Spring IOC 源码解析（持续）

如何查看源码

Spring源码下载https://github.com/spring-projects/spring-framework/tags?after=v3.1.0.RC1

eclipse关联源码 自己百度吧

源代码结构组织

Build-spring-framework是整个Spring源代码的构建目录，里面是项目的构建脚本，如果要自己动手构建Spring，可以进入这个目录使用ANT进行构建。

l  org.springframework.context是IoC容器的源代码目录

l  org.springframework.aop是AOP实现的源代码目录

l  org.springframework.jdbc是JDBC的源代码部分

l  org.springframework.orm是O/R Mapping对应的源代码实现部分

SpringIOC源码分析

IOC初始化

1、 XmlBeanFactory(屌丝IOC)的整个流程

2、 FileSystemXmlApplicationContext 的IOC容器流程

1、高富帅IOC解剖

2、 设置资源加载器和资源定位

3、AbstractApplicationContext的refresh函数载入Bean定义过程：

4、AbstractApplicationContext子类的refreshBeanFactory()方法：

5、AbstractRefreshableApplicationContext子类的loadBeanDefinitions方法：

6、AbstractBeanDefinitionReader读取Bean定义资源：

7、资源加载器获取要读入的资源：

8、XmlBeanDefinitionReader加载Bean定义资源：

9、DocumentLoader将Bean定义资源转换为Document对象：

10、XmlBeanDefinitionReader解析载入的Bean定义资源文件：

11、DefaultBeanDefinitionDocumentReader对Bean定义的Document对象解析：

12、BeanDefinitionParserDelegate解析Bean定义资源文件中的<Bean>元素：

13、BeanDefinitionParserDelegate解析<property>元素：

14、解析<property>元素的子元素：

15、解析<list>子元素：

16、解析过后的BeanDefinition在IoC容器中的注册：

17、DefaultListableBeanFactory向IoC容器注册解析后的BeanDefinition：

IOC体系

BeanFactory

Spring Bean的创建是典型的工厂模式，这一系列的Bean工厂，也即IOC容器为开发者管理对象间的依赖关系提供了很多便利和基础服务，在Spring中有许多的IOC容器的实现供用户选择和使用，其相互关系如下：

BeanFactory

BeanFactory定义了 IOC 容器的最基本形式，并提供了 IOC 容器应遵守的的最基本的接口，也就是Spring IOC 所遵守的最底层和最基本的编程规范。在  Spring 代码中， BeanFactory 只是个接口，并不是 IOC容器的具体实现，但是 Spring 容器给出了很多种实现，如 DefaultListableBeanFactory 、 XmlBeanFactory 、ApplicationContext 等，都是附加了某种功能的实现。

大体思路是 反射+DOM4J, 解析配置文件，通过beanId查找bean是否存在

存在的话，获取该节点class地址，使用反射机制初始化。

Spring 使用了很多抽象类

Spring核心jar包：

SpringCore -- Spring 核心jar

SpringContext--上下文IOC具体实现

Spring-Bean --  Spring实例

Spring-jdbc

SpringAOP

BeanFactory接口： ctrl+T

核心方法查看：Bean的工厂

定义接口去进行规范

public interface BeanFactory {
    //这里是对FactoryBean的转义定义，因为如果使用bean的名字检索FactoryBean得到的对象是工厂生成的对象，
  //如果需要得到工厂本身，需要转义
    //转义符“&”用来获取FactoryBean本身
    String FACTORY_BEAN_PREFIX = "&";
//根据bean的名字进行获取bean的实例，这是IOC最大的抽象方法
    Object getBean(String name) throws BeansException;
//根据bean的名字和Class类型进行获取Bean的实例,和上面方法不同的是，bean名字和Bean 的class类型不同时候会爆出异常
    <T> T getBean(String name, Class<T> requiredType) throws BeansException;
    <T> T getBean(Class<T> requiredType) throws BeansException;
    Object getBean(String name, Object... args) throws BeansException;
//检测这个IOC容器中是否含有这个Bean
boolean containsBean(String name);
//判断这个Bean是不是单利

