How to Fix UnsupportedTemporalTypeException when formatting Java 8 Instant to String

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The Java 8 Instant is a single instantaneous point in the timeline used to record event time stamps.

You can add timezone value(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss z").withZone(ZoneId.systemDefault())) in order resolve the UnsupportedTemporalTypeException when formatting Instant to String

In this tutorial, you will learn possible ways to resolve the UnsupportedTemporalTypeException when formatting Instant to String in Java.

Add Time Zone to DateTimeFormatter

The DateTimeFormatter in Java is used for parsing date-time objects.

Cause of Error
When parsing Instant value to String, Instant value requires time zone value . If the time zone value is not specified, then UnsupportedTemporalTypeException will be thrown.

Code

    import java.time.Instant;  
    import java.time.format.DateTimeFormatter;  

    Instant instant = Instant.now();
    DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss z");  
    String date = dateTimeFormatter.format(instant);  
    System.out.println(date);

Output

    Exception in thread "main" java.time.temporal.UnsupportedTemporalTypeException: Unsupported field: YearOfEra
    at java.base/java.time.Instant.getLong(Instant.java:605)

In the above example, the time zone value is not set when parsing an Instant value to String, resulting in an UnsupportedTemporalTypeException.

You can add a time zone value to the DateTimeFormatter to avoid the UnsupportedTemporalTypeException error, as shown below,

Code

    import java.time.Instant;  
    import java.time.ZoneId;  
    import java.time.ZoneOffset;  
    import java.time.format.DateTimeFormatter;  
    import java.time.format.FormatStyle;  
    import java.util.Locale;

    Instant instant = Instant.now();  
    DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss z").withZone(ZoneId.systemDefault());  
    String date = dateTimeFormatter .format(instant);  
    System.out.println(date);  //2023-01-29 20:02:39 GMT    

    DateTimeFormatter dateTimeFormatter1 =  
            DateTimeFormatter.ofLocalizedDateTime( FormatStyle.FULL )  
                    .withLocale( Locale.US )  
                    .withZone( ZoneOffset.UTC );  

    String date1 = dateTimeFormatter1.format(instant);  
    System.out.println(date1);  //Sunday, January 29, 2023 at 9:30:17 PM Z

Use Predefined ISO date-time formatter

The ISO default set of date-time format can also be used to avoid the UnsupportedTemporalTypeException when parsing Instant value to String.

You can find different predefined ISO date-time formatter with examples in this tutorial, How to parse/format dates with Java 8 LocalDateTime
Code

    import java.time.Instant;  
    import java.time.ZoneId;  
    import java.time.ZoneOffset;  
    import java.time.format.DateTimeFormatter;  

    Instant instant = Instant.now();
    DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME.withZone(ZoneId.from(ZoneOffset.UTC));  
    String date = dateTimeFormatter.format(instant);  
    System.out.println(date);  //2023-01-29T21:23:05.5036373

Use LocalDateTime instead of Instant

Using LocalDateTime instead of Instant, as shown below, can also help achieve the same objective without the UnsupportedTemporalTypeException error.

Code

    import java.time.LocalDateTime;  
    import java.time.format.DateTimeFormatter;  

    LocalDateTime datetime = LocalDateTime.now();  
    String date = DateTimeFormatter.ofPattern(""yyyy-MM-dd HH:mm:ss").format(datetime);  
    System.out.println(date);  //2023-01-29 21:36:14

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