将Java Date转换为UTC String

Question

该java.util.Date toString()方法显示本地时区的日期.

有几种常见的情况我们希望以UTC格式打印数据,包括日志,数据导出和与外部程序的通信.

• java.util.Date在UTC中创建字符串表示形式的最佳方法是什么？
• 如何用更好的toString()格式替换juDate的格式,这是不可排序的(谢谢@JonSkeet!)？

附录

我认为以自定义格式和时区打印日期的标准方法非常繁琐:

final Date date = new Date();
final String ISO_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSS zzz";
final SimpleDateFormat sdf = new SimpleDateFormat(ISO_FORMAT);
final TimeZone utc = TimeZone.getTimeZone("UTC");
sdf.setTimeZone(utc);
System.out.println(sdf.format(date));

我正在寻找一个单线像:

System.out.println(prettyPrint(date, "yyyy-MM-dd'T'HH:mm:ss.SSS zzz", "UTC"));

Answer 1

java.time

在Java 8及更高版本中,我们内置了新的java.time包(教程).灵感来自Joda-Time,由JSR 310定义,并由ThreeTen-Extra项目扩展.

最好的解决方案是对日期时间对象而不是字符串进行排序.但如果您必须使用字符串,请继续阅读.

An Instant代表时间轴上的一个时刻,基本上是UTC(有关详细信息,请参阅类doc).该toString实现DateTimeFormatter.ISO_INSTANT默认使用该格式.此格式包括所需的零,三,六或九位数字,以显示秒至纳秒精度的分数.

String output = Instant.now().toString(); // Example: '2015-12-03T10:15:30.120Z'

如果必须与旧Date类互操作,则通过添加到旧类的新方法转换为java.time或从java.time转换.示例:Date::toInstant.

myJavaUtilDate.toInstant().toString()

如果您需要在小数秒内保持一致的位数,或者您不需要小数秒,则可能需要使用备用格式化程序.

如果要截断一秒的分数,则另一个路径是使用ZonedDateTime而不是Instant调用其方法将分数更改为零.

请注意,我们必须为ZonedDateTime(因此名称)指定时区.在我们的情况下,这意味着UTC.的子类ZoneID,为UTC提供ZoneOffset了一个方便的常量.如果我们省略时区,则会隐式应用JVM的当前默认时区.

String output = ZonedDateTime.now( ZoneOffset.UTC ).withNano( 0 ).toString();  // Example: 2015-08-27T19:28:58Z

乔达时间

更新: Joda -Time项目现在处于维护模式,团队建议迁移到java.time类.

我正在寻找一个单线

使用Joda-Time 2.3库很容易.ISO 8601是默认格式.

时区

在下面的代码示例中,请注意我指定的是时区而不是默认时区.在这种情况下,我根据您的问题指定UTC.在Z上月底,口语为"祖鲁",意味着没有UTC的时区偏移.

示例代码

// import org.joda.time.*;

String output = new DateTime( DateTimeZone.UTC );

输出...

2013-12-12T18:29:50.588Z

Answer 2

根据有用的评论,我完全重建了日期格式化程序.用法应该是:

• 要短(一个班轮)
• 将一次性对象(时区,格式)表示为字符串
• 从包装盒中支持有用的,可排序的ISO格式和传统格式

如果您认为此代码有用,我可以在github中发布源代码和JAR.

用法

// The problem - not UTC
Date.toString()                      
"Tue Jul 03 14:54:24 IDT 2012"

// ISO format, now
PrettyDate.now()        
"2012-07-03T11:54:24.256 UTC"

// ISO format, specific date
PrettyDate.toString(new Date())         
"2012-07-03T11:54:24.256 UTC"

// Legacy format, specific date
PrettyDate.toLegacyString(new Date())   
"Tue Jul 03 11:54:24 UTC 2012"

// ISO, specific date and time zone
PrettyDate.toString(moonLandingDate, "yyyy-MM-dd hh:mm:ss zzz", "CST") 
"1969-07-20 03:17:40 CDT"

// Specific format and date
PrettyDate.toString(moonLandingDate, "yyyy-MM-dd")
"1969-07-20"

// ISO, specific date
PrettyDate.toString(moonLandingDate)
"1969-07-20T20:17:40.234 UTC"

// Legacy, specific date
PrettyDate.toLegacyString(moonLandingDate)
"Wed Jul 20 08:17:40 UTC 1969"

