Spring 容器初始化

初始化代码

 @Test
    public void testInit2(){
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:beans.xml");
        Car car= (Car) context.getBean("car");
        System.out.println(car.getBrand());
    }

ClassPathXmlApplicationContext代码结构图

SpringIOC容器初始化代码结构图

ClassPathXmlApplicationContext初始化代码

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

        super(parent);
        //解析配置文件，例如（多个配置文件路径解析成字符串数组，将路径前后的空格去掉）
        setConfigLocations(configLocations);
        if (refresh) {
        //Spring IOC容器初始化的核心方法
            refresh();
        }
    }

核心方法refresh()代码解析

public void refresh() throws BeansException, IllegalStateException {
        //此处增加Synchronized字段，给容器refresh加锁，避免容器处在refresh阶段时，容器进行了初始化或者销毁的操作
        synchronized (this.startupShutdownMonitor) {
            //refresh容器时的一些准备工作，设置容器的状态(close设置为false，active设置为true)
            prepareRefresh();
            //重点方法：
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            //准备 Bean 容器: prepareBeanFactory
            prepareBeanFactory(beanFactory);

            try {
                // 允许子类这册子自定义的后置处理器
                postProcessBeanFactory(beanFactory);

                // 调用子类的后置处理器
                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;
            }
        }
    }

obtainFreshBeanFactory()方法解析【refresh中核心方法】

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        //如果有旧的BeanFactory则销毁旧的BeanFactory，然后创建一个新的BeanFactory，加载Bean、注册Bean等等
        refreshBeanFactory();
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }
    

//refreshBeanFactory()方法代码解析
protected final void refreshBeanFactory() throws BeansException {
        //如果有BeanFactory，销毁和关闭BeanFactory
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {
            //创建一个DefaultListableBeanFactory对象
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            //设置beanFactory的的序列化ID
            beanFactory.setSerializationId(getId());
            //定义BeanFactory的属性(Bean可覆盖，Bean循环引用)
            customizeBeanFactory(beanFactory);
            //加载Bean
            loadBeanDefinitions(beanFactory);
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }
    

BeanDefinition 的覆盖问题可能会有开发者碰到这个坑，就是在配置文件中定义 bean 时使用了相同的 id 或 name，默认情况下，allowBeanDefinitionOverriding 属性为 null，如果在同一配置文件中重复了，会抛错，但是如果不是同一配置文件中，会发生覆盖

为什么使用DafaultListableBeanFactory初始化BeanFactory

BeanFactory代码结构

从上图可以看出DefaultListableBeanFactory类和所有的BeanFactory类或者接口都有关系，因此这个类是最强大的BeanFactory。

加载 Bean: loadBeanDefinitions。这个方法根据配置加载各个Bean，然后将Bean放置到BeanFactory中。读取配置的操作在 XmlBeanDefinitionReader 中，其负责加载配置、解析。

/**
     * Loads the bean definitions via an XmlBeanDefinitionReader.
     */
    @Override
    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        // 为BeanFacotry创建一个获取Bean信息的XmlBeanDefinitionReader对象
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
        //给XmlBeanDefinitionReader配置上下文的资源环境
        beanDefinitionReader.setEnvironment(this.getEnvironment());
        beanDefinitionReader.setResourceLoader(this);
        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
    
        //允许子类提供自定义初始化BeanFactory的reader
        // Allow a subclass to provide custom initialization of the reader,
        // then proceed with actually loading the bean definitions.
        //初始化加载Bean definitions的Reader，默认的实现是空的(让子类提供定制的初始化)
        initBeanDefinitionReader(beanDefinitionReader);
        //加载BeanDefinitionReader
        loadBeanDefinitions(beanDefinitionReader);
    }

加载BeanDefinitionReader的加载方法loadBeanDefinitions

/**
     *通过XmlBeanDefinitionReader加载bean definitions,bean *factory的生命周期通过refreshBeanFactory方法来处理。这个方法应该来加*载或者注册bean definitions
     */
    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
    //以Resources的方式获取配置文件的资源位置
        Resource[] configResources = getConfigResources();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
    //以String的形式获取配置文件的位置
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            reader.loadBeanDefinitions(configLocations);
        }
    }

