我有一个表示日期的字符串。
String date_s = "2011-01-18 00:00:00.0";
我想把它转换成一个日期,并以YYYY-MM-DD格式输出。
2011-01-18
我怎样才能做到这一点呢?
好吧,根据我在下面找到的答案,以下是我尝试过的一些方法:
String date_s = " 2011-01-18 00:00:00.0";
SimpleDateFormat dt = new SimpleDateFormat("yyyyy-mm-dd hh:mm:ss");
Date date = dt.parse(date_s);
SimpleDateFormat dt1 = new SimpleDateFormat("yyyyy-mm-dd");
System.out.println(dt1.format(date));
但是它输出02011-00-1而不是所需的2011-01-18。我做错了什么?
答案当然是创建一个SimpleDateFormat对象,并使用它来解析“字符串到日期”并将“日期到字符串”格式化。如果您已经尝试了SimpleDateFormat,它没有工作,那么请显示您的代码和您可能收到的任何错误。
附录:String格式中的“mm”与“mm”不一样。用MM表示月,用MM表示分钟。另外,yyyyy和yyyy也不一样。例如,:
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class FormateDate {
public static void main(String[] args) throws ParseException {
String date_s = "2011-01-18 00:00:00.0";
// *** note that it's "yyyy-MM-dd hh:mm:ss" not "yyyy-mm-dd hh:mm:ss"
SimpleDateFormat dt = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Date date = dt.parse(date_s);
// *** same for the format String below
SimpleDateFormat dt1 = new SimpleDateFormat("yyyy-MM-dd");
System.out.println(dt1.format(date));
}
}
其他答案是正确的,基本上你在你的图案中有错误数量的“y”字符。
时区
还有一个问题,你没有提到时区。如果你指的是UTC,那么你应该这么说。如果不是,说明答案不完整。如果您只需要日期部分而不需要时间,那么没有问题。但是如果您要做的进一步工作可能涉及到时间,那么您应该指定一个时区。
乔达时间
下面是相同类型的代码,但是使用了第三方开源的Joda-Time 2.3库
// © 2013 Basil Bourque. This source code may be used freely forever by anyone taking full responsibility for doing so.
String date_s = "2011-01-18 00:00:00.0";
org.joda.time.format.DateTimeFormatter formatter = org.joda.time.format.DateTimeFormat.forPattern( "yyyy-MM-dd' 'HH:mm:ss.SSS" );
// By the way, if your date-time string conformed strictly to ISO 8601 including a 'T' rather than a SPACE ' ', you could
// use a formatter built into Joda-Time rather than specify your own: ISODateTimeFormat.dateHourMinuteSecondFraction().
// Like this:
//org.joda.time.DateTime dateTimeInUTC = org.joda.time.format.ISODateTimeFormat.dateHourMinuteSecondFraction().withZoneUTC().parseDateTime( date_s );
// Assuming the date-time string was meant to be in UTC (no time zone offset).
org.joda.time.DateTime dateTimeInUTC = formatter.withZoneUTC().parseDateTime( date_s );
System.out.println( "dateTimeInUTC: " + dateTimeInUTC );
System.out.println( "dateTimeInUTC (date only): " + org.joda.time.format.ISODateTimeFormat.date().print( dateTimeInUTC ) );
System.out.println( "" ); // blank line.
// Assuming the date-time string was meant to be in Kolkata time zone (formerly known as Calcutta). Offset is +5:30 from UTC (note the half-hour).
org.joda.time.DateTimeZone kolkataTimeZone = org.joda.time.DateTimeZone.forID( "Asia/Kolkata" );
org.joda.time.DateTime dateTimeInKolkata = formatter.withZone( kolkataTimeZone ).parseDateTime( date_s );
System.out.println( "dateTimeInKolkata: " + dateTimeInKolkata );
System.out.println( "dateTimeInKolkata (date only): " + org.joda.time.format.ISODateTimeFormat.date().print( dateTimeInKolkata ) );
// This date-time in Kolkata is a different point in the time line of the Universe than the dateTimeInUTC instance created above. The date is even different.
System.out.println( "dateTimeInKolkata adjusted to UTC: " + dateTimeInKolkata.toDateTime( org.joda.time.DateTimeZone.UTC ) );
运行时……
dateTimeInUTC: 2011-01-18T00:00:00.000Z
dateTimeInUTC (date only): 2011-01-18
dateTimeInKolkata: 2011-01-18T00:00:00.000+05:30
dateTimeInKolkata (date only): 2011-01-18
dateTimeInKolkata adjusted to UTC: 2011-01-17T18:30:00.000Z