Add getSmallestWithDate factory method to ObjectId

JAVA-3683

Author: jyemin

bson/src/main/org/bson/types/ObjectId.java

@@ -74,6 +74,21 @@ public static ObjectId get() {
         return new ObjectId();
     }
 
+    /**
+     * Gets a new object id with the give date value and all other bits zeroed.
+     * <p>
+     * The returned object id will compare as less than or equal to any other object id within the same second as the given date, and
+     * less than any later date.
+     * </p>
+     *
+     * @param date the date
+     * @return the ObjectId
+     * @since 4.1
+     */
+    public static ObjectId getSmallestWithDate(final Date date) {
+        return new ObjectId(dateToTimestampSeconds(date), 0, (short) 0, 0, false);
+    }
+
     /**
      * Checks if a string could be an {@code ObjectId}.
      *

bson/src/test/unit/org/bson/types/ObjectIdTest.java

@@ -91,6 +91,16 @@ public void testBytesRoundtrip() {
         assertEquals("41d91c58988b09375cc1fe9f", expected.toString());
     }
 
+    @Test
+    public void testGetSmallestWithDate() {
+        Date date = new Date(1588467737760L);
+        byte[] expectedBytes = new byte[]{94, -82, 24, 25, 0, 0, 0, 0, 0, 0, 0, 0};
+        ObjectId objectId = ObjectId.getSmallestWithDate(date);
+        assertArrayEquals(expectedBytes, objectId.toByteArray());
+        assertEquals(date.getTime() / 1000 * 1000, objectId.getDate().getTime());
+        assertEquals(-1, objectId.compareTo(new ObjectId(date)));
+    }
+
     @Test
     public void testGetTimeZero() {
         assertEquals(0L, new ObjectId(0, 0).getDate().getTime());