在测试可在系统之间映射日期时间类型的Web服务时，我注意到在公历开始时间之前发送任何日期会导致转换为最终类型时准确性下降，最终结果总是在该范围内稍早一些几天。

我将问题缩小到确切的范围，但是我仍然无法弄清为什么要这样进行转换，从documentation中可以看出，儒略历用于公历开始前的日期时间:1582年10月15日。

问题行在从XMLGregorianCalendar到GregorianCalendar的强制转换，第78行:calendarDate = argCal.toGregorianCalendar();从第86行的calendarDate提取时间时:cal.setTime(calendarDate.getTime());时间比原定时间提前2天，即1月03日而不是1月1日，如您从以下程序的输出中看到的那样。

这是我制作的一个示例程序，用来展示类型转换过程的端到端:

import java.sql.Date;
import java.util.Calendar;
import java.util.GregorianCalendar;

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.XMLGregorianCalendar;



public class TestDateConversions {

    public static void main(String[] args)
    {
        TestDateConversions testDates = new TestDateConversions();
        try
        {
            XMLGregorianCalendar testDate1 = DatatypeFactory.newInstance().newXMLGregorianCalendar();
            testDate1.setYear(0001);
            testDate1.setMonth(01);
            testDate1.setDay(01);
            System.out.println("Start date: "+testDate1.toString() +"\n**********************");

            testDates.setXMLGregorianCalendar(testDate1);
            System.out.println("\nNull given \n"+ "**********");
            testDates.setXMLGregorianCalendar(null);
        }
        catch(Exception e)
        {
            System.out.println(e);
        }
    }


    public void setXMLGregorianCalendar(XMLGregorianCalendar argCal)
    {
        GregorianCalendar calendarDate;
        if (argCal != null)
        {
            calendarDate = argCal.toGregorianCalendar();
            System.out.println("XMLGregorianCalendar time: " + argCal.getHour() + ":"+argCal.getMinute()+":"+argCal.getSecond());
            System.out.println("XMLGregorianCalendar time(ms): "+argCal.getMillisecond());
            System.out.println("XMLGregorianCalendar -> GregorianCalendar: "+calendarDate.get(GregorianCalendar.YEAR) + "-"+(calendarDate.get(GregorianCalendar.MONTH)+1) + "-"+calendarDate.get(GregorianCalendar.DAY_OF_MONTH));
            System.out.println("!!!!PROBLEM AREA!!!!");
            Calendar cal = Calendar.getInstance();
            System.out.println("-- New Calendar instance: "+cal.get(Calendar.YEAR) + "-"+(cal.get(Calendar.MONTH)+1)+"-"+cal.get(Calendar.DAY_OF_MONTH));
            System.out.println("-- Calling Calendar.setTime(GregorianCalendar.getTime())");
            cal.setTime(calendarDate.getTime());
            System.out.println("-- calendarDate.getTime() = " + calendarDate.getTime() + " <-- time is incorrect");
            System.out.println("-- Calendar with time set from GregorianCalendar: "+cal.get(Calendar.YEAR) + "-"+(cal.get(Calendar.MONTH)+1)+"-"+cal.get(Calendar.DAY_OF_MONTH) + " <-- day is increased here");
            setCalendar(cal);
        }
        else 
        {
            setCalendar(null);
        }
    }

    public void setCalendar(Calendar argCal)
    {
        if (argCal != null)
        {
            Date date = new Date(argCal.getTimeInMillis());
            System.out.println("Calendar to Date: "+date);
            setDate(date);
        }
        else
        {
            setDate(null);
        }

    }

    public void setDate(Date argDate)
    {
        try
        {
            if (argDate == null)
            {
                Calendar cal  = new GregorianCalendar(1,0,1);
                Date nullDate = new Date(cal.getTimeInMillis());
                System.out.println("Null Calendar created: "+cal.get(Calendar.YEAR) + "-"+(cal.get(Calendar.MONTH)+1)+"-"+cal.get(Calendar.DAY_OF_MONTH));
                System.out.println("Null Date created: "+nullDate);
            }
            else 
            {
                System.out.println("Final date type: "+argDate);
            }
        }
        catch (Exception  ex)
        {
            System.out.println(ex);
        }
    }
}

最佳答案

摘自 XMLGregorianCalendar.toGregorianCalendar() JavaDoc，介绍了它们如何创建GregorianCalendar实例:

Obtain a pure Gregorian Calendar by invoking GregorianCalendar.setGregorianChange( new Date(Long.MIN_VALUE)).

Calendar calendar = Calendar.getInstance();
((GregorianCalendar) calendar).setGregorianChange(new Date(Long.MIN_VALUE));

// Get XML gregorian calendar
XMLGregorianCalendar xmlCalendar = DatatypeFactory.newInstance().newXMLGregorianCalendar();
xmlCalendar.setYear(1); // Watch for octal number representations (you had there 0001)
xmlCalendar.setMonth(1);
xmlCalendar.setDay(1);

// Convert to Calendar as it is easier to work with it
Calendar calendar = xmlCalendar.toGregorianCalendar(); // Proleptic for old dates

// Convert to default calendar (will misinterpret proleptic for Julian, but it is a workaround)
Calendar result = Calendar.getInstance();
result.setTimeZone(calendar.getTimeZone());
result.set(Calendar.YEAR, calendar.get(Calendar.YEAR));
result.set(Calendar.MONTH, calendar.get(Calendar.MONTH));
result.set(Calendar.DAY_OF_MONTH, calendar.get(Calendar.DAY_OF_MONTH));
result.set(Calendar.HOUR_OF_DAY, calendar.get(Calendar.HOUR_OF_DAY));
result.set(Calendar.MINUTE, calendar.get(Calendar.MINUTE));
result.set(Calendar.SECOND, calendar.get(Calendar.SECOND));
result.set(Calendar.MILLISECOND, calendar.get(Calendar.MILLISECOND));

System.out.println(result.getTime());

关于java - 从XMLGregorianCalendar转换为Calendar时的日期更改，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16321193/