Repurposed Fallback provider

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

@@ -104,6 +104,11 @@ public LocaleProviderAdapter.Type getAdapterType() {
         return LocaleProviderAdapter.Type.CLDR;
     }
 
+    @Override
+    public BreakIteratorProvider getBreakIteratorProvider() {
+        return null;
+    }
+
     @Override
     public CalendarDataProvider getCalendarDataProvider() {
         if (calendarDataProvider == null) {
@@ -142,6 +147,11 @@ public CalendarNameProvider getCalendarNameProvider() {
         return calendarNameProvider;
     }
 
+    @Override
+    public CollatorProvider getCollatorProvider() {
+        return null;
+    }
+
     @Override
     public TimeZoneNameProvider getTimeZoneNameProvider() {
         if (timeZoneNameProvider == null) {

src/java.base/share/classes/sun/util/locale/provider/FallbackLocaleProviderAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2023, 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
@@ -25,29 +25,19 @@
 
 package sun.util.locale.provider;
 
-import java.util.Collections;
-import java.util.Locale;
 import java.util.Set;
 
-/**
- * FallbackProviderAdapter implementation.
+/*
+ * FallbackProviderAdapter implementation. Fallback provider serves the
+ * following purposes:
  *
- * @author Naoto Sato
+ * - Locale data for ROOT, in case CLDR provider is absent.
+ * - Locale data for BreakIterator/Collator resources for all locales.
+ * - "Gan-nen" support for SimpleDateFormat (provides "FirstYear" for
+ *   Japanese locales.
  */
 public class FallbackLocaleProviderAdapter extends JRELocaleProviderAdapter {
 
-    /**
-     * Supported language tag set.
-     */
-    private static final Set<String> rootTagSet =
-        Collections.singleton(Locale.ROOT.toLanguageTag());
-
-    /**
-     * Fallback provider only provides the ROOT locale data.
-     */
-    private final LocaleResources rootLocaleResources =
-        new LocaleResources(this, Locale.ROOT);
-
     /**
      * Returns the type of this LocaleProviderAdapter
      */
@@ -56,18 +46,13 @@ public LocaleProviderAdapter.Type getAdapterType() {
         return Type.FALLBACK;
     }
 
-    @Override
-    public LocaleResources getLocaleResources(Locale locale) {
-        return rootLocaleResources;
-    }
-
     @Override
     protected Set<String> createLanguageTagSet(String category) {
-        return rootTagSet;
-    }
-
-    @Override
-    public boolean isSupportedProviderLocale(Locale locale, Set<String>langtags) {
-        return Locale.ROOT.equals(locale);
+        return switch (category) {
+            case "BreakIteratorInfo", "BreakIteratorRules", "CollationData"
+                    -> super.createLanguageTagSet(category);
+            case "FormatData" -> Set.of("ja-JP", "ja", "und");
+            default -> Set.of("und");
+        };
     }
 }

src/java.base/share/classes/sun/util/locale/provider/LocaleProviderAdapter.java

@@ -140,16 +140,12 @@ public String getTextResourcesPackage() {
             }
         }
 
-        if (!typeList.isEmpty()) {
-            // bona fide preference exists
-            if (!typeList.contains(Type.CLDR)) {
-                // Append FALLBACK as the last resort when no ResourceBundleBasedAdapter is available.
-                typeList.add(Type.FALLBACK);
-            }
-        } else {
+        if (typeList.isEmpty()) {
             // Default preference list.
             typeList.add(Type.CLDR);
         }
+        // always append FALLBACK
+        typeList.add(Type.FALLBACK);
         adapterPreference = Collections.unmodifiableList(typeList);
 
         // Emit logs, if any, after 'adapterPreference' is initialized which is needed

src/jdk.localedata/share/classes/sun/text/resources/ext/FormatData_ja.java

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 1996, 2023, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * (C) Copyright Taligent, Inc. 1996, 1997 - All Rights Reserved
+ * (C) Copyright IBM Corp. 1996 - 1999 - All Rights Reserved
+ *
+ * The original version of this source code and documentation
+ * is copyrighted and owned by Taligent, Inc., a wholly-owned
+ * subsidiary of IBM. These materials are provided under terms
+ * of a License Agreement between Taligent and Sun. This technology
+ * is protected by multiple US and International patents.
+ *
+ * This notice and attribution to Taligent may not be removed.
+ * Taligent is a registered trademark of Taligent, Inc.
+ *
+ */
+
+/*
+ * COPYRIGHT AND PERMISSION NOTICE
+ *
+ * Copyright (C) 1991-2012 Unicode, Inc. All rights reserved. Distributed under
+ * the Terms of Use in http://www.unicode.org/copyright.html.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of the Unicode data files and any associated documentation (the "Data
+ * Files") or Unicode software and any associated documentation (the
+ * "Software") to deal in the Data Files or Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, and/or sell copies of the Data Files or Software, and
+ * to permit persons to whom the Data Files or Software are furnished to do so,
+ * provided that (a) the above copyright notice(s) and this permission notice
+ * appear with all copies of the Data Files or Software, (b) both the above
+ * copyright notice(s) and this permission notice appear in associated
+ * documentation, and (c) there is clear notice in each modified Data File or
+ * in the Software as well as in the documentation associated with the Data
+ * File(s) or Software that the data or software has been modified.
+ *
+ * THE DATA FILES AND SOFTWARE ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+ * KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF
+ * THIRD PARTY RIGHTS. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR HOLDERS
+ * INCLUDED IN THIS NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL INDIRECