在理解Spring AOP的实现之前，先理解一些Spring AOP的相干概念
AOP的相干概念
在应用Spring进行AOP相干的编程时，咱们常常应用Advice (告诉), PointCut (切点), Advisor (告诉器)来实现咱们须要的性能。
Advice
Advice是AOP联盟定义的一个接口，定义了咱们能够在切点做些什么，即咱们心愿织入的加强逻辑，为切面加强提供织入的入口。在Spring中，Advice作为一个对立的接口，Spring在Advice的根底上定义了具体的告诉类型，比方,
- BeforeAdvice: 前置加强接口，在指标办法调用之前回调。
- AfterAdvice : 后置加强接口，在指标办法调用完结并胜利返回时回调。
- ThrowAdvice : 在抛出异样时回调。
- Interceptor: 示意一个通用的拦截器，能够在办法的调用前后进行加强。
- DynamicIntroductionAdvice: 与下面的Advice和Interceptor不同，DynamicIntroductionAdvice不对办法进行加强，而是动静的引入新的接口实现。咱们能够为指标类增加一个接口的实现（原来指标类未实现某个接口）,那么通过DynamicIntroductionAdvice加强能够为指标类创立实现某接口的代理。
Pointcut
Pointcut 决定Advice能够作用于哪些连接点，即通过Pointcut咱们能够定义须要加强的办法的汇合。这些办法的汇合能够通过Pointcut中定义的规定来选取，当办法合乎Pointcut定义的规定时，返回true。这些规定可是正则表达式，也能够是字符串的匹配等。
Spring定义了Pointcut的接口，Pointcut接口中定义了用于获取类过滤器和办法匹配器的形象办法。
public interface Pointcut {
/**
* Return the ClassFilter for this pointcut.
* @return the ClassFilter (never {@code null})
*/
ClassFilter getClassFilter();
/**
* Return the MethodMatcher for this pointcut.
* @return the MethodMatcher (never {@code null})
*/
MethodMatcher getMethodMatcher();
/**
* Canonical Pointcut instance that always matches.
*/
Pointcut TRUE = TruePointcut.INSTANCE;
}然而有了类过滤器和办法匹配器，咱们还须要晓得如何应用类过滤器和办法匹配器，因而在实现Pointcut的同时也须要实现MethodMatcher。MethodMatcher定义了matches办法，即用于规定匹配的办法。
public interface MethodMatcher {
/**
* Perform static checking whether the given method matches.
* <p>If this returns {@code false} or if the {@link #isRuntime()}
* method returns {@code false}, no runtime check (i.e. no
* {@link #matches(java.lang.reflect.Method, Class, Object[])} call)
* will be made.
* @param method the candidate method
* @param targetClass the target class
* @return whether or not this method matches statically
*/
boolean matches(Method method, Class<?> targetClass);
/**
* Is this MethodMatcher dynamic, that is, must a final call be made on the
* {@link #matches(java.lang.reflect.Method, Class, Object[])} method at
* runtime even if the 2-arg matches method returns {@code true}?
* <p>Can be invoked when an AOP proxy is created, and need not be invoked
* again before each method invocation,
* @return whether or not a runtime match via the 3-arg
* {@link #matches(java.lang.reflect.Method, Class, Object[])} method
* is required if static matching passed
*/
boolean isRuntime();
/**
* Check whether there a runtime (dynamic) match for this method,
* which must have matched statically.
* <p>This method is invoked only if the 2-arg matches method returns
* {@code true} for the given method and target class, and if the
* {@link #isRuntime()} method returns {@code true}. Invoked
* immediately before potential running of the advice, after any
* advice earlier in the advice chain has run.
* @param method the candidate method
* @param targetClass the target class
* @param args arguments to the method
* @return whether there's a runtime match
* @see MethodMatcher#matches(Method, Class)
*/
boolean matches(Method method, Class<?> targetClass, Object... args);
/**
* Canonical instance that matches all methods.
