validator array zf2

f.php

    public function create($data = null) {
        $json = "{ \"artist\":\"ergsern\", \"title\":\"enruy7u\" }";
        $array = \Zend\Json\Decoder::decode($json);

        $artist = new Input('artist');
        $artist->getValidatorChain()->addValidator(new Validator\StringLength(array('min' => '5', 'max' => '20')));

        $title = new Input('title');
        $title->getValidatorChain()->addValidator(new Validator\StringLength(array('min' => '5', 'max' => '20')));
        $inputFilter = new InputFilter();
        $inputFilter->add($artist);
        $inputFilter->add($title);
        $inputFilter->setData((array)$array);
        if ($inputFilter->isValid()) {
            echo "is valid\n";
        } else {
            echo "is not valid\n";
            foreach ($inputFilter->getInvalidInput() as $error) {
                print_r ($error->getMessages());
            }
        }
        //  var_dump($array);
    }