElement

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        //处理不同类型的子节点 比如<import />  <alias />  <bean />
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            importBeanDefinitionResource(ele);
        }
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            processAliasRegistration(ele);
        }
        //这是处理<bean /> ,进入该方法
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            processBeanDefinition(ele, delegate);
        }
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
    }

进入processBeanDefinition方法

    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        //将element节点解析为BeanDefinitionHolder，BeanDefinitionHolder包含BeanDefinition，beanName，aliases
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
                //注册beanDefination，alias，也就是将beanDefination，alias放到HashMap中 进入该方法
　　　　　　　　　 BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +
                        bdHolder.getBeanName() + "'", ele, ex);
            }
            // Send registration event.
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }

进入registerBeanDefination方法

public static void registerBeanDefinition(
            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {
　　　　　//注册BeanDefination，进入该方法后可以看到，将beandefination放到currentHashMap中　
        // Register bean definition under primary name.
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
        //注册alias，也是将alias放到currentHashMap中
        // Register aliases for bean name, if any.
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
    }

到此，如果是默认的命名空间，则走parseDefaultElement这个方法，已经结束。如果不是默认的命名空间,走parseCustomElement这个方法，接下来我们就进入parseCustomElement这个方法看看。

public BeanDefinition parseCustomElement(Element ele) {
        return parseCustomElement(ele, null);
    }

    public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
        String namespaceUri = getNamespaceURI(ele);
        NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
        if (handler == null) {
            error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
            return null;
        }
        //解析过程在这个方法里 
        return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
    }