fix(bigquery-jdbc): parse scientific-notation epoch TIMESTAMPs

java-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryTemporalUtility.java

@@ -150,14 +150,12 @@ public static Time boxTime(String val, ZoneId zoneId) {
    * the Calendar timezone is explicitly ignored per JDBC 4.2 spec.
    */
   public static Timestamp boxTimestamp(String val) {
-    // Check if the value is a numeric float string (e.g. "1680174859.8202269" from JSON API)
-    try {
-      if (val.indexOf('-') < 0
-          || (val.startsWith("-")
-              && val.indexOf('-', 1) < 0)) { // Quick check to ensure it's not a date string
+    // Epoch decimals never contain ':' but may contain '-' (e.g. "1.0E-6"), so key on ':'.
+    if (val.indexOf(':') < 0) {
+      try {
         return Timestamp.from(parseEpochDecimalToInstant(val));
+      } catch (NumberFormatException ignored) {
       }
-    } catch (NumberFormatException ignored) {
     }
 
     String iso = val;

java-bigquery-jdbc/src/test/java/com/google/cloud/bigquery/jdbc/BigQueryTemporalUtilityTest.java

@@ -272,6 +272,16 @@ public void testBoxTimestamp() {
     Timestamp picosIsoTs =
         BigQueryTemporalUtility.boxTimestamp("2026-08-24T15:30:45.123456789012Z");
     assertThat(picosIsoTs.getNanos()).isEqualTo(123456789);
+
+    // JSON API uses scientific notation for |t| < 1 ms
+    assertThat(BigQueryTemporalUtility.boxTimestamp("1.0E-6").toInstant())
+        .isEqualTo(Instant.parse("1970-01-01T00:00:00.000001Z"));
+    assertThat(BigQueryTemporalUtility.boxTimestamp("9.99E-4").toInstant())
+        .isEqualTo(Instant.parse("1970-01-01T00:00:00.000999Z"));
+    assertThat(BigQueryTemporalUtility.boxTimestamp("-1.0E-6").toInstant())
+        .isEqualTo(Instant.parse("1969-12-31T23:59:59.999999Z"));
+    assertThat(BigQueryTemporalUtility.boxTimestamp("-1.0E-4").toInstant())
+        .isEqualTo(Instant.parse("1969-12-31T23:59:59.999900Z"));
   }
 
   @Test

java-bigquery-jdbc/src/test/java/com/google/cloud/bigquery/jdbc/it/ITTimestampTimeZoneTest.java

@@ -73,7 +73,10 @@ public class ITTimestampTimeZoneTest extends ITBase {
           + " DATE '2025-01-01' AS d,"
           + " TIME '12:34:56' AS t,"
           + " [TIMESTAMP '2025-01-01 12:34:56.123 UTC'] AS ts_array,"
-          + " STRUCT(TIMESTAMP '2025-01-01 12:34:56.123 UTC' AS ts) AS ts_struct";
+          + " STRUCT(TIMESTAMP '2025-01-01 12:34:56.123 UTC' AS ts) AS ts_struct,"
+          // REST API sends these as scientific notation ("1.0E-6", "-1.0E-6").
+          + " TIMESTAMP '1970-01-01 00:00:00.000001 UTC' AS ts_post_epoch,"
+          + " TIMESTAMP '1969-12-31 23:59:59.999999 UTC' AS ts_pre_epoch";
 
   // Same coercion as an INSERT into a TIMESTAMP column, for TIMESTAMP and STRING parameters.
   private static final String PROBE_TIMESTAMP = "SELECT UNIX_MILLIS(CAST(? AS TIMESTAMP))";
@@ -321,7 +324,17 @@ public void testGetTimestampAndGetObject_returnMoment(String zone) throws SQLExc
               assertEquals(
                   Timestamp.from(REF),
                   rs.getObject("ts"),
-                  label(zone, "getObject must return a Timestamp of the stored moment")));
+                  label(zone, "getObject must return a Timestamp of the stored moment")),
+          () ->
+              assertEquals(
+                  Instant.parse("1970-01-01T00:00:00.000001Z"),
+                  rs.getTimestamp("ts_post_epoch").toInstant(),
+                  label(zone, "getTimestamp just after the epoch")),
+          () ->
+              assertEquals(
+                  Instant.parse("1969-12-31T23:59:59.999999Z"),
+                  rs.getTimestamp("ts_pre_epoch").toInstant(),
+                  label(zone, "getTimestamp just before the epoch")));
     }
   }
 
@@ -500,7 +513,17 @@ public void testGetString_returnsUtcDigits(String zone) throws SQLException {
               assertEquals(
                   "{\"ts\":\"2025-01-01 12:34:56.123\"}",
                   rs.getString("ts_struct"),
-                  label(zone, "getString on STRUCT<TIMESTAMP> must return UTC digits")));
+                  label(zone, "getString on STRUCT<TIMESTAMP> must return UTC digits")),
+          () ->
+              assertEquals(
+                  "1970-01-01 00:00:00.000001",
+                  rs.getString("ts_post_epoch"),
+                  label(zone, "getString just after the epoch")),
+          () ->
+              assertEquals(
+                  "1969-12-31 23:59:59.999999",
+                  rs.getString("ts_pre_epoch"),
+                  label(zone, "getString just before the epoch")));
     }
   }