Why Is It Difficult to Parse ISO 8601 Strings in Java 8 When the Offset Lacks a Colon?

Difficulty Parsing ISO 8601 String in Java 8: Missing Colon in Offset

Java's date and time parsing functionality can be frustrating, especially when dealing with ISO 8601 formatted strings that lack a colon in the offset. Let's explore this issue and provide solutions using the new java.time API.

Problem Description:

When attempting to parse a date string like "2018-02-13T10:20:12.120 0000" using the legacy java.util.Date class, the process succeeds smoothly.

Date date = new SimpleDateFormat("yyyy-MM-dd'T'hh:mm:ss.SSSZZZ")
                      .parse("2018-02-13T10:20:12.120+0000");

However, the same format fails when using the newer ZonedDateTime class from java.time.

ZonedDateTime dateTime = ZonedDateTime.parse("2018-02-13T10:20:12.120+0000",
                   DateTimeFormatter.ofPattern("yyyy-MM-dd'T'hh:mm:ss.SSSZZZ"));

Solution:

The problem lies in using the incorrect class for parsing. Instead of ZonedDateTime, which represents a full time zone, you should use OffsetDateTime for cases involving only an offset from UTC.

OffsetDateTime odt = OffsetDateTime.parse( 
    "2018-02-13T10:20:12.120+0000" , 
    DateTimeFormatter.ofPattern( "uuuu-MM-dd'T'HH:mm:ss.SSSX" )
);

Temporary Bug Workaround:

Unfortunately, due to a bug in Java 8, you might encounter issues when parsing offset strings that omit the colon between hours and minutes. As a workaround, you can do one of the following:

1. Hack: Replace the missing colon in the input string.

   String input = "2018-02-13T10:20:12.120+0000".replace( "+0000" , "+00:00" );

2. Define Formatting Pattern: Use an explicit formatting pattern when constructing the DateTimeFormatter.

   String input = "2018-02-13T10:20:12.120+0000" ;
   DateTimeFormatter f = DateTimeFormatter.ofPattern( "uuuu-MM-dd'T'HH:mm:ss.SSSX" );

Additional Considerations:

If you need a value in UTC, extract an Instant object. For a localized time, apply a time zone using the ZonedDateTime class.

Conclusion:

By understanding the appropriate classes and handling bugs, you can effectively parse and manipulate dates in ISO 8601 format using the java.time API. Remember to utilize the newer classes whenever possible to avoid legacy date formatting issues.

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