1.配置通知器
其实如何配置拦截器的问题，可以转化为拦截器元素是从哪来的，又在哪边配置的问题。看过上章Aop拦截器调用解析的博文的朋友肯定有印象存在着一行代码
// 获得该方法定义好的连接器链.
List这里的advised是AdvisedSupport对象，我们来看一下它的具体实现
//这里运用缓存，存入了Map>
//key：Method ; value: advisor chain List
public List DefaultAdvisorChainFactory的getInterceptorsAndDynamicInterceptionAdvice方法
//获取通知
@Override
public List在ProxyFactoryBean的getObject方法中对advisor进行初始化时，从XML配置中获取了Advisor通知器。在初始化Advisor中，可以看到对IOC容器的一个getBean回调来得到配置好的Advisor通知器。那么ProxyFactoryBean是如何获得IOC容器，然后通过回调来获得Advisor的呢？对于IOC容器的使用，如果需要回调容器，前提是当前的Bean实现BeanFactoryAware接口，并实现setBeanFactory方法，同时设置一个属性来持有IOC容器，就可以在Bean中取得IOC容器并进行回调了，而ProxyFactoryBean就实现了这个接口。ProxyFactoryBean给出通知器的名字（这些名字在XML中interceptorNames的list中），在IOC对FactoryBean进行依赖注入的时候，会直接注入到FactoryBean的interceptorNames的属性中。完成这个过程以后，ProxyFactoryBean就获得了配置的通知器。
2.Advice的通知实现
首先我们来看下如何获取通知器的通知，我们在解析如何获取配置通知器的时候出现过如下这行代码
AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
因为AdvisorAdapterRegistry是一个接口，我们来看一下它的默认实现类DefaultAdvisorAdapterRegistry
public class DefaultAdvisorAdapterRegistry implements AdvisorAdapterRegistry, Serializable {
//通知器适配器集合
private final List adapters = new ArrayList(3);
/**
* 构造方法,只有3种通知器适配器.
*/
public DefaultAdvisorAdapterRegistry() {
registerAdvisorAdapter(new MethodBeforeAdviceAdapter());
registerAdvisorAdapter(new AfterReturningAdviceAdapter());
registerAdvisorAdapter(new ThrowsAdviceAdapter());
}
//将通知封装为通知器
@Override
public Advisor wrap(Object adviceObject) throws UnknownAdviceTypeException {
if (adviceObject instanceof Advisor) {
return (Advisor) adviceObject;
}
if (!(adviceObject instanceof Advice)) {
throw new UnknownAdviceTypeException(adviceObject);
}
Advice advice = (Advice) adviceObject;
if (advice instanceof MethodInterceptor) {
return new DefaultPointcutAdvisor(advice);
}
for (AdvisorAdapter adapter : this.adapters) {
//检查符合的advice.
if (adapter.supportsAdvice(advice)) {
return new DefaultPointcutAdvisor(advice);
}
}
throw new UnknownAdviceTypeException(advice);
}
//获得通知器的通知
@Override
public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
List interceptors = new ArrayList(3);
//获取advice通知
Advice advice = advisor.getAdvice();
//如果通知是MethodInterceptor类型，则加入interceptors
if (advice instanceof MethodInterceptor) {
interceptors.add((MethodInterceptor) advice);
}
//对通知进行适配，从适配器（MethodBeforeAdviceAdapter，AfterReturningAdviceAdapter，ThrowsAdviceAdapter）中取出封装好AOP编织功能的拦截器
for (AdvisorAdapter adapter : this.adapters) {
if (adapter.supportsAdvice(advice)) {
interceptors.add(adapter.getInterceptor(advisor));
}
}
if (interceptors.isEmpty()) {
throw new UnknownAdviceTypeException(advisor.getAdvice());
}
return interceptors.toArray(new MethodInterceptor[interceptors.size()]);
}
//注册通知适配器
@Override
public void registerAdvisorAdapter(AdvisorAdapter adapter) {
this.adapters.add(adapter);
}
}
我们以MethodBeforeAdviceAdapter为例，看一下MethodBeforeAdviceAdapter的具体实现
class MethodBeforeAdviceAdapter implements AdvisorAdapter, Serializable {
@Override
public boolean supportsAdvice(Advice advice) {
return (advice instanceof MethodBeforeAdvice);
}
@Override
public MethodInterceptor getInterceptor(Advisor advisor) {
MethodBeforeAdvice advice = (MethodBeforeAdvice) advisor.getAdvice();
return new MethodBeforeAdviceInterceptor(advice);
}
}
public class MethodBeforeAdviceInterceptor implements MethodInterceptor, Serializable {
private MethodBeforeAdvice advice;
/**
* Create a new MethodBeforeAdviceInterceptor for the given advice.
* @param advice the MethodBeforeAdvice to wrap
*/
public MethodBeforeAdviceInterceptor(MethodBeforeAdvice advice) {
Assert.notNull(advice, "Advice must not be null");
this.advice = advice;
}
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );
return mi.proceed();
}
}
如代码所示，MethodBeforeAdviceInterceptor 完成的是对MethodBeforeAdvice 通知的封装，可以在MethodBeforeAdviceInterceptor 设计的invoke回调方法中，看到首先触发了advice的before方法，然后才是MethodInvocation的proceed方法调用。而proceed方法已经在第十一章中分析完毕。以上则是Spring AOP的所有内容。