我试图定义一个切入点表达式以匹配包含用特定注释注释的参数的方法,而不管该参数位于什么位置。在我的情况下,我正在寻找@Constraint注释。例如:
@Constraint
匹配方式:
public void method1(@Constraint Car car) public void method2(String id, @Constraint Plane plane) public void method3(Wheel wheel, @Constraint List<Train> trains, @Constraint Plane plane) public void method4(Motor motor, @Constraint Set<Train> trains, Bicycle bike, Wheel wheel) public void method5(Wing wing, Motorcycle moto, @Constraint Truck truck, Bicycle bike, Wheel wheel)
到目前为止,我还没有尝试过以下表达式:
@Before("execution(public * *.*(..)) and @args(com.example.Constraint)") // there can be only one parameter @Before("execution(public * *.*(..)) and @args(..,com.example.Constraint)") // parameter must be in last position @Before("execution(public * *.*(..)) and @args(com.example.Constraint,..)") // parameter must be in first position @Before("execution(public * *.*(..)) and (@args(com.example.Constraint,..) or @args(..,com.example.Constraint))") // parameter must be in first or last position, nothing in between @Before("execution(public * *.*(..)) and @args(..,com.example.Constraint,..)") // Invalid
有人可以指出正确的解决方案吗?有可能吗?
你不能通过args()AspectJ 中的任意位置绑定参数,因为这可能会导致歧义。试想一下,你有两个或多个相同类型的参数(在这种情况下,使用相同的注释类型进行了注释)。应将其中哪一个绑定到命名args()参数?所以当
execution(public * (.., @Deprecated (), ..)) 可以作为独立的表达式(请注意星号的括号),不能与组合使用args()。因此,如果你不仅要拦截方法本身的执行,而且要查找具有给定批注的第一个或所有参数,则需要执行我在另一篇文章中所展示的。我有点重复自己,但是为了不再次删除答案是这样的:
import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; @Retention(RetentionPolicy.RUNTIME) public @interface Constraint {}
import java.util.ArrayList; import java.util.HashSet; import java.util.List; import java.util.Set; public class Application { public void method1(@Constraint int i) {} public void method2(String id, @Constraint float f) {} public void method3(int i, @Constraint List<String> strings, @Constraint String s) {} public void method4(int i, @Constraint Set<Integer> numbers, float f, boolean b) {} public void method5(boolean b, String s, @Constraint String s2, float f, int i) {} public void notIntercepted(boolean b, String s, String s2, float f, int i) {} public static void main(String[] args) { List<String> strings = new ArrayList<String>(); strings.add("foo"); strings.add("bar"); Set<Integer> numbers = new HashSet<Integer>(); numbers.add(11); numbers.add(22); numbers.add(33); Application app = new Application(); app.method1(1); app.method2("foo", 1f); app.method3(1, strings, "foo"); app.method4(1, numbers, 1f, true); app.method5(false, "foo", "bar", 1f, 1); app.notIntercepted(false, "foo", "bar", 1f, 1); } }
import java.lang.annotation.Annotation; import org.aspectj.lang.SoftException; import org.aspectj.lang.reflect.MethodSignature; public aspect ArgCatcherAspect { before() : execution(public * *(.., @Constraint (*), ..)) { System.out.println(thisJoinPointStaticPart); MethodSignature signature = (MethodSignature) thisJoinPoint.getSignature(); String methodName = signature.getMethod().getName(); Class<?>[] parameterTypes = signature.getMethod().getParameterTypes(); Annotation[][] annotations; try { annotations = thisJoinPoint.getTarget().getClass(). getMethod(methodName, parameterTypes).getParameterAnnotations(); } catch (Exception e) { throw new SoftException(e); } int i = 0; for (Object arg : thisJoinPoint.getArgs()) { for (Annotation annotation : annotations[i]) { if (annotation.annotationType() == Constraint.class) System.out.println(" " + annotation + " -> " + arg); } i++; } } }
如你所见,获取给定参数的注释不仅是声明的类型,还有些棘手,但是基本上它的工作方式与我之前的文章相同,即遍历参数列表。