spring源码浅析 - IOC

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　　　　原文链接： spring源码浅析——IOC   转载请注明出处！

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在读之前应该明白其重点：读spring读的不是其具体的技术实现，读的是其系统层面的结构和设计! spring漂亮就漂亮在她的结构，包括接口和抽象类的灵活使用！

　　IOC模块只是spring框架中的一个模块，这里只对该模块进行分析(使用版本：spring-framework-4.0.0.RELEASE-dist)。

　　IOC(Inversion of Control,控制反转)，“控制对象的创建或销毁不再由调用处进行控制，而是由spring容器进行管理和控制”，“控制”就是指对程序中的对象实体的生命周期的控制。“反转”本来是由调用处进行控制的，现在调用处不管了，反倒由spring进行管理，所以叫做bean的管理“反转”了，合在一起也就是所谓的“控制反转”。很不喜欢这四个字来描述！刚接触spring的朋友对这个概念比较难以理解，我当时接触的时候就感觉无法理解，直到后来一遍一遍的琢磨之后才理解其含义。

IOC涉及到的类比较多，结构较为复杂，在分析之前需要先抓住九个关键的类系（之所以用类系来形容是因为下面所列出来的不是某个具体的实现类，而是从接口到抽象类等一些系列相关类/接口）：

　　BeanFactory：bean的管理工厂，所有的bean都在该对象中进行创建、存储和销毁。

　　DefaultListableBeanFactory:beanFactory具体实现类

　　Resource：spring的配置信息，该信息可能来源于xml文件，可能来源于网络，也可能来源于数据流中。不管他从哪里来的，都封装为Resource对象。

　　BeanDefinition:bean的所有信息在该对象中进行封装，包括bean的参数值、方法名、是否懒加载、是否为单例等各种信息

　　BeanDefinitionReader：见名知意，构建BeanDefinition的reader，也就是通过该Reader从Resource中读取信息封装为BeanDefinition。

　　ApplicationContext：俗称“上下文”和“控制反转”一样晦涩难懂，据我猜测之所以这样命名，是因为context继承了太多的接口，具有各种各样的功能，可以称为万能的上帝。并且所有的需要用到的bean都可以在其中取到，起到沟通上下的桥梁的作用，所以叫做“上下文”。这里可以看出其特性是：实现了各种功能接口，封装了各种bean对象。

　　Environment：运行环境配置信息，也就是一些配置属性，来源于：properties文件，JVM properties，system环境变量，JNDI, servlet context parameters上下文参数,专门的Properties对象，Maps等等

　　Document：从xml文件文件中抽取出来的本文对象。

　　Element：从Document中取出的node节点

　　上面的描述暂时理解不了没关系，只要心里面有这几个模块的概念就可以，在进行分析代码的时候能够意识到相关bean的功能即可，如需深入理解相关类系，需要深入对代码进行剖析。

下面我们就从一个小例子进入对IOC模块的分析。

　　Spring配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.springframework.org/schema/beans"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

    <bean id="person" class="com.zpj.bean.Person">
        <property name="name" value="xingoo" />
        <property name="age" value="12" />
    </bean>

</beans>


　　程序入口

public class SpringTest {
    public static void main(String[] args) {
        //获取context上下文对象，该上下文是ClassPathXmlApplicationContext类
        ApplicationContext context = new ClassPathXmlApplicationContext("springConfig.xml");
        //从容器中取出名为"person"的对象
        Person person = context.getBean("person", Person.class);
        //调用person.info()方法。
        person.info();
    }
}


在进入ClassPathXmlApplicationContext构造方法之后，一直调用this()找到被重载的构造方法

public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
        this(new String[] {configLocation}, true, null);
    }
//this（）进入重载的构造方法
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)throws BeansException {
        super(parent);
        setConfigLocations(configLocations);
        if (refresh) {
            refresh();
        }
    }


