Date list improvements

src/main/java/net/fortuna/ical4j/model/DateList.java

@@ -53,6 +53,9 @@ public class DateList<T extends Temporal> implements Serializable {
 
 	private static final long serialVersionUID = -3700862452550012357L;
 
+    @SuppressWarnings("rawtypes")
+    public static final DateList EMPTY_LIST = new DateList();
+
     private final List<TemporalAdapter<T>> dates;
 
     /**
@@ -65,12 +68,21 @@ public DateList() {
     /**
      * Constructs a new date list of the specified type containing
      * the dates in the specified list.
-     * @param list a list of dates to include in the new list
+     * @param dates a list of dates to include in the new list
      */
-    public DateList(final List<TemporalAdapter<T>> list) {
-        this.dates = list;
+    public DateList(final T...dates) {
+        this.dates = Arrays.stream(dates).map(TemporalAdapter::new).collect(Collectors.toList());
     }
 
+    public DateList(TimeZoneRegistry timeZoneRegistry, T...dates) {
+        this.dates = Arrays.stream(dates).map(date -> new TemporalAdapter<>(date, timeZoneRegistry))
+                .collect(Collectors.toList());
+    }
+
+    private DateList(List<TemporalAdapter<T>> dates) {
+        this.dates = dates;
+    }
+
     /**
      * Parse a string representation of a date/time list.
      *
@@ -79,20 +91,44 @@ public DateList(final List<TemporalAdapter<T>> list) {
      * @throws DateTimeParseException
      */
     public static DateList<? extends Temporal> parse(String value) {
+        if (value == null || value.isEmpty()) {
+            return emptyList();
+        }
+
         List<TemporalAdapter<Temporal>> dates = Arrays.stream(value.split(","))
                 .parallel().map(TemporalAdapter::parse)
                 .collect(Collectors.toList());
 
         return new DateList<>(dates);
     }
 
+    public static DateList<? extends Temporal> parse(String value, ZoneId zoneId) {
+        if (value == null || value.isEmpty()) {
+            return emptyList();
+        }
+
+        List<TemporalAdapter<ZonedDateTime>> dates = Arrays.stream(value.split(","))
+                .parallel().map(s -> TemporalAdapter.parse(s, zoneId))
+                .collect(Collectors.toList());
+        return new DateList<>(dates);
+    }
+
     public static DateList<ZonedDateTime> parse(String value, TzId tzId, TimeZoneRegistry timeZoneRegistry) {
+        if (value == null || value.isEmpty()) {
+            return emptyList();
+        }
+
         List<TemporalAdapter<ZonedDateTime>> dates = Arrays.stream(value.split(","))
                 .parallel().map(s -> TemporalAdapter.parse(s, tzId, timeZoneRegistry))
                 .collect(Collectors.toList());
         return new DateList<>(dates);
     }
 
+    @SuppressWarnings("unchecked")
+    public static <T extends Temporal> DateList<T> emptyList() {
+        return (DateList<T>) EMPTY_LIST;
+    }
+
     @Override
     public String toString() {
         if (dates.isEmpty()) {

src/test/groovy/net/fortuna/ical4j/model/DateListTestSpec.groovy

@@ -0,0 +1,91 @@
+/*
+ *  Copyright (c) 2022, Ben Fortuna
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions
+ *  are met:
+ *
+ *   o Redistributions of source code must retain the above copyright
+ *  notice, this list of conditions and the following disclaimer.
+ *
+ *   o Redistributions in binary form must reproduce the above copyright
+ *  notice, this list of conditions and the following disclaimer in the
+ *  documentation and/or other materials provided with the distribution.
+ *
+ *   o Neither the name of Ben Fortuna nor the names of any other contributors
+ *  may be used to endorse or promote products derived from this software
+ *  without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ *  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ *  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ *  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ *  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ *  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ *  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ *  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ *  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ *  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ *  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+package net.fortuna.ical4j.model
+
+import net.fortuna.ical4j.model.component.VTimeZone
+import net.fortuna.ical4j.model.property.TzId
+import spock.lang.Specification
+
+import java.time.LocalDate
+import java.time.LocalDateTime
+import java.time.ZoneId
+import java.time.ZoneOffset
+import java.time.zone.ZoneRulesProvider
+
+class DateListTestSpec extends Specification {
+
+    def 'test date list string parsing'() {
+        expect: 'parsed string produces expected date list'
+        DateList.parse(value) == expectedDateList
+
+        where:
+        value               | expectedDateList
+        ''                  | DateList.emptyList()
+        '20220617'          | new DateList<>(LocalDate.of(2022, 06, 17))
+        '20220617,20220618' | new DateList<>(LocalDate.of(2022, 06, 17), LocalDate.of(2022, 06, 18))
+        '20220617T140000'   | new DateList<>(LocalDateTime.of(2022, 06, 17, 14, 0))
+        '20220617T140000Z'  | new DateList<>(LocalDateTime.of(2022, 06, 17, 14, 0).toInstant(ZoneOffset.UTC))
+    }
+
+    def 'test date list string parsing in another timezone'() {
+        expect: 'parsed string produces expected date list'
+        DateList.parse(value, ZoneId.of(zoneId)) == expectedDateList
+
+        where:
+        value               | zoneId            | expectedDateList
+        '20220617T140000'   | 'Europe/London'   | new DateList<>(LocalDateTime.of(2022, 06, 17, 14, 0).atZone(ZoneId.of('Europe/London')))
+    }
+
+    def 'test date list string parsing with a custom timezone'() {
+        given: 'a custom timezone registry'
+        TimeZoneRegistry timeZoneRegistry = new TimeZoneRegistryImpl()
+
+        and: 'a custom timezone'
+        VTimeZone vTimeZone = timeZoneRegistry.getTimeZone('Europe/Amsterdam').getVTimeZone()
+        vTimeZone.replace(new TzId('Europe/Atlantis'))
+
+        TimeZone timeZone = new TimeZone(vTimeZone)
+        timeZoneRegistry.register(timeZone)
+
+        and: 'registered zone rules provider'
+        ZoneRulesProvider.registerProvider(new ZoneRulesProviderImpl(timeZoneRegistry));
+
+        and: 'corresponding tzid parameter'
+        net.fortuna.ical4j.model.parameter.TzId tzIdParam = new net.fortuna.ical4j.model.parameter.TzId('Europe/Atlantis')
+
+        expect: 'parsed string produces expected date list'
+        DateList dateList = DateList.parse('20220617T140000', tzIdParam, timeZoneRegistry)
+        dateList.dates == new DateList<>(LocalDateTime.of(2022, 06, 17, 14, 0).atZone(timeZoneRegistry.getZoneId('Europe/Atlantis'))).dates
+    }
+}