如何使用php判断服务器是否是HTTPS连接

代码如下:
if ($_SERVER['HTTPS'] != "on") {
 echo "This is not HTTPS";
}else{
 echo "This is HTTPS";
}if ($_SERVER['HTTPS'] != "on") {
 echo "This is not HTTPS";
}else{
 echo "This is HTTPS";
}