The JSTL formatting library doesn't work at all if there is no Accept-Language header

browser display
2014/7/1

php curl display with no Accept-Language header
2014-07-01 00:00:00.0

php curl display with Accept-Language header
2014/7/1

 php code

$url = "http://localhost/index.jsp";
$ch = curl_init();
$header = array();
$header[] = "Accept-Language: zh-tw,en;q=0.5";  //You can comment this line, the effects of different places 
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
curl_exec($ch);
curl_close($ch);

explain:

9.9 <fmt:formatdate></fmt:formatdate>

Null & Error Handling

• If value is null, remove the scoped variable if it is specified (see attributes var and scope).
• If timeZone is null or empty, it is handled as if it was missing.
• If this action fails to determine a formatting locale, it uses java.util.Date.toString() as the output format.

Reference:
http://stackoverflow.com/questions/23627158/the-jstl-formatting-library-http-java-sun-com-jsp-jstl-fmt-doesnt-work-at