Java 将 Joda-Time DateTime - ISO 8601 格式日期转换为另一种日期格式
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Convert Joda-Time DateTime - ISO 8601 format date to another date format
提问by MChan
Inside my Java app I am using Joda-Timeto convert the app user entered date from MM/dd/yyyy to ISO 8601 format in order to save it in DB.
在我的 Java 应用程序中，我使用Joda-Time将应用程序用户输入的日期从 MM/dd/yyyy 转换为 ISO 8601 格式，以便将其保存在 DB 中。
Can someone please tell me how I can convert the ISO 8601date back to MM/dd/yyyy format using Joda-Time?
有人可以告诉我如何使用 Joda-Time将ISO 8601日期转换回 MM/dd/yyyy 格式吗？
My code convert user date to ISO 8601 date format:
我的代码将用户日期转换为 ISO 8601 日期格式：
String date1 = "05/05/2013";
DateTimeFormatter parser1 = DateTimeFormat.forPattern("MM/dd/yyyy");
DateTime dateTimeObj1 = DateTime.parse(date1,parser1);
DateTimeFormatter isoDateFormat = ISODateTimeFormat.dateTime();
String isoDateStr = isoDateFormat.print(dateTimeObj1);
System.out.println(isoDateStr);
采纳答案by Basil Bourque
Use Same Formatter
使用相同的格式化程序
You use the same DateTimeFormatterobject to parse as to print(render a string) in Joda-Time2.3.
您在Joda-Time2.3 中使用相同的 DateTimeFormatter对象来解析print（渲染字符串）。
Time Zone
时区
Note that your code neglected to address a time zone. In that case you get the JVM's default time zone. Not a good practice.
请注意，您的代码忽略了对时区的寻址。在这种情况下，您将获得 JVM 的默认时区。不是一个好习惯。
A DateTime represents both a date and a time. When parsing a string for only the date portion, the time portion is automatically set to first moment of the day. That first moment varies by time zone. So applying a different time zone gives a different result, a different point along the timeline of the Universe, a different milliseconds-since-epoch.
DateTime 表示日期和时间。仅解析日期部分的字符串时，时间部分会自动设置为当天的第一时刻。第一个时刻因时区而异。因此，应用不同的时区会产生不同的结果，沿着宇宙时间线的不同点，不同的毫秒数。
Note the call to withZonewhen defining the formatter.
请注意withZone定义格式化程序时的调用。
Strings
字符串
Keep in mind that DateTime objects are notStrings. You can generate a string representation of the date-time information contained inside a DateTime by either:
请记住，DateTime 对象不是字符串。您可以通过以下任一方式生成包含在 DateTime 中的日期时间信息的字符串表示形式：
- Call the
toStringmethod on the DateTime instance.
Every DateTime has a built-in ISO 8601formatter, used automatically by the "toString" method. - Instantiate your own
DateTimeFormatterinstance.
- 调用
toStringDateTime 实例上的方法。
每个 DateTime 都有一个内置的ISO 8601格式化程序，由“toString”方法自动使用。 - 实例化您自己的
DateTimeFormatter实例。
Both of these string-generation techniques are seen in the example code below.
在下面的示例代码中可以看到这两种字符串生成技术。
Example Code
示例代码
// Usually better to specify a time zone than rely on default.
DateTimeZone timeZone = DateTimeZone.forID( "Asia/Hong_Kong" );
DateTimeFormatter formatter = DateTimeFormat.forPattern( "MM/dd/yyyy" ).withZone( timeZone );
// Parse string into a DateTime. Define the format.
String input = "05/05/2013";
DateTime dateTime = formatter.parseDateTime( input ); // Defaults to first moment of the day.
// Render date-time as an ISO 8601 string. The "toString" method on DateTime defaults to a built-in ISO 8601 formatter.
// A DateTime object is not itself a string. But a DateTime can generate a string by calling its "toString" method.
String iso8601String = dateTime.toString();
// Parse string into a DateTime. Passing to constructor conveniently uses the built-in ISO 8601 parser built into DateTime class.
DateTime dateTime2 = new DateTime( iso8601String, timeZone );
// Render date-time as a string in a particular format.
String output = formatter.print( dateTime2 );
Rather than hard-code a specific format, you can soft-code a localized format.
您可以对本地化格式进行软编码，而不是对特定格式进行硬编码。
String outputUS = DateTimeFormat.forStyle( "S-" ).withLocale( Locale.US ).print( dateTime2 );
String outputQuébécois = DateTimeFormat.forStyle( "F-" ).withLocale( Locale.CANADA_FRENCH ).print( dateTime2 );
Dump to console…
转储到控制台...
System.out.println( "dateTime: " + dateTime ); // Implicit call to "toString" method in DateTime class generates a new string using a built-in formatter for ISO 8601 format.
System.out.println( "iso8601String: " + iso8601String );
System.out.println( "dateTime2: " + dateTime2 ); // Another implicit call to "toString" method on DateTime class. Generates a new string in ISO format.
System.out.println( "output: " + output );
When run…
运行时…
dateTime: 2013-05-05T00:00:00.000+08:00
iso8601String: 2013-05-05T00:00:00.000+08:00
dateTime2: 2013-05-05T00:00:00.000+08:00
output: 05/05/2013
String Is Not a Date-Time
字符串不是日期时间
Do not think of date-time objects as strings.
不要将日期时间对象视为字符串。
A DateTimehas no format. That class can parse a String in ISO 8601 format to instantiate a date-time object. Likewise a DateTimeFormattercan parse a String to instantiate a date-time object.
ADateTime没有格式。该类可以解析 ISO 8601 格式的字符串以实例化日期时间对象。同样，DateTimeFormatter可以解析 String 以实例化日期时间对象。
Going the opposite direction, a DateTimehas a toStringimplementation that generates a String representation of the date-time object's value. Likewise a DateTimeFormattercan generate a String representation of the date-time object's value.
相反，aDateTime有一个toString实现，它生成日期时间对象值的字符串表示。同样， aDateTimeFormatter可以生成日期时间对象值的字符串表示。
In all these cases the String representation is entirely different and separate from the date-time object.
在所有这些情况下，字符串表示完全不同并且与日期时间对象分开。
