SPRING技术内幕：深入解析SPRING架构与设计原理(第2版)-笔记（一）IOC解析

开始之前先说一下Beanfactory的结构原理：

下图是springIOC解析的整个过程：

IOC容器分为3个步骤：
1、定位
(1)Resource resource = resourceLoader.getResource(location);
int loadCount = loadBeanDefinitions(resource);
(2)loadBeanDefinitions委派为子类XmlBeanDefinitionReader的重写方法
(3)定位：在方法loadBeanDefinitions(String location, Set actualResources)中语句：
Resource resource = resourceLoader.getResource(location)，resourceLoader调用其实现类DefaultResourceLoader的getResource(String location)方法的getResourceByPath(location)定位加载资源，getResourceByPath(location)在FileSystemXmlApplicationContext已经重写，即，调用的FileSystemXmlApplicationContext的实现方法。这也解释了FileSystemXmlApplicationContext有一个getResourceByPath方法的原因（委派机制）。
2、载入
主要实现类：
BeanDefinitionParserDelegate.parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean):

/** * Parse the bean definition itself, without regard to name or aliases. May return * <code>null</code> if problems occured during the parse of the bean definition. */
    public AbstractBeanDefinition parseBeanDefinitionElement(
            Element ele, String beanName, BeanDefinition containingBean) {

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

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

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

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

            parseMetaElements(ele, bd);
            parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
            parseReplacedMethodSubElements(ele, bd.getMethodOverrides());

            parseConstructorArgElements(ele, bd);
            parsePropertyElements(ele, bd);
            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;
    }

3、注册
主要实现类：
DefaultListableBeanFactory.registerBeanDefinition(String beanName, BeanDefinition beanDefinition)

//---------------------------------------------------------------------
    // Implementation of BeanDefinitionRegistry interface
    //---------------------------------------------------------------------

    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);
            }
        }

        synchronized (this.beanDefinitionMap) {
            Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
            if (oldBeanDefinition != null) {
                if (!this.allowBeanDefinitionOverriding) {
                    throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                            "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
                            "': There is already [" + oldBeanDefinition + "] bound.");
                }
                else {
                    if (this.logger.isInfoEnabled()) {
                        this.logger.info("Overriding bean definition for bean '" + beanName +
                                "': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                    }
                }
            }
            else {
                this.beanDefinitionNames.add(beanName);
                this.frozenBeanDefinitionNames = null;
            }
            this.beanDefinitionMap.put(beanName, beanDefinition);

            resetBeanDefinition(beanName);
        }
    }