spring4.0源码分析━━━（AOP实现）

• AOP的概念

         AOP为Aspect Oriented Programming的缩写，意为：面向切面编程（也叫面向方面）。这就让一些问题很简单化了，例如：开始我们实现了一些逻辑并上线了，现在客户又来了一个新的需求。要在每次交易之前统计下，或者记录下他们的交易简单资料。而你发现你其他模块可能正好有这部分的功能。那AOP就可以用得上了，使用AOP就可以在不修改源代码的情况下新增这些功能。就是在交易前这个切面，新装你的一些功能。这有点像拦截器和Filter。其实都是一个原理。前面说了解析xml和Bean的实例化。

         而AOP的实现的话都是在我前面两篇spring3.0源码分析的基础上实现。其实AOP算是对自己本身IOC的实例，你学好弄懂AOP。基本IOC的也是懂了。但是这里的AOP也用到了一些新的东西，像Aspect，还有JVM的反射和动态代理。还有CGLIB这里也是有用到的。但是默认的实现是用JVM的动态代理。

 

• AOP的实例

        AOP用起来还是很简单的。就把xml配置好就算完工了。有Advisor和aspect两种方式来完成。如果是用Advisor的话需要实现AfterReturningAdvice，MethodBeforeAdvice，ThrowsAdvice等接口。而如果用aspect的话则不用继承或者实现其他的类，一个普通的类即可。

     

public class LogAop {
	private final static Log log = LogFactory.getLog(LogAop.class);
	public void addLog(){
		log.info("add log ========================");
	}
}

 

public class BeforeAdvisor implements MethodBeforeAdvice {
	private final static Log log =LogFactory.getLog(BeforeAdvisor.class);
	
	private int testSEL;

	@Override
	public void before(Method method, Object[] args, Object target)
			throws Throwable {
		log.info("in before advice and method="+method.getName()+ " args "+args.length);
	}
 ..........

 

public class AfterAdvisor implements AfterReturningAdvice {
	private final static Log log =LogFactory.getLog(AfterAdvisor.class);
	
........

	@Override
	public void afterReturning(Object returnValue, Method method,
			Object[] args, Object target) throws Throwable {
		// TODO Auto-generated method stub
		log.info("test sel the testSEL "+testSEL);
		log.info("after return advice");
	}

}

 

 

     而配置文件如下：

	<bean id="LogAop" class="com.zzx.study.aop.LogAop" />
	<bean id="beforeAdvisor" class="com.zzx.study.aop.BeforeAdvisor" >
	   <property name="testSEL" value="11"/>
	</bean>
	<bean id="beforeAdvisor2" class="com.zzx.study.aop.BeforeAdvisor2" >
	   <property name="testSEL" value="23"/>
	</bean>
	<bean id="afterAdvisor" class="com.zzx.study.aop.AfterAdvisor" >
	   <property name="testSEL" value="11"/>
	</bean>
	<aop:config>
	   <aop:pointcut expression="execution(* com.zzx.study.di.BankSecurityDaoImpl.add(..))" id="target" />
	   <aop:pointcut expression="execution(* com.zzx.study.di.Ban*.ad*(..))" id="nonePointCutTest" />
	   <aop:advisor id="bid" pointcut-ref="target" advice-ref="beforeAdvisor" />
	   <aop:advisor id="noAdvisor" pointcut-ref="nonePointCutTest" advice-ref="beforeAdvisor2" />
	   <aop:advisor id="aid" pointcut-ref="target" advice-ref="afterAdvisor" />
	   <aop:aspect ref="LogAop" >
	       <aop:after method="addLog"  pointcut-ref="target"/>
	   </aop:aspect>
	</aop:config>  

       向上面实现后则如果执行BankSecurityDaoImpl的add方法前就会执行BeforeAdvisor的before方法，然后执行add方法，最后是LogAop的addLog方法，AfterAdvisor的afterReturning方法。这里还可以让Advisor实现Order定义这些执行的前后。

public class BeforeAdvisor implements MethodBeforeAdvice,Ordered {
	............

	@Override
	public int getOrder() {
		// TODO Auto-generated method stub
		return 2;
	}

}

 

      这里的有一个getOrder方法，返回int值，越小则越先执行。

 

• AOP在spring中的实现

       在解析xml的时候说过，如果发现不是bean标签，则会是不同的类来解析。解析aop的为http\://www.springframework.org/schema/aop=org.springframework.aop.config.AopNamespaceHandler。也就是AopNamespaceHandler类。进去到AopNamespaceHandler类中parse方法，实际是调用其父类的NamespaceHandlerSupport的parse方法。

private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
		String localName = parserContext.getDelegate().getLocalName(element);
		BeanDefinitionParser parser = this.parsers.get(localName);
		if (parser == null) {
			parserContext.getReaderContext().fatal(
					"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
		}
		return parser;
}

 这里的parses是在解析xml的时候初始化。

public void init() {
		// In 2.0 XSD as well as in 2.1 XSD.
		registerBeanDefinitionParser("config", new ConfigBeanDefinitionParser());
		registerBeanDefinitionParser("aspectj-autoproxy", new AspectJAutoProxyBeanDefinitionParser());
		registerBeanDefinitionDecorator("scoped-proxy", new ScopedProxyBeanDefinitionDecorator());

		// Only in 2.0 XSD: moved to context namespace as of 2.1
		registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
}

 

 

