Breaking change in Avro 1.12.1 affects parquet-avro users: logical types now deserialize to different Java types

[laymain]

Summary

Avro 1.12.1 introduces a breaking change that affects parquet-avro users. Multiple logical types are now deserialized to their proper Java types instead of their underlying primitive types when using ReflectData, causing ClassCastException in existing code.

Background

• Upstream issue: https://issues.apache.org/jira/browse/AVRO-3989
• Pull request: AVRO-3989: [java] add conversion classes to default instance of SpecificData avro#3354
• Avro version affected: 1.12.1 (released as a patch version)

Problem

The fix in AVRO-3989 changed the deserialization behavior for ALL logical types. When using parquet-avro's ReflectData class, these fields now return their logical Java type objects instead of their underlying primitive types from GenericRecord.

Affected logical types and conversions:

Logical Type	Old Type (≤1.12.0)	New Type (1.12.1)
timestamp-millis	Long	Instant
timestamp-micros	Long	Instant
date	Integer	LocalDate
time-millis	Integer	LocalTime
time-micros	Long	LocalTime
local-timestamp-millis	Long	LocalDateTime
local-timestamp-micros	Long	LocalDateTime
uuid	String	UUID
decimal	ByteBuffer	BigDecimal

This breaks existing code that expects primitive values:

// This used to work in Avro 1.12.0
Long timestamp = (Long) genericRecord.get("timestamp_field");
Integer date = (Integer) genericRecord.get("date_field");
String uuid = (String) genericRecord.get("uuid_field");

// In Avro 1.12.1, all of these throw ClassCastException
// because values are now Instant, LocalDate, UUID, etc.

Impact

• Widespread breakage: Affects anyone using parquet-avro with ANY logical types
• Code that has worked for years suddenly breaks after a patch version update
• The breaking nature wasn't clearly documented in Avro's changelog
• This is a significant behavior change that affects the entire logical type system

Heads up for future avro updates

I apologize if this isn't the right place to report this, please feel free to redirect me if there's a better venue for this discussion. My main goal is to ensure that when parquet-java does consider updating Avro, the team and users are aware of this significant behavioral change.

For Current Users

If you're using parquet-avro and explicitly upgrading Avro to 1.12.1+ in your project, be aware of this breaking change. You'll need to update code that reads logical type fields from GenericRecord.