Update DateTimeUtils#parse to support date strings

CHANGELOG.md

@@ -34,6 +34,9 @@ will use `Uniqueness.NONE`. This class's documentation was also updated to provi
 Updated `AttributeDefinition.toString()` to print a JSON model of the object to be consistent with
 all other SCIM objects in the library.
 
+Updated `DateTimeUtils.parse()` to support date strings without timestamps (e.g., "1970-01-01").
+The time values will always be set to the start of the day.
+
 ## 6.0.0 - 2026-May-11
 The UnboundID SCIM SDK has been updated to use version 3 of the Jackson library (this release ships
 with v3.1.3). This change aligns the SCIM SDK with HTTP libraries such as Spring Framework 7/Spring

scim2-sdk-common/src/main/java/com/unboundid/scim2/common/utils/DateTimeUtils.java

@@ -32,21 +32,35 @@
 package com.unboundid.scim2.common.utils;
 
 import com.unboundid.scim2.common.annotations.NotNull;
-import java.time.DateTimeException;
+import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.time.ZoneOffset;
 import java.time.temporal.ChronoUnit;
+import java.time.temporal.TemporalAccessor;
+import java.time.temporal.TemporalQueries;
 import java.util.Calendar;
 import java.util.Date;
+import java.util.Objects;
 import java.util.TimeZone;
 
+import static java.time.format.DateTimeFormatter.ISO_DATE;
 import static java.time.format.DateTimeFormatter.ISO_OFFSET_DATE_TIME;
 
 /**
  * Utility methods for handling SCIM 2 DateTime values. The SCIM 2 DateTime
  * type is defined as a valid {@code xsd:dateTime} in
  * <a href="https://datatracker.ietf.org/doc/html/rfc7643#section-2.3.5">
  * RFC 7643, section 2.3.5</a>.
+ * <br><br>
+ *
+ * This class is primarily used during JSON deserialization of date-time values
+ * within this SDK. However, it may be used as a general utility class to
+ * perform conversions between date-time strings (e.g., "1970-01-01T00:00:00Z")
+ * and Java objects. The primary entry points to this class are:
+ * <ul>
+ *   <li> {@link #parse(String)}: Converts a timestamp string to a Java object.
+ *   <li> {@link #format(Calendar) format()}: Converts an object to a string.
+ * </ul>
  */
 public final class DateTimeUtils
 {
@@ -135,31 +149,21 @@ public static String format(@NotNull final Calendar calendar)
    * @param dateStr A SCIM 2 DateTime string.
    * @return The DateTime string as a Calendar value.
    * @throws IllegalArgumentException if the string cannot be parsed as an
-   * xsd:dateTime value.
+   *                                  {@code xsd:dateTime} value.
    */
   @NotNull
   public static Calendar parse(@NotNull final String dateStr)
       throws IllegalArgumentException
   {
-    OffsetDateTime parsedTime;
-    try
-    {
-      parsedTime = OffsetDateTime.parse(dateStr);
-    }
-    catch (DateTimeException e)
-    {
-      // Re-throw as an IllegalArgumentException for backward compatibility with
-      // previous releases of the SCIM SDK.
-      throw new IllegalArgumentException(e);
-    }
+    OffsetDateTime parsedTime = asOffsetDateTime(dateStr);
 
     // In previous releases, the default region was "GMT+00:00".
     ZoneOffset offset = parsedTime.getOffset();
     TimeZone zone = USE_GMT_CALENDARS && offset.equals(ZoneOffset.ofHours(0))
         ? GMT : TimeZone.getTimeZone(offset);
 
     Calendar calendar = Calendar.getInstance(zone);
-    calendar.setTime(Date.from(parsedTime.toInstant()));
+    calendar.setTimeInMillis(parsedTime.toInstant().toEpochMilli());
     return calendar;
   }
 
@@ -180,4 +184,38 @@ public static Calendar parse(final long timestampMillis)
     c.setTimeInMillis(timestampMillis);
     return c;
   }
+
+  /**
+   * Converts the provided string timestamp into a Java object.
+   */
+  @NotNull
+  private static OffsetDateTime asOffsetDateTime(@NotNull final String dateStr)
+      throws IllegalArgumentException
+  {
+    Exception original;
+    try
+    {
+      // Parse timestamps of the form: 1970-01-01T00:00:00Z
+      return OffsetDateTime.parse(dateStr);
+    }
+    catch (Exception e)
+    {
+      original = e;
+    }
+
+    try
+    {
+      // Fall back to a date parser without a time: 1970-01-01
+      TemporalAccessor parsedDate = ISO_DATE.parse(dateStr);
+      ZoneOffset offset = Objects.requireNonNullElse(
+          parsedDate.query(TemporalQueries.offset()), ZoneOffset.UTC);
+
+      return LocalDate.from(parsedDate).atStartOfDay().atOffset(offset);
+    }
+    catch (Exception e)
+    {
+      // Use the original exception, as it is more likely to have relevant info.
+      throw new IllegalArgumentException(original);
+    }
+  }
 }