本文转自博客：https://blog.csdn.net/luanlouis/article/details/51095702 特此申明！
1、Spring内部创建代理对象的过程
在Spring的底层，如果我们配置了代理模式，Spring会为每一个Bean创建一个对应的ProxyFactoryBean的FactoryBean来创建某个对象的代理对象。
假定我们现在有一个接口TicketService及其实现类RailwayStation，我们打算创建一个代理类，在执行TicketService的方法时的各个阶段，插入对应的业务代码。
public interface TicketService {
//售票
public void sellTicket();
//问询
public void inquire();
//退票
public void withdraw();
}
public class RailwayStation implements TicketService {
public void sellTicket(){
System.out.println("售票............");
}
public void inquire() {
System.out.println("问询.............");
}
public void withdraw() {
System.out.println("退票.............");
}
}下面是各种Advice类
public class TicketServiceBeforeAdvice implements MethodBeforeAdvice {
public void before(Method method, Object[] args, Object target) throws Throwable {
System.out.println("BEFORE_ADVICE: 欢迎光临代售点....");
}
}
public class TicketServiceAfterReturningAdvice implements AfterReturningAdvice {
@Override
public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
System.out.println("AFTER_RETURNING：本次服务已结束....");
}
}
public class TicketServiceThrowsAdvice implements ThrowsAdvice {
public void afterThrowing(Exception ex){
System.out.println("AFTER_THROWING....");
}
public void afterThrowing(Method method, Object[] args, Object target, Exception ex){
System.out.println("调用过程出错啦！！！！！");
}
}
public class TicketServiceAroundAdvice implements MethodInterceptor {
@Override
public Object invoke(MethodInvocation invocation) throws Throwable {
System.out.println("AROUND_ADVICE:BEGIN....");
Object returnValue = invocation.proceed();
System.out.println("AROUND_ADVICE:END.....");
return returnValue;
}
}
现在，我们来手动使用ProxyFactoryBean来创建Proxy对象，并将相应的几种不同的Advice加入这个proxy对应的各个执行阶段中：
public class App {
public static void main(String[] args) throws Exception {
//1.针对不同的时期类型，提供不同的Advice
Advice beforeAdvice = new TicketServiceBeforeAdvice();
Advice afterReturningAdvice = new TicketServiceAfterReturningAdvice();
Advice aroundAdvice = new TicketServiceAroundAdvice();
Advice throwsAdvice = new TicketServiceThrowsAdvice();
RailwayStation railwayStation = new RailwayStation();
//2.创建ProxyFactoryBean,用以创建指定对象的Proxy对象
ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
//3.设置Proxy的接口
proxyFactoryBean.setInterfaces(TicketService.class);
//4. 设置RealSubject
proxyFactoryBean.setTarget(railwayStation);
//5.使用JDK基于接口实现机制的动态代理生成Proxy代理对象，如果想使用CGLIB，需要将这个flag设置成true
proxyFactoryBean.setProxyTargetClass(true);
//6. 添加不同的Advice
proxyFactoryBean.addAdvice(afterReturningAdvice);
proxyFactoryBean.addAdvice(aroundAdvice);
proxyFactoryBean.addAdvice(throwsAdvice);
proxyFactoryBean.addAdvice(beforeAdvice);
proxyFactoryBean.setProxyTargetClass(false);
//7通过ProxyFactoryBean生成Proxy对象
