如何使用反射检查给定对象是否是方法的有效参数(其中参数和对象是泛型类型)？

为了获得一些背景知识，这就是我想要实现的目标:

在玩反射方法调用时，我认为调用具有特定类型参数的所有方法会很好。这适用于原始类型，因为您可以调用 isAssignableFrom(Class<?> c)在他们的类对象上。但是，当您开始将泛型加入混合中时，突然变得不那么容易了，因为泛型不是反射原始设计的一部分，并且是因为类型删除。

问题更大，但基本上归结为以下几点:

理想的解决方案

理想情况下的代码

import java.lang.reflect.*;
import java.util.*;


public class ReflectionAbuse {

    public static void callMeMaybe(List<Integer> number) {
        System.out.println("You called me!");
    }

    public static void callMeAgain(List<? extends Number> number) {
        System.out.println("You called me again!");
    }

    public static void callMeNot(List<Double> number) {
        System.out.println("What's wrong with you?");
    }

    public static <T> void reflectiveCall(List<T> number){
        for(Method method : ReflectionAbuse.class.getDeclaredMethods()) {
            if(method.getName().startsWith("call")) {
                if(canBeParameterOf(method, number)) {
                    try {
                        method.invoke(null, number);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    public static <T> boolean canBeParameterOf(Method method, List<T> number) {
        // FIXME some checks missing
        return true;
    }

    public static void main(String[] args) {
        reflectiveCall(new ArrayList<Integer>());
    }

}

You called me!
You called me again!

import java.lang.reflect.*;
import java.util.*;


public class ReflectionAbuse {

            public static void callMeMaybe(ArrayList<Integer> number) {
                System.out.println("You called me!");
            }

            public static void callMeAgain(ArrayList<? extends Number> number) {
                System.out.println("You called me again!");
            }

            public static void callMeNot(ArrayList<Double> number) {
                System.out.println("What's wrong with you?");
            }

    public static <T> void reflectiveCall(List<T> number){
        for(Method method : ReflectionAbuse.class.getDeclaredMethods()) {
            if(method.getName().startsWith("call")) {
                if(canBeParameterOf(method, number)) {
                    try {
                        method.invoke(null, number);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    public static <T> boolean canBeParameterOf(Method method, List<T> number) {
        return method.getGenericParameterTypes()[0].equals(number.getClass().getGenericSuperclass());
    }

    public static void main(String[] args) {
        reflectiveCall(new ArrayList<Integer>(){});
    }

}

You called me!

import java.lang.reflect.*;
import java.util.*;


public class ReflectionAbuse {

    public static void callMeMaybe(List<Integer> number) {
        System.out.println("You called me!");
    }

    public static void callMeAgain(List<? extends Number> number) {
        System.out.println("You called me again!");
    }

    public static void callMeNot(List<Double> number) {
        System.out.println("What's wrong with you?");
    }

    public static <T> void reflectiveCall(List<T> number, Class<T> clazz){
        for(Method method : ReflectionAbuse.class.getDeclaredMethods()) {
            if(method.getName().startsWith("call")) {
                Type n = number.getClass().getGenericSuperclass();
                if(canBeParameterOf(method, clazz)) {
                    try {
                        method.invoke(null, number);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    public static <T> boolean canBeParameterOf(Method method, Class<T> clazz) {
        Type type = ((ParameterizedType)method.getGenericParameterTypes()[0]).getActualTypeArguments()[0];
        if (type instanceof WildcardType) {
            return ((Class<?>)(((WildcardType) type).getUpperBounds()[0])).isAssignableFrom(clazz);
        }
        return ((Class<?>)type).isAssignableFrom(clazz);
    }

    public static void main(String[] args) {
        reflectiveCall(new ArrayList<Integer>(), Integer.class);
    }

}

最佳答案

Am I stuck with either using anonymous subclasses or passing the type parameter?

public static <T> void reflectiveCall(TypeToken<T> type, T value)

reflectiveCall(new TypeToken<List<Integer>>() {}, new ArrayList<Integer>());

public static boolean canBeParameterOf(Method method, TypeToken<?> givenType) {
    Type[] argTypes = method.getGenericParameterTypes();

    return argTypes.length != 0 && 
        TypeToken.of(argTypes[0]).isAssignableFrom(givenType);
}

关于java - 反射性地检查对象是否是方法的有效泛型参数，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16450569/