Expose Arrow `Struct` columns as JDBC `STRUCT` metadata in the Flight SQL JDBC driver.

Bắt đầu tại flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/utils/SqlTypes.java, nơi ArrowType.Struct được ánh xạ tới Types.JAVA_OBJECT, và xem xét triển khai liên quan của ArrowFlightJdbcStructVectorAccessor.java. Cập nhật ánh xạ siêu dữ liệu để các cột Struct báo cáo JDBC STRUCT và xác minh rằng ResultSetMetaData trả về STRUCT và "STRUCT" cho các cột đó.

Describe the enhancement requested

Please expose Arrow Struct columns as JDBC STRUCT metadata in the Flight SQL JDBC driver.

Today, Arrow Struct is mapped to java.sql.Types.JAVA_OBJECT, which makes
ResultSetMetaData report:

• getColumnType(...) == Types.JAVA_OBJECT
• getColumnTypeName(...) == "JAVA_OBJECT"

This hides the fact that the column is structurally a JDBC STRUCT, even though the driver
already has struct-specific accessor support.

Why this matters

JDBC clients often rely on ResultSetMetaData to understand result schemas before reading
rows. When STRUCT columns are reported as JAVA_OBJECT, clients cannot distinguish:

• struct/object-like columns
• generic opaque objects

This makes schema inspection, BI tooling, ORM adapters, and generic JDBC consumers harder.

Current upstream evidence

In
flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/utils/SqlTypes.java:

• ArrowType.Struct maps to Types.JAVA_OBJECT

In flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/accessor/impl/comple x/ArrowFlightJdbcStructVectorAccessor.java:

• getStruct() is already implemented
• but getObjectClass() returns Map.class
• getObject() returns a Map

So the data path knows about structs, but metadata does not expose them as JDBC STRUCT.

Expected behavior

For Arrow Struct columns:

• ResultSetMetaData.getColumnType(...) should return java.sql.Types.STRUCT
• ResultSetMetaData.getColumnTypeName(...) should return STRUCT

Optionally, getObject() / object-class behavior could also be aligned with JDBC Struct, but
the most important gap is metadata.

Actual behavior

Arrow Struct columns are exposed as:

• Types.JAVA_OBJECT
• "JAVA_OBJECT"

Version

Observed with:

• Arrow Flight SQL JDBC driver 18.2.0

Confirmed in current upstream code and latest published artifact line:

• 19.0.0