TicketService ticketService = (TicketService) proxyFactoryBean.getObject();
ticketService.sellTicket();
}
}不出意外的话，你会得到如下的输出结果：
你会看到，我们成功地创建了一个通过一个ProxyFactoryBean和真实的实例对象创建出了对应的代理对象，并将各个Advice加入到proxy代理对象中。
你会发现，在调用RailwayStation的sellticket()之前，成功插入了BeforeAdivce逻辑，而调用RailwayStation的sellticket()之后，AfterReturning逻辑也成功插入了。
AroundAdvice也成功包裹了sellTicket()方法，只不过这个AroundAdvice发生的时机有点让人感到迷惑。实际上，这个背后的执行逻辑隐藏了Spring AOP关于AOP的关于Advice调度最为核心的算法机制，这个将在本文后面详细阐述。
另外，本例中ProxyFactoryBean是通过JDK的针对接口的动态代理模式生成代理对象的，具体机制，请看下面关于ProxyFactoryBean的介绍。
2、Spring AOP的核心—ProxyFactoryBean
上面我们通过了纯手动使用ProxyFactoryBean实现了AOP的功能。现在来分析一下上面的代码：我们为ProxyFactoryBean提供了如下信息：
1). Proxy应该感兴趣的Adivce列表；
2). 真正的实例对象引用ticketService;
3).告诉ProxyFactoryBean使用基于接口实现的JDK动态代理机制实现proxy:
4). Proxy应该具备的Interface接口：TicketService;
根据这些信息，ProxyFactoryBean就能给我们提供我们想要的Proxy对象了！那么，ProxyFactoryBean帮我们做了什么？
Spring 使用工厂Bean模式创建每一个Proxy，对应每一个不同的Class类型，在Spring中都会有一个相对应的ProxyFactoryBean. 以下是ProxyFactoryBean的类图。
如上所示，对于生成Proxy的工厂Bean而言，它要知道对其感兴趣的Advice信息，而这类的信息，被维护到Advised中。Advised可以根据特定的类名和方法名返回对应的AdviceChain，用以表示需要执行的Advice串。
3、基于JDK面向接口的动态代理JdkDynamicAopProxy生成代理对象
JdkDynamicAopProxy类实现了AopProxy，能够返回Proxy，并且，其自身也实现了InvocationHandler角色。也就是说，当我们使用proxy时，我们对proxy对象调用的方法，都最终被转到这个类的invoke()方法中。
4、基于Cglib子类继承方式的动态代理CglibAopProxy生成代理对象
5、各种Advice是的执行顺序是如何和方法调用进行结合的？
JdkDynamicAopProxy 和CglibAopProxy只是创建代理方式的两种方式而已，实际上我们为方法调用添加的各种Advice的执行逻辑都是统一的。在Spring的底层，会把我们定义的各个Adivce分别 包裹成一个 MethodInterceptor,这些Advice按照加入Advised顺序，构成一个AdivseChain.
比如我们上述的代码：
//5. 添加不同的Advice
proxyFactoryBean.addAdvice(afterReturningAdvice);
proxyFactoryBean.addAdvice(aroundAdvice);
proxyFactoryBean.addAdvice(throwsAdvice);
proxyFactoryBean.addAdvice(beforeAdvice);
proxyFactoryBean.setProxyTargetClass(false);
//通过ProxyFactoryBean生成
TicketService ticketService = (TicketService) proxyFactoryBean.getObject();
ticketService.sellTicket();
当我们调用 ticketService.sellTicket()时，Spring会把这个方法调用转换成一个MethodInvocation对象，然后结合上述的我们添加的各种Advice,组成一个ReflectiveMethodInvocation:
各种Advice本质而言是一个方法调用拦截器，现在让我们看看各个Advice拦截器都干了什么？
/**
* 包裹MethodBeforeAdvice的方法拦截器
* Interceptor to wrap am {@link org.springframework.aop.MethodBeforeAdvice}.
* Used internally by the AOP framework; application developers should not need
* to use this class directly.
*
* @author Rod Johnson
*/
@SuppressWarnings("serial")
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 {
//在调用方法之前，先执行BeforeAdvice
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );
return mi.proceed();
}
}
/**
* 包裹AfterReturningAdvice的方法拦截器
* Interceptor to wrap am {@link org.springframework.aop.AfterReturningAdvice}.
* Used internally by the AOP framework; application developers should not need
* to use this class directly.