*/
MethodMatcher TRUE = TrueMethodMatcher.INSTANCE;
}下图给出了Spring中一些Pointcut的继承关系，能够看到具体的实现都集成了Pointcut接口和MethodMatcher接口。
Advisor
后面介绍了Advice的加强逻辑，Pointcut定义了办法的汇合，然而哪些办法应用什么样的加强逻辑仍旧没有关联起来，Advisor就是将Advice和Pointcut联合起来，通过Advisor，能够定义在某个Pointcut连接点上应用哪个Advice。
Spring 提供了一个DefaultPointcutAdvisor, 在DefaultPointcutAdvisor中有两个属性，别离为advice和pointcut用来配置Advice 和Pointcut。 其实现如下所示。
public class DefaultPointcutAdvisor extends AbstractGenericPointcutAdvisor implements Serializable {
private Pointcut pointcut = Pointcut.TRUE;
/**
* Create an empty DefaultPointcutAdvisor.
* <p>Advice must be set before use using setter methods.
* Pointcut will normally be set also, but defaults to {@code Pointcut.TRUE}.
*/
public DefaultPointcutAdvisor() {
}
/**
* Create a DefaultPointcutAdvisor that matches all methods.
* <p>{@code Pointcut.TRUE} will be used as Pointcut.
* @param advice the Advice to use
*/
public DefaultPointcutAdvisor(Advice advice) {
this(Pointcut.TRUE, advice);
}
/**
* Create a DefaultPointcutAdvisor, specifying Pointcut and Advice.
* @param pointcut the Pointcut targeting the Advice
* @param advice the Advice to run when Pointcut matches
*/
public DefaultPointcutAdvisor(Pointcut pointcut, Advice advice) {
this.pointcut = pointcut;
setAdvice(advice);
}
/**
* Specify the pointcut targeting the advice.
* <p>Default is {@code Pointcut.TRUE}.
* @see #setAdvice
*/
public void setPointcut(@Nullable Pointcut pointcut) {
this.pointcut = (pointcut != null ? pointcut : Pointcut.TRUE);
}
@Override
public Pointcut getPointcut() {
return this.pointcut;
}
@Override
public String toString() {
return getClass().getName() + ": pointcut [" + getPointcut() + "]; advice [" + getAdvice() + "]";
}
}Spring AOP的实现
后面曾经介绍了Spring AOP的相干概念，然而Spring AOP是如何对办法的调用进行拦挡的呢？上面就Spring AOP的实现进行剖析。
同样以Spring中的单元测试开始Spring AOP的实现剖析。
通过以下代码开始Spring AOP的实现剖析。
@Test
public void testProxyFactory() {
TestBean target = new TestBean();
ProxyFactory pf = new ProxyFactory(target);
NopInterceptor nop = new NopInterceptor();
CountingBeforeAdvice cba = new CountingBeforeAdvice();
Advisor advisor = new DefaultPointcutAdvisor(cba);
pf.addAdvice(nop);
pf.addAdvisor(advisor);
ITestBean proxied = (ITestBean) pf.getProxy();
proxied.setAge(5);
assertThat(cba.getCalls()).isEqualTo(1);
assertThat(nop.getCount()).isEqualTo(1);
assertThat(pf.removeAdvisor(advisor)).isTrue();
assertThat(proxied.getAge()).isEqualTo(5);
assertThat(cba.getCalls()).isEqualTo(1);
assertThat(nop.getCount()).isEqualTo(2);
}
上述的代码中创立了一个TestBean，NopInterceptor, CountingBeforeAdvice对象，并应用TestBean初始化了ProxyFactory，CountingBeforeAdvice对象初始化DefaultPointcutAdvisor，同时将NopInterceptorDefaultPointcutAdvisor增加到ProxyFactory中。能够看到上述的代码中没有指明Pointcut, 也就意味着应用了默认的Pointcut.TRUE, 即对所有的办法都进行加强。
首先来看一下ProxyFactory的继承关系。
从上往下看，首先是TargetClassAware, 定义了一个getTargetClass()办法用来获取指标对象的Class，Advised继承了该接口，Advised接口定义了获取和设置AOP 代理工厂(Aop proxy factory)配置的办法,具体代码如下：
public interface Advised extends TargetClassAware {
boolean isFrozen();
boolean isProxyTargetClass();
Class<?>[] getProxiedInterfaces();
boolean isInterfaceProxied(Class<?> intf);
void setTargetSource(TargetSource targetSource);
TargetSource getTargetSource();
void setExposeProxy(boolean exposeProxy);
boolean isExposeProxy();
void setPreFiltered(boolean preFiltered);
boolean isPreFiltered();
Advisor[] getAdvisors();
default int getAdvisorCount() {
return getAdvisors().length;
}
void addAdvisor(Advisor advisor) throws AopConfigException;
void addAdvisor(int pos, Advisor advisor) throws AopConfigException;
boolean removeAdvisor(Advisor advisor);
