[ARROW-11114] [Java] Metadata serialization is broken for Field class

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.0
• Fix Version/s: 3.0.0
• Component/s: Java
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/27025
• Assignee: Unassigned
• Reporter: Nick Bruno
• Created: 03/Jan/21 08:07
• Updated: 11/Jan/23 08:17
• Resolved: 08/Jan/21 01:59

Description

org.apache.arrow.vector.types.pojo.Field uses asymmetric serialization and deserialization for the metadata field, causing it to fail to deserialize with the following error:

Exception in thread "main" com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of START_OBJECT tokenException in thread "main" com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of START_OBJECT token at [Source: (File); line: 10, column: 20] (through reference chain: org.apache.arrow.vector.types.pojo.Schema["fields"]->java.util.ArrayList[0]->org.apache.arrow.vector.types.pojo.Field["metadata"]) 

This is because the class serializes metadata as Map<String, String> but expects to deserialize it as List<Map<String, String>>. 

MCVE: https://gist.github.com/nbruno/983cb7faf41dc20a0810ae80fe33562d

Issue Links

• links to: GitHub Pull Request #9088