无论是上面获取的是Resource还是String形式的资源地址，最后加载资源的加载方法都是下面的loadBeanDefinitions方法

/**
     * 从特别的xml文件来加载bean definition
     */
    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());
        }
        //用ThreadLocal来存放当前的资源
        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 {
        //将Resource转换成XML实体的单一输入源InputSource
            InputStream inputStream = encodedResource.getResource().getInputStream();
            try {
                InputSource inputSource = new InputSource(inputStream);
                if (encodedResource.getEncoding() != null) {
                    inputSource.setEncoding(encodedResource.getEncoding());
                }
                //处理InputSource的方法
                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();
            }
        }
    }

处理inputSource的doLoadBeanDefinitions方法

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {
        try {
            //将inputSource转换成Document对象
            Document doc = doLoadDocument(inputSource, resource);
            //下面方法是对BeanDefinition解析的详细过程，这个解析会使用到Spring的Bean配置规则
            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);
        }
    }

加载Spring Bean的方法registerBeanDefinitions解析

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        //这里得到BeanDefinitionDocumentReader来对XML的BeanDefinition进行解析
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        documentReader.setEnvironment(getEnvironment());
        int countBefore = getRegistry().getBeanDefinitionCount();
        //具体的解析过程在这个registerBeanDefinitions中完成
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }
    
/**
     *根据Spring-beans的XSD来解析bean definitions
     */
    @Override
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        Element root = doc.getDocumentElement();
        //从xml根节点来解析
        doRegisterBeanDefinitions(root);
    }
    
/**
     * 
     * 通过给定的root来注册每个定义的bean
     */
    protected void doRegisterBeanDefinitions(Element root) {
    //通过BeanDefinitionParserDelegate类来解析Bean定义
        BeanDefinitionParserDelegate parent = this.delegate;
    //这里为什么要定义一个 parent? 看到后面就知道了，是递归问题，
   // 因为 <beans /> 内部是可以定义 <beans /> 的，所以这个方法的 root 其实不一定就是 xml 的根节点，也可以是嵌套在里面的 <beans /> 节点，从源码分析的角度，我们当做根节点就好了
        this.delegate = createDelegate(getReaderContext(), root, parent);

        if (this.delegate.isDefaultNamespace(root)) {
        // 这块说的是根节点 <beans ... profile="dev" /> 中的 profile 是否是当前环境需要的，
      // 如果当前环境配置的 profile 不包含此 profile，那就直接 return 了，不对此 <beans /> 解析
            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)) {
                    return;
                }
            }
        }

        //钩子方法
        preProcessXml(root);
        //重点方法
        parseBeanDefinitions(root, this.delegate);
        //钩子方法
        postProcessXml(root);
        this.delegate = parent;
    }
    
    /**
     * 解析document中的标签如下
     * "import", "alias", "bean".
     */
    protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        if (delegate.isDefaultNamespace(root)) {
            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)) {
                    //处理默认的namespace
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                    //处理其他的namespace
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

/**
 *处理默认的namespace
 *
 */
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
        //处理import标签
            importBeanDefinitionResource(ele);
        }
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
        //处理alias标签
            processAliasRegistration(ele);
        }
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
        //处理bean标签
            processBeanDefinition(ele, delegate);
        }
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // 如果是嵌套beans标签，采用递归方式解析
            doRegisterBeanDefinitions(ele);
        }
    }

这里具体解析处理bean标签的解析器,processBeanDefinition方法分析

/**
     *解析bean definition然后注册
     */
    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
    //将bean中的信息提取出来，封装到一个BeanDefinitionHolder对象中
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                //注册最后的装饰实例(封装完成的BeanDefinition)
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +
                        bdHolder.getBeanName() + "'", ele, ex);
            }
            //发送注册事件
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }
    
    /**
     *解析bean标签中的信息，然后将信息封装进BeanDefinitionHolder对象中 
     */
    public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
        //获取id的属性值
        String id = ele.getAttribute(ID_ATTRIBUTE);
        //获取name的属性值
        String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

        List<String> aliases = new ArrayList<String>();
        if (StringUtils.hasLength(nameAttr)) {
            String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
            aliases.addAll(Arrays.asList(nameArr));
        }

