在多个方面修改参数,提供建议

Question

我有两个方面,每个方面修改方法参数.当两个方面都应用于同一个方法时,我希望将方面的执行链接起来,并且我希望第一个方面中修改的参数可用于第二个方面.joinPoint.getArgs();但是,似乎每个方面只获得原始论点; 第二个方面永远不会看到修改后的值.我设计了一个例子:

测试类:

public class AspectTest extends TestCase {
    @Moo
    private void foo(String boo, String foo) {
        System.out.println(boo + foo);
    }

    public void testAspect() {
        foo("You should", " never see this");
    }
}

方法foo()由两个方面建议:

@Aspect
public class MooImpl {

    @Pointcut("execution(@Moo * *(..))")
    public void methodPointcut() {}

    @Around("methodPointcut()")
    public Object afterMethodInControllerClass(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("MooImpl is being called");
        Object[] args = joinPoint.getArgs();
        args[0] = "don't";
        return joinPoint.proceed(args);
    }
}

和...

@Aspect
public class DoubleMooImpl {

    @Pointcut("execution(@Moo * *(..))")
    public void methodPointcut() {}

    @Around("methodPointcut()")
    public Object afterMethodInControllerClass(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("DoubleMooImpl is being called");
        Object[] args = joinPoint.getArgs();
        args[1] = " run and hide";
        return joinPoint.proceed(args);
    }
}

我希望输出为:

MooImpl is being called
DoubleMooImpl is being called
don't run and hide

...但是:

MooImpl is being called
DoubleMooImpl is being called
You should run and hide

我是否使用正确的方法通过建议修改参数？

Answer 1

这听起来不像是方面排序问题，它更多的是如何在 java 中处理方法参数 - 对参数的引用是按值传递的，因为你的第一个参数是一个字符串，通过修改字符串引用指向你不是确实以任何方式影响原始字符串，因此被传递。

您可以尝试传入 StringBuilder 或其他可变类型，然后修改状态，然后状态更改应该得到正确反映。

更新：

我使用可变类型进行了测试，它按预期更改：

@Moo
private void foo(StringBuilder boo, StringBuilder foo) {
    System.out.println(boo.toString() + foo.toString());
}

public void testAspect() {
    foo(new StringBuilder("You should"), new StringBuilder(" never see this"));
}

与 MooImpl 方面：

@Aspect
public class MooImpl {

    @Pointcut("execution(@Moo * *(..))")
    public void methodPointcut() {}

    @Around("methodPointcut()")
    public Object afterMethodInControllerClass(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("MooImpl is being called");
        Object[] args = joinPoint.getArgs();
        ((StringBuilder)args[0]).append("****");
        return joinPoint.proceed(args);
    }
}

和 DoubleMooImpl：

@Aspect
public class DoubleMooImpl {

    @Pointcut("execution(@Moo * *(..))")
    public void methodPointcut() {}

    @Around("methodPointcut()")
    public Object afterMethodInControllerClass(ProceedingJoinPoint joinPoint) throws Throwable {
        System.out.println("DoubleMooImpl is being called");
        Object[] args = joinPoint.getArgs();
        ((StringBuilder)args[1]).append("****");
        return joinPoint.proceed(args);
    }
}

并得到这个输出：

MooImpl is being called
DoubleMooImpl is being called
You should**** never see this****