一、方法功能概述

// Tell the subclass to refresh the internal bean factory.
// 告诉子类刷新内部bean工厂
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

获得一个刷新后的bean工厂，返回一个ConfigurableListableBeanFactory对象，主要包含如下的操作：

• 如果bean工厂了,就销毁掉,关闭掉

• 创建一个新的bean工厂

• 设置序列化id和两个属性

• 加载BeanDefinition（解析xml中的bean，封装成BeanDefinition，放置到beanDefinition的map中）（重点！！！）

二、整体代码展示

//AbstractApplicationContext
/**
 * Tell the subclass to refresh the internal bean factory.
 * 告诉子类刷新内部bean工厂
 * @return the fresh BeanFactory instance
 * 返回刷新后的bean工厂实例
 * @see #refreshBeanFactory()
 * @see #getBeanFactory()
 */
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    //刷新bean工厂
    refreshBeanFactory();
    return getBeanFactory();
}

//refreshBeanFactory是一个抽象方法
//我们进入到其子类AbstractRefreshableApplicationContext中
//这边有个注意的点,如果是springmvc项目的话,会进到子类GenericApplicationContext中
@Override
protected final void refreshBeanFactory() throws BeansException {
    //如果bean工厂了,就销毁掉,关闭掉
    if (hasBeanFactory()) {
        //其实就是调用一些集合的clear方法,解除对一些实例的引用
        destroyBeans();
        //关闭当前的beanFactory,其实就是将成员变量beanFactory设置为null
        closeBeanFactory();
    }
    try {
        //创建新的BeanFactory
        DefaultListableBeanFactory beanFactory = createBeanFactory();
        //为了序列话指定id,如果需要的话,让这个BeanFactory从id反序列化到BeanFactory对象
        beanFactory.setSerializationId(getId());
        /**
         * 设置两个属性：
         * 1. 是否允许覆盖同名称的不同定义的对象
         * 2. 是否允许bean之间存在循环依赖
    	 * 如果想改这两个属性值,在子类中重写该方法,设置属性
         */
        customizeBeanFactory(beanFactory);
        //根据配置,加载各个Bean,然后放到BeanFactory中
        //注意,该方法的具体实现在子类中,所以xml和注解方式实现不同
        loadBeanDefinitions(beanFactory);
        synchronized (this.beanFactoryMonitor) {
            this.beanFactory = beanFactory;
        }
    }
    catch (IOException ex) {
        throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
    }
}

三、详细代码解读、loadBeanDefinitions（重点！！！）

加载BeanDefinition

先看下调用流程图

这边loadBeanDefinitions有一堆重载方法，需要注意，容易乱

1、我们点击loadBeanDefinitions，进到子类AbstractXmlApplicationContext中

//AbstractXmlApplicationContext
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
    XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

    beanDefinitionReader.setEnvironment(this.getEnvironment());
    beanDefinitionReader.setResourceLoader(this);
    /**
     * 这个EntityResolver是jdk包里sax下的一个接口(SAX:Simple API for XML)
     * 根据该类上的注解可知,这是一个解析实体的基础接口,实体其实代表的是xml中的标签对象
     *
	 * 这个操作是：设置一个实现了EntityResolver的类,用来读取本地的xsd或者dtd文件,来完成相关的
     * 解析工作
     */
    beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
	//初始化beanDefinitionReader对象,此处设置配置文件是否需要验证
    initBeanDefinitionReader(beanDefinitionReader);
    //点这里
    loadBeanDefinitions(beanDefinitionReader);
}

2、继续点loadBeanDefinitions（这是方法的重载！）

//AbstractXmlApplicationContext
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
    Resource[] configResources = getConfigResources();
    //这里一般是进不来了,取决于构造函数是否调用了设置configResources的那个
    if (configResources != null) {
        reader.loadBeanDefinitions(configResources);
    }
    String[] configLocations = getConfigLocations();
    if (configLocations != null) {
        //点这里
        reader.loadBeanDefinitions(configLocations);
    }
}

3、这里分Resource和String，点String进到AbstractBeanDefinitionReader类中

//AbstractBeanDefinitionReader
@Override
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
    Assert.notNull(locations, "Location array must not be null");
    int count = 0;
    //循环每一个对象
    for (String location : locations) {
        //点这里
        count += loadBeanDefinitions(location);
    }
    return count;
}

4、继续点loadBeanDefinitions

//AbstractBeanDefinitionReader
@Override
public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
    //第二个参数叫实际资源
    return loadBeanDefinitions(location, null);
}

