带有子类参数的Java getMethod

本文介绍了带有子类参数的Java getMethod的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 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(); } } }