** 什么是ISO 8601**
国际标准化组织的国际标准ISO 8601是日期和时间表示方法，全称为<<数据存储和交互形式 信息交换 日期和时间的表示方法>>。目前最新为第三版ISO8601:2004, 第一版为ISO8601:1988, 第二版为ISO8601:2000。
日期和时间的组合表示法：
合并表示时，要在时间前面加一大写字母T, 如要表示北京时间2004年5月3日下午5点30分8秒，可以写成2004-05-03T17:30:08+08:00或20040503T173008+08。
详细内容请查阅百度百科
或https://en.wikipedia.org/wiki/ISO_8601
erlang时间与日期处理
http://www.cnblogs.com/me-sa/archive/2012/05/17/erlang-calendar-date-time.html
** iso8601库**
下面把德国时间转换为北京时间
世界各国时间转换网址：
http://cn.piliapp.com/time-now/converter/
使用iso8601库进行转换结果： 
代码如下：
-module(iso8601).
-export([add_time/4,
format/1,
parse/1,
parse_exact/1]).
-export_types([timestamp/0]).
-define(MIDNIGHT, {0,0,0}).
-define(V, proplists:get_value).
-type datetime_plist() :: list({atom(), integer()}).
-type maybe(A) :: undefined | A.
-type timestamp() :: {MegaSecs::integer(),
Secs::integer(),
MicroSecs::integer() | float()}.
%% API
-spec add_time (calendar:datetime(), integer(), integer(), integer())
-> calendar:datetime().
%% @doc Add some time to the supplied `calendar:datetime()'.
add_time(Datetime, H, M, S) ->
apply_offset(Datetime, H, M, S).
-spec format (calendar:datetime() | timestamp()) -> binary().
%% @doc Convert a `util:timestamp()' or a calendar-style `{date(), time()}'
%% tuple to an ISO 8601 formatted string. Note that this function always
%% returns a string with no offset (i.e., ending in "Z").
format({_,_,_}=Timestamp) ->
format(calendar:now_to_datetime(Timestamp));
format({{Y,Mo,D}, {H,Mn,S}}) when is_float(S) ->
FmtStr = "~4.10.0B-~2.10.0B-~2.10.0BT~2.10.0B:~2.10.0B:~9.6.0fZ",
IsoStr = io_lib:format(FmtStr, [Y, Mo, D, H, Mn, S]),
list_to_binary(IsoStr);
format({{Y,Mo,D}, {H,Mn,S}}) ->
FmtStr = "~4.10.0B-~2.10.0B-~2.10.0BT~2.10.0B:~2.10.0B:~2.10.0BZ",
IsoStr = io_lib:format(FmtStr, [Y, Mo, D, H, Mn, S]),
list_to_binary(IsoStr).
-spec parse (string()) -> calendar:datetime().
%% @doc Convert an ISO 8601 formatted string to a
parse(Bin) when is_binary(Bin) ->
parse(binary_to_list(Bin));
parse(Str) ->
{{Date, {H, M, S}}, Subsecond} = year(Str, []),
{Date, {H, M, S + round(Subsecond)}}.
-spec parse_exact (string()) -> calendar:datetime().
%% @doc Convert an ISO 8601 formatted string to a `{date(), time()}'
%% tuple with seconds precision to 3 decimal palces
parse_exact(Bin) when is_binary(Bin) ->
parse_exact(binary_to_list(Bin));
parse_exact(Str) ->
{{Date, {H, M, S}}, SecondsDecimal} = year(Str, []),
{Date, {H, M, S + SecondsDecimal}}.
%% Private functions
year([Y1,Y2,Y3,Y4|Rest], Acc) ->
acc([Y1,Y2,Y3,Y4], Rest, year, Acc, fun month_or_week/2);
year(_, _) ->
error(badarg).
month_or_week([], Acc) ->
datetime(Acc);
month_or_week([$-,$W,W1,W2|Rest], Acc) ->
acc([W1,W2], Rest, week, Acc, fun week_day/2);
month_or_week([$-,D1,D2,D3], Acc) ->
%% ordinal date, no time
io:format("Ordinal date, no time!~n"),
acc_ordinal_date(D1, D2, D3, [], Acc, fun hour/2);
month_or_week([$-,D1,D2,D3,$T|Rest], Acc) ->
%% ordinal date with time
io:format("Ordinal date, time is ~p!~n", [Rest]),
acc_ordinal_date(D1, D2, D3, [$T|Rest], Acc, fun hour/2);
month_or_week([$-,M1,M2|Rest], Acc) ->
acc([M1,M2], Rest, month, Acc, fun month_day/2);
month_or_week([$W,W1,W2|Rest], Acc) ->
acc([W1,W2], Rest, week, Acc, fun week_day_no_hyphen/2);
month_or_week([M1,M2|Rest], Acc) ->
acc([M1,M2], Rest, month, Acc, fun month_day_no_hyphen/2);
month_or_week(_, _) ->
error(badarg).
week_day([], Acc) ->
datetime(Acc);
week_day([$-,D|Rest], Acc) ->
acc([D], Rest, week_day, Acc, fun hour/2);
week_day(_, _) ->
error(badarg).
