将参数动态传递到Method.Invoke

Question

I have methods in a class

public class ReflectionClass {
    public int add(int a, int b) {
        return a + b;
    }
    public int add(int a, int b, int c) {
        return a + b + c;
    }
    public String concatenate (String a, String b, String c){
        return a + b + c;
    }
}

I'm trying to call these methods through reflection. All I have in hand are - the method name and the parameters. Is there a way to pass the parameters into the Method.Invoke() method dynamically based on the number/type of parameters I have in hand?

Answer 1

正如你在docs中看到的那样， public Object invoke(Object obj, Object... args)接受一个varargs参数 - 所以你可以简单地传递一个参数数组。

Answer 2

You need to create an instance, get the methods, get the parameters, check the parameters by checking the type and how many... then call invoke depending of what

Example:

public static void main(String[] args) throws Exception {
    Class<?> cls = Class.forName("com.ReflectionClass");
    Object obj = cls.newInstance();
    for (Method m : cls.getDeclaredMethods()) {
        if (m.getParameterCount() == 3 && Arrays.asList(m.getParameterTypes()).contains(String.class)) {
            String a = "A";
            String b = "B";
            String c = "C";
            Object returnVal = m.invoke(obj, a, b, c);
            System.out.println((String) returnVal);
        } else if (m.getParameterCount() == 2 && Arrays.asList(m.getParameterTypes()).contains(int.class)) {
            int a = 5;
            int b = 3;
            Object returnVal = m.invoke(obj, a, b);
            System.out.println(returnVal);
    } else if (m.getParameterCount() == 3 && Arrays.asList(m.getParameterTypes()).contains(int.class)) {
            int a = 5;
            int b = 3;
            int c = 3;
            Object returnVal = m.invoke(obj, a, b, c);
            System.out.println(returnVal);
    }
}
}