import java.util.Random;

public class KeyGenerator {

public static final long WEAK_KEY = 0xFFFFFFF0000000L;
public static final long STRONG_KEY = 0xACDF03F590AE56L;

public long getKey() {
Random rand = new Random();
int x = rand.nextInt(3);

if(x == 1) {
return WEAK_KEY;
} else {
return STRONG_KEY;
}
}
}


////////////////////////////////////////////////////////

import java.lang.reflect.Method;

import org.springframework.aop.AfterReturningAdvice;

public class WeakKeyCheckAdvice implements AfterReturningAdvice {

public void afterReturning(Object returnValue, Method method,
Object[] args, Object target) throws Throwable {

if ((target instanceof KeyGenerator)
&& ("getKey".equals(method.getName()))) {
long key = ((Long) returnValue).longValue();

if (key == KeyGenerator.WEAK_KEY) {
throw new SecurityException(
"Key Generator generated a weak key. Try again");
}
}
}

}

////////////////////////////////////////////////////////
import org.springframework.aop.framework.ProxyFactory;

public class AfterAdviceExample {

public static void main(String[] args) {
KeyGenerator keyGen = getKeyGenerator();

for(int x = 0; x < 10; x++) {
try {
long key = keyGen.getKey();
System.out.println("Key: " + key);
} catch(SecurityException ex) {
System.out.println("Weak Key Generated!");
}
}

}

private static KeyGenerator getKeyGenerator() {

KeyGenerator target = new KeyGenerator();

ProxyFactory factory = new ProxyFactory();
factory.setTarget(target);
factory.addAdvice(new WeakKeyCheckAdvice());

return (KeyGenerator)factory.getProxy();
}
}