[英]Java getMethod with subclass parameter
I'm writing a library that uses reflection to find and call methods dynamically.我正在编写一个使用反射来动态查找和调用方法的库。 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.
给定一个对象、一个方法名称和一个参数列表,我需要调用给定的方法,就好像方法调用是在代码中显式编写的一样。
I've been using the following approach, which works in most cases:我一直在使用以下方法,该方法在大多数情况下都有效:
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);
}
However, when one of the parameters is a subclass of one of the supported types for the method, the reflection API throws a NoSuchMethodException
.但是,当其中一个参数是该方法支持的类型之一的子类时,反射 API 将
NoSuchMethodException
。 For example, if the receiver's class has testMethod(Foo)
defined, the following fails:例如,如果接收者的类定义了
testMethod(Foo)
,则以下操作失败:
receiver.getClass().getMethod("testMethod", FooSubclass.class).invoke(receiver, new FooSubclass());
even though this works:即使这有效:
receiver.testMethod(new FooSubclass());
How do I resolve this?我该如何解决? 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.
如果方法调用是硬编码的,则没有问题 - 编译器只是使用重载算法来选择要使用的最佳适用方法。 It doesn't work with reflection, though, which is what I need.
但是,它不适用于反射,这正是我所需要的。
Thanks in advance!提前致谢!
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.它比您开始时的要长一点,但这可以满足您的要求......此外还有一点 - 例如, callMethod(receiver, "voidMethod") 其中 voidMethod 不带任何参数也有效。
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();
}
}
}
receiver.testMethod(new FooSubclass());
even though this works:
If your testMethod
function has parameter of FooSuperClass
type:如果您的
testMethod
函数具有FooSuperClass
类型的参数:
public void testMethod(FooSuperClass object){}
then, while you are trying to get a matching method with reflection: getClass().getMethod("testMethod", FooSubclass.class)
will result in NoSuchMethodException
.然后,当您尝试使用反射获取匹配方法时:
getClass().getMethod("testMethod", FooSubclass.class)
将导致NoSuchMethodException
。 Because this getMethod(String name, Class<?>... parameterTypes
function returns a Method
object which is a public member method with the given name
where parameterTypes
parameter is an array of Class objects that identify the method's formal parameter types . There is actually no such method is declared with signature testMedthod(FooSubClass object)
as the formal parameter type of the function is FooSuperClass
. So, the correct invocation is:因为这个
getMethod(String name, Class<?>... parameterTypes
函数返回一个Method
对象,它是一个具有给定name
的公共成员方法,其中parameterTypes
参数是标识方法形式参数类型的 Class 对象数组。实际上有没有用签名testMedthod(FooSubClass object)
声明这样的方法,因为函数的FooSuperClass
参类型是FooSuperClass
。所以,正确的调用是:
receiver.getClass().getMethod("testMethod", FooSuperClass.class)
.invoke(receiver, new FooSubclass());
or , passing the super class by calling SubClass.class.getSuperClass()
as follows:或者,通过调用
SubClass.class.getSuperClass()
传递超类,如下所示:
receiver.getClass().getMethod("testMethod", FooSubClass.class.getSuperclass())
.invoke(receiver, new FooSubclass());
or , changing the method signature to: public void testMethod(FooSubClass object){}
and then invoke as you are doing now:或者,将方法签名更改为:
public void testMethod(FooSubClass object){}
然后像现在一样调用:
receiver.getClass().getMethod("testMethod", FooSubclass.class)
.invoke(receiver, new FooSubclass());
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