第一个super()一直向上找到AbstractApplicationContext，该类中实现了大部分的标准操作。

    public AbstractApplicationContext(ApplicationContext parent) {
        this();
        setParent(parent);
    }
    //先看this方法，this()进入该方法对resourcePatternResolver进行赋值
    public AbstractApplicationContext() {
        this.resourcePatternResolver = getResourcePatternResolver();
    }
    //这里需要注意的是getResourcePatternResolver()中返回的是PathMatchingResourcePatternResolver对象，并把this作为参数赋值给resolver中的resourceLoader。
    protected ResourcePatternResolver getResourcePatternResolver() {
        return new PathMatchingResourcePatternResolver(this);
    }
    //在PathMatchingResourcePatternResolver中，this被赋值给resourceLoader。上面传进来的是context，怎么用resourceLoader进行接收了呢？
    //因为Context实现了ResourceLoader的接口（这里需要记住）
    private final ResourceLoader resourceLoader;//resourceLoader的定义
    public PathMatchingResourcePatternResolver(ResourceLoader resourceLoader) {
        Assert.notNull(resourceLoader, "ResourceLoader must not be null");
        this.resourceLoader = resourceLoader;
    }
//************************分析完this（），下面看setParent(parent);（这里parent是个null值，这里我们进入看看都进行了哪些操作）**************************************************************   
    @Override
    public void setParent(ApplicationContext parent) {
        this.parent = parent;
        if (parent != null) {
            //注意这里，说明是从AbstractApplicationContext中取得的EnvEnvironment对象
            Environment parentEnvironment = parent.getEnvironment();
            if (parentEnvironment instanceof ConfigurableEnvironment) {
                //merge()对取得的parentEnvironment和当前的Environment进行合并。
                getEnvironment().merge((ConfigurableEnvironment) parentEnvironment);
            }
        }
    }
   
//    再AbstractApplicationContext中，如果存在则直接返回，如果不存在则进行创建操作
//    注意该方法，后面有多次进行获取environment
    public ConfigurableEnvironment getEnvironment() {
        if (this.environment == null) {
            //这里创建同时保存在了当前类AbstractApplicationContext中
            this.environment = createEnvironment();
        }
        return this.environment;
    }
    //创建的时候返回以StandardEnvironment实现类进行创建
    protected ConfigurableEnvironment createEnvironment() {
        return new StandardEnvironment();
    }
//    至此，ClassPathXmlApplicationContext构造方法中super()的操作结束
   


　　这里对ClassPathXmlApplicationContext构造方法的super操作进行汇总：

　　　　1、AbstractApplicationContext中对resourcePatternResolver设值，并把自身当做resourceLoader设置给resourcePatternResolver。

　　　　2、AbstractApplicationContext中对environment进行了设值

　　　　3、把parent的environment和自己的environment进行了合并

这里需要注意的是，进行到这一步environment和resourcePatternResolver都已经有值了，在后面就可以进行get使用了。

下面进入到setConfigLocations(configLocations) 操作

    public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)throws BeansException {
        super(parent);
        //对该方法进行分析，这里configLocations的值为[springConfig.xml]
        setConfigLocations(configLocations);
        if (refresh) {
            refresh();
        }
    }
    //进入void org.springframework.context.support.AbstractRefreshableConfigApplicationContext.setConfigLocations(String... locations)

    public void setConfigLocations(String... locations) {
        if (locations != null) {
            //这句断言攒在的意义是什么？上面已经进行了不为空判断，如果为null根本就执行不到这一步
            Assert.noNullElements(locations, "Config locations must not be null");
            this.configLocations = new String[locations.length];
            for (int i = 0; i < locations.length; i++) {
                //该方法主要目的就是对configLocations进行解析设值
                this.configLocations[i] = resolvePath(locations[i]).trim();
            }
        }
        else {
            this.configLocations = null;
        }
    }
//    进入resolvePath，这里调用了Environment的resolveRequiredPlaceholders方法（上面已经说过Environment已经进行了设值）
    protected String resolvePath(String path) {
        return getEnvironment().resolveRequiredPlaceholders(path);
    }
//    该方法全名为：String org.springframework.core.env.AbstractEnvironment.resolveRequiredPlaceholders(String text) throws IllegalArgumentException
//是实现在StandardEnvironment的父类AbstractEnvironment中
    @Override
    public String resolveRequiredPlaceholders(String text) throws IllegalArgumentException {
        //    这里又进行了调用
        return this.propertyResolver.resolveRequiredPlaceholders(text);
    }
//    这里的需要注意的是propertyResolver的实例化在哪里进行的。
//    在该类中有三个全局变量：
    protected final Log logger = LogFactory.getLog(getClass());
    private final MutablePropertySources propertySources = new MutablePropertySources(this.logger);
    private final ConfigurablePropertyResolver propertyResolver =new PropertySourcesPropertyResolver(this.propertySources);
//    所以propertyResolver在生成new StandEnvironment()的时候就同时创建了
//    这里不再继续进行跟进去，this.propertyResolver.resolveRequiredPlaceholders(text);主要是对占位符进行了替换操作，把${name}替换为其实际值。
//    至此setConfigLocations()操作结束


