假设我有一个方面

public aspect Hack {

pointcut authHack(String user, String pass): call(* Authenticator.authenticate(String,String)) && args(user,pass);

boolean around(String user, String pass): authHack(user,pass) {
    out("$$$ " + user + ":" + pass + " $$$");
    return false;
}

}

Authenticator.authenticate 方法很重要。黑客拦截对此方法的调用。

是否可以编写第二个方面来取消/禁用 Hack 方面的 authHack 建议？

我可以捕捉到 around authHack 建议的执行，但是如果我想继续身份验证，我需要再次调用 Authenticator.authenticate，这会创建一个无限循环..

最佳答案

为了模拟您的情况，我编写了以下 Authenticator 代码:

public class Authenticator {

    public boolean authenticate(String user, String pass) {
        System.out.println("User: '" + user + "', pass: '" + pass + "'");
        return true;
    }

}

这是我的主类:

public class Main {

    public static void main(String[] args) {

        Authenticator authenticator = new Authenticator();

        boolean status = authenticator.authenticate("Yaneeve", "12345");
        System.out.println("Status: '" + status + "'");
    }

}

输出是:

User: 'Yaneeve', pass: '12345'
Status: 'true'

我添加了你的 Hack 方面:

public aspect Hack {

    pointcut authHack(String user, String pass): call(* Authenticator.authenticate(String,String)) && args(user,pass);

    boolean around(String user, String pass): authHack(user,pass) {
        System.out.println("$$$ " + user + ":" + pass + " $$$");
        return false;
    }
}

现在的输出是:

$$$ Yaneeve:12345 $$$
Status: 'false'

解决方案:

我创建了以下 HackTheHack 方面:

public aspect HackTheHack {

    declare precedence: "HackTheHack", "Hack";

    pointcut authHack(String user, String pass): call(* Authenticator.authenticate(String,String)) && args(user,pass);

    boolean around(String user, String pass): authHack(user,pass) {
        boolean status = false;
        try {
            Class<?> klass = Class.forName("Authenticator");
            Object newInstance = klass.newInstance();
            Method authMethod = klass.getDeclaredMethod("authenticate", String.class, String.class);
            status = (Boolean) authMethod.invoke(newInstance, user, pass);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (SecurityException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        }
        return status;
    }
}

输出又是:

User: 'Yaneeve', pass: '12345'
Status: 'true'

这仅在 Hack 方面的原始切入点是“调用”而不是“执行”时有效，因为执行实际上捕获了反射。

解释:

我使用方面优先级在 Hack 之前调用 HackTheHack:

declare precedence: "HackTheHack", "Hack";

然后我使用反射(注意可以而且应该进行优化以减少方法的重复查找)来简单地调用原始方法，而无需 Hack around 建议。由于两件事，这成为可能:

1. authHack 切入点:切入点 authHack(String user, String pass): call(* Authenticator.authenticate(String,String)) && args(user,pass); 使用(在两个方面) call() 而不是 execution()
2. 我没有在 HackTheHack 中调用 proceed()

我想向您推荐Manning's AspectJ in Action, Second Edition这让我走上了正确的轨道:

6.3.1 Ordering of advice

As you’ve just seen, with multiple aspects present in a system, pieces of advice in the different aspects can often apply to a single join point. When this happens, AspectJ uses the following precedence rules to determine the order in which the advice is applied. Later, you’ll see how to control precedence:

1 The aspect with higher precedence executes its before advice on a join point before the aspect with lower precedence.

2 The aspect with higher precedence executes its after advice on a join point after the aspect with lower precedence.

3 The around advice in the higher-precedence aspect encloses the around advice in the lower-precedence aspect. This kind of arrangement allows the higher- precedence aspect to control whether the lower-precedence advice will run by controlling the call to proceed(). If the higher-precedence aspect doesn’t call proceed() in its advice body, not only will the lower-precedence aspects not execute, but the advised join point also won’t execute.

关于java - 在 AspectJ 中禁用/避免建议执行，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10194951/