void removeAdvisor(int index) throws AopConfigException;
int indexOf(Advisor advisor);
boolean replaceAdvisor(Advisor a, Advisor b) throws AopConfigException;
void addAdvice(Advice advice) throws AopConfigException;
void addAdvice(int pos, Advice advice) throws AopConfigException;
boolean removeAdvice(Advice advice);
int indexOf(Advice advice);
String toProxyConfigString();
}而ProxyConfig则保留了AOP 代理工厂的局部属性，能够看成是一个数据基类，如下：
public class ProxyConfig implements Serializable {
...
private boolean proxyTargetClass = false;
private boolean optimize = false;
boolean opaque = false;
boolean exposeProxy = false;
private boolean frozen = false;
...
}AdvisedSupport 继承了ProxyConfig同时实现了Advised接口，封装了AOP对Advice和Advisor的相干操作。
/** The AdvisorChainFactory to use. */
AdvisorChainFactory advisorChainFactory = new DefaultAdvisorChainFactory();
/** Cache with Method as key and advisor chain List as value. */
private transient Map<MethodCacheKey, List<Object>> methodCache;
/**
* Interfaces to be implemented by the proxy. Held in List to keep the order
* of registration, to create JDK proxy with specified order of interfaces.
*/
private List<Class<?>> interfaces = new ArrayList<>();
/**
* List of Advisors. If an Advice is added, it will be wrapped
* in an Advisor before being added to this List.
*/
private List<Advisor> advisors = new ArrayList<>();ProxyCreatorSupport 则提供了设置ProxyFactory和创立代理对象的办法，创立的具体的代理对象则交给具体的ProxyFactory实现。
最上面的则是三个具体的ProxyFactory的实现，别离为：
- ProxyFactory，能够在IOC容器中应用申明式配置AOP。
- ProxyFactoryBean，须要编程式的应用AOP
- AspectProxyFactory， 对于应用AspectJ的AOP利用，集成了Spring和AspectJ。
理解了ProxyFactory的继承关系后，持续往下看，咱们曾经晓得了具体的代理的对象的创立交给具体的ProxyFactory。
咱们次要关注上面用于获取代理对象的这行代码：
ITestBean proxied = (ITestBean) pf.getProxy();ProxyFactory 的getProxy的实现如下：
public Object getProxy() {
return createAopProxy().getProxy();
}getProxy()调用ProxyCreatorSupport的createAopProxy()用于创立AopProxy。
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
return getAopProxyFactory().createAopProxy(this);
}createAopProxy()先通过getAopProxyFactory()获取AopProxyFactory。getAopProxyFactory()间接返回一个DefaultAopProxyFactory的对象，而后调用DefaultAopProxyFactory的createAopProxy()办法创立具体的AopProxy，并传入this指针，即ProxyFactory对象自身，因为ProxyFactory继承了AdvisedSupport。
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (!NativeDetector.inNativeImage() &&
(config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config))) {
Class<?> targetClass = config.getTargetClass();
if (targetClass == null) {
throw new AopConfigException("TargetSource cannot determine target class: " +
"Either an interface or a target is required for proxy creation.");
}
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
return new JdkDynamicAopProxy(config);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}
private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
Class<?>[] ifcs = config.getProxiedInterfaces();
return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
}- config.isOptimize()：示意是否应用了优化策略，配置的属性optimize值决定；
- config.isProxyTargetClass()：示意是否是代理指标类，配置的属性proxy-target-class值决定；
- hasNoUserSuppliedProxyInterfaces()：就是在判断代理的对象是否有实现接口
当代理的是接口时，则应用JdkDynamicAopProxy，否则应用ObjenesisCglibAopProxy()。
JdkDynamicAopProxy保留了config和须要代理的接口。
public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
Assert.notNull(config, "AdvisedSupport must not be null");
if (config.getAdvisorCount() == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
throw new AopConfigException("No advisors and no TargetSource specified");
}
this.advised = config;
this.proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(this.proxiedInterfaces);