这里对ClassPathXmlApplicationContext构造方法的setConfigLocations(configLocations) 操作进行汇总：

　　1、xml对配置文件名称进行了解析，解析之后存储在String[] org.springframework.context.support.AbstractRefreshableConfigApplicationContext.configLocations数组中。

到这一步，xml配置文件路径已经进行了存储，下面就该对xml进行读取，加载、解析等操作。

下面进入到void org.springframework.context.support.AbstractApplicationContext.refresh() throws BeansException, IllegalStateException操作

@Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            //对context的刷新进行准备操作           
            prepareRefresh();
           
            // Tell the subclass to refresh the internal bean factory.
            //告诉子类刷新内部bean工厂
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
           
            // Prepare the bean factory for use in this context.
            //对beanFactory进行准备操作，以便于context的后续使用
            prepareBeanFactory(beanFactory);
            try {
                // Allows post-processing of the bean factory in context subclasses.
                //在对beanFactory进行标准化处理之后，允许子类对beanFactory进行后处理操作，子类覆写该方法进行特殊操作
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                //在上下文中调用作为bean注册的工厂处理器。
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
                //注册拦截bean创建的bean处理器，这里只是进行注册操作
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                //为上下文初始化message，即对国际化资源文件进行初始化
                initMessageSource();

                // Initialize event multicaster for this context.
                //初始化应用消息广播器
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                //子类覆写该方法，进行自己的初始化操作
                onRefresh();

                // Check for listener beans and register them.
                //查找所用已经注册过的listener bean并注册到广播器中
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                //初始化剩下的单实例（非惰性）
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                //最后一步：完成刷新过程，通知生命周期处理器lifecycleProcessor刷新过程，同时发出ContextRefreshEvent事件，通知其他监听者
                finishRefresh();
            }

            catch (BeansException ex) {
                logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);

                // Destroy already created singletons to avoid dangling resources.
                //发生异常销毁已经创建的单利bean
                destroyBeans();

                // Reset 'active' flag.
                //关闭刷新操作
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }
        }
    }


beanFactory的创建和初始化操作都在该方法中进行，下面逐个方法进行分析



   
//    进入void org.springframework.context.support.AbstractApplicationContext.prepareRefresh()
    protected void prepareRefresh() {
        this.startupDate = System.currentTimeMillis();
        this.active.set(true);
        if (logger.isInfoEnabled()) {
            logger.info("Refreshing " + this);
        }
        // Initialize any placeholder property sources in the context environment
        //留给子类覆写，实现其特有的占位符初始化操作，这里方法体为空
        initPropertySources();

        // Validate that all properties marked as required are resolvable
        // see ConfigurablePropertyResolver#setRequiredProperties
        //验证系统所必须的关键性配置参数是否已经加载到environment中，如果没有则抛出MissingRequiredPropertiesException异常
        getEnvironment().validateRequiredProperties();
    }
/**
* void org.springframework.context.support.AbstractApplicationContext.prepareRefresh()汇总：
*         1、让子类进行自身特有的占位符初始化操作
*         2、验证必须的配置参数是否已经加载
*/
   
//    进入ConfigurableListableBeanFactory org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory()
    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        //刷新beanFactory
        refreshBeanFactory();
        //获取beanFactory并进行返回
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }
   
    //这里进行刷新操作，该方法实现于：void org.springframework.context.support.AbstractXmlApplicationContext.loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException
    @Override
    protected final void refreshBeanFactory() throws BeansException {
        if (hasBeanFactory()) {//    判断方式：return (this.beanFactory != null);
            //如果已经存在则进行销毁同时关闭，至于怎么销毁和关闭的就不详解
            destroyBeans();
            closeBeanFactory();
        }
        try {
            //创建beanFactory，该方法直接return new DefaultListableBeanFactory(getInternalParentBeanFactory());这里需要注意的是beanFactory的实现类是DefaultListableBeanFactory
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            //设置序列化唯一id
            beanFactory.setSerializationId(getId());
            //设置beanFactory相关属性，是否允许覆盖同名称的不同定义的对象、是否允许循环依赖，可以被子类进行覆写
            customizeBeanFactory(beanFactory);
            //重点！！！加载beanDefinition 加载分两步：1、解析Document  2、注册BeanDefinition
            loadBeanDefinitions(beanFactory);
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }
//    这里进入关键方法loadBeanDefinitions，该方法实现于：void org.springframework.context.support.AbstractXmlApplicationContext.loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException
    @Override
    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        // Create a new XmlBeanDefinitionReader for the given BeanFactory.
        //这里是使用xml文件进行配置的，所以这里使用的是XmlBeanDefinitionReader作为beanDefinitionReader，
        //这里beanFactory作为BeanDefinitionRegistry实例传入beanDefinitionReader.XmlBeanDefinitionReader.XmlBeanDefinitionReader(BeanDefinitionRegistry registry);
        //注意beanDefinitionReader中的registry
        //提醒:还记得文章开始部分定义的BeanDefinition是什么吗？bean的所有信息在该对象中进行封装，包括bean的参数值、方法名、是否懒加载、是否为单例等各种信息
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

