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。

@Testpublic 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:

  1. Advice, Pointcut,Advisor的实现
  2. 指标对象代理对象的生成。
  3. 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。