GH-1293: Use floor division when splitting epoch millis into day and time

DateTimeUtils.getTimestampValue split epoch millis into an epoch day and a
time-of-day remainder using `/` and `%`, which truncate toward zero. Only the
remainder half compensated for negative input, so for any negative value that
was not an exact multiple of a day the two halves described different days and
the returned timestamp was one day later than the instant given. This is
reachable from ArrowFlightJdbcDateVectorAccessor.getDate(Calendar), where the
calendar offset shifts a day-aligned date value off that alignment, making
every pre-1970 date come back a day late.

Use Math.floorDiv and Math.floorMod for both halves, which keeps the day and
the remainder on the same day and makes the manual negative adjustment
redundant. Positive input is unaffected, since both functions agree with `/`
and `%` there.

Closes #1293.

Author: AbhishekPathania

flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/utils/DateTimeUtils.java

@@ -55,15 +55,12 @@ public static long applyCalendarOffset(long milliseconds, Calendar calendar) {
    * @return a {@link Timestamp} object representing the given Epoch millis
    */
   public static Timestamp getTimestampValue(long millisWithCalendar) {
-    long milliseconds = millisWithCalendar;
-    if (milliseconds < 0) {
-      // LocalTime#ofNanoDay only accepts positive values
-      milliseconds -= ((milliseconds / MILLIS_PER_DAY) - 1) * MILLIS_PER_DAY;
-    }
-
+    // Millis are negative before 1970, where only floor semantics keep the epoch day
+    // and the time-of-day remainder on the same day (and the remainder non-negative).
     return Timestamp.valueOf(
         LocalDateTime.of(
-            LocalDate.ofEpochDay(millisWithCalendar / MILLIS_PER_DAY),
-            LocalTime.ofNanoOfDay(TimeUnit.MILLISECONDS.toNanos(milliseconds % MILLIS_PER_DAY))));
+            LocalDate.ofEpochDay(Math.floorDiv(millisWithCalendar, MILLIS_PER_DAY)),
+            LocalTime.ofNanoOfDay(
+                TimeUnit.MILLISECONDS.toNanos(Math.floorMod(millisWithCalendar, MILLIS_PER_DAY)))));
   }
 }

flight/flight-sql-jdbc-core/src/test/java/org/apache/arrow/driver/jdbc/utils/DateTimeUtilsTest.java

@@ -95,4 +95,15 @@ public void testShouldGetTimestampNegative() {
 
     assertThat(expected, is(actual));
   }
+
+  @Test
+  public void testShouldGetTimestampNegativeNotAlignedToDay() {
+    final long epochMilli = negativeEpochMilli + 3600000L; // 1950-06-01 01:00:00 UTC
+    final Instant instant = Instant.ofEpochMilli(epochMilli);
+
+    final Timestamp expected = Timestamp.from(instant);
+    final Timestamp actual = DateTimeUtils.getTimestampValue(epochMilli);
+
+    assertThat(expected, is(actual));
+  }
 }