[SPARK-57855][SQL] Refactor JDBC value getters into a sealed type for readability

[Gamal72]

What changes were proposed in this pull request?

JdbcUtils.makeGetter builds a per-column reader (JDBCValueGetter) that reads a column from a ResultSet, converts it to Spark's internal representation, and stores it into an InternalRow. JDBCValueGetter was a private type alias for (ResultSet, InternalRow, Int) => Unit, so makeGetter returned an anonymous closure per column.

This PR makes the getter an explicit type:

• Adds JDBCValueGetter.scala with a private[jdbc] sealed trait JDBCValueGetter (single apply(rs, row, pos) method) and one named case per getter in its companion object — case object for stateless getters, final case class for parameterized ones — plus the getter-only helpers nullSafeConvert / arrayConverter.
• JdbcUtils.makeGetter becomes a straightforward DataType -> getter selection.

Class hierarchy (sealed):

JDBCValueGetter
 ├─ BooleanGetter, DoubleGetter, FloatGetter, IntGetter, LongGetter, ShortGetter,
 │  ByteGetter, StringGetter, RowIdGetter, BytesGetter, BinaryLongGetter,
 │  BinaryBitGetter, TimeGetter, LogicalTimeGetter, PostgresBitArrayGetter, NullGetter   (case object)
 └─ DateGetter, DecimalGetter, TimestampGetter, LogicalTimeNTZGetter, TimestampNTZGetter,
    YearMonthIntervalGetter, DayTimeIntervalGetter, ArrayGetter                          (final case class)

Each getter's body is transcribed unchanged from the corresponding match arm, and the selection order and guards in makeGetter are unchanged.

Why are the changes needed?

Because JDBCValueGetter was only a function alias, the getter chosen for a column was not expressed in the type system: makeGetter read as a large match returning indistinguishable closures, and an individual getter could not be named or referred to. Turning it into a sealed trait with one named case per getter makes the set of getters explicit and self-documenting, and reduces makeGetter to a simple selection over the column's DataType, separating "which getter to use" from "what each getter does".

Does this PR introduce any user-facing change?

No. This is an internal, behavior-preserving refactor of private (private[jdbc]) symbols; the per-column read/convert/store logic is unchanged, and there is no public API or binary-compatibility (MiMa) impact.

How was this patch tested?

Existing JDBC test suites (JDBCSuite, JDBCV2Suite, JDBCWriteSuite, JdbcUtilsSuite, etc.). This is a behavior-preserving refactor with no new behavior, so no new tests were added — the getter logic is a direct transcription of the previous match arms.

Was this patch authored or co-authored using generative AI tooling?

Generated-by: Claude Code

[cloud-fan]

0 blocking, 0 non-blocking, 1 nits.
A clean, faithful, behavior-preserving refactor. Transcription verified arm-by-arm; every old match arm matches its new getter case, including ArrayGetter's error args (dt -> arrayType) and the case object singletons being stateless.

Nits: 1 minor item (see inline comments).

[cloud-fan]

thanks, merging to master/4.x

[cloud-fan]

Merge Summary:

• merged into master 589e007
• merged into branch-4.x e993c29

Posted by merge_spark_pr.py