8347955: TimeZone methods to stream the available timezone IDs

Reviewed-by: naoto, rriggs

src/java.base/share/classes/java/util/TimeZone.java

@@ -41,6 +41,7 @@ package java.util;
 import java.io.Serializable;
 import java.time.ZoneId;
 import java.time.ZoneOffset;
+import java.util.stream.Stream;
 
 import jdk.internal.util.StaticProperty;
 import sun.util.calendar.ZoneInfo;
@@ -615,24 +616,63 @@ public abstract class TimeZone implements Serializable, Cloneable {
     /**
      * Gets the available IDs according to the given time zone offset in milliseconds.
      *
+     * @apiNote Consider using {@link #availableIDs(int)} which returns
+     * a stream of the available time zone IDs according to the given offset.
+     *
      * @param rawOffset the given time zone GMT offset in milliseconds.
      * @return an array of IDs, where the time zone for that ID has
      * the specified GMT offset. For example, "America/Phoenix" and "America/Denver"
      * both have GMT-07:00, but differ in daylight saving behavior.
      * @see #getRawOffset()
+     * @see #availableIDs(int)
      */
     public static String[] getAvailableIDs(int rawOffset) {
         return ZoneInfo.getAvailableIDs(rawOffset);
     }
 
     /**
-     * Gets all the available IDs supported.
-     * @return an array of IDs.
+     * {@return an array of the available IDs supported}
+     *
+     * @apiNote Consider using {@link #availableIDs()} which returns
+     * a stream of the available time zone IDs.
+     *
+     * @see #availableIDs()
      */
     public static String[] getAvailableIDs() {
         return ZoneInfo.getAvailableIDs();
     }
 
+    /**
+     * Gets the available IDs according to the given time zone offset in milliseconds.
+     *
+     * @implNote Unlike {@link #getAvailableIDs(int)}, this method does
+     * not create a copy of the {@code TimeZone} IDs array.
+     *
+     * @param rawOffset the given time zone GMT offset in milliseconds.
+     * @return a stream of IDs, where the time zone for that ID has
+     * the specified GMT offset. For example, "America/Phoenix" and "America/Denver"
+     * both have GMT-07:00, but differ in daylight saving behavior.
+     * @see #getRawOffset()
+     * @see #getAvailableIDs(int)
+     * @since 25
+     */
+    public static Stream<String> availableIDs(int rawOffset) {
+        return ZoneInfo.availableIDs(rawOffset);
+    }
+
+    /**
+     * {@return a stream of the available IDs supported}
+     *
+     * @implNote Unlike {@link #getAvailableIDs()}, this method does
+     * not create a copy of the {@code TimeZone} IDs array.
+     *
+     * @since 25
+     * @see #getAvailableIDs()
+     */
+    public static Stream<String> availableIDs() {
+        return ZoneInfo.availableIDs();
+    }
+
     /**
      * Gets the platform defined TimeZone ID.
      **/

src/java.base/share/classes/sun/util/calendar/ZoneInfo.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -31,6 +31,7 @@ import java.util.Date;
 import java.util.Map;
 import java.util.SimpleTimeZone;
 import java.util.TimeZone;
+import java.util.stream.Stream;
 
 /**
  * <code>ZoneInfo</code> is an implementation subclass of {@link
@@ -562,6 +563,27 @@ public class ZoneInfo extends TimeZone {
         return ZoneInfoFile.getZoneIds(rawOffset);
     }
 
+    /**
+     * Gets all available IDs supported in the Java run-time.
+     *
+     * @return a stream of time zone IDs.
+     */
+    public static Stream<String> availableIDs() {
+        return ZoneInfoFile.zoneIds();
+    }
+
+    /**
+     * Gets all available IDs that have the same value as the
+     * specified raw GMT offset.
+     *
+     * @param rawOffset the GMT offset in milliseconds. This
+     * value should not include any daylight saving time.
+     * @return a stream of time zone IDs.
+     */
+    public static Stream<String> availableIDs(int rawOffset) {
+        return ZoneInfoFile.zoneIds(rawOffset);
+    }
+
     /**
      * Gets the ZoneInfo for the given ID.
      *

src/java.base/share/classes/sun/util/calendar/ZoneInfoFile.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -45,6 +45,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.SimpleTimeZone;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.stream.Stream;
 import java.util.zip.CRC32;
 
 import jdk.internal.util.StaticProperty;
@@ -59,7 +60,7 @@ public final class ZoneInfoFile {
     /**
      * Gets all available IDs supported in the Java run-time.
      *
-     * @return a set of time zone IDs.
+     * @return an array of time zone IDs.
      */
     public static String[] getZoneIds() {
         var shortIDs = ZoneId.SHORT_IDS.keySet();
@@ -92,11 +93,35 @@ public final class ZoneInfoFile {
         // sorted list, though the specification does not
         // specify it. Keep the same behavior for better
         // compatibility.
-        String[] list = ids.toArray(new String[ids.size()]);
+        String[] list = ids.toArray(new String[0]);
         Arrays.sort(list);
         return list;
     }
 
+    /**
+     * Gets all available IDs supported in the Java run-time.
+     *
+     * @return a stream of time zone IDs.
+     */
+    public static Stream<String> zoneIds() {
+        return Stream.concat(Arrays.stream(regions),
+                ZoneId.SHORT_IDS.keySet().stream());
+    }
+
+    /**
+     * Gets all available IDs that have the same value as the
+     * specified raw GMT offset.
+     *
+     * @param rawOffset  the GMT offset in milliseconds. This
+     *                   value should not include any daylight saving time.
+     * @return a stream of time zone IDs.
+     */
+    public static Stream<String> zoneIds(int rawOffset) {
+        return zoneIds()
+                .filter(id -> getZoneInfo(id).getRawOffset() == rawOffset)
+                .sorted(); // Sort the IDs, see getZoneIds(int)
+    }
+
     public static ZoneInfo getZoneInfo(String zoneId) {
         if (zoneId == null) {
             return null;

src/java.base/share/classes/sun/util/cldr/CLDRTimeZoneNameProviderImpl.java

@@ -55,7 +55,7 @@ public class CLDRTimeZoneNameProviderImpl extends TimeZoneNameProviderImpl {
     private static final String NO_INHERITANCE_MARKER = "\u2205\u2205\u2205";
     private static class AVAILABLE_IDS {
         static final String[] INSTANCE =
-            Arrays.stream(ZoneInfoFile.getZoneIds())
+                ZoneInfoFile.zoneIds()
                 .sorted()
                 .toArray(String[]::new);
     }