Java reflection for private static method with parameters

Question

I have a problem using the invoke method in java.

I have a method to use to provide me a Method object and it looks like:

 public static Method provideMethod(String methodName, Class targetClass) throws NoSuchMethodException {
    Method method = targetClass.getDeclaredMethod(methodName,null);

    //Set accessible provide a way to access private methods too
    method.setAccessible(true);

    return method;
}

Ok this method works perfectly when I'm trying to access methods, from any context (static, or non static), that have no arguments.

Now the problem is that I can't call invoke and pass arguments to a method that have arguments, for instance:

I have the following method :

private static boolean createDirectory(String path, String fileName) {
  ... 
}

And I want to invoke it like this:

 Boolean created = (Boolean) DataUtils.provideMethod("createDirectory", FileUtils.class).
            invoke(null, String.class, String.class);

But I'm getting java.lang.NoSuchMethodException: createDirectory [].

Does somebody knows how can I invoke a private static method that have parameters ?

And, how can I pass values to that methods arguments?

Thanks, Arkde

Answer 1

You're explicitly calling a reflection method which looks for a method declared with the given parameter types - but you're not providing any parameter types.

If you want to find any method with the given name, use getDeclaredMethods() and just filter by name... but then when you call invoke, you need to provide the string values, not the parameter types.

Alternatively, change your provideMethod call to also accept the parameter types, so you can use:

DataUtils.provideMethod("createDirectory", FileUtils.class,
                        String.class, String.class)
         .invoke(null, "foo", "bar")

Answer 2

You're specifically only looking up methods with no arguments when you call

Method method = targetClass.getDeclaredMethod(methodName,null)

In order to find the createDirectory method, you'd need to call

targetClass.getDeclaredMethod("createDirectory", String.class, String.class)

but at present your provideMethod method has no way of doing this.

I would suggest that you change the signature of provideMethod so that it allows the caller to pass in the classes of the arguments that they're looking for, like so:

public static Method provideMethod(String methodName, Class targetClass, Class... parameterTypes) throws NoSuchMethodException {
    Method method = targetClass.getDeclaredMethod(methodName, parameterTypes);

    //Set accessible provide a way to access private methods too
    method.setAccessible(true);

    return method;
}