将字符串转成变量

$__logFile = __FILE__;
$__logFileRequestMethod = $_SERVER['REQUEST_METHOD'];
$data = '_'.$__logFileRequestMethod;//注意，前面不能有$符号哦
$__logFileData = json_encode(${$data},302);
log::DEBUG("request record,method:[{$__logFileRequestMethod}],path:[{$__logFile}],