各平台获取北京时间

安卓

方法一：

SimpleDateFormat dff = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
dff.setTimeZone(TimeZone.getTimeZone("GMT+08"));
String ee = dff.format(new Date());
这个方法获取的结果是24小时制的，月份也正确

方法二：

Calendar calendar = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("dd-MMM-yyyy hh:mm:ss");
sdf.setTimeZone(TimeZone.getTimeZone("GMT+8"));
String rt = sdf.format(calendar.getTime());

这个方法获取的结果是不是24小时制的，月份也正确

方法三：

public static String getLocalDatetimeString(String local) {
Calendar cal = new GregorianCalendar(TimeZone.getTimeZone(local));
cal.setTimeInMillis(Calendar.getInstance().getTimeInMillis());
String date = cal.get(Calendar.YEAR) + "-" + (cal.get(Calendar.MONTH) + 1) + "-" + cal.get(Calendar.DAY_OF_MONTH);
String time = cal.get(Calendar.HOUR_OF_DAY) + ":" + cal.get(Calendar.MINUTE) + ":" + cal.get(Calendar.SECOND);
return date + " " + time;
}
String tt = getLocalDatetimeString("GMT+8");

 代码里也看出来了，这个在月份上加了一个1, 24小时制

网上流传的还有这个方法：

Time t=new Time("GMT+8"); // or Time t=new Time("GMT+8"); 加上Time Zone资料。

t.setToNow(); // 取得系统时间。
int year1 = t.year;
int month1 = t.month;
int date2 = t.monthDay;
int hour = t.hour; // 0-23
int minute = t.minute;
int second = t.second;

这个月份上也是少了一个1，需要再加1，如 int month1 = t.month + 1；;

但是 hour 获取的值不对，不知为何

windows

flutter

flutter的 DataTime.parse(formattedString)能接收一个格式化后的时间(如 "2019-02-12 12:22:33"), 并返回DateTime格式的一个时间.

但是如何将一个utc格式的时间转为本地时间(北京时间,东8区时间)呢?

例如我需要将UTC时间 "2019-03-02T12:25:55.010Z"转化为(北京时间,东8区时间).

解决思路:

1. 查看flutter的DataTime.parse的源代码,可以发现这一段注解

   • • An optional time-zone offset part,
   • possibly separated from the previous by a space.
   • The time zone is either ‘z’ or ‘Z’, or it is a signed two digit hour
   • part and an optional two digit minute part. The sign must be either
   • "+" or "-", and can not be omitted.
   • The minutes may be separated from the hours by a ‘:’.
   • Examples: "Z", "-10", "01:30", "1130".
   • This includes the output of both [toString] and [toIso8601String], which
   • will be parsed back into a DateTime object with the same time as the
   • original.
   • The result is always in either local time or UTC.
   • If a time zone offset other than UTC is specified,
   • the time is converted to the equivalent UTC time.
   • Examples of accepted strings:
   • • "2012-02-27 13:27:00"
   • • "2012-02-27 13:27:00.123456z"
   • • "2012-02-27 13:27:00,123456z"
   • • "20120227 13:27:00"
   • • "20120227T132700"
   • • "20120227"
   • • "+20120227"
   • • "2012-02-27T14Z"
   • • "2012-02-27T14+00:00"
   • • "-123450101 00:00:00 Z": in the year -12345.
   • • "2002-02-27T14:00:00-0500": Same as "2002-02-27T19:00:00Z"
       */

看到_`"2002-02-27T14:00:00-0500"`: Same as `"2002-02-27T19:00:00Z"`_这一段,就是说14点偏移往前5个小时就是19点了;

那么, 我需要转化UTC时间 "2019-03-02T12:25:55.010Z", 就必须要符合它上面列出来的格式.

首先要把".010Z"删除, 加上"-0800", ("-"代表向东边偏移,"+"代表向西边偏移,"08"代表8个小时,"00"代表分钟);

String utcTime="2019-03-02T12:25:55.010Z";
DataTime beijingTime=DateTime.parse("${utcTime.substring(0,19)}-0800");

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参考资料：
https://blog.csdn.net/dearlaoyuan/article/details/9900967
https://zhuanlan.zhihu.com/p/58135333