java獲取格林威治時間

Calendar cd = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.US);
sdf.setTimeZone(TimeZone.getTimeZone("GMT")); // 設置時區為GMT
String str = sdf.format(cd.getTime());
System.out.println(str);