}当advised没有实现SpringProxy，Advised, DecoratingProxy 接口AopProxyUtils.completeProxiedInterfaces()会别离增加这三个接口。
到这里AopProxyFactory就实例化实现了。持续看getProxy()做了什么。
public Object getProxy() {
return getProxy(ClassUtils.getDefaultClassLoader());
}
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
return Proxy.newProxyInstance(classLoader, this.proxiedInterfaces, this);
}通过将classLoader, proxiedInterfaces和this传入到newProxyInstance中去创立了指标对象的代理对象。JdkDynamicAopProxy实现了InvocationHandler接口，因而能够将this指针传进去创立代理对象。
代理对象创立实现之后，当咱们调用代理对象的办法时，就会回调JdkDynamicAopProxy的invoke()办法。到这里咱们只看见了代理对象的创立，仍旧没有看到怎么对办法进行加强的逻辑，因为对代码进行加强的实现就在invoke()办法外面。
接下来看一下invoke()办法。
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Object target = null;
try {
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// The target does not implement the hashCode() method itself.
return hashCode();
}
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
return AopProxyUtils.ultimateTargetClass(this.advised);
}
else 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;
}
// Get as late as possible to minimize the time we "own" the target,
// in case it comes from a pool.
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
// 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.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// We need to create a method invocation...
MethodInvocation 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.
Class<?> returnType = method.getReturnType();
if (retVal != null && retVal == target &&
returnType != Object.class && returnType.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;
}
else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
throw new AopInvocationException(
"Null return value from advice does not match primitive return type for: " + method);
}
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
// Must have come from TargetSource.
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}invoke()的入参为代理对象，调用的办法，以及调用办法的参数。invoke()方首先查看method是不是equal，hashCode办法，以及declaringClass是不是DecoratingProxy，是不是须要将proxy设置到AopContext外面。做完这一系列的查看之后，通过getInterceptorsAndDynamicInterceptionAdvice(）获取Interceptor和Advice保留到chain中，如果chain为空，示意没有interceptor和Advice,则间接通过反射的办法调用指标办法，invokeJoinpointUsingReflection()办法封装反射调用的逻辑。如果非空，则结构一个ReflectiveMethodInvocation对象，ReflectiveMethodInvocation对象的proceed办法封装了Advice办法的加强逻辑。
先来看一下getInterceptorsAndDynamicInterceptionAdvice(）的实现：
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, @Nullable Class<?> targetClass) {
MethodCacheKey cacheKey = new MethodCacheKey(method);
List<Object> cached = this.methodCache.get(cacheKey);
if (cached == null) {
cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(
this, method, targetClass);
this.methodCache.put(cacheKey, cached);
}
return cached;
}先将method封装成MethodCacheKey，而后尝试从缓存中获取这个key对应的缓存，如果没有，则通过advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(）去获取，这里的advisorChainFactory的默认实现是DefaultAdvisorChainFactory，看一下getInterceptorsAndDynamicInterceptionAdvice()的实现。
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
Advised config, Method method, @Nullable Class<?> targetClass) {
// This is somewhat tricky... We have to process introductions first,
// but we need to preserve order in the ultimate list.
AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
Advisor[] advisors = config.getAdvisors();
List<Object> interceptorList = new ArrayList<>(advisors.length);
Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
Boolean hasIntroductions = null;
for (Advisor advisor : advisors) {
if (advisor instanceof PointcutAdvisor) {
// Add it conditionally.
PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
boolean match;
if (mm instanceof IntroductionAwareMethodMatcher) {
if (hasIntroductions == null) {
hasIntroductions = hasMatchingIntroductions(advisors, actualClass);
}
match = ((IntroductionAwareMethodMatcher) mm).matches(method, actualClass, hasIntroductions);
}
else {
match = mm.matches(method, actualClass);
}
if (match) {
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
if (mm.isRuntime()) {
// Creating a new object instance in the getInterceptors() method
// isn't a problem as we normally cache created chains.
for (MethodInterceptor interceptor : interceptors) {
interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
}
}
else {
interceptorList.addAll(Arrays.asList(interceptors));
}
}
}
}
else if (advisor instanceof IntroductionAdvisor) {
IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
Interceptor[] interceptors = registry.getInterceptors(advisor);
interceptorList.addAll(Arrays.asList(interceptors));
}
}
else {
Interceptor[] interceptors = registry.getInterceptors(advisor);
interceptorList.addAll(Arrays.asList(interceptors));
}
}
return interceptorList;
}上述的代码首先通过GlobalAdvisorAdapterRegistry.getInstance()获取了DefaultAdvisorAdapterRegistry的实例，DefaultAdvisorAdapterRegistry注册了三种Adviced的适配器，用于将Advice适配成Interceptor。
public DefaultAdvisorAdapterRegistry() {
registerAdvisorAdapter(new MethodBeforeAdviceAdapter());
registerAdvisorAdapter(new AfterReturningAdviceAdapter());
registerAdvisorAdapter(new ThrowsAdviceAdapter());
}而后对咱们增加的Advisor一一遍历，首先判断是不是PointcutAdvisor，而后判断是不是IntroductionAdvisor，如果都不是则认为是Interceptor。如果以后的advisor是PointcutAdvisor，则先判断是不是提前过滤过了，或者class是否合乎ClassFilter中定义的规定，如果进一步判断MethodMatcher的类型以及method是否匹配。无论是PointcutAdvisor，IntroductionAdvisor还是Interceptor， 最初都通过 registry.getInterceptors()办法对advisor进行适配，将advisor对象通过响应的适配器适配成MethodInterceptor的一个实例。具体的实现如下所示：
public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
List<MethodInterceptor> interceptors = new ArrayList<>(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[0]);
}看一下其中一个adapter的实现。
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, BeforeAdvice, Serializable {
private final MethodBeforeAdvice advice;
public MethodBeforeAdviceInterceptor(MethodBeforeAdvice advice) {
Assert.notNull(advice, "Advice must not be null");
this.advice = advice;
}
@Override
@Nullable
public Object invoke(MethodInvocation mi) throws Throwable {
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
return mi.proceed();
}
}能够看到对于BeforeAdvice最终被是配成了MethodBeforeAdviceInterceptor，实现了MethodInterceptor接口，其中invoke办法就是前面拦截器链的入口。
持续看proceed的实现。
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;
Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());
if (dm.methodMatcher.matches(this.method, 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);
}
}从索引为-1开始递增，如果所有的Interceptor或者Advice都调用结束，则通过反射调用指标函数。如果以后的interceptorOrInterceptionAdvice是InterceptorAndDynamicMethodMatcher的实例，则先通matches办法进行匹配，如果匹配胜利，则调用interceptor的invoke办法，否则跳过，如果不是InterceptorAndDynamicMethodMatcher的实例则时示意是一个interceptor,也间接调用invoke办法。
联合上述的MethodInterceptor的invoke办法，能够看到所有的Advice和interceptor串成了一条拦截器链，从头开始，通过matches办法进行匹配，匹配胜利则进行加强，否则持续往下查找，直到尾部，调用指标办法，整个过程就是对指标办法的加强过程，也是AOP的实现原理。
总结
本文以ProxyFactory为例剖析了Spring AOP的实现，其实现原理大抵能够分为三个局部：
- Advice, Pointcut,Advisor的实现
- 指标对象代理对象的生成。
- 对Advice进行适配，并组装成一条拦截器链，通过拦截器链对指标办法进行加强。
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