java - 如何使用 Aspectj 捕获和抑制 Java 类抛出的异常
问题描述
我想处理从Circle.getArea()
使用 Aspectj 的方法抛出的异常。
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;
}
}
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 :(");
}
}
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());
}
}
}
解决.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:(”,并且我需要在最后获取圆形对象的实际区域。但是,我无法更改任何 .java 文件。所有更改应使用 Resolve.aj 文件。
解决方案
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
通知拦截给定的连接点,并且可以在该连接点之前、之后和代替该连接点注入新的行为。是一项特殊功能,允许通知继续执行.proceed
around
joinpoint
从AspectJ 支持的建议类型(即 、 before
和after
)around
中,around
建议是唯一允许返回值和/或使用proceed
. 这使得一个around
通知可以多次执行同一个连接点,或者根本不执行它。此外,您甚至可以使用不同的上下文执行截获的连接点(例如,更改方法参数的值)。
有关建议和继续工作的更多信息,请参阅此 SO Thread。
我们的around
通知将拦截类中方法的所有执行连接点Circle
,并相应地处理这些方法抛出的异常。