今天看了一下《spring技术内幕》，看了下spring IOC容器的加载过程，但是里面的代码很杂，就自己用源码的测试用例debug了一下看了下过程

测试用例

@Test    public void testSingleConfigLocation() throws IOException {        ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext(FQ_SIMPLE_CONTEXT);        assertTrue(ctx.containsBean("someMessageSource"));        LazyBean bean = ctx.getBean(LazyBean.class);        Environment environment =ctx.getEnvironment();        String[] profiles =environment.getDefaultProfiles();        for(String s :profiles){            System.out.println(s);        }        CollectionBean bean2 = (CollectionBean) ctx.getBean("collection");        SingletonBean bean3 = ctx.getBean(SingletonBean.class);        SingletonBean bean4 = ctx.getBean(SingletonBean.class);        if (bean != null) {            System.out.println(bean.getTestFiled());        }        if (bean2 != null) {            System.out.println(bean2.getList());        }        if (bean3 != null) {            bean3.process();        }        if (bean4 != null) {            bean4.process();        }        System.out.println(ctx.getBeanDefinitionCount());        /*         * System.out.println(ctx.getBean("lazyBean"));         * System.out.println(ctx.getBean("lazyBean"));         */        ctx.close();    }

加载过程

• 首先会调用父类AbstractApplicationContext的静态初始化块

static {        // Eagerly load the ContextClosedEvent class to avoid weird classloader issues        // on application shutdown in WebLogic 8.1. (Reported by Dustin Woods.)        ContextClosedEvent.class.getName();    }

大概就是说为了避免一些奇怪的问题会首先发布一个ContextClosedEvent事件，然后按照正常的初始化依次初始化父类。

• 调用构造方法中的refresh方法，这个方法也是上下文初始化的开始

public ClassPathXmlApplicationContext(            String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)            throws BeansException {        super(parent);        setConfigLocations(configLocations);        if (refresh) {            refresh();        }    }

• refresh方法会调用AbstractRefreshableApplicationContext中的refreshBeanFactory方法创建一个DefaultListableBeanFactory实例，作为上下文的容器

protected final void refreshBeanFactory() throws BeansException {        if (hasBeanFactory()) {            destroyBeans();            closeBeanFactory();        }        try {            DefaultListableBeanFactory beanFactory = createBeanFactory();            beanFactory.setSerializationId(getId());            customizeBeanFactory(beanFactory);            loadBeanDefinitions(beanFactory);            synchronized (this.beanFactoryMonitor) {                this.beanFactory = beanFactory;            }        }        catch (IOException ex) {            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);        }    }

• 创建了容器之后就要从xml文件中加载和注册bean的定义，上面的loadBeanDefinition方法在AbstractXmlApplicationContext中的实现会被调用

@Override    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {        // Create a new XmlBeanDefinitionReader for the given BeanFactory.        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);        // Configure the bean definition reader with this context's        // resource loading environment.        beanDefinitionReader.setEnvironment(this.getEnvironment());        beanDefinitionReader.setResourceLoader(this);        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));        // Allow a subclass to provide custom initialization of the reader,        // then proceed with actually loading the bean definitions.        initBeanDefinitionReader(beanDefinitionReader);        loadBeanDefinitions(beanDefinitionReader);    }    /**     * Initialize the bean definition reader used for loading the bean     * definitions of this context. Default implementation is empty.     * 
Can be overridden in subclasses, e.g. for turning off XML validation     * or using a different XmlBeanDefinitionParser implementation.     * @param reader the bean definition reader used by this context     * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setDocumentReaderClass     */    protected void initBeanDefinitionReader(XmlBeanDefinitionReader reader) {        reader.setValidating(this.validating);    }    /**     * Load the bean definitions with the given XmlBeanDefinitionReader.     * 
The lifecycle of the bean factory is handled by the {
    @link #refreshBeanFactory}     * method; hence this method is just supposed to load and/or register bean definitions.     * @param reader the XmlBeanDefinitionReader to use     * @throws BeansException in case of bean registration errors     * @throws IOException if the required XML document isn't found     * @see #refreshBeanFactory     * @see #getConfigLocations     * @see #getResources     * @see #getResourcePatternResolver     */    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {        Resource[] configResources = getConfigResources();        if (configResources != null) {            reader.loadBeanDefinitions(configResources);        }        String[] configLocations = getConfigLocations();        if (configLocations != null) {            reader.loadBeanDefinitions(configLocations);        }    }

• 这两个方法会用来加载并注册BeanDefiniton，它们又会使用XmlBeanDefinitionReader来加载xml中的bean的定义，bean定义的解析会使用DefaultBeanDefinitionDocumentReader，它又会使用BeanDefinitionParserDelegate类委托解析bean的定义

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
    //委托BeanDefinitionParserDelegate进行解析        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);        if (bdHolder != null) {            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);            try {                // Register the final decorated instance.                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());            }            catch (BeanDefinitionStoreException ex) {                getReaderContext().error("Failed to register bean definition with name '" +                        bdHolder.getBeanName() + "'", ele, ex);            }            // Send registration event.            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));        }    }

上面黑体标注的是将解析的BeanDefinition注册到上下文中的过程，我之前没找到这个方法很奇怪loadBeanDefinition返回的都是int我就在想，BeanDefinition哪去了。静态方法会调用BeanDefinitionRegistry

接口的registerBeanDefinition方法。而DefaultListableBeanFactory实现了这个接口，

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

到此BeanDefinition就被注册到了ClassPathXmlApplicationContext中，还有很多细节没贴出来，自己debug一下很有意思的