Nick B created ARROW-11114:
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Summary: [Java] Metadata serialization is broken for Field class
Key: ARROW-11114
URL: https://issues.apache.org/jira/browse/ARROW-11114
Project: Apache Arrow
Issue Type: Bug
Components: Java
Affects Versions: 2.0.0
Reporter: Nick B
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:
{noformat}
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"])
{noformat}
This is because the class [serializes
metadata|https://github.com/apache/arrow/blob/dfef236f7587e4168ac1e07bd09e42d9373beb70/java/vector/src/main/java/org/apache/arrow/vector/types/pojo/Field.java#L274]
as {{Map<String, String>}} but [expects to deserialize
it|https://github.com/apache/arrow/blob/dfef236f7587e4168ac1e07bd09e42d9373beb70/java/vector/src/main/java/org/apache/arrow/vector/types/pojo/Field.java#L87]
as {{List<Map<String, String>>}}.
MCVE: [https://gist.github.com/nbruno/983cb7faf41dc20a0810ae80fe33562d]
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