Magento2:Magento2 - 如何从Controller获取JSON响应

我已经创建了自定义控制器，我希望返回使用JSON格式化的结果.我总是得到一个JSON解析错误"JSON.parse：JSON数据第1行第1列的意外字符"，结果总是采用以下格式：

array(0) { } {"Test-Message":""}

我尝试过以下代码变体，但没有解决问题

public function execute()
{
    $message = "";
    $userName = $this->_request->getParam('user_name');
    try
    {
        //Check user name
        $result = $helper->checkUserName($userName);
        if ($result)
        {
            $message = "Test";
        }
    }
    catch(\Exception $e)
    {
        $message = $e;
    } 
    //$this->getResponse()->setBody($message);
/*
    $arr = array('result' => $message);
    $jsonData = json_encode(array($arr));
    $this->getResponse()->setHeader('Content-type', 'application/json');
    $this->getResponse()->setBody($jsonData);               
*/
/*      
   $this->getResponse()->clearHeaders()->setHeader('Content-type', 'application/json', true);
   $this->getResponse()->clearBody();
    echo $this->getResponse()->getBody();
*/
/*
    $arr = array('result' => $message);
    $jsonData = json_encode(array($arr));
    $this->getResponse()->clearHeaders();
    $this->getResponse()->representJson($jsonData);
*/
/*
    $result = $this->resultJsonFactory->create();
    return $result->setData(['message' => $message]);       
*/
   /** @var \Magento\Framework\Controller\Result\Json $result */
    $result = $this->resultJsonFactory->create();
    /** You may introduce your own constants for this custom REST API */
    $result->setData(['Test-Message' => $message]);
    return $result;     
 }