Invoke method with an array parameter using reflection

Question

I am attempting to write a method the executes a static method from another class by passing an array of strings as arguments to the method.

Here's what I have:

public static void
executeStaticCommand(final String[] command, Class<?> provider)
{
    Method[] validMethods = provider.getMethods();

    String javaCommand = TextFormat.toCamelCase(command[0]);

    for (Method method : validMethods) {
        if (method.getName().equals(javaCommand)) {
            try {
                method.invoke(null, new Object[] { new Object[] { command } });
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                Throwable ex = e.getCause();
                ex.printStackTrace();
            }
            break;
        }
    }
}

Such that this:

String[] args = new String[] { "methodName", "arg1", "arg2" }; 
executeStaticCommand(args, ClassName.class);

Should execute this:

public class ClassName {
    public static void methodName(String[] args) {
        assert args[1].equals("arg1");
    }
}

However I'm getting IllegalArgumentExceptions.

Community · Accepted Answer · 2017-05-23 10:29:49Z

25

You have two problems:

The target parameter type is String[], but you're passing in a Object[]
You're passing in the whole command array as arguments, which includes the method name

The problems are all in the inner try block, so I show only that code.

String[] args = Arrays.copyOfRange(command, 1, command.length - 1);
method.invoke(null, new Object[]{args}); // must prevent expansion into varargs

Thanks to Perception for reminding me of the varargs issue

edited May 23, 2017 at 10:29

CommunityBot

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answered Apr 11, 2013 at 14:48

Bohemian♦

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6 Comments

Perception Over a year ago

Was just typing this up, plus one additional enhancement he can make. You need to change the invoke to method.invoke(null, new Object[] {args}) for this to work.

Bohemian Over a year ago

@Perception but the target method parameter is String[], not String, String. Won't this work (I don't have a java editor handy here)?

Perception Over a year ago

It doesnt work because the array gets expanded into the varargs, causing both the signature and argument types to mismatch.

azz Over a year ago

Point 2 is intentional, and method.invoke(null, new Object[]{ command }); is what I originally had (before wrapping it in another new Object[]{}). It only works when there is one element in the String[] array.

Bohemian Over a year ago

Can you try Pshemo's suggestion of (Object)args? Also, passing in the method name as a parameter to the method seems a bad idea. Why would the method want to be passed its own name?

|

Lavanya · Accepted Answer · 2013-04-11 14:41:08Z

1

The method your trying to invoke is expecting String array, however you are passing Object array as param. Change it to String array Or you can pass any type if the method expects Object.

method.invoke(null,(Object) command );

answered Apr 11, 2013 at 14:41

Lavanya

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1 Comment

azz Over a year ago

When I use (Object)command, if command.length is 1, the method is correctly called, bit if it is > 1, no method is called.

Community · Accepted Answer · 2017-05-23 11:55:15Z

0

Based on this question, it looks like the call should be

 method.invoke(null, command);

edited May 23, 2017 at 11:55

CommunityBot

11 silver badge

answered Apr 11, 2013 at 14:41

Zim-Zam O'Pootertoot

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