反射 – Groovy：在调用任何方法之前和之后,执行代码是透明的

说明：

下面的metaClass实现从GroovyObject开始覆盖invokeMethod.由于所有groovy对象都继承自GroovyObject,因此我们可以灵活地操作/拦截方法调用,甚至可以指定我们自己的methodMissing实现.我们需要一个覆盖静态方法和一个非静态方法.基本上,invokeMethod拦截对定义它的Class上的每个方法的调用.我们最终得到了每种方法的一些前后功能.使用反射,下面的实现能够通过其名称和参数找出方法,并在运行时调用它.

注意：-

>确保从闭包中返回方法调用的返回值
>可能是一个昂贵的类有很多方法与繁重的实现
>如果需要选择性执行,则检查方法名称,然后拦截呼叫

执行：

class Dummy {
    def method1() { System.out.println "In method 1" }
    def method2(String str) { System.out.println "In method 2" }
    static def method3(int a,int b) { 
        System.out.println "In static method 3" 
    }    
}

Dummy.metaClass.invokeMethod = {String name,args ->
   def result

   System.out.println(
     "Do something before $name is called with args $args")

   try {
      result = delegate.metaClass.getMetaMethod(name,args)
                                 .invoke(delegate,args)
   } catch(Exception e) {
       System.out.println "Handling exception for method $name"
   }

   System.out.println(
      "Do something after $name was called with args $args n")

   result
}

Dummy.metaClass.'static'.invokeMethod = {String name,args ->
   def result

   System.out.println(
     "Do something before static method $name is called with args $args")

   try {
      result = delegate.metaClass.getMetaMethod(name,args)
   } catch(Exception e) {
       System.out.println "Handling exception for method $name"
   }

   System.out.println(
     "Do something after static method $name was called with args $args n")

   result
}

def dummy = new Dummy()
dummy.method1()
dummy.method2('Test')
Dummy.method3(1,2)