aop—如何捕获和抑制使用aspectj从java类抛出的异常

00jrzges  于 2021-06-29  发布在  Java
关注(0)|答案(1)|浏览(496)

我想处理从 Circle.getArea() 方法使用aspectj。
形状.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;
        }
    }

矩形.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;
        }
    }

圆圈.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 :(");
        }
    }

主.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());
                }
        }
    }

解析.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");
        }
    }

电流输出为:

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“error:oops,我不知道如何计算:(”,我需要得到圆对象的真实面积。但是,我不能更改任何.java文件。所有更改都应使用resolve.aj文件。

ruoxqz4g

ruoxqz4g1#

你需要使用 around 建议而不是后面的建议:

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

为什么我们要用周围的建议而不是后面的建议?
非常非正式地说 around advice截获给定的joinpoint,并可以在joinpoint之前、之后和之后注入新行为,而不是该joinpoint。这个 proceed 是允许 around 建议继续执行 joinpoint .
从aspectj支持的通知类型(即。, before , after ,和 around ),的 around 通知是唯一允许返回值和/或使用 proceed . 这就使得 around 建议多次执行同一连接点,或根本不执行。此外,您甚至可以使用不同的上下文执行截获的joinpoint(例如,更改方法参数的值)。
有关建议和继续如何工作的更多信息可以在此so线程上找到。
我们的 around 通知将截获类中所有方法的执行连接点 Circle ,并将相应地处理这些方法引发的异常。

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