 如果是config标签，则是用ConfigBeanDefinitionParser类了，如果是aspectj-autoproxy标签则是用AspectJAutoProxyBeanDefinitionParser类来解析了。其实这两个的解析最终都是向DefaultListableBeanFactory中注册class为AspectJAwareAdvisorAutoProxyCreator的BeanDefinition。而AspectJAwareAdvisorAutoProxyCreator是有实现BeanPostProcessor、BeanFactoryAware接口的。而实例化一个bean的时候会经过这些BeanPostProcessor的处理。也就是这些BeanPostProcessor最终实现了把目标对象代理掉，而用代理前后spring就会调用到配置的这些Advisor来处理一些业务逻辑了。其中的BeanFactoryAware接口是把BeanFactory注入到AspectJAwareAdvisorAutoProxyCreator这个类中，而最终执行方法前通过这里注入的BeanFactory得到这些Advisor类并调用。

 

这里讲使用java动态代理的实现。在JdkDynamicAopProxy类中。使用到了责任链的模式，会先得到一个Advisor的list，然后在list中用链的方式执行下去。如果chain不是空的则会到ReflectiveMethodInvocation类中执行processed方法。

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		MethodInvocation invocation;
		Object oldProxy = null;
		boolean setProxyContext = false;

		TargetSource targetSource = this.advised.targetSource;
		Class targetClass = null;
		Object target = null;

		try {
			if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
				// The target does not implement the equals(Object) method itself.
				return equals(args[0]);
			}
			if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
				// The target does not implement the hashCode() method itself.
				return hashCode();
			}
			if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
					method.getDeclaringClass().isAssignableFrom(Advised.class)) {
				// Service invocations on ProxyConfig with the proxy config...
				return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
			}

			Object retVal;

			if (this.advised.exposeProxy) {
				// Make invocation available if necessary.
				oldProxy = AopContext.setCurrentProxy(proxy);
				setProxyContext = true;
			}

			// May be null. Get as late as possible to minimize the time we "own" the target,
			// in case it comes from a pool.
			target = targetSource.getTarget();
			if (target != null) {
				targetClass = target.getClass();
			}

			// Get the interception chain for this method.
			List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

			// Check whether we have any advice. If we don't, we can fallback on direct
			// reflective invocation of the target, and avoid creating a MethodInvocation.
			if (chain.isEmpty()) {
				// We can skip creating a MethodInvocation: just invoke the target directly
				// Note that the final invoker must be an InvokerInterceptor so we know it does
				// nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
				retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args);
			}
			else {
				// We need to create a method invocation...
				invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
				// Proceed to the joinpoint through the interceptor chain.
				retVal = invocation.proceed();
			}

			// Massage return value if necessary.
			if (retVal != null && retVal == target && method.getReturnType().isInstance(proxy) &&
					!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
				// Special case: it returned "this" and the return type of the method
				// is type-compatible. Note that we can't help if the target sets
				// a reference to itself in another returned object.
				retVal = proxy;
			}
			return retVal;
		}
		finally {
			if (target != null && !targetSource.isStatic()) {
				// Must have come from TargetSource.
				targetSource.releaseTarget(target);
			}
			if (setProxyContext) {
				// Restore old proxy.
				AopContext.setCurrentProxy(oldProxy);
			}
		}
}

 

 

public Object proceed() throws Throwable {
		//	We start with an index of -1 and increment early.
		if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
			return invokeJoinpoint();
		}

		Object interceptorOrInterceptionAdvice =
		    this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
		if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
			// Evaluate dynamic method matcher here: static part will already have
			// been evaluated and found to match.
			InterceptorAndDynamicMethodMatcher dm =
			    (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
			if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
				return dm.interceptor.invoke(this);
			}
			else {
				// Dynamic matching failed.
				// Skip this interceptor and invoke the next in the chain.
				return proceed();
			}
		}
		else {
			// It's an interceptor, so we just invoke it: The pointcut will have
			// been evaluated statically before this object was constructed.
			return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
		}
}

 

这里的interceptorOrInterceptionAdvice都是MethodInterceptor类型。因为解析xml的时候，会把<aop:advisor>最终生成class为DefaultBeanFactoryPointcutAdvisor类的BeanDefinition类，而<aop:aspect>会生成class为AspectJPointcutAdvisor的BeanDefinition。又通过DefaultAdvisorAdapterRegistry类把Advisor转换为MethodInterceptor类。

public class DefaultAdvisorAdapterRegistry implements AdvisorAdapterRegistry, Serializable {

...........................


	public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
		List<MethodInterceptor> interceptors = new ArrayList<MethodInterceptor>(3);
		Advice advice = advisor.getAdvice();
		if (advice instanceof MethodInterceptor) {
			interceptors.add((MethodInterceptor) advice);
		}
		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()]);
	}

	public void registerAdvisorAdapter(AdvisorAdapter adapter) {
		this.adapters.add(adapter);
	}

}

    像beforeAdvisor则转换为MethodBeforeAdviceInterceptor这样的拦截器了。在这个拦截器中的invoke方法中会发现会先调用自己advice的before方法，也就是你自己实现的业务类。接着又会调用processed，也就是连接链的方式，一直调用下去，知道chain中所有都执行完成。

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;
	}

	public Object invoke(MethodInvocation mi) throws Throwable {
		this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );
		return mi.proceed();
	}

}

     

       这里的advice