将DateTime对象转换为字符串

Question

I have a simple question. How can I convert an ISO-8601 Date to an String? I'm using a Date with the following format: 2019-02-05T08:21:15.000+01:00 and want to convert this Date Object to an String. I tried the following:

String startString = (String) jsonObjectMap2.get("created_on"); 
//startString = "2019-02-21T09:47:58.699004+00:00"`

DateTime start = ISODateTimeFormat.dateTimeParser().parseDateTime(startString);
DateFormat dateFormat = new SimpleDateFormat("yyyy-mm-dd'T'hh:mm:ss.SSSZ+|-hh:mm"); 
String formatedStartString = dateFormat.format(start);`

But Iam getting the following error:

java.lang.IllegalArgumentException: Cannot format given Object as a Date.

What is the corrrect form of the DateFormat? I hope you can help me, thank you in advance.

Answer 1

为什么不在DateTime对象上使用toString（）？

Answer 2

tl;dr

java.time.OffsetDateTime.parse( "2019-02-21T09:47:58.699004+00:00" )

java.time

What class is DateTime ? If you are using Joda-Time, know that the Joda-Time project is now in maintenance-mode. Its creator, Stephen Colbourne, went on to lead JSR 310 and implement the java.time classes built into Java.

No need for formatting pattern

Your input string is in standard ISO 8601 format. The java.time classes use the ISO 8601 formats by default when parsing/generating strings.

String input = "2019-02-21T09:47:58.699004+00:00" ;  // Standard ISO 8601 format.

OffsetDateTime

Your input string indicates an offset-from-UTC but not a time zone. So the appropriate class to represent this value is OffsetDateTime .

OffsetDateTime odt = OffsetDateTime.parse( input ) ;

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8 , Java SE 9 , Java SE 10 , Java SE 11 , and later - Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP… .

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval , YearWeek , YearQuarter , and more .

Answer 3

As Thomas alluded to in the comments, DateTime.format() consumes a Date object, not a DateTime object; hence the IllegalArgumentException . Judging by the format of your date you could try parsing your startString using the in-built java.time.ZonedDateTime class:

ZonedDateTime dateTime = ZonedDateTime.parse(startString) //it can parse ISO-8601 date-times

You could then format your dateTime object using java.time.DateTimeFormatter 's static ofPattern() method which takes a String pattern to apply to your date-time and returns the formatted date as a String:

String formattedDateTime = dateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'hh:mm:ss.SSSZ+|-hh:mm"));

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EDIT

As Basil pointed out, the OP's DateTime object includes a time offset which is not necessarily a time zone offset--as is represented by the ZonedDateTime class. Thus the most appropriate class to use in this scenario is OffsetDateTime which provides the same capabilities but is more suited for the given use case. See Basil Bourque's answer

Answer 4

I am not certain that this will solve your problem, But mm should be uppercase ie MM, Because MM describes months while mm describes minutes.

see the following code:

DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'hh:mm:ss.SSSZ+|- 
    hh:mm");

Answer 5

I have found the following to work for me

DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSS[XXX]");
String formatted = zonedDateTime.format(dateTimeFormatter);