如何使用 Aspectj 捕获和抑制从 Java Class 抛出的异常

Question

我想使用 Aspectj 处理从 Circle.getArea() 方法抛出的异常。

Shape.java

    package Shapes;
    
    public class Circle {
        private double radius;
        public Circle(double radius) {
               this.radius = radius;
        }
        public double getPerimeter(){
               return 2 * Math.PI * this.radius;
        }
        public double getArea(){
            return Math.PI * this.radius * this.radius;
        }
    }

Rectangle.java


    package Shapes;
    
    public class Rectangle {
        private double width, height;
        public Rectangle(double width, double height) {
             this.width = width;
             this.height = height;
        }
        public double getPerimeter() {
               return 2 * (this.width + this.height);
        }
        public double getArea() {
               return this.width * this.height;
        }
    }

Circle.java


    package Shapes;
    
    public class Circle {
        private double radius;
        public Circle(double radius) {
            this.radius = radius;
        }
        public double getPerimeter() {
            return 2 * Math.PI * this.radius;
        }
        public double getArea() {
            throw new RuntimeException("Oops, I don't know how to calculate this :(");
        }
    }

Main.java


    package Shapes;
    
    public class Main {
    
        public static void main(String[] args) {
            try {
                Shape s;
                s = (Shape) new Rectangle(2, 10);
                System.out.println("The area of " + s + " is " + s.getArea());
                
                s = (Shape) new Rectangle(-2, 10);
                System.out.println("The perimeter of " + s +" is " + s.getPerimeter());
                
                s = (Shape) new Circle(-2);
                System.out.println("The perimeter of " + s +" is " + s.getPerimeter());
                
                s = (Shape) new Circle(2);
                System.out.println("The area of " + s + " is " + s.getArea());
                }
                catch(Exception e) {
                    System.out.println("Error: " + e.getMessage());
                }
        }
    }

Resolve.aj


    package Shapes;
    
    privileged public aspect Resolve {
        declare parents: Rectangle implements Shape;
        declare parents: Circle implements Shape;
        
        public String Rectangle.getName(){
            return "Rectangle";
        }
        
        public String Circle.getName(){
            return "Circle";
        }
        
        public String Rectangle.toString(){
            return this.getName()+"("+this.width+","+this.height+")";
        }
        public String Circle.toString(){
            return this.getName()+"("+this.radius+")";
        }
        
    
        after() throwing(RuntimeException e) : execution(* Circle.*()){
            handleException();
        }   
    
        protected void handleException()
        {
            System.out.println("Error detected");
        }
    }

当前输出为：

The area of Rectangle(2.0,10.0) is 20.0

The perimeter of Rectangle(-2.0,10.0) is 16.0

The perimeter of Circle(-2.0) is -12.566370614359172

Error detected

Error: Oops, I don't know how to calculate this :(

我想避免打印“错误：糟糕，我不知道如何计算这个:(”，最后我需要得到圆形对象的真实面积。但是，我无法更改任何 .java 文件。所有更改都应使用 Resolve.aj 文件。

Answer 1

您需要使用 around 建议而不是 after:

     Object around () : execution(* Circle.*()){
         try {
              return proceed();
         } 
         catch(Exception e) 
         {
            handleException();
         }
         return null;
    }

代码输出：

The area of Rectangle(2.0,10.0) is 20.0
The perimeter of Rectangle(-2.0,10.0) is 16.0
The perimeter of Circle(-2.0) is -12.566370614359172
Error detected
The area of Circle(2.0) is 0.0

为什么我们使用 around 建议而不是 after？

非常非正式地，around建议拦截给定的连接点，并且可以注入新行为 before、after 和 instead of that joinpoint。 proceed 是一个特殊的 feature 允许 around advice 继续执行 joinpoint .

来自 AspectJ 支持的 advice 类型（即 before、after 和 around), around advice 是唯一允许 return 一个值 and/or 使用 proceed。这使得 around advice 可以多次执行相同的 joinpoint，或者根本不执行。此外，您甚至可以使用不同的上下文执行拦截的 joinpoint（例如，更改方法参数的值）。

可以在 .

上找到有关建议和程序如何工作的更多信息

我们的around建议会拦截class[=]中方法的所有执行joinpoint 24=]，并将相应地处理这些方法抛出的异常。

如何使用 Aspectj 捕获和抑制从 Java Class 抛出的异常

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