*
* @author Rod Johnson
*/
@SuppressWarnings("serial")
public class AfterReturningAdviceInterceptor implements MethodInterceptor, AfterAdvice, Serializable {
private final AfterReturningAdvice advice;
/**
* Create a new AfterReturningAdviceInterceptor for the given advice.
* @param advice the AfterReturningAdvice to wrap
*/
public AfterReturningAdviceInterceptor(AfterReturningAdvice advice) {
Assert.notNull(advice, "Advice must not be null");
this.advice = advice;
}
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
//先调用invocation
Object retVal = mi.proceed();
//调用成功后，调用AfterReturningAdvice
this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
return retVal;
}
}
/**
* Interceptor to wrap an after-throwing advice.
*
* <p>The signatures on handler methods on the {@code ThrowsAdvice}
* implementation method argument must be of the form:<br>
*
* {@code void afterThrowing([Method, args, target], ThrowableSubclass);}
*
* <p>Only the last argument is required.
*
* <p>Some examples of valid methods would be:
*
* <pre class="code">public void afterThrowing(Exception ex)</pre>
* <pre class="code">public void afterThrowing(RemoteException)</pre>
* <pre class="code">public void afterThrowing(Method method, Object[] args, Object target, Exception ex)</pre>
* <pre class="code">public void afterThrowing(Method method, Object[] args, Object target, ServletException ex)</pre>
*
* <p>This is a framework class that need not be used directly by Spring users.
*
* @author Rod Johnson
* @author Juergen Hoeller
*/
public class ThrowsAdviceInterceptor implements MethodInterceptor, AfterAdvice {
private static final String AFTER_THROWING = "afterThrowing";
private static final Log logger = LogFactory.getLog(ThrowsAdviceInterceptor.class);
private final Object throwsAdvice;
/** Methods on throws advice, keyed by exception class */
private final Map<Class<?>, Method> exceptionHandlerMap = new HashMap<Class<?>, Method>();
/**
* Create a new ThrowsAdviceInterceptor for the given ThrowsAdvice.
* @param throwsAdvice the advice object that defines the exception
* handler methods (usually a {@link org.springframework.aop.ThrowsAdvice}
* implementation)
*/
public ThrowsAdviceInterceptor(Object throwsAdvice) {
Assert.notNull(throwsAdvice, "Advice must not be null");
this.throwsAdvice = throwsAdvice;
Method[] methods = throwsAdvice.getClass().getMethods();
for (Method method : methods) {
//ThrowsAdvice定义的afterThrowing方法是Handler方法
if (method.getName().equals(AFTER_THROWING) &&
(method.getParameterTypes().length == 1 || method.getParameterTypes().length == 4) &&
Throwable.class.isAssignableFrom(method.getParameterTypes()[method.getParameterTypes().length - 1])
) {
// Have an exception handler
this.exceptionHandlerMap.put(method.getParameterTypes()[method.getParameterTypes().length - 1], method);
if (logger.isDebugEnabled()) {
logger.debug("Found exception handler method: " + method);
}
}
}
if (this.exceptionHandlerMap.isEmpty()) {
throw new IllegalArgumentException(
"At least one handler method must be found in class [" + throwsAdvice.getClass() + "]");
}
}
public int getHandlerMethodCount() {
return this.exceptionHandlerMap.size();
}
/**
* Determine the exception handle method. Can return null if not found.
