PHP用CURL发送Content-type为application/json的HTTP/HTTPS请求

$headers = [
    "Content-type: application/json;charset='utf-8'",
    "Accept: application/json",
    "Cache-Control: no-cache",
    "Pragma: no-cache"
];
$curl = curl_init();
$url = '';
$data = '';
curl_setopt($curl, CURLOPT_URL, $url);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, FALSE);
if (!empty($data)) {
    curl_setopt($curl, CURLOPT_POST, 1);
    curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
}
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, TRUE);
$output = curl_exec($curl);
curl_close($curl);
return $output;

其中CURLOPT_HTTPHEADER为设置header参数，CURLOPT_RETURNTRANSFER 不设置  curl_exec返回TRUE 设置  curl_exec返回json(此处) 失败都返回FALSE