5、继续点loadBeanDefinitions

//AbstractBeanDefinitionReader
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
    ResourceLoader resourceLoader = getResourceLoader();
    if (resourceLoader == null) {
        throw new BeanDefinitionStoreException(
                "Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
    }

    if (resourceLoader instanceof ResourcePatternResolver) {
        try {
            //获取资源,这里要注意,AbstractApplicationContext实例化的时候会设置resourcePatternResolver为PathMatchingResourcePatternResolver这个类,所以这里往里点的时候,最终会到这个类中的getResources,具体作用就是匹配文件,整理成Resource对象
            Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
            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 {
        Resource resource = resourceLoader.getResource(location);
        //点这里
        int count = loadBeanDefinitions(resource);
        if (actualResources != null) {
            actualResources.add(resource);
        }
        if (logger.isTraceEnabled()) {
            logger.trace("Loaded " + count + " bean definitions from location [" + location + "]");
        }
        return count;
    }
}

6、继续点loadBeanDefinitions，进到类BeanDefinitionReader的子类XmlBeanDefinitionReader中

//XmlBeanDefinitionReader
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
    return loadBeanDefinitions(new EncodedResource(resource));
}


public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
    Assert.notNull(encodedResource, "EncodedResource must not be null");
    if (logger.isTraceEnabled()) {
        logger.trace("Loading XML bean definitions from " + encodedResource);
    }

    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 {
        //开始从Resource中获取inputStream
        InputStream inputStream = encodedResource.getResource().getInputStream();
        try {
            InputSource inputSource = new InputSource(inputStream);
            if (encodedResource.getEncoding() != null) {
                inputSource.setEncoding(encodedResource.getEncoding());
            }
            //核心逻辑
            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();
        }
    }
}

7、这里的doLoadBeanDefinitions才算进入到核心方法，之前的都是方法的重载，熟悉设计模式的同学还能发现其中运用了一些适配器的设计思想

//XmlBeanDefinitionReader
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {

    try {
        //将流读取成一个文档对象
        //内部有个getValidationModeForResource方法会分辨文件是dtd还是xsd
        //内部其实就是解析xml文件返回文档对象,不必深究,有兴趣的可以看看
        Document doc = doLoadDocument(inputSource, resource);
        //把文档中各种节点读取出来解析成beanDefinition对象
        int count = registerBeanDefinitions(doc, resource);
        if (logger.isDebugEnabled()) {
            logger.debug("Loaded " + count + " bean definitions from " + resource);
        }
        return count;
    }
    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);
    }
}

8、点击registerBeanDefinitions进去看

//XmlBeanDefinitionReader
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
    //创建一个解析器
    BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    //记录下初始数量
    int countBefore = getRegistry().getBeanDefinitionCount();
    //解析
    documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    return getRegistry().getBeanDefinitionCount() - countBefore;
}

9、点击registerBeanDefinitions进入子类DefaultBeanDefinitionDocumentReader中看

//DefaultBeanDefinitionDocumentReader
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
    this.readerContext = readerContext;
    //真正做解析的方法
    doRegisterBeanDefinitions(doc.getDocumentElement());
}

10、继续点击doRegisterBeanDefinitions进去

//DefaultBeanDefinitionDocumentReader
protected void doRegisterBeanDefinitions(Element root) {
    BeanDefinitionParserDelegate parent = this.delegate;
    this.delegate = createDelegate(getReaderContext(), root, parent);

	//是否默认命名空间
    if (this.delegate.isDefaultNamespace(root)) {
        //是否包含profile属性
        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,给子类扩展实现
    preProcessXml(root);
	//解析BeanDefinition,传入根节点
    parseBeanDefinitions(root, this.delegate);
	//空方法,给子类扩展实现
    postProcessXml(root);

    this.delegate = parent;
}

11、点击parseBeanDefinitions进去

//DefaultBeanDefinitionDocumentReader
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
    if (delegate.isDefaultNamespace(root)) {
        //获取子节点
        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)) {
                    //有些是spring默认带的,<import />、<alias />、<bean />、<beans />这些
                    parseDefaultElement(ele, delegate);
                }
                else {
                    //其他标签,比如<mvc />、<task />、<context />、<aop />这些
                    delegate.parseCustomElement(ele);
                }
            }
        }
    }
    else {
        delegate.parseCustomElement(root);
    }
}

12、点击parseDefaultElement进去可以看到默认命名空间

//DefaultBeanDefinitionDocumentReader
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)) {
        //处理<beans />标签
        doRegisterBeanDefinitions(ele);
    }
}

public static final String ALIAS_ATTRIBUTE = "alias";

public static final String IMPORT_ELEMENT = "import";

public static final String BEAN_ELEMENT = "bean";

public static final String NESTED_BEANS_ELEMENT = "beans";

13、我们重点关注标签，所以点击processBeanDefinition进去

//DefaultBeanDefinitionDocumentReader
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
    //BeanDefinitionHolder里包含了BeanDefinition、bean的名字和别名,用于向容器注册
    //此处是通过BeanDefinitionParserDelegate对xml中元素解析得到BeanDefinitionHolder
    BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
    if (bdHolder != null) {
        bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
        try {
            // 注册
            BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
        }
        catch (BeanDefinitionStoreException ex) {
            getReaderContext().error("Failed to register bean definition with name '" +
                    bdHolder.getBeanName() + "'", ele, ex);
        }
        getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
    }
}

