使用joda时间将一个时区转换为另一个时区 [英] convert one time zone to another using joda time

问题描述

有一个国家的下拉菜单，用户将选择国家，然后是时区下拉，用户将选择用户所选择的国家/地区可用的时区，然后用户将进入当地日期（例如：2014年12月26日）和时间（23:11）（24小时），此输入的日期和时间是所选国家和时区。
现在我必须将这个日期和时间转换为GMT时区。如何使用joda时间来执行此操作？

there is a form having a drop down for country ,user will select the country ,then there is a drop down for time zone ,user will select the time zone which are available in country selected by the user.Then user will enter the local date( eg: 26-Dec-2014) and time( 23:11)(24 hours time) this entered date and time is for the selected country and time zone. now i have to convert this date and time to GMT time zone. how can i do this using joda time

如何计算夏令时（DST）？

how the daylight saving time(DST) will be calculate?

我已经做了一个接收参数的函数，从时区到时区，日期

i have made a function which accepts the parameters as from time zone,to time zone,date

public static String convertTimeZones( String fromTimeZoneString, 
             String toTimeZoneString, String fromDateTime) {
         DateTimeZone fromTimeZone = DateTimeZone.forID(fromTimeZoneString);
         DateTimeZone toTimeZone = DateTimeZone.forID(toTimeZoneString);
         DateTime dateTime = new DateTime(fromDateTime, fromTimeZone);

         DateTimeFormatter outputFormatter 
            = DateTimeFormat.forPattern("dd-MMM-yyyy HH:mm").withZone(toTimeZone);
        return outputFormatter.print(dateTime);
    }

我想以日期格式（24-Feb -2014 12:34）但是不采取这种格式

i want to pass the date to this function in a format (24-Feb-2014 12:34) but it is not taking this format

推荐答案

//so we can get the local date
//UTC = true, translate from UTC time to local
//UTC = false, translate from local to UTC

public static String formatUTCToLocalAndBackTime(String datetime, boolean UTC) { 
    String returnTimeDate = "";
    DateTime dtUTC = null;
    DateTimeZone timezone = DateTimeZone.getDefault();
    DateTimeFormatter formatDT = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm:ss");
    DateTime dateDateTime1 = formatDT.parseDateTime(datetime);
    DateTime now = new DateTime();
    DateTime nowUTC = new LocalDateTime(now).toDateTime(DateTimeZone.UTC);
    long instant = now.getMillis();
    long instantUTC = nowUTC.getMillis();
    long offset = instantUTC - instant;

    if (UTC) { 
        //convert to local time
        dtUTC = dateDateTime1.withZoneRetainFields(DateTimeZone.UTC);
        //dtUTC = dateDateTime1.toDateTime(timezone);
        dtUTC = dtUTC.plusMillis((int) offset);
    } else { 
        //convert to UTC time
        dtUTC = dateDateTime1.withZoneRetainFields(timezone);
        dtUTC = dtUTC.minusMillis((int) offset);        
    }

    returnTimeDate = dtUTC.toString(formatDT);



    return returnTimeDate;
}

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