带有子类参数的Java getMethod [英] Java getMethod with subclass parameter

问题描述

我正在编写一个使用反射来动态查找和调用方法的库。只给出一个对象，一个方法名和一个参数列表，我需要调用给定的方法，好像方法调用是在代码中明确写出的一样。

I'm writing a library that uses reflection to find and call methods dynamically. Given just an object, a method name, and a parameter list, I need to call the given method as though the method call were explicitly written in the code.

我'我一直在使用以下方法，它适用于大多数情况：

I've been using the following approach, which works in most cases:

static void callMethod(Object receiver, String methodName, Object[] params) {
    Class<?>[] paramTypes = new Class<?>[params.length];
    for (int i = 0; i < param.length; i++) {
        paramTypes[i] = params[i].getClass();
    }
    receiver.getClass().getMethod(methodName, paramTypes).invoke(receiver, params);
}

但是，其中一个参数是子类该方法支持的类型之一，反射API抛出 NoSuchMethodException 。例如，如果接收者的类定义了 testMethod（Foo），则以下操作失败：

However, when one of the parameters is a subclass of one of the supported types for the method, the reflection API throws a NoSuchMethodException. For example, if the receiver's class has testMethod(Foo) defined, the following fails:

receiver.getClass().getMethod("testMethod", FooSubclass.class).invoke(receiver, new FooSubclass());

即使有效：

receiver.testMethod(new FooSubclass());

如何解决此问题？如果方法调用是硬编码的，则没有问题 - 编译器只使用重载算法来选择最适用的方法。但它不适用于反射，这就是我需要的。

How do I resolve this? If the method call is hard-coded there's no issue - the compiler just uses the overloading algorithm to pick the best applicable method to use. It doesn't work with reflection, though, which is what I need.

提前致谢！

推荐答案

这比你开始的时间要长一点，但是这样做你要求的......还有一点 - 例如，callMethod（接收器，voidMethod），其中voidMethod没有参数也可以。

It's a bit longer than what you started with, but this does what you asked for... and a little more besides - for example, callMethod(receiver, "voidMethod") where voidMethod takes no arguments also works.

static void callMethod(Object receiver,
      String methodName, Object... params) {
  if (receiver == null || methodName == null) {
    return;
  }
  Class<?> cls = receiver.getClass();
  Method[] methods = cls.getMethods();
  Method toInvoke = null;
  methodLoop: for (Method method : methods) {
    if (!methodName.equals(method.getName())) {
      continue;
    }
    Class<?>[] paramTypes = method.getParameterTypes();
    if (params == null && paramTypes == null) {
      toInvoke = method;
      break;
    } else if (params == null || paramTypes == null
        || paramTypes.length != params.length) {
      continue;
    }

    for (int i = 0; i < params.length; ++i) {
      if (!paramTypes[i].isAssignableFrom(params[i].getClass())) {
        continue methodLoop;
      }
    }
    toInvoke = method;
  }
  if (toInvoke != null) {
    try {
      toInvoke.invoke(receiver, params);
    } catch (Exception t) {
      t.printStackTrace();
    }
  }
}

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