Java – Invoke method with an array parameter using reflection

javamethod-invocationreflection

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.

Best Answer

You have two problems:

  1. The target parameter type is String[], but you're passing in a Object[]
  2. 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

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