Add DateTimeUtils conversion methods

util/src/main/java/google/registry/util/DateTimeUtils.java

@@ -19,6 +19,8 @@
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Ordering;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
 import org.joda.time.DateTime;
 import org.joda.time.DateTimeZone;
 
@@ -86,4 +88,23 @@ public static DateTime leapSafeSubtractYears(DateTime now, int years) {
     checkArgument(years >= 0);
     return years == 0 ? now : now.minusYears(1).minusYears(years - 1);
   }
+
+  /**
+   * Converts a Joda {@link DateTime} object to an equivalent java.time {@link ZonedDateTime}
+   * object.
+   */
+  public static ZonedDateTime toZonedDateTime(DateTime dateTime) {
+    java.time.Instant instant = java.time.Instant.ofEpochMilli(dateTime.getMillis());
+    return ZonedDateTime.ofInstant(instant, ZoneId.of(dateTime.getZone().getID()));
+  }
+
+  /**
+   * Converts a java.time {@link ZonedDateTime} object to an equivalent Joda {@link DateTime}
+   * object.
+   */
+  public static DateTime toJodaDateTime(ZonedDateTime zonedDateTime) {
+    return new DateTime(
+        zonedDateTime.toInstant().toEpochMilli(),
+        DateTimeZone.forID(zonedDateTime.getZone().getId()));
+  }
 }

util/src/test/java/google/registry/util/DateTimeUtilsTest.java

@@ -24,9 +24,14 @@
 import static google.registry.util.DateTimeUtils.latestOf;
 import static google.registry.util.DateTimeUtils.leapSafeAddYears;
 import static google.registry.util.DateTimeUtils.leapSafeSubtractYears;
+import static google.registry.util.DateTimeUtils.toJodaDateTime;
+import static google.registry.util.DateTimeUtils.toZonedDateTime;
 
 import com.google.common.collect.ImmutableList;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
 import org.joda.time.DateTime;
+import org.joda.time.DateTimeZone;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -94,4 +99,36 @@ public void testFailure_earliestOfEmpty() {
   public void testFailure_latestOfEmpty() {
     assertThrows(IllegalArgumentException.class, () -> earliestOf(ImmutableList.of()));
   }
+
+  @Test
+  public void testSuccess_toZonedDateTime() {
+    DateTime dateTime = DateTime.now(DateTimeZone.UTC);
+    ZonedDateTime zonedDateTime = toZonedDateTime(dateTime);
+    assertThat(zonedDateTime.toInstant().toEpochMilli()).isEqualTo(dateTime.getMillis());
+    assertThat(zonedDateTime.getZone().getId()).isEqualTo("UTC");
+  }
+
+  @Test
+  public void testSuccess_toZonedDateTime_preservesTimeZone() {
+    DateTime dateTime = DateTime.now(DateTimeZone.forID("America/Los_Angeles"));
+    ZonedDateTime zonedDateTime = toZonedDateTime(dateTime);
+    assertThat(zonedDateTime.toInstant().toEpochMilli()).isEqualTo(dateTime.getMillis());
+    assertThat(zonedDateTime.getZone().getId()).isEqualTo("America/Los_Angeles");
+  }
+
+  @Test
+  public void testSuccess_toJodaDateTime() {
+    ZonedDateTime zonedDateTime = ZonedDateTime.now(ZoneId.of("UTC"));
+    DateTime dateTime = toJodaDateTime(zonedDateTime);
+    assertThat(dateTime.getMillis()).isEqualTo(zonedDateTime.toInstant().toEpochMilli());
+    assertThat(dateTime.getZone().getID()).isEqualTo("UTC");
+  }
+
+  @Test
+  public void testSuccess_toJodaDateTime_preservesTimeZone() {
+    ZonedDateTime zonedDateTime = ZonedDateTime.now(ZoneId.of("America/Los_Angeles"));
+    DateTime dateTime = toJodaDateTime(zonedDateTime);
+    assertThat(dateTime.getMillis()).isEqualTo(zonedDateTime.toInstant().toEpochMilli());
+    assertThat(dateTime.getZone().getID()).isEqualTo("America/Los_Angeles");
+  }
 }