    boolean isSingleton(String name) throws NoSuchBeanDefinitionException;
//判断这个Bean是不是原型
    boolean isPrototype(String name) throws NoSuchBeanDefinitionException;
//查询指定的bean的名字和Class类型是不是指定的Class类型
    boolean isTypeMatch(String name, Class targetType) throws NoSuchBeanDefinitionException;
//这里对得到bean实例的Class类型
    Class<?> getType(String name) throws NoSuchBeanDefinitionException;
//这里得到bean的别名，如果根据别名检索，那么其原名也会被检索出来
    String[] getAliases(String name);
}

BeanDefinition

这个接口，可以理解为xml bean元素的数据载体。通过对比xml bean标签的属性列表和BeanDefinition的属性列表一看便知。
我的理解，是解析XML的过程，就是 xml <bean>元素内容 转换为BeanDefinition对象的过程。而且这个接口，支持层级，对应对象的继承。
有一个类BeanDefinitionHolder,BeanDefinitionHolder，根据名称或者别名持有beanDefinition，它承载了name和BeanDefinition的映射信息。
BeanWarpper:
提供对标准javabean的分析和操作方法：单个或者批量获取和设置属性值，获取属性描述符，查询属性的可读性和可写性等。支持属性的嵌套设置，深度没有限制。
AbstractRefreshableApplicationContext的refreshBeanFactory()这个方法

核心类：

核心方法：

 这个接口主要做xml解析的

封装xml解析Spring Bean文件的解析封装 （可以get出来个Bean属性哈哈）

方法：

一：

/**
     * Return the current bean class name of this bean definition.
     * <p>Note that this does not have to be the actual class name used at runtime, in
     * case of a child definition overriding/inheriting the class name from its parent.
     * Also, this may just be the class that a factory method is called on, or it may
     * even be empty in case of a factory bean reference that a method is called on.
     * Hence, do <i>not</i> consider this to be the definitive bean type at runtime but
     * rather only use it for parsing purposes at the individual bean definition level.
     * @see #getParentName()
     * @see #getFactoryBeanName()
     * @see #getFactoryMethodName()
     */
    @Nullable
    String getBeanClassName();

获取bean的class文件地址  id = xx  class=“”com.tooc5.car“

二：

/**
* Override the target scope of this bean, specifying a new scope name.
* @see #SCOPE_SINGLETON
* @see #SCOPE_PROTOTYPE
*/
void setScope(@Nullable String scope);

xml的配置的范围属性

分析看一个类： 分析要分析父类 一直追踪。核心的都封装在父类

点击进入这个抽象类 AbstractRefreshableApplicationContext

看它的方法：refreshBeanFactory()

protected final void refreshBeanFactory() throws BeansException {
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {
            DefaultListableBeanFactory beanFactory = createBeanFactory();//创建IOC容器（Bean工厂）！！！！！！
            beanFactory.setSerializationId(getId());
            customizeBeanFactory(beanFactory);
            loadBeanDefinitions(beanFactory);    //载入loadBeanDefinitions  直接把工厂传入进去了
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

点进入看：

 loadBeanDefinitions(beanFactory); 

实现类：

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

        // Configure the bean definition reader with this context's
        // resource loading environment.
        beanDefinitionReader.setEnvironment(this.getEnvironment());
        beanDefinitionReader.setResourceLoader(this);  //获取到当前上下文
        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);
    }

继续点进去看：

loadBeanDefinitions(beanDefinitionReader);    加载配置文件

    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        Resource[] configResources = getConfigResources();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
        String[] configLocations = getConfigLocations();  //数组形式 可以加载多个配置文件
        if (configLocations != null) {
            reader.loadBeanDefinitions(configLocations);
        }
    }

持续点击：

 reader.loadBeanDefinitions(configLocations);   