* @param exception the exception thrown
* @return a handler for the given exception type
*/
private Method getExceptionHandler(Throwable exception) {
Class<?> exceptionClass = exception.getClass();
if (logger.isTraceEnabled()) {
logger.trace("Trying to find handler for exception of type [" + exceptionClass.getName() + "]");
}
Method handler = this.exceptionHandlerMap.get(exceptionClass);
while (handler == null && exceptionClass != Throwable.class) {
exceptionClass = exceptionClass.getSuperclass();
handler = this.exceptionHandlerMap.get(exceptionClass);
}
if (handler != null && logger.isDebugEnabled()) {
logger.debug("Found handler for exception of type [" + exceptionClass.getName() + "]: " + handler);
}
return handler;
}
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
//使用大的try，先执行代码，捕获异常
try {
return mi.proceed();
}
catch (Throwable ex) {
//获取异常处理方法
Method handlerMethod = getExceptionHandler(ex);
//调用异常处理方法
if (handlerMethod != null) {
invokeHandlerMethod(mi, ex, handlerMethod);
}
throw ex;
}
}
private void invokeHandlerMethod(MethodInvocation mi, Throwable ex, Method method) throws Throwable {
Object[] handlerArgs;
if (method.getParameterTypes().length == 1) {
handlerArgs = new Object[] { ex };
}
else {
handlerArgs = new Object[] {mi.getMethod(), mi.getArguments(), mi.getThis(), ex};
}
try {
method.invoke(this.throwsAdvice, handlerArgs);
}
catch (InvocationTargetException targetEx) {
throw targetEx.getTargetException();
}
}
}
关于AroundAdivce,其本身就是一个MethodInterceptor，所以不需要额外做转换了。
细心的你会发现，在拦截器串中，每个拦截器最后都会调用MethodInvocation的proceed()方法。如果按照简单的拦截器的执行串来执行的话，MethodInvocation的proceed()方法至少要执行N次(N表示拦截器Interceptor的个数)，因为每个拦截器都会调用一次proceed()方法。更直观地讲，比如我们调用了ticketService.sellTicket()方法，那么，按照这个逻辑，我们会打印出四条记录：
售票............
售票............
售票............
售票............这样我们肯定不是我们需要的结果！！！！因为按照我们的理解，只应该有一条”售票…………”才对。真实的Spring的方法调用过程能够控制这个逻辑按照我们的思路执行，Spring将这个整个方法调用过程连同若干个Advice组成的拦截器链组合成ReflectiveMethodInvocation对象，让我们来看看这一执行逻辑是怎么控制的：
public class ReflectiveMethodInvocation implements ProxyMethodInvocation, Cloneable {
protected final Object proxy;
protected final Object target;
protected final Method method;
protected Object[] arguments;
private final Class<?> targetClass;
/**
* Lazily initialized map of user-specific attributes for this invocation.
*/
private Map<String, Object> userAttributes;
/**
* List of MethodInterceptor and InterceptorAndDynamicMethodMatcher
* that need dynamic checks.
*/
protected final List<?> interceptorsAndDynamicMethodMatchers;
/**
* Index from 0 of the current interceptor we're invoking.
* -1 until we invoke: then the current interceptor.
*/
private int currentInterceptorIndex = -1;
/**
* Construct a new ReflectiveMethodInvocation with the given arguments.
* @param proxy the proxy object that the invocation was made on
* @param target the target object to invoke
* @param method the method to invoke
* @param arguments the arguments to invoke the method with
* @param targetClass the target class, for MethodMatcher invocations
* @param interceptorsAndDynamicMethodMatchers interceptors that should be applied,
* along with any InterceptorAndDynamicMethodMatchers that need evaluation at runtime.
* MethodMatchers included in this struct must already have been found to have matched
* as far as was possibly statically. Passing an array might be about 10% faster,
* but would complicate the code. And it would work only for static pointcuts.
*/
protected ReflectiveMethodInvocation(
Object proxy, Object target, Method method, Object[] arguments,
Class<?> targetClass, List<Object> interceptorsAndDynamicMethodMatchers) {
this.proxy = proxy;//proxy对象
this.target = target;//真实的realSubject对象
this.targetClass = targetClass;//被代理的类类型
this.method = BridgeMethodResolver.findBridgedMethod(method);//方法引用
this.arguments = AopProxyUtils.adaptArgumentsIfNecessary(method, arguments);//调用参数
this.interceptorsAndDynamicMethodMatchers = interceptorsAndDynamicMethodMatchers;//Advice拦截器链
}
@Override
public final Object getProxy() {
return this.proxy;
}
@Override
public final Object getThis() {
return this.target;
}
@Override
public final AccessibleObject getStaticPart() {
return this.method;
}
/**
* Return the method invoked on the proxied interface.