        // Configure the bean definition reader with this context's resource loading environment.
        beanDefinitionReader.setEnvironment(this.getEnvironment());
        //注意这个ResourceLoader参数，此处的this指的是AbstractXmlApplicationContext，而AbstractBeanDefinitionReader.setResourceLoader(ResourceLoader resourceLoader)中接收的是ResourceLoader
        //所以说AbstractXmlApplicationContext实现了ResourceLoader接口（上面已经说过）
        beanDefinitionReader.setResourceLoader(this);
        //设置实体解析器，该ResourceEntityResolver还是用ResourceLoader接收的this
        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

        // Allow a subclass to provide custom initialization of the reader,
        // then proceed with actually loading the bean definitions.
        //对defintionReader进行初始化操作，运训子类进行覆盖，然后开始进行实际加载bean definition
        initBeanDefinitionReader(beanDefinitionReader);
        //重点！！！进行BeanDefinitions的加载操作
        loadBeanDefinitions(beanDefinitionReader);
    }
//    这里进入关键方法loadBeanDefinitions，该方法实现于：void org.springframework.context.support.AbstractXmlApplicationContext.loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException
    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        //取得ClassPathResource并进行加载
        Resource[] configResources = getConfigResources();
        if (configResources != null) {
            //标识位置：loadBeanDefinitions_Resource
            reader.loadBeanDefinitions(configResources);
        }
        //取得ConfigLocations并进行加载（这里的ConfigLocations就是上面解析出来的String[] configLocations,存储着配置文件的路径）
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            //标识位置：loadBeanDefinitions_String
            reader.loadBeanDefinitions(configLocations);
        }
    }
//    这里的loadBeanDefinitions_String和loadBeanDefinitions_Resource进行加载的方法是一样的，都是调用int org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException
//    进行加载。只是loadBeanDefinitions_String在进行加载之前多了一步操作，把String转化为Resource，然后进行加载，这里就从loadBeanDefinitions_String跟进去
   
//    进入loadBeanDefinitions方法，该方法实现于：int org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException
    @Override
    public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
        Assert.notNull(locations, "Location array must not be null");
        int counter = 0;
        for (String location : locations) {
            //循环对locations进行加载
            counter += loadBeanDefinitions(location);
        }
        return counter;
    }
//进入loadBeanDefinitions，该方法实现于：int org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(String location) throws BeanDefinitionStoreException
    @Override
    public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
        //继续调用加载
        return loadBeanDefinitions(location, null);
    }
//进入loadBeanDefinitions，该方法实现于： int org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException
    public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
        //还记得这个resourceLoader什么时候赋值的吗？赋值的又是谁呢？AbstractXmlApplicationContext
        ResourceLoader resourceLoader = getResourceLoader();
        if (resourceLoader == null) {
            throw new BeanDefinitionStoreException(
                    "Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
        }
        //这里根据resourceLoader进行划分，不同的resourceLoader从不同的源加载resource。
        if (resourceLoader instanceof ResourcePatternResolver) {
            // Resource pattern matching available.
            try {
                Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
                int loadCount = loadBeanDefinitions(resources);
                if (actualResources != null) {
                    for (Resource resource : resources) {
                        //把resource进行缓存
                        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.
            //只能加载从绝对URL加载单例资源，xml走的是这里,进入之后区分类路径资源、URL资源和文件系统资源（xml属于该种），这里不再对封装resource进行分析
            Resource resource = resourceLoader.getResource(location);
            //进行记载definition，这里调用的方法和标识位置：loadBeanDefinitions_Resource调用的加载方法就相同了
            int loadCount = loadBeanDefinitions(resource);
            if (actualResources != null) {
                //把resource进行缓存
                actualResources.add(resource);
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
            }
            return loadCount;
        }
    }
    //进入loadBeanDefinitions，该方法实现于：int org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException
   
