SimpleDateFormat sdf3 = new SimpleDateFormat("yyyy/MM/dd"); // string轉date

SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd"); // string轉date
Calendar now = Calendar.getInstance(); // 獲取當前系統時間
String nowYear = String.valueOf(now.get(Calendar.YEAR)); // 年
String nowMonth = StringUtils.leftPad(String.valueOf(now.get(Calendar.MONTH) + 1), 2, "0"); // 月
String nowDay = StringUtils.leftPad(String.valueOf(now.get(Calendar.DAY_OF_MONTH)), 2, "0"); // 日
Date nowDate = sdf.parse(nowYear + nowMonth + nowDay); // 20180608
 

這時候就會報錯Unparseable date: "20180608"。因為我string轉date時格式是"yyyy/MM/dd"，而呼叫給的引數是"20180608"，長度是不一致的，所以報錯。應該這樣寫最後一句

Date nowDate = sdf.parse(nowYear +"/"+ nowMonth +"/"+ nowDay);

總結：SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd"); 給的引數長度和格式一定要跟"yyyy/MM/dd"一致