Add Date to LocalDateTime conversion methods and test cases

This commit enhances the DateUtils class by adding two new methods to convert
java.util.Date to java.time.LocalDateTime, supporting both default and specified
time zones. The implementation leverages Java 8's date-time API for accurate
time zone handling, including:

- `toLocalDateTime(Date date)`: Uses the system's default time zone
- `toLocalDateTime(Date date, TimeZone tz)`: Explicitly specifies time zone via TimeZone parameter

Key improvements:
- Proper null checking with Objects.requireNonNull()
- Direct conversion via Instant and ZoneId for timezone accuracy
- Maintains parity with existing DateUtils method naming conventions

Test cases added in DateUtilsTest:
- Default time zone conversion (Asia/Shanghai example)
- Specified time zone conversion (America/New_York)
- Null input validation (throws NullPointerException)
- Daylight saving time handling (America/New_York DST case)
- Extreme time zone test (Pacific/Kiritimati, UTC+14)

These changes enable seamless integration between legacy Date APIs and modern
LocalDateTime, while ensuring robust timezone handling across different environments.

Author: yuyu1025

src/main/java/org/apache/commons/lang3/time/DateUtils.java

@@ -18,6 +18,8 @@
 
 import java.text.ParseException;
 import java.text.ParsePosition;
+import java.time.LocalDateTime;
+import java.time.ZoneId;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.Iterator;
@@ -1625,6 +1627,29 @@ public static Calendar toCalendar(final Date date, final TimeZone tz) {
         return c;
     }
 
+    /**
+     * Converts a {@link Date} into a {@link LocalDateTime}, using the default time zone.
+     * @param date the date to convert to a LocalDateTime
+     * @return the created LocalDateTime
+     * @throws NullPointerException if {@code date} is null
+     * @since 3.18
+     */
+    public static LocalDateTime toLocalDateTime(final Date date) {
+        return toLocalDateTime(date, TimeZone.getDefault());
+    }
+
+    /**
+     * Converts a {@link Date} into a {@link LocalDateTime}
+     * @param date the date to convert to a LocalDateTime
+     * @param tz the time zone of the {@code date}
+     * @return the created LocalDateTime
+     * @throws NullPointerException if {@code date} is null
+     * @since 3.18
+     */
+    public static LocalDateTime toLocalDateTime(final Date date, final TimeZone tz) {
+        return Objects.requireNonNull(date, "date").toInstant().atZone(ZoneId.of(tz.getID())).toLocalDateTime();
+    }
+
     /**
      * Truncates a date, leaving the field specified as the most
      * significant field.

src/test/java/org/apache/commons/lang3/time/DateUtilsTest.java

@@ -28,6 +28,9 @@
 import java.text.DateFormat;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
+import java.time.Instant;
+import java.time.LocalDateTime;
+import java.time.ZoneOffset;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.GregorianCalendar;
@@ -1285,6 +1288,67 @@ public void testToCalendarWithTimeZoneNull() {
         assertThrows(NullPointerException.class, () -> DateUtils.toCalendar(date1, null));
     }
 
+    @Test
+    void shouldConvertDateToLocalDateTimeUsingDefaultTimeZone() {
+        TimeZone.setDefault(TimeZone.getTimeZone("Asia/Shanghai"));
+
+        Instant instant = LocalDateTime.of(2023, 1, 1, 0, 0)
+                .atOffset(ZoneOffset.UTC)
+                .toInstant();
+        Date date = Date.from(instant);
+
+        LocalDateTime expected = LocalDateTime.of(2023, 1, 1, 8, 0);
+
+        assertEquals(expected, DateUtils.toLocalDateTime(date));
+    }
+
+    @Test
+    void shouldConvertDateToLocalDateTimeUsingSpecifiedTimeZone() {
+        Instant instant = LocalDateTime.of(2023, 1, 1, 0, 0)
+                .atOffset(ZoneOffset.UTC)
+                .toInstant();
+        Date date = Date.from(instant);
+
+        TimeZone newYorkTimeZone = TimeZone.getTimeZone("America/New_York");
+        LocalDateTime expected = LocalDateTime.of(2022, 12, 31, 19, 0);
+
+        assertEquals(expected, DateUtils.toLocalDateTime(date, newYorkTimeZone));
+    }
+
+    @Test
+    void shouldThrowNullPointerExceptionWhenDateIsNull() {
+        assertThrows(NullPointerException.class, () -> DateUtils.toLocalDateTime(null));
+        assertThrows(NullPointerException.class, () -> DateUtils.toLocalDateTime(null, TimeZone.getDefault()));
+    }
+
+    @Test
+    void shouldHandleDaylightSavingTimeCorrectly() {
+        Instant instant = LocalDateTime.of(2023, 3, 12, 7, 0)
+                .atOffset(ZoneOffset.UTC)
+                .toInstant();
+        Date date = Date.from(instant);
+
+        TimeZone newYorkTimeZone = TimeZone.getTimeZone("America/New_York");
+        LocalDateTime expected = LocalDateTime.of(2023, 3, 12, 3, 0);
+
+        assertEquals(expected, DateUtils.toLocalDateTime(date, newYorkTimeZone));
+    }
+
+    @Test
+    void shouldHandleExtremeTimeZoneCorrectly() {
+        Instant instant = LocalDateTime.of(2023, 1, 1, 0, 0)
+                .atOffset(ZoneOffset.UTC)
+                .toInstant();
+        Date date = Date.from(instant);
+
+        TimeZone extremeTimeZone = TimeZone.getTimeZone("Pacific/Kiritimati");
+        LocalDateTime expected = LocalDateTime.of(2023, 1, 1, 14, 0);
+
+        assertEquals(expected, DateUtils.toLocalDateTime(date, extremeTimeZone));
+    }
+
+
+
     /**
      * Tests various values with the trunc method
      *