* May or may not correspond with a method invoked on an underlying
* implementation of that interface.
*/
@Override
public final Method getMethod() {
return this.method;
}
@Override
public final Object[] getArguments() {
return (this.arguments != null ? this.arguments : new Object[0]);
}
@Override
public void setArguments(Object... arguments) {
this.arguments = arguments;
}
@Override
public Object proceed() throws Throwable {
// 没有拦截器，则直接调用Joinpoint上的method，即直接调用MethodInvocation We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
// 取得第拦截器链上第N个拦截器
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
//PointcutInterceptor会走这个逻辑
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
//当前拦截器是符合拦截规则，每个拦截器可以定义是否特定的类和方法名是否符合拦截规则
//实际上PointCut定义的方法签名最后会转换成这个MethodMatcher，并置于拦截器中
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
//符合拦截规则，调用拦截器invoke()
return dm.interceptor.invoke(this);
}
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
// 当前方法不需要拦截器操作，则直接往前推进
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
//直接调用拦截器，
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
/**
* Invoke the joinpoint using reflection.
* Subclasses can override this to use custom invocation.
* @return the return value of the joinpoint
* @throws Throwable if invoking the joinpoint resulted in an exception
*/
protected Object invokeJoinpoint() throws Throwable {
return AopUtils.invokeJoinpointUsingReflection(this.target, this.method, this.arguments);
}
上述的代码比较冗杂，解释起来比较繁琐，请看下面一张图，你就知道这段代码的思路了：
实例分析
根据上面的执行链上的逻辑，我们将我们上面举的例子的输出结果在整理一下：
Advice拦截器的添加顺序:
proxyFactoryBean.addAdvice(afterReturningAdvice);
proxyFactoryBean.addAdvice(aroundAdvice);
proxyFactoryBean.addAdvice(throwsAdvice);
proxyFactoryBean.addAdvice(beforeAdvice);第一个拦截器：AfterReturningAdvice
第一个添加的是afterReturningAdivce,它所处的位置是第一个拦截器，执行的操作就是：
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
Object retVal = mi.proceed();
this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
return retVal;
}
也就是说，先完成MethodInvocation的proceed()方法再执行相应的advice；而调用了mi.proceed()方法，导致了当前的调用链后移，进行和后续的操作，也就是说，AfterReturningAdvice只能等到整个拦截器链上所有执行完毕后才会生效，所以：AFTER_RETURNING:本次服务已结束…. 这句话排在了最后：
第二个拦截器：AroundAdvice
@Override
public Object invoke(MethodInvocation invocation) throws Throwable {
System.out.println("AROUND_ADVICE:BEGIN....");
Object returnValue = invocation.proceed();
System.out.println("AROUND_ADVICE:END.....");
return returnValue;
}
现在执行到了第二个拦截器，首先输出了”AROUND_ADVICE:BEGIN……”，接着调用Invocation.proceed(),等到剩余的执行完后，再输出”AROUND_ADVICE:END…..”：
第三个拦截器：ThrowsAdvice:
ThrowsAdvice拦截器的处理模式是：
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
try {
//先执行invocation.proceed();
return mi.proceed();
}
catch (Throwable ex) {
//捕捉错误，调用afterThrowing()方法
Method handlerMethod = getExceptionHandler(ex);
if (handlerMethod != null) {
invokeHandlerMethod(mi, ex, handlerMethod);
}
throw ex;
}
}
上述的逻辑是，先执行Invocation.proceed();如果这个过程中抛出异常，则调用ThrowsAdvice。