14、点击parseBeanDefinitionElement进去，到类BeanDefinitionParserDelegate中

//BeanDefinitionParserDelegate
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
    return parseBeanDefinitionElement(ele, null);
}

@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
    //解析id
    String id = ele.getAttribute(ID_ATTRIBUTE);
    //解析name
    String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

    //如果有别名,对别名分割解析
    List<String> aliases = new ArrayList<>();
    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.isTraceEnabled()) {
            logger.trace("No XML 'id' specified - using '" + beanName +
                    "' as bean name and " + aliases + " as aliases");
        }
    }

    if (containingBean == null) {
        //判断名字是否唯一,在同一个xml中不能出现重复的bean名称
        checkNameUniqueness(beanName, aliases, ele);
    }

    //方法的重载
    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);

                    String beanClassName = beanDefinition.getBeanClassName();
                    if (beanClassName != null &&
                            beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
                            !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                        aliases.add(beanClassName);
                    }
                }
                if (logger.isTraceEnabled()) {
                    logger.trace("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;
}

15、继续点击parseBeanDefinitionElement进去

//BeanDefinitionParserDelegate
@Nullable
public AbstractBeanDefinition parseBeanDefinitionElement(
        Element ele, String beanName, @Nullable BeanDefinition containingBean) {

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

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

    try {
        //创建BeanDefinition,实际创建的是AbstractBeanDefinition的子类对象GenericBeanDefinition
        AbstractBeanDefinition bd = createBeanDefinition(className, parent);

        //解析bean标签的其他属性
        parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
        //设置description属性,description标签
        bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
        //解析<meta />标签
        parseMetaElements(ele, bd);
        //解析<lookup-method />标签
        parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
        //解析<replaced-method />标签
        parseReplacedMethodSubElements(ele, bd.getMethodOverrides());

        //解析<constructor-arg />标签
        parseConstructorArgElements(ele, bd);
        //解析<property />标签
        parsePropertyElements(ele, bd);
        //解析<qualifier />标签
        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;
}

16、至此BeanDefinitionHolder创建完成，下面回到第13步，点击registerBeanDefinition看下，到类BeanDefinitionReaderUtils中

//BeanDefinitionReaderUtils
public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException {

    String beanName = definitionHolder.getBeanName();
    //注册BeanDefinition
    registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

    //注册别名,不然根据别名找不到bean
    String[] aliases = definitionHolder.getAliases();
    if (aliases != null) {
        for (String alias : aliases) {
            registry.registerAlias(beanName, alias);
        }
    }
}

17、再点击registerBeanDefinition，进到DefaultListableBeanFactory类的registerBeanDefinition方法

//DefaultListableBeanFactory
@Override
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 existingDefinition = this.beanDefinitionMap.get(beanName);
    //处理已经注册的bean的情况,如果包含了相同名称的bean
    if (existingDefinition != null) {
        //如果不允许覆盖,就抛异常
        if (!isAllowBeanDefinitionOverriding()) {
            throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
        }
        else if (existingDefinition.getRole() < beanDefinition.getRole()) {
            if (logger.isInfoEnabled()) {
                logger.info("Overriding user-defined bean definition for bean '" + beanName +
                        "' with a framework-generated bean definition: replacing [" +
                        existingDefinition + "] with [" + beanDefinition + "]");
            }
        }
        else if (!beanDefinition.equals(existingDefinition)) {
            if (logger.isDebugEnabled()) {
                logger.debug("Overriding bean definition for bean '" + beanName +
                        "' with a different definition: replacing [" + existingDefinition +
                        "] with [" + beanDefinition + "]");
            }
        }
        else {
            if (logger.isTraceEnabled()) {
                logger.trace("Overriding bean definition for bean '" + beanName +
                        "' with an equivalent definition: replacing [" + existingDefinition +
                        "] with [" + beanDefinition + "]");
            }
        }
        //放到map里去
        this.beanDefinitionMap.put(beanName, beanDefinition);
    }
    else {
        //如果map里没有
        if (hasBeanCreationStarted()) {
            synchronized (this.beanDefinitionMap) {
                this.beanDefinitionMap.put(beanName, beanDefinition);
                List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
                updatedDefinitions.addAll(this.beanDefinitionNames);
                updatedDefinitions.add(beanName);
                this.beanDefinitionNames = updatedDefinitions;
                if (this.manualSingletonNames.contains(beanName)) {
                    Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
                    updatedSingletons.remove(beanName);
                    this.manualSingletonNames = updatedSingletons;
                }
            }
        }
        else {
            this.beanDefinitionMap.put(beanName, beanDefinition);
            this.beanDefinitionNames.add(beanName);
            this.manualSingletonNames.remove(beanName);
        }
        this.frozenBeanDefinitionNames = null;
    }

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