对于springAOP的源码分析，我打算分三部分来讲解：1.配置文件的解析，解析为BeanDefination和其他信息然后注册到BeanFactory中；2.为目标对象配置增强行为以及代理对象的生成，可以理解为AOP的准备阶段；3.代理对象调用方法，增强行为的触发执行，此时是AOP生效的阶段。我们可以把1,2理解为IOC阶段；2,3理解为AOP阶段。
我们先看第一部分：BeanDefination的解析注册过程
由一个demo进入源码分析，创建一个接口UserDao
public interface UserDao {
void addUser();
void deleteUser();
}
创建UserDaoImpl类
public class UserDaoImpl implements UserDao{
public void addUser() {
System.out.println("add user ");
}
public void deleteUser() {
System.out.println("delete user ");
}
}
创建一个Logger类
public class Logger {
public void recordBefore(){
System.out.println("recordBefore");
}
public void recordAfter(){
System.out.println("recordAfter");
}
}
在aop.xml中添加配置信息
<bean id="userDao" class="com.demo.aop.sourcecode.UserDaoImpl"/>
<bean id="logger" class="com.demo.aop.sourcecode.Logger" />
<!-- 切面：切入点和通知 -->
<aop:config>
<aop:aspect id="logger" ref="logger">
<aop:pointcut expression="execution(* com.demo.aop.sourcecode..*.*(..))" id="udpateUserMethod" />
<aop:before method="recordBefore" pointcut-ref="udpateUserMethod" />
<aop:after method="recordAfter" pointcut-ref="udpateUserMethod" />
</aop:aspect>
</aop:config>
写测试方法
@Test
public void testAop(){
ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("aop.xml");//BeanDefination的解析注册，代理对象的生成
UserDao userDao = (UserDao) applicationContext.getBean("userDao");//可以看到userDao类型是以$Proxy开头的，说明是通过JDK动态代理的方式获取的
userDao.addUser();//增强行为发生的时刻
}
进入到AbstractApplicationContext类中的refresh方法
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//BeanDefination的解析注册在这个方法中发生，进入这个方法
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
通过一步步追踪，我们可以进入DefaultBeanDefinitionDocumentReader类中的parseBeanDefinitions方法
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//判断是否是默认的命名空间，默认的命名空间是 http://www.springframework.org/schema/beans
if (delegate.isDefaultNamespace(root)) {
//获取所有的子节点，然后循环处理
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)) {
//在aop.xml文件中，对userDao和logger的定义将在这里处理
parseDefaultElement(ele, delegate);
}
else {
//对<aop:config>的定义在这里处理，因为它的命名空间是 http://www.springframework.org/schema/aop 进入该方法
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
进入parseCustomElement方法，然后可以追踪到以下方法
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(ele);
//此处的handler为AopNamespaceHandler，接下来将用它对<aop:config>进行解析
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
//进入该方法
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
进入NamespaceHandlerSupport类中的parse方法
public BeanDefinition parse(Element element, ParserContext parserContext) {
return findParserForElement(element, parserContext).parse(element, parserContext);
}
由于<aop:config>的解析是由ConfigBeanDefinitionParser类来完成的，所以进入该类的parse方法，看解析过程
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
CompositeComponentDefinition compositeDef =
new CompositeComponentDefinition(element.getTagName(), parserContext.extractSource(element));
parserContext.pushContainingComponent(compositeDef); configureAutoProxyCreator(parserContext, element);
//获取子节点，根据aop.xml文件中的配置，子节点为<aop:aspect>
List<Element> childElts = DomUtils.getChildElements(element);
for (Element elt: childElts) {
String localName = parserContext.getDelegate().getLocalName(elt);
if (POINTCUT.equals(localName)) {
parsePointcut(elt, parserContext);
}
else if (ADVISOR.equals(localName)) {
parseAdvisor(elt, parserContext);
}
else if (ASPECT.equals(localName)) {
//进入该方法，解析<aop:aspect>
parseAspect(elt, parserContext);
}
} parserContext.popAndRegisterContainingComponent();
return null;
}
进入parseAspect方法
private void parseAspect(Element aspectElement, ParserContext parserContext) {
//获取定义的切面ID和ref
String aspectId = aspectElement.getAttribute(ID);
String aspectName = aspectElement.getAttribute(REF);
try {
//将获取到的切面ID和ref封装到AspectEntry这个类中
this.parseState.push(new AspectEntry(aspectId, aspectName));
//把<aop:before>等通知相关的信息封装到AspectJPointcutAdvisor中，然后放到该集合里
List<BeanDefinition> beanDefinitions = new ArrayList<BeanDefinition>();
//把ref相关的信息如aop.xml中的logger，updateUserMethod等封装到RunTimeBeanReference中，然后放到这个集合中
List<BeanReference> beanReferences = new ArrayList<BeanReference>();
List<Element> declareParents = DomUtils.getChildElementsByTagName(aspectElement, DECLARE_PARENTS);
for (int i = METHOD_INDEX; i < declareParents.size(); i++) {
Element declareParentsElement = declareParents.get(i);
beanDefinitions.add(parseDeclareParents(declareParentsElement, parserContext));
}
// We have to parse "advice" and all the advice kinds in one loop, to get the
// ordering semantics right.
NodeList nodeList = aspectElement.getChildNodes();
boolean adviceFoundAlready = false;
//循环切面的子节点，然后判断是否是通知，然后进行对应的处理
for (int i = 0; i < nodeList.getLength(); i++) {
Node node = nodeList.item(i);
if (isAdviceNode(node, parserContext)) {
if (!adviceFoundAlready) {
adviceFoundAlready = true;
if (!StringUtils.hasText(aspectName)) {
parserContext.getReaderContext().error(
"<aspect> tag needs aspect bean reference via 'ref' attribute when declaring advices.",
aspectElement, this.parseState.snapshot());
return;
}
//封装ref信息
beanReferences.add(new RuntimeBeanReference(aspectName));
}
//把通知相关信息封装到AspectJPointcutAdvisor这个类中，同时封装ref信息然后放到BeanReferences中
//这个是解析通知的方法，可以进入看看
AbstractBeanDefinition advisorDefinition = parseAdvice(
aspectName, i, aspectElement, (Element) node, parserContext, beanDefinitions, beanReferences);
beanDefinitions.add(advisorDefinition);
}
}
//把切面信息和通知信息封装到这个类中
AspectComponentDefinition aspectComponentDefinition = createAspectComponentDefinition(
aspectElement, aspectId, beanDefinitions, beanReferences, parserContext);
parserContext.pushContainingComponent(aspectComponentDefinition);
//解析切入点，然后封装信息
List<Element> pointcuts = DomUtils.getChildElementsByTagName(aspectElement, POINTCUT);
for (Element pointcutElement : pointcuts) {
//这个是具体解析切入点的方法
parsePointcut(pointcutElement, parserContext);
}
parserContext.popAndRegisterContainingComponent();
}
finally {
this.parseState.pop();
}
}
其实我们可以看到，这个方法的目的就是解析<aop:aspect>中的配置信息然后封装到类中，最终都存放在了containingComponents这个栈中，方便后面使用，这就是整个解析过程。
在接下来的一篇博文中，我们讲解代理对象的生成，如何给目标对象配置增强行为的，也就是第二个阶段。