- AOP的概念
spring4.0源码分析━━━（AOP实现）
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