码

(此代码也是Code Review stackexchange问​​题的主题)

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

/**
 * Formats dates to sortable UTC strings in compliance with ISO-8601.
 * 
 * @author Adam Matan <adam@matan.name>
 * @see http://stackoverflow.com/questions/11294307/convert-java-date-to-utc-string/11294308
 */
public class PrettyDate {
    public static String ISO_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSS zzz";
    public static String LEGACY_FORMAT = "EEE MMM dd hh:mm:ss zzz yyyy";
    private static final TimeZone utc = TimeZone.getTimeZone("UTC");
    private static final SimpleDateFormat legacyFormatter = new SimpleDateFormat(LEGACY_FORMAT);
    private static final SimpleDateFormat isoFormatter = new SimpleDateFormat(ISO_FORMAT);
    static {
        legacyFormatter.setTimeZone(utc);
        isoFormatter.setTimeZone(utc);
    }

    /**
     * Formats the current time in a sortable ISO-8601 UTC format.
     * 
     * @return Current time in ISO-8601 format, e.g. :
     *         "2012-07-03T07:59:09.206 UTC"
     */
    public static String now() {
        return PrettyDate.toString(new Date());
    }

    /**
     * Formats a given date in a sortable ISO-8601 UTC format.
     * 
     * <pre>
     * <code>
     * final Calendar moonLandingCalendar = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
     * moonLandingCalendar.set(1969, 7, 20, 20, 18, 0);
     * final Date moonLandingDate = moonLandingCalendar.getTime();
     * System.out.println("UTCDate.toString moon:       " + PrettyDate.toString(moonLandingDate));
     * >>> UTCDate.toString moon:       1969-08-20T20:18:00.209 UTC
     * </code>
     * </pre>
     * 
     * @param date
     *            Valid Date object.
     * @return The given date in ISO-8601 format.
     * 
     */

    public static String toString(final Date date) {
        return isoFormatter.format(date);
    }

    /**
     * Formats a given date in the standard Java Date.toString(), using UTC
     * instead of locale time zone.
     * 
     * <pre>
     * <code>
     * System.out.println(UTCDate.toLegacyString(new Date()));
     * >>> "Tue Jul 03 07:33:57 UTC 2012"
     * </code>
     * </pre>
     * 
     * @param date
     *            Valid Date object.
     * @return The given date in Legacy Date.toString() format, e.g.
     *         "Tue Jul 03 09:34:17 IDT 2012"
     */
    public static String toLegacyString(final Date date) {
        return legacyFormatter.format(date);
    }

    /**
     * Formats a date in any given format at UTC.
     * 
     * <pre>
     * <code>
     * final Calendar moonLandingCalendar = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
     * moonLandingCalendar.set(1969, 7, 20, 20, 17, 40);
     * final Date moonLandingDate = moonLandingCalendar.getTime();
     * PrettyDate.toString(moonLandingDate, "yyyy-MM-dd")
     * >>> "1969-08-20"
     * </code>
     * </pre>
     * 
     * 
     * @param date
     *            Valid Date object.
     * @param format
     *            String representation of the format, e.g. "yyyy-MM-dd"
     * @return The given date formatted in the given format.
     */
    public static String toString(final Date date, final String format) {
        return toString(date, format, "UTC");
    }

    /**
     * Formats a date at any given format String, at any given Timezone String.
     * 
     * 
     * @param date
     *            Valid Date object
     * @param format
     *            String representation of the format, e.g. "yyyy-MM-dd HH:mm"
     * @param timezone
     *            String representation of the time zone, e.g. "CST"
     * @return The formatted date in the given time zone.
     */
    public static String toString(final Date date, final String format, final String timezone) {
        final TimeZone tz = TimeZone.getTimeZone(timezone);
        final SimpleDateFormat formatter = new SimpleDateFormat(format);
        formatter.setTimeZone(tz);
        return formatter.format(date);
    }
}

Answer 3

基于上面接受的答案,以下简化代码对我有用:

public class GetSync {
    public static String ISO_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSS zzz";
    private static final TimeZone utc = TimeZone.getTimeZone("UTC");
    private static final SimpleDateFormat isoFormatter = new SimpleDateFormat(ISO_FORMAT);
    static {
        isoFormatter.setTimeZone(utc);
    }

    public static String now() {
        return isoFormatter.format(new Date()).toString();
    }
}

我希望这有助于某人.