    @Override
    public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {  //可以传递多个路径进入
        Assert.notNull(locations, "Location array must not be null");
        int count = 0;
        for (String location : locations) {
            count += loadBeanDefinitions(location);
        }
        return count;
    }

持续点击：

loadBeanDefinitions(location);
循环读取配置文件

@Override
public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
return loadBeanDefinitions(location, null);
}

持续点击：

loadBeanDefinitions(location, null);

/**
     * Load bean definitions from the specified resource location.
     * <p>The location can also be a location pattern, provided that the
     * ResourceLoader of this bean definition reader is a ResourcePatternResolver.
     * @param location the resource location, to be loaded with the ResourceLoader
     * (or ResourcePatternResolver) of this bean definition reader
     * @param actualResources a Set to be filled with the actual Resource objects
     * that have been resolved during the loading process. May be {@code null}
     * to indicate that the caller is not interested in those Resource objects.
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of loading or parsing errors
     * @see #getResourceLoader()
     * @see #loadBeanDefinitions(org.springframework.core.io.Resource)
     * @see #loadBeanDefinitions(org.springframework.core.io.Resource[])
     */
    public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
        ResourceLoader resourceLoader = getResourceLoader();   //获取到当配置路径
        if (resourceLoader == null) {
            throw new BeanDefinitionStoreException(
                    "Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
        }

        if (resourceLoader instanceof ResourcePatternResolver) {
            // Resource pattern matching available.
            try {
                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 {  //////// 看这里
            // Can only load single resources by absolute URL.
            Resource resource = resourceLoader.getResource(location);  //获取资源文件
            int count = loadBeanDefinitions(resource);
            if (actualResources != null) {
                actualResources.add(resource);
            }
            if (logger.isTraceEnabled()) {
                logger.trace("Loaded " + count + " bean definitions from location [" + location + "]");
            }
            return count;
        }
    }

拿到resource后继续读取，点击

int count = loadBeanDefinitions(resource);

点击xml的 不是配置 文件的

    /**
     * Load bean definitions from the specified XML file.
     * @param resource the resource descriptor for the XML file
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of loading or parsing errors
     */
    @Override
    public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
        return loadBeanDefinitions(new EncodedResource(resource));
    }

持续点击：

 return loadBeanDefinitions(new EncodedResource(resource));

    /**
     * Load bean definitions from the specified XML file.
     * @param encodedResource the resource descriptor for the XML file,
     * allowing to specify an encoding to use for parsing the file
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of loading or parsing errors
     */
    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 {
            InputStream inputStream = encodedResource.getResource().getInputStream();  //拿到input流
            try {
                InputSource inputSource = new InputSource(inputStream);  //读取input流
                if (encodedResource.getEncoding() != null) {
                    inputSource.setEncoding(encodedResource.getEncoding());  //进行转码
                }
                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();
            }
        }
    }

拿到文件流之后？ 持续点击
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());

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

        try {  //XML的DOM4J解析
            Document doc = doLoadDocument(inputSource, resource);
            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);
        }
    }

如何解析的？持续点击：

/**
     * Actually load bean definitions from the specified XML file.
     * @param inputSource the SAX InputSource to read from
     * @param resource the resource descriptor for the XML file
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of loading or parsing errors
     * @see #doLoadDocument
     * @see #registerBeanDefinitions
     */
    protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {

        try {
            Document doc = doLoadDocument(inputSource, resource);  //解析出doc
            int count = registerBeanDefinitions(doc, resource);    //注册bean
            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);
        }
    }

拿到：doc 和 resource后，注册bean：持续点击

 int count = registerBeanDefinitions(doc, resource); 

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        int countBefore = getRegistry().getBeanDefinitionCount();
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource)); // 作bean的注册
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }

持续点击：

documentReader.registerBeanDefinitions(doc, createReaderContext(resource)); 

    @Override
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        doRegisterBeanDefinitions(doc.getDocumentElement());
    }