    //当前进行加载的resources存储于这个ThreadLocal线程局部变量中
    private final ThreadLocal<Set<EncodedResource>> resourcesCurrentlyBeingLoaded = new NamedThreadLocal<Set<EncodedResource>>("XML bean definition resources currently being loaded");
    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);
            //操作之前先把currentResources放在resourcesCurrentlyBeingLoaded中，注意下面加载操作完成之后进行了remove
            this.resourcesCurrentlyBeingLoaded.set(currentResources);
        }
        //这里把encodedResource放进currentResources中，后面依旧会remove
        if (!currentResources.add(encodedResource)) {
            throw new BeanDefinitionStoreException(
                    "Detected cyclic loading of " + encodedResource + " - check your import definitions!");
        }
        try {
            //获取inputStream
            InputStream inputStream = encodedResource.getResource().getInputStream();
            try {
                //封装为InputSource
                InputSource inputSource = new InputSource(inputStream);
                if (encodedResource.getEncoding() != null) {
                    //为inputSource设置resource的编码方式
                    inputSource.setEncoding(encodedResource.getEncoding());
                }
                //这里才是真正进行BeanDefinitions的加载操作，前面的都是进行预处理封装inputSource
                return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
            }
            finally {
                inputStream.close();
            }
        }
        catch (IOException ex) {
            throw new BeanDefinitionStoreException(
                    "IOException parsing XML document from " + encodedResource.getResource(), ex);
        }
        finally {
            //操作之后把currentResources从resourcesCurrentlyBeingLoaded中移除出去，注意上面加载操之前的add
            currentResources.remove(encodedResource);
            if (currentResources.isEmpty()) {
                this.resourcesCurrentlyBeingLoaded.remove();
            }
        }
    }
//    进入doLoadBeanDefinitions，该方法实现于：int org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException
    protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {
        try {
            //关键方法两步：取得Document;注册BeanDefinition
            //这里就不再解析怎么加载Document的了，Spring是使用SAX进行xml解析的，可以自己详细了解
            Document doc = doLoadDocument(inputSource, resource);
            //把BeanDefinition注册到context中           
            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);
        }
    }
//    进入registerBeanDefinitions，该方法实现于： int org.springframework.beans.factory.xml.XmlBeanDefinitionReader.registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException
    public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        //创建documentReader这里返回的是    return BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        documentReader.setEnvironment(this.getEnvironment());
        //这个countBefore是为了统计从Document中加载的beanDefinition的个数
        int countBefore = getRegistry().getBeanDefinitionCount();
        //进行注册BeanDefinition操作
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }
//    进入registerBeanDefinitions，该方法实现于：void org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.registerBeanDefinitions(Document doc, XmlReaderContext readerContext)
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        Element root = doc.getDocumentElement();
        //取出root节点，从root节点遍历所有节点进行注册
        doRegisterBeanDefinitions(root);
    }
//    进入doRegisterBeanDefinitions，该方法实现于：void org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(Element root)
    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(this.readerContext, root, parent);

        if (this.delegate.isDefaultNamespace(root)) {
            String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
            if (StringUtils.hasText(profileSpec)) {
                Assert.state(this.environment != null, "Environment must be set for evaluating profiles");
                String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
                        profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
                if (!this.environment.acceptsProfiles(specifiedProfiles)) {
                    return;
                }
            }
        }
        //为子类预留，覆写进行解析之前的特殊操作
        preProcessXml(root);
        //通过代理进行解析
        parseBeanDefinitions(root, this.delegate);
        //为子类预留，覆写进行解析之后的特殊操作
        postProcessXml(root);

        this.delegate = parent;
    }
//    进入postProcessXml，该方法实现于：void org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate)
    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)) {
                        //循环所有的Element节点进行解析
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }
//    进入postProcessXml，该方法实现于： void org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate)
    private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        //对“import”标签进行解析注册
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            importBeanDefinitionResource(ele);
        }
        //对“alias”标签进行解析注册
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            processAliasRegistration(ele);
        }
        //对“bean”标签进行解析注册,这里从这里面进去分析，这里的分支思路大同小异
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            processBeanDefinition(ele, delegate);
        }
        //对“beans”标签进行解析注册
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
    }
//    进入processBeanDefinition，该方法实现于： void org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate)
    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        //对ele进行解析，把id、name、aliases进行封装
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            //如果需要则使用bdHolder的代理进行操作
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
                //对definition的最终注册，注意该方法的第二个参数：Registry
                //设置readerContext位置：documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
                //设置Registry位置（第五个参数this）：return new XmlReaderContext(resource, this.problemReporter, this.eventListener,this.sourceExtractor, this, getNamespaceHandlerResolver());
                //该this指代的是XmlBeanDefinitionReader实例
                //而他的Registry设置位置是：XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
                //所以该Registry就是beanFactory
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +
                        bdHolder.getBeanName() + "'", ele, ex);
            }
            // Send registration event.
            //发送注册event给监听者
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }
//    进入BeanDefinitionReaderUtils.registerBeanDefinition，该方法实现于： void org.springframework.beans.factory.support.BeanDefinitionReaderUtils.registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)