week_day_no_hyphen([], Acc) ->
datetime(Acc);
week_day_no_hyphen([D|Rest], Acc) ->
acc([D], Rest, week_day, Acc, fun hour/2);
week_day_no_hyphen(_, _) ->
error(badarg).
month_day([], Acc) ->
datetime(Acc);
month_day([$-,D1,D2|Rest], Acc) ->
acc([D1,D2], Rest, month_day, Acc, fun hour/2);
month_day(_, _) ->
error(badarg).
month_day_no_hyphen([], _) ->
error(badarg); % omission of day disallowed by spec in this case
month_day_no_hyphen([D1,D2|Rest], Acc) ->
acc([D1,D2], Rest, month_day, Acc, fun hour/2);
month_day_no_hyphen(_, _) ->
error(badarg).
hour([], Acc) ->
datetime(Acc);
hour([$T,H1,H2,$.|Rest], Acc) ->
acc([H1,H2], Rest, hour, Acc, fun hour_decimal/2);
hour([$T,H1,H2,$,|Rest], Acc) ->
acc([H1,H2], Rest, hour, Acc, fun hour_decimal/2);
hour([$T,H1,H2|Rest], Acc) ->
acc([H1,H2], Rest, hour, Acc, fun minute/2);
hour(_, _) ->
error(badarg).
hour_decimal(Str, Acc) ->
decimal(Str, Acc, hour_decimal).
minute([], Acc) ->
datetime(Acc);
minute([$:,M1,M2,$.|Rest], Acc) ->
acc([M1,M2], Rest, minute, Acc, fun minute_decimal/2);
minute([$:,M1,M2,$,|Rest], Acc) ->
acc([M1,M2], Rest, minute, Acc, fun minute_decimal/2);
minute([$:,M1,M2|Rest], Acc) ->
acc([M1,M2], Rest, minute, Acc, fun second/2);
minute([M1,M2,$.|Rest], Acc) ->
acc([M1,M2], Rest, minute, Acc, fun minute_decimal/2);
minute([M1,M2,$,|Rest], Acc) ->
acc([M1,M2], Rest, minute, Acc, fun minute_decimal/2);
minute([M1,M2|Rest], Acc) ->
acc([M1,M2], Rest, minute, Acc, fun second_no_colon/2);
minute(_, _) ->
error(badarg).
minute_decimal(Str, Acc) ->
decimal(Str, Acc, minute_decimal).
second([], Acc) ->
datetime(Acc);
second([$:,S1,S2,$.|Rest], Acc) ->
acc([S1,S2], Rest, second, Acc, fun second_decimal/2);
second([$:,S1,S2,$,|Rest], Acc) ->
acc([S1,S2], Rest, second, Acc, fun second_decimal/2);
second([$:,S1,S2|Rest], Acc) ->
acc([S1,S2], Rest, second, Acc, fun offset_hour/2);
second(_, _) ->
error(badarg).
second_no_colon([], Acc) ->
datetime(Acc);
second_no_colon([S1,S2,$.|Rest], Acc) ->
acc([S1,S2], Rest, second, Acc, fun second_decimal/2);
second_no_colon([S1,S2,$,|Rest], Acc) ->
acc([S1,S2], Rest, second, Acc, fun second_decimal/2);
second_no_colon([S1,S2|Rest], Acc) ->
acc([S1,S2], Rest, second, Acc, fun offset_hour/2);
second_no_colon(_, _) ->
error(badarg).
second_decimal(Str, Acc) ->
decimal(Str, Acc, second_decimal).
decimal([], _, _) ->
error(badarg);
decimal(Str, Acc, Key) ->
F = fun(X) when is_integer(X), X >= $0, X =< $9 ->
true;
(_) ->
false
end,
{Parts, Rest} = lists:splitwith(F, Str),
acc_float([$0,$.|Parts], Rest, Key, Acc, fun offset_hour/2).
offset_hour([], Acc) ->
datetime(Acc);
offset_hour([$Z], Acc) ->
datetime(Acc);
offset_hour([$+,H1,H2|Rest], Acc) ->
acc([H1,H2], Rest, offset_hour, Acc, fun offset_minute/2);
offset_hour([$-,H1,H2|Rest], Acc) ->
acc([H1,H2], Rest, offset_hour, [{offset_sign, -1}|Acc], fun offset_minute/2);
offset_hour(_, _) ->
error(badarg).
offset_minute([], Acc) ->
datetime(Acc);
offset_minute([$:,M1,M2], Acc) ->
acc([M1,M2], [], offset_minute, Acc, fun datetime/2);
offset_minute([M1,M2], Acc) ->
acc([M1,M2], [], offset_minute, Acc, fun datetime/2);
offset_minute(_, _) ->
error(badarg).
acc(IntStr, Rest, Key, Acc, NextF) ->
Acc1 = [{Key, list_to_integer(IntStr)}|Acc],
NextF(Rest, Acc1).
acc_float(FloatStr, Rest, Key, Acc, NextF) ->
Acc1 = [{Key, list_to_float(FloatStr)}|Acc],
NextF(Rest, Acc1).
