xsavikx/jdk-zone-parsing-inconsistency

A companion repository for showcasing inconsistency in JDK `DateTimeFormatter` parsing behavior. JDK issues are https://bit.ly/JDK-8257667 and https://bit.ly/JDK-8257647.

JDK ZoneId parsing inconsistency

This repository contains a reproducible example of the Java time API usage inconsistency across different JDK versions.

The problem

The UTC time zone specified in a String with date and time is parsed to a different ZoneId in Java11+ rather than in Java8.

Consider the following pattern MM/dd/yyyy hh:mm a z used to create a DateTimeFormatter with the US locale.

When a date string such as e.g. 05/17/2021 09:23 PM UTC is parsed to a ZonedDateTime using the formatter, the ZoneId value of the ZonedDateTime is different when different JDK versions are used.

For JDK 8-10 and 12-14 the value of the ZoneId is UTC. But for JDK 11 and JDK 15 the value is equal to Etc/UTC.

Environments

Windows Server 2019, macOS 10.15, Ubuntu 18.04.

Java 11, Java 15.

Steps to reproduce

The easiest way to reproduce the issue is to clone the repository and run ./gradlew build.

Otherwise, you may follow the steps below.

1. Create DateTimeFormatter with the MM/dd/yyyy hh:mm a z pattern:

   DateTimeFormatter ZONED_FORMATTER = DateTimeFormatter.ofPattern("MM/dd/yyyy hh:mm a z", Locale.US);
   

2. Parse date-time string 05/17/2021 09:23 PM UTC to a ZonedDateTime object:

   ZonedDateTime result = ZONED_FORMATTER.parse(dateString, ZonedDateTime::from);
   

3. Check ZoneId value of the result:

   assert result.getZone().equals(ZoneId.of("UTC"));
   

Here's a full compilable example that fails in Java 11 and Java 15 environments.

final class ZonedParser {

    public static void main(String[] args) {
        DateTimeFormatter ZONED_FORMATTER = DateTimeFormatter.ofPattern("MM/dd/yyyy hh:mm a z", Locale.US);
        ZonedDateTime result = ZONED_FORMATTER.parse("05/17/2021 09:23 PM UTC", ZonedDateTime::from);
        if (!result.getZone().equals(ZoneId.of("UTC"))) {
            throw new IllegalStateException("Zone ID must be equal to `UTC`.");
        }
    }
}