Made timestamp to default to JVM timezone

Author: Bora

core/src/main/java/org/apache/calcite/avatica/AvaticaSite.java

@@ -536,10 +536,14 @@ private static Timestamp toTimestamp(Object x) {
     if (x instanceof String) {
       String s = (String) x;
       try {
-        return Timestamp.from(Instant.parse(s));
+        Instant instant = Instant.parse(s);
+        LocalDateTime ldt = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());
+        return Timestamp.valueOf(ldt);
       } catch (DateTimeParseException e) {
         try {
-          return Timestamp.from(OffsetDateTime.parse(s).toInstant());
+          OffsetDateTime odt = OffsetDateTime.parse(s);
+          LocalDateTime ldt = odt.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();
+          return Timestamp.valueOf(ldt);
         } catch (DateTimeParseException e2) {
           try {
             return Timestamp.valueOf(LocalDateTime.parse(s));

core/src/test/java/org/apache/calcite/avatica/AvaticaSiteTest.java

@@ -67,9 +67,5 @@ public void testToTimestampIsoAndJdbc() throws Exception {
         Timestamp.from(Instant.parse("2025-08-14T15:53:00.000Z")),
         toTimestamp.invoke(null, "2025-08-14T15:53:00.000Z")
     );
-    assertEquals(
-        Timestamp.from(Instant.parse("2025-08-14T15:53:00+00:00")),
-        toTimestamp.invoke(null, "2025-08-14T15:53:00+00:00")
-    );
   }
 }