Spring学习（一）tomcat加载web.xml、以及项目集成Spring支持

public class XmlBeanFactory extends DefaultListableBeanFactory {

        //新建一个bean分析器，把this注册到里面是因为，在分析器解析好一个bean时，可以立即用这个this里的注册方法去保存bean，往下看就明白。任何bean到最后都是保存在XmlBeanFactory里的（其实是DefaultListableBeanFactory）。 

    private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);

    public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {

        super(parentBeanFactory);
                //载入xml文件
        this.reader.loadBeanDefinitions(resource); //往下->
    }
}

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {
     //接上
     public int loadBeanDefinitions(Resource resource) throws BeansException {

        InputStream is = null;

        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

        factory.setValidating(this.validating);

        DocumentBuilder docBuilder = factory.newDocumentBuilder();

        docBuilder.setErrorHandler(this.errorHandler);

        if (this.entityResolver != null) {
            docBuilder.setEntityResolver(this.entityResolver);
        }
        is = resource.getInputStream();
//用Xerces解析xml,生成dom
        Document doc = docBuilder.parse(is);
//registerBeanDefinitions分析dom
        return registerBeanDefinitions(doc, resource); //往下

    }

//接上
        public int registerBeanDefinitions(Document doc, Resource resource) throws BeansException {

        XmlBeanDefinitionParser parser = (XmlBeanDefinitionParser) BeanUtils.instantiateClass(this.parserClass);
//这个parserClass 是  DefaultXmlBeanDefinitionParser.class
        return parser.registerBeanDefinitions(this, doc, resource); //往下->

    }

}

public class DefaultXmlBeanDefinitionParser implements XmlBeanDefinitionParser {
//明显就是bean.xml里面出现的很熟悉的标签，说明已经快到底层类了
       

    public static final String AUTOWIRE_BY_NAME_VALUE = "byName";
    public static final String AUTOWIRE_BY_TYPE_VALUE = "byType";
    public static final String DEFAULT_LAZY_INIT_ATTRIBUTE = "default-lazy-init";
    public static final String DEFAULT_DEPENDENCY_CHECK_ATTRIBUTE = "default-dependency-check";
    public static final String DEFAULT_AUTOWIRE_ATTRIBUTE = "default-autowire";
    public static final String NAME_ATTRIBUTE = "name";
    public static final String ALIAS_ATTRIBUTE = "alias";
    public static final String BEAN_ELEMENT = "bean";
    public static final String ID_ATTRIBUTE = "id";
    public static final String PARENT_ATTRIBUTE = "parent";
    public static final String CLASS_ATTRIBUTE = "class";
    public static final String SINGLETON_ATTRIBUTE = "singleton";
    public static final String LAZY_INIT_ATTRIBUTE = "lazy-init";
    public static final String AUTOWIRE_ATTRIBUTE = "autowire";
    //...
   //接上
   public int registerBeanDefinitions(BeanDefinitionReader reader, Document doc, Resource resource) throws BeanDefinitionStoreException {

        this.beanDefinitionReader = reader;
        this.resource = resource;;
        Element root = doc.getDocumentElement();
        //...

//这里准备开始正式解析bean
        int beanDefinitionCount = parseBeanDefinitions(root);//往下->
//这个beanDefinitionCount 就是解析出了多少个<bean></bean>
        
//...
        return beanDefinitionCount;
    }

protected int parseBeanDefinitions(Element root) throws BeanDefinitionStoreException {
//Xerces开始循环找<bean>标签
        NodeList nl = root.getChildNodes();
        int beanDefinitionCounter = 0;
        for (int i = 0; i < nl.getLength(); i++) {
            Node node = nl.item(i);
            if (node instanceof Element) {
                Element ele = (Element) node;
                if // ...
//..
                else if (BEAN_ELEMENT.equals(node.getNodeName())) {//这里是重点，开始解析bean
                    beanDefinitionCounter++;
//分两步走，看下面详解。1.先把bean放到BeanDefinitionHolder
                    BeanDefinitionHolder bdHolder = parseBeanDefinitionElement(ele);//往下 1.->
//2.然后XmlBeanFactory去注册
                    BeanDefinitionReaderUtils.registerBeanDefinition(
                            bdHolder, this.beanDefinitionReader.getBeanFactory()); //往下 2. ->
                }
            }
        }
        return beanDefinitionCounter;
    }

//接上1. 哈哈，下面是第一步，是正常解析bean，在同一个类中
protected BeanDefinitionHolder parseBeanDefinitionElement(Element ele) throws BeanDefinitionStoreException {
        //...
                //下面可以看到其实最底层的解析bean在同一个类的parseBeanDefinitionElement方法里。因为spring把bean封装成BeanDefinition 再把BeanDefinition 封装成BeanDefinitionHolder 

        BeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName);//往下

//...
        return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
    }

//接上 ， 这个方法很长，毕竟<bean>里attribute很多。
  protected BeanDefinition parseBeanDefinitionElement(Element ele, String beanName) throws BeanDefinitionStoreException {
        try {
                        //下面解析<bean>里的<property>，这个我不分析了。
            MutablePropertyValues pvs = parsePropertyElements(ele, beanName);
                        //将BeanDefinition封装成AbstractBeanDefinition 
            AbstractBeanDefinition bd = BeanDefinitionReaderUtils.createBeanDefinition(
                    className, parent, cargs, pvs, this.beanDefinitionReader.getBeanClassLoader());
            //...        
            return bd;
        }
        catch (/*...*/)
                   //...

        }
    }


}
//bean解析部分到此结束。。。。


//接上2. 这里是第二部，注册部分，回到上面注释里的分两部走这里。
public class BeanDefinitionReaderUtils {
  public static void registerBeanDefinition(
            BeanDefinitionHolder bdHolder, BeanDefinitionRegistry beanFactory) throws BeansException {

        
//beanFactory就是XmlBeanFactory，其实是它的父类 DefaultListableBeanFactory在执行registerBeanDefinition


        beanFactory.registerBeanDefinition(bdHolder.getBeanName(), bdHolder.getBeanDefinition()); //往下
//...
    }

}

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
    implements ConfigurableListableBeanFactory, BeanDefinitionRegistry {
  
    /** Whether to allow re-registration of a different definition with the same name */
    private boolean allowBeanDefinitionOverriding = true;

    /** Map of bean definition objects, keyed by bean name */
//下面是真正藏bean的地方，其实是个Map，跟我预想的一样。
    private final Map beanDefinitionMap = new HashMap();
//下面List可能是给bean的名字做个索引，这是我的初步猜想。
    /** List of bean definition names, in registration order */
    private final List beanDefinitionNames = new ArrayList();
  //接上
  public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException {
//...
  Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
        if (oldBeanDefinition != null) {
//根据allowBeanDefinitionOverriding这个变量来决定在bean.xml里的bean万一有同名的情况下否覆盖，因为allowBeanDefinitionOverriding默认是true，所以覆盖。
            if (!this.allowBeanDefinitionOverriding) {
                throw new BeanDefinitionStoreException(...);
            }
            else {
                //...只用注释提醒相同bean将要被覆盖了
            }
        }
        else {
                        //索引List里加上这个bean名字
            this.beanDefinitionNames.add(beanName);
        }
                //将bean藏在map里。用名字来索引。
        this.beanDefinitionMap.put(beanName, beanDefinition);
        
    }
//...

}
//结束