    public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)throws BeanDefinitionStoreException {
        // Register bean definition under primary name.
        //取得beanName注册beanDefinition
        String beanName = definitionHolder.getBeanName();
        //注册beanDefinition
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
        // Register aliases for bean name, if any.
        //取得对该beanName注册aliases,这里关联的是aliases--beanName,所以通过aliase进行取值的时候需要先由aliase找到beanName，然后根据beanName找到beanDefinition
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String aliase : aliases) {
                registry.registerAlias(beanName, aliase);
            }
        }
    }
//    进入registerBeanDefinition.registerBeanDefinition，该方法实现于：void org.springframework.beans.factory.support.DefaultListableBeanFactory.registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException
//注意该方法的实现位置：DefaultListableBeanFactory
   
    private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);
    @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 oldBeanDefinition;

        //加锁同步
        //注意该上面的beanDefinitionMap
        synchronized (this.beanDefinitionMap) {
            oldBeanDefinition = this.beanDefinitionMap.get(beanName);
            if (oldBeanDefinition != null) {
                //如果已经存在该beanDefinition则判断是否允许覆盖
                if (!this.allowBeanDefinitionOverriding) {
                    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 {
                //如果不存在该bean则注册beanName
                this.beanDefinitionNames.add(beanName);
                this.frozenBeanDefinitionNames = null;
            }
            //把bean加入缓存beanDefinitionMap,这里完成注册
            this.beanDefinitionMap.put(beanName, beanDefinition);
        }

        if (oldBeanDefinition != null || containsSingleton(beanName)) {
            //重置该beanDefinition的所有缓存 Reset all bean definition caches for the given bean
            resetBeanDefinition(beanName);
        }
    }
//至此，beanFactory构建完成， ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();结束。


beanFactory创建完成之后，缓存中已经存储有配置bean的beanDefinition。

在void org.springframework.context.support.AbstractApplicationContext.refresh() throws BeansException, IllegalStateException中的其他方法是对beanFactory以及context的其他操作，主要是为子类覆写一些方法、注册一些监听、处理一下国际化资源文件等，这里就不再进行详细分析。

至此，该方法中的context 创建完成。

public class SpringTest {
    public static void main(String[] args) {
        //获取context上下文对象，该上下文是ClassPathXmlApplicationContext类
        ApplicationContext context = new ClassPathXmlApplicationContext("springConfig.xml");
        //从容器中取出名为"person"的对象
        Person person = context.getBean("person", Person.class);
        //调用person.info()方法。
        person.info();
    }
}

　　spring用着方便，但是实现起来确实很复杂，里面涉及了大量的设计模式，装饰模式、代理模式、工厂模式、模板方法等，对于学习系统设计有很大的帮助。

　　文章中只简单的介绍了一下beanFactory的创建，其中忽略了大量的细节，比如对单利bean的管理，beanDefinition到bean的创建，此外，对beanFactory的后期处理，Listeners的添加、MessageSource的初始化等。有兴趣的朋友可以深入研究一下，这里就不再继续分析，能力有限，很多东西我也不是太明白，还需要继续学习。建议刚接触该模块源码的朋友一定要多进行debug读源码，对源码进行分析，如果能在熟练使用sping的基础上读源码效果会更好，最好自己亲自绘制一下该模块的类图，这样可以对该模块的整体结构有一个比较清晰的认识，对上面的九个关键的类系就能够有更好的理解。

在学习的过程中遇到一本讲解比较详细的书，这里分享给大家，里面还有绘制的相关类图，用powerdesigner进行打开。

链接在此：学习资源分享  文件名分别为：spring源码深度解析   spring-IOC相关类图



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转：https://www.cnblogs.com/PerkinsZhu/p/6500837.html