第四个拦截器:BeforeAdvice:
这个拦截器的工作逻辑如下：
@Override
public Object invoke(MethodInvocation mi) throws Throwable {
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );//先执行Advice
return mi.proceed();//后执行Invocation
}
综上所有的拦截器过程，我们就能理解，为什么我们刚开始的输出为什么是下面这样了：
6、PointCut与Advice的结合——Adivce的条件执行
上面我们提供了几个Adivce，你会发现，这些Advice是无条件地加入了我们创建的对象中。无论调用Target的任何方法，这些Advice都会被触发到。
那么，我们可否告诉Advice，只让它对特定的方法或特定类起作用呢？ 这个实际上是要求我们添加一个过滤器，如果满足条件，则Advice生效，否则无效。Spring将这个过滤器抽象成如下的接口：
public interface MethodMatcher {
/**
* 提供方法签名和所属的Class类型，判断是否支持
* Perform static checking whether the given method matches. 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 (may be {@code null}, in which case
* the candidate class must be taken to be the method's declaring 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 (may be {@code null}, in which case
* the candidate class must be taken to be the method's declaring 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;
}
将这个匹配器MethodMatcher和拦截器Interceptor 结合到一起，就构成了一个新的类InterceptorAndDynamicMethodMatcher ：
/**
* Internal framework class, combining a MethodInterceptor instance
* with a MethodMatcher for use as an element in the advisor chain.
*
* @author Rod Johnson
*/
class InterceptorAndDynamicMethodMatcher {
final MethodInterceptor interceptor;
final MethodMatcher methodMatcher;
public InterceptorAndDynamicMethodMatcher(MethodInterceptor interceptor, MethodMatcher methodMatcher) {
this.interceptor = interceptor;
this.methodMatcher = methodMatcher;
}
}
我们再将上述的包含整个拦截器执行链逻辑的ReflectiveMethodInvocation实现的核心代码在过一遍：
@Override
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);
//起到一定的过滤作用，如果不匹配，则直接skip
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
//满足匹配规则，则拦截器Advice生效
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.
//拦截器尚未生效，直接skip
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);
}
}
实战：
我们现在实现一个PointcutAdisor，PointcutAdvisor表示拥有某个Pointcut的Advisor。
package org.luanlouis.meditations.thinkinginspring.aop;
import org.aopalliance.aop.Advice;
import org.springframework.aop.Pointcut;
import org.springframework.aop.PointcutAdvisor;
/**
* 实现一个PointcutAdvisor，通过提供的Pointcut,对Advice的执行进行过滤
* Created by louis on 2016/4/16.
*/
public class FilteredAdvisor implements PointcutAdvisor {
private Pointcut pointcut;
private Advice advice;
public FilteredAdvisor(Pointcut pointcut, Advice advice) {
this.pointcut = pointcut;
this.advice = advice;
}
/**
* Get the Pointcut that drives this advisor.
*/
@Override
public Pointcut getPointcut() {
return pointcut;
}
@Override
public Advice getAdvice() {
return advice;
}
@Override
public boolean isPerInstance() {
return false;
}
}
package org.luanlouis.meditations.thinkinginspring.aop;
import org.aopalliance.aop.Advice;
import org.springframework.aop.aspectj.AspectJExpressionPointcut;
import org.springframework.aop.framework.ProxyFactoryBean;
/**
* 通过ProxyFactoryBean 手动创建 代理对象
* Created by louis on 2016/4/14.
