spring 加载bean过程源码简易解剖
这一篇主要是讲用载入bean的过程。其实就是IOC.低调 低调。。
我把重要的都挑出来了。一步步往下看就明白spring载入bean.xml里面bean的原理 。
感觉像候杰的 MFC深入浅出，哈哈。
观看规则
接下 表示下一层代码。
接上 表示最近上面要调用的代码的详细部分。
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domDocument doc = docBuilder.parse(is);//registerBeanDefinitions分析domreturn 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.classreturn 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beanint 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beanbeanDefinitionCounter++;//分两步走，看下面详解。1.先把bean放到BeanDefinitionHolderBeanDefinitionHolder 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registerBeanDefinitionbeanFactory.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