Advice接口
### 1.Advice接口
上图为AOP中通知（Advice）接口的实现与继承关系。
最常用的两个 BeforeAdvice 与AfterAdvice，AfterAdvice又被AfterReturnAdvice与ThrowsAdvice接口继承
### 2.BeforeAdvice的实现方式
1.实现了BeforeAdvice接口要重写Before方法
```
/**
* method为被代理的方法，就是要在这个方法前面执行一些操作
* args 为参数列表
* target 为被代理的类的一个对象
**/
public void before(Method method, Object[] args, Object target) throws Throwable {
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
```
2.以AspectJMethodBeforeAdvice类为例
before方法调用了AbstractAspectJAdvice类中的invokeAdviceMethod(getJoinPointMatch(), null, null);
```
/**
* 调用
* @param 获取连接点信息
* @param 返回类型
* @param 异常
* @return the invocation result
* @throws Throwable in case of invocation failure
*/
protected Object invokeAdviceMethod(JoinPointMatch jpMatch, Object returnValue, Throwable ex) throws Throwable {
return invokeAdviceMethodWithGivenArgs(argBinding(getJoinPoint(), jpMatch, returnValue, ex));
}
```
其中第一参数连接点JoinPoint接口，就是用来将代理对象与目标对象进行连接的一个接口
AspectJ中的切入点匹配的执行点称作连接的（JoinPoint），
在通知方法中可以声明一个JoinPoint类型的参数。通过JoinPoint可以访问连接点的细节。
下面简要介绍JponPoint的方法：
==连接点是在什么时候生成的????==
```
1.java.lang.Object[] getArgs()：获取连接点方法运行时的入参列表；
2.Signature getSignature() ：获取连接点的方法签名对象；
3.java.lang.Object getTarget() ：获取连接点所在的目标对象；
4.java.lang.Object getThis() ：获取代理对象本身；
```
ProceedingJoinPoint继承JoinPoint子接口，它新增了两个用于执行连接点方法的方法：
```
5.java.lang.Object proceed() throws java.lang.Throwable：通过反射执行目标对象的连接点处的方法；
6.java.lang.Object proceed(java.lang.Object[] args) throws java.lang.Throwable：通过反射执行目标对象连接点处的方法，不过使用新的参数替换原来的参数。
```
3.执行相关的函数
```
protected Object invokeAdviceMethod(JoinPointMatch jpMatch, Object returnValue, Throwable ex) throws Throwable {
return invokeAdviceMethodWithGivenArgs(argBinding(getJoinPoint(), jpMatch, returnValue, ex));
}
```
其中argBinding(getJoinPoint(), jpMatch, returnValue, ex)
```
/**
* Take the arguments at the method execution join point and output a set of arguments
* to the advice method
* @param jp the current JoinPoint
* @param jpMatch the join point match that matched this execution join point
* @param returnValue the return value from the method execution (may be null)
* @param ex the exception thrown by the method execution (may be null)
* @return the empty array if there are no arguments
*/
protected Object[] argBinding(JoinPoint jp, JoinPointMatch jpMatch, Object returnValue, Throwable ex) {
calculateArgumentBindings();
// AMC start
Object[] adviceInvocationArgs = new Object[this.adviceInvocationArgumentCount];
int numBound = 0;
if (this.joinPointArgumentIndex != -1) {
adviceInvocationArgs[this.joinPointArgumentIndex] = jp;
numBound++;
}
else if (this.joinPointStaticPartArgumentIndex != -1) {
adviceInvocationArgs[this.joinPointStaticPartArgumentIndex] = jp.getStaticPart();
numBound++;
}
if (!CollectionUtils.isEmpty(this.argumentBindings)) {
// binding from pointcut match
if (jpMatch != null) {
PointcutParameter[] parameterBindings = jpMatch.getParameterBindings();
for (PointcutParameter parameter : parameterBindings) {
String name = parameter.getName();
Integer index = this.argumentBindings.get(name);
adviceInvocationArgs[index] = parameter.getBinding();
numBound++;
}
}
// binding from returning clause
if (this.returningName != null) {
Integer index = this.argumentBindings.get(this.returningName);
adviceInvocationArgs[index] = returnValue;
numBound++;
}
// binding from thrown exception
if (this.throwingName != null) {
Integer index = this.argumentBindings.get(this.throwingName);
adviceInvocationArgs[index] = ex;
numBound++;
}
}
if (numBound != this.adviceInvocationArgumentCount) {
throw new IllegalStateException("Required to bind " + this.adviceInvocationArgumentCount
+ " arguments, but only bound " + numBound + " (JoinPointMatch " +
(jpMatch == null ? "was NOT" : "WAS") +
" bound in invocation)");
}
```
最后执行
```
protected Object invokeAdviceMethodWithGivenArgs(Object[] args) throws Throwable {
Object[] actualArgs = args;
if (this.aspectJAdviceMethod.getParameterTypes().length == 0) {
actualArgs = null;
}
try {
ReflectionUtils.makeAccessible(this.aspectJAdviceMethod);
// TODO AopUtils.invokeJoinpointUsingReflection
return this.aspectJAdviceMethod.invoke(this.aspectInstanceFactory.getAspectInstance(), actualArgs);
}
catch (IllegalArgumentException ex) {
throw new AopInvocationException("Mismatch on arguments to advice method [" +
this.aspectJAdviceMethod + "]; pointcut expression [" +
this.pointcut.getPointcutExpression() + "]", ex);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
```