acc_ordinal_date(D1, D2, D3, Rest, Acc, NextF) ->
Days = list_to_integer([D1, D2, D3]),
Days > 0 orelse error(badarg),
Year = ?V(year, Acc),
Year =/= undefined orelse error(badarg),
DaysInMonths = days_in_months_for_year(Year),
{ Month, Day } = unpack_ordinal_date(Days, DaysInMonths),
Acc1 = [{ month, Month }, { month_day, Day }|Acc],
NextF(Rest, Acc1).
unpack_ordinal_date(Days, DaysInMonths) -> unpack_ordinal_date(1, Days, DaysInMonths).
unpack_ordinal_date(_Month, _Days, []) -> error(badarg), { 0, 0 };
unpack_ordinal_date(_Month, Days, _DaysInMonths) when Days < 0 -> error(badarg), { 0, 0 };
unpack_ordinal_date(Month, Days, [DaysThisMonth|DaysInMonths]) ->
case Days > DaysThisMonth of
true -> unpack_ordinal_date(Month + 1, Days - DaysThisMonth, DaysInMonths);
_ -> { Month, Days }
end.
days_in_months_for_year(Year) ->
case is_leap_year(Year) of
true -> [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
false -> [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
end.
is_leap_year(Year) ->
case Year rem 100 of
0 -> Year rem 400 =:= 0;
_ -> Year rem 4 =:= 0
end.
add_decimal(Datetime, Plist) ->
HDecimal = ?V(hour_decimal, Plist, 0.0),
MDecimal = ?V(minute_decimal, Plist, 0.0),
apply_offset(Datetime, HDecimal, MDecimal, 0.0).
datetime(Plist) ->
{Date, WeekOffsetH} = make_date(Plist),
Time = {?V(hour, Plist, 0), ?V(minute, Plist, 0), ?V(second, Plist, 0)},
Datetime = add_decimal({Date, Time}, Plist),
OffsetSign = ?V(offset_sign, Plist, 1),
OffsetH = -1 * OffsetSign * ?V(offset_hour, Plist, 0),
OffsetM = -1 * OffsetSign * ?V(offset_minute, Plist, 0),
{ apply_offset(Datetime, WeekOffsetH+OffsetH, OffsetM, 0), ?V(second_decimal, Plist, 0.0) }.
datetime(_, Plist) ->
datetime(Plist).
-spec make_date (datetime_plist())
-> {Date::calendar:date(), WeekOffsetH::non_neg_integer()}.
%% @doc Return a `tuple' containing a date and, if the date is in week format,
%% an offset in hours that can be applied to the date to adjust it to midnight
%% of the day specified. If month format is used, the offset will be zero.
make_date(Plist) ->
Year = ?V(year, Plist),
Year =/= undefined orelse error(badarg),
make_date(Year, ?V(month, Plist, 1), ?V(week, Plist), Plist).
-spec make_date (non_neg_integer(),
maybe(pos_integer()),
maybe(pos_integer()),
datetime_plist())
-> {calendar:date(), non_neg_integer()}.
%% @doc Return a `tuple' containing a date and - if the date is in week format
%% (i.e., `Month' is undefined, `Week' is not) - an offset in hours that can be
%% applied to the date to adjust it to midnight of the day specified. If month
%% format is used (i.e., `Week' is undefined, `Month' is not), the offset will
%% be zero.
make_date(Year, Month, undefined, Plist) ->
Date = {Year, Month, ?V(month_day, Plist, 1)},
{Date, 0};
make_date(Year, _, Week, Plist) ->
Weekday = ?V(week_day, Plist, 1),
OffsetH = ((Week-1)*7 + (Weekday-1))*24, % week/weekday offset in hours
{date_at_w01_1(Year), OffsetH}.
-spec date_at_w01_1(pos_integer()) -> calendar:date().
%% @doc Calculate the `calendar:date()' at ISO week 1, day 1 in the supplied
%% year.
date_at_w01_1(Year) ->
case calendar:day_of_the_week({Year,1,1}) of
1 -> {Year, 1, 1};
2 -> {Year-1, 12, 31};
3 -> {Year-1, 12, 30};
4 -> {Year-1, 12, 29};
5 -> {Year, 1, 4};
6 -> {Year, 1, 3};
7 -> {Year, 1, 2}
end.
-spec apply_offset (calendar:datetime(), number(), number(), number())
-> calendar:datetime().
%% @doc Add the specified number of hours, minutes and seconds to `Datetime'.
apply_offset(Datetime, H, M, S) ->
OffsetS = S + (60 * (M + (60 * H))),
Gs = round(OffsetS) + calendar:datetime_to_gregorian_seconds(Datetime),
calendar:gregorian_seconds_to_datetime(Gs).实例：
13> G = "2020-04-28T06:09:00.000Z".
"2020-04-28T06:09:00.000Z"
14> iso8601:format(iso8601:add_time(iso8601:parse(G),8,0,0)).
<<"2020-04-28T14:09:00Z">>
15>
来源：oschina
链接：https://my.oschina.net/summergao/blog/4278575