        String beanName = id;
        if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
            beanName = aliases.remove(0);
            if (logger.isDebugEnabled()) {
                logger.debug("No XML 'id' specified - using '" + beanName +
                        "' as bean name and " + aliases + " as aliases");
            }
        }

        if (containingBean == null) {
            checkNameUniqueness(beanName, aliases, ele);
        }

        AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
        if (beanDefinition != null) {
            if (!StringUtils.hasText(beanName)) {
                try {
                    if (containingBean != null) {
                        beanName = BeanDefinitionReaderUtils.generateBeanName(
                                beanDefinition, this.readerContext.getRegistry(), true);
                    }
                    else {
                        beanName = this.readerContext.generateBeanName(beanDefinition);
                        // Register an alias for the plain bean class name, if still possible,
                        // if the generator returned the class name plus a suffix.
                        // This is expected for Spring 1.2/2.0 backwards compatibility.
                        String beanClassName = beanDefinition.getBeanClassName();
                        if (beanClassName != null &&
                                beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
                                !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                            aliases.add(beanClassName);
                        }
                    }
                    if (logger.isDebugEnabled()) {
                        logger.debug("Neither XML 'id' nor 'name' specified - " +
                                "using generated bean name [" + beanName + "]");
                    }
                }
                catch (Exception ex) {
                    error(ex.getMessage(), ele);
                    return null;
                }
            }
            String[] aliasesArray = StringUtils.toStringArray(aliases);
            return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        }

        return null;
    }
    

    /**
     * 创建beanDefinition实例
     */
    public AbstractBeanDefinition parseBeanDefinitionElement(
            Element ele, String beanName, BeanDefinition containingBean) {

        this.parseState.push(new BeanEntry(beanName));

        String className = null;
        if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
            className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
        }

        try {
            String parent = null;
            if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
                parent = ele.getAttribute(PARENT_ATTRIBUTE);
            }
            AbstractBeanDefinition bd = createBeanDefinition(className, parent);

            parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));

            // 解析 <meta />
            parseMetaElements(ele, bd);
            // 解析 <lookup-method />
            parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
            // 解析 <replaced-method />
            parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
            // 解析 <constructor-arg />
            parseConstructorArgElements(ele, bd);
            // 解析 <property />
            parsePropertyElements(ele, bd);
            // 解析 <qualifier />
            parseQualifierElements(ele, bd);

            bd.setResource(this.readerContext.getResource());
            bd.setSource(extractSource(ele));

            return bd;
        }
        catch (ClassNotFoundException ex) {
            error("Bean class [" + className + "] not found", ele, ex);
        }
        catch (NoClassDefFoundError err) {
            error("Class that bean class [" + className + "] depends on not found", ele, err);
        }
        catch (Throwable ex) {
            error("Unexpected failure during bean definition parsing", ele, ex);
        }
        finally {
            this.parseState.pop();
        }

        return null;
    }

bean标签解析成功之后，进行注册

/**
     *
     * 鉴于bean factory来注册bean definition
     */
    public static void registerBeanDefinition(
            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {

        // 注册bean使用最原始的名称
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

        // 如果有别名就使用别名来注册
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
    }
    
//注册别名
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");

        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }

        BeanDefinition oldBeanDefinition;
        //查看beanName名称是否被注册
        oldBeanDefinition = this.beanDefinitionMap.get(beanName);
        if (oldBeanDefinition != null) {
        //如果beanName名称已经被注册过，并且没有bean覆盖标识则抛出异常
            if (!isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
                        "': There is already [" + oldBeanDefinition + "] bound.");
            }
            else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
                            "' with a framework-generated bean definition: replacing [" +
                            oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
            else {
                if (this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean '" + beanName +
                            "': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
        }
        else {
            this.beanDefinitionNames.add(beanName);
            this.manualSingletonNames.remove(beanName);
            this.frozenBeanDefinitionNames = null;
        }
        //所有的bean信息都会放进该map中，这个map用来保存所有的beanDefinition信息
        this.beanDefinitionMap.put(beanName, beanDefinition);

        if (oldBeanDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
    }

==总结==:到了当前的阶段，xml中的Bean信息已经被解析完毕，Bean容器已经被初始化。Bean标签中的相关配置也装换成相应的BeanDefinition对象，已经注册到BeanDefinition中心，注册事件也已经发布成功。