*/
public class App {
public static void main(String[] args) throws Exception {
//1.针对不同的时期类型，提供不同的Advice
Advice beforeAdvice = new TicketServiceBeforeAdvice();
Advice afterReturningAdvice = new TicketServiceAfterReturningAdvice();
Advice aroundAdvice = new TicketServiceAroundAdvice();
Advice throwsAdvice = new TicketServiceThrowsAdvice();
RailwayStation railwayStation = new RailwayStation();
//2.创建ProxyFactoryBean,用以创建指定对象的Proxy对象
ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
//3.设置Proxy的接口
proxyFactoryBean.setInterfaces(TicketService.class);
//4. 设置RealSubject
proxyFactoryBean.setTarget(railwayStation);
//5.使用JDK基于接口实现机制的动态代理生成Proxy代理对象，如果想使用CGLIB，需要将这个flag设置成true
proxyFactoryBean.setProxyTargetClass(true);
//5. 添加不同的Advice
proxyFactoryBean.addAdvice(afterReturningAdvice);
proxyFactoryBean.addAdvice(aroundAdvice);
proxyFactoryBean.addAdvice(throwsAdvice);
//proxyFactoryBean.addAdvice(beforeAdvice);
proxyFactoryBean.setProxyTargetClass(false);
//手动创建一个pointcut,专门拦截sellTicket方法
AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
pointcut.setExpression("execution( * sellTicket(..))");
//传入创建的beforeAdvice和pointcut
FilteredAdvisor sellBeforeAdvior = new FilteredAdvisor(pointcut,beforeAdvice);
//添加到FactoryBean中
proxyFactoryBean.addAdvisor(sellBeforeAdvior);
//通过ProxyFactoryBean生成
TicketService ticketService = (TicketService) proxyFactoryBean.getObject();
ticketService.sellTicket();
System.out.println("---------------------------");
ticketService.inquire();
}
}
这个时候，你会看到输出：
从结果中你可以清晰地看到，我们可以对某一个Advisor(即Advice)添加一个pointcut限制，这样就可以针对指定的方法执行Advice了！本例中使用了PointcutAdvisor,实际上，带底层代码中，Spring会将PointcutAdvisor转换成InterceptorAndDynamicMethodMatcher 参与ReflectiveMethodInvocation关于拦截器链的执行逻辑：
public class DefaultAdvisorChainFactory implements AdvisorChainFactory, Serializable {
@Override
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
Advised config, Method method, Class<?> targetClass) {
// This is somewhat tricky... We have to process introductions first,
// but we need to preserve order in the ultimate list.
List<Object> interceptorList = new ArrayList<Object>(config.getAdvisors().length);
Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
for (Advisor advisor : config.getAdvisors()) {
//PointcutAdvisor向 InterceptorAndDynamicMethodMatcher 的转换
if (advisor instanceof PointcutAdvisor) {
// Add it conditionally.
PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) {
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;
}
/**
* Determine whether the Advisors contain matching introductions.
*/
private static boolean hasMatchingIntroductions(Advised config, Class<?> actualClass) {
for (int i = 0; i < config.getAdvisors().length; i++) {
Advisor advisor = config.getAdvisors()[i];
if (advisor instanceof IntroductionAdvisor) {
IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
if (ia.getClassFilter().matches(actualClass)) {
return true;
}
}
}
return false;
}
}
7、总结
至此，你已经了解了Spring的AOP的精髓，以及Spring的整个工作机制。我个人认为,想要理解Spring AOP，你需要从ProxyFactoryBean 开始，逐步地分析整个代理的构建过程：
1. 代理对象是怎么生成的(JDK or Cglib)
2. Advice链(即拦截器链)的构造过程以及执行机制
3. 如何在Advice上添加pointcut,并且这个pointcut是如何工作的(实际上起到的过滤作用)
最后再讲一下性能问题，如上面描述的，Spring创建Proxy的过程逻辑虽然很清晰，但是你也看到，对于我们每一个方法调用，都会经过非常复杂的层层Advice拦截判断，是否需要拦截处理，这个开销是非常大的。记得Spring的documentation介绍，如果使用Spring的AOP，对项目而言会造成10%的性能消耗，So，用AOP之前要仔细考虑一下性能问题~~~~~