继续点击进入： 从根目录获取到配置文件document。拿到根路径后正式做解析。

    /**
     * Register each bean definition within the given root {@code <beans/>} element.
     */
    @SuppressWarnings("deprecation")  // for Environment.acceptsProfiles(String...)
    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);
                // We cannot use Profiles.of(...) since profile expressions are not supported
                // in XML config. See SPR-12458 for details.
                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;
                }
            }
        }

        preProcessXml(root);
        parseBeanDefinitions(root, this.delegate);  //做documet解析
        postProcessXml(root);

        this.delegate = parent;
    }

持续点击：

  parseBeanDefinitions(root, this.delegate);  //做documet解析  从根路径开始解析 遍历节点 

/**
     * Parse the elements at the root level in the document:
     * "import", "alias", "bean".
     * @param root the DOM root element of the document
     */
    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)) {
                        parseDefaultElement(ele, delegate);  //默认解析节点
                    }
                    else {
                        delegate.parseCustomElement(ele);   //自定义解析
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

持续点击进入默认解析：

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {    // input解析
            importBeanDefinitionResource(ele);
        }
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {  //别名解析
            processAliasRegistration(ele);
        }
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {    //解析beans
            processBeanDefinition(ele, delegate);
        }
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
    }

持续查看解析bean：

 processAliasRegistration(ele);

    /**
     * Process the given bean element, parsing the bean definition
     * and registering it with the registry.
     */
    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());  //可以持续点击查看这里
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +
                        bdHolder.getBeanName() + "'", ele, ex);
            }
            // Send registration event.
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }

可以持续点击查看这里

BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry()); 

/**
     * Register the given bean definition with the given bean factory.
     * @param definitionHolder the bean definition including name and aliases
     * @param registry the bean factory to register with
     * @throws BeanDefinitionStoreException if registration failed
     */
    public static void registerBeanDefinition(
            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {

        // Register bean definition under primary name.
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());  //beanName beanId的名称 

        // Register aliases for bean name, if any.
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
    }

beanName beanId的名称 是通过

   String beanName = definitionHolder.getBeanName();

获取的：点击查看 BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);

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

        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;    //通过beanId 找
        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) {
            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.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;
    }

回退 查看注册的代码，持续点击进入：
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());

/**
     * Register the given bean definition with the given bean factory.
     * @param definitionHolder the bean definition including name and aliases
     * @param registry the bean factory to register with
     * @throws BeanDefinitionStoreException if registration failed
     */
    public static void registerBeanDefinition(
            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {

        // Register bean definition under primary name.
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());  //重点！！！

        // Register aliases for bean name, if any.
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
    }

重点点击：

好几种注册方式：

选择一种：

@Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "'beanName' must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");
        this.beanDefinitionMap.put(beanName, beanDefinition);
    }

下面插入一段反射代码：

从这里点击进入：

点击：

持续点击进入：

持续点击：

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

        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) {
            checkNameUniqueness(beanName, aliases, ele);
        }

        AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);  //正式开始注册！！！！！！
        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.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;
    }

持续点击关键代码 注册bean：
核心代码：

持续点击：

持续点击：

public static AbstractBeanDefinition createBeanDefinition(
            @Nullable String parentName, @Nullable String className, @Nullable ClassLoader classLoader) throws ClassNotFoundException {

        GenericBeanDefinition bd = new GenericBeanDefinition();
        bd.setParentName(parentName);
        if (className != null) {
            if (classLoader != null) {
                bd.setBeanClass(ClassUtils.forName(className, classLoader));   //反射机制初始化bean！
            }
            else {
                bd.setBeanClassName(className);
            }
        }
        return bd;
    }

注意啊 不要点击classPatxXmlApplicationContext  里面没有！ 核心 在父类！

很多方法写成了一个类 ，一层一个类。看起类是挺不爽的，下伙伴耐心看昂。

可以参考：

https://www.cnblogs.com/ITtangtang/p/3978349.html