使用Java反射在Scala中获取具有方面特定注释的方法参数

Question

I am using aop in scala using aspectj . I have a method

def delete(@Id id:Long, name:String)

How can I get the value of id in my aspect file.

@Around("execution (* com.myapp.Employee.delete(..))")   
def message(joinPoint: ProceedingJoinPoint): Object = {    
  val methodSignature =joinPoint.getSignature.asInstanceOf[MethodSignature] 
  //get the value of the field id
  joinPoint.proceed   
}

I am not able to get the values.

If I try

val res = methodSignature.getMethod.getParameterAnnotations
res.map(annotations => println("size = "+annotations.length))

It is always printing the size as 0.

EDIT: Now I am getting the size correctly. The method was in object . But I think there are some problems with java reflection to read object . I changed to class and now able to get the annotations. But how can I get the parameter which is annotated with that annotation?

Answer 1

Here is some Java sample code showing how to get method annotations and also parameter annotations along with paramater types (parameter names are unavailable as cchantep already mentioned). I guess you can easily convert it into Scala by yourself.

package de.scrum_master.aspect;

import java.lang.annotation.Annotation;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.reflect.MethodSignature;

@Aspect
public class MyAspect {
    @Before("execution (* com.myapp.Employee.delete(..))")
    public void myAdvice(JoinPoint joinPoint) throws Throwable {
        System.out.println(joinPoint);
        MethodSignature signature = (MethodSignature) joinPoint.getSignature();
        String methodName = signature.getMethod().getName();
        Class<?>[] parameterTypes = signature.getMethod().getParameterTypes();

        System.out.println("Method annotations:");
        Annotation[] methodAnnotations = joinPoint.getTarget().getClass().getMethod(methodName, parameterTypes).getAnnotations();
        for (Annotation annotation : methodAnnotations)
            System.out.println("  " + annotation);

        System.out.println("Parameter annotations:");
        Annotation[][] parameterAnnotations = joinPoint.getTarget().getClass().getMethod(methodName, parameterTypes).getParameterAnnotations();
        int parameterIndex = 0;
        for (Annotation[] annotationsPerParameter : parameterAnnotations) {
            System.out.println("  Parameter of type " + parameterTypes[parameterIndex++].getName() + ":");
            for (Annotation annotation : annotationsPerParameter)
                System.out.println("    " + annotation);
        }
    }
}

---

Update:

Well, in Java 8 there is a way to determine parameter names if you compile your classes with the -parameters option. There is also a compiler switch in Eclipse for that if you use a Java 8 JRE/JDK:

You should also use a Java 8-compliant AspectJ version such as the current 1.8.5. Then your aspect can look as follows:

package de.scrum_master.aspect;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.reflect.MethodSignature;

@Aspect
public class MyAspect {
    @Before("execution(!static * *..Application.*(..))")
    public void myAdvice(JoinPoint joinPoint) throws Throwable {
        System.out.println(joinPoint);
        MethodSignature signature = (MethodSignature) joinPoint.getSignature();
        Method method = signature.getMethod();
        Parameter[] parameters = method.getParameters();

        System.out.println("Method annotations:");
        Annotation[] methodAnnotations = method.getAnnotations();
        for (Annotation annotation : methodAnnotations)
            System.out.println("  " + annotation);

        System.out.println("Parameter annotations:");
        for (Parameter parameter : parameters) {
            System.out.println("  " + parameter.getType().getName() + " " + parameter.getName());
            for (Annotation annotation : parameter.getAnnotations())
                System.out.println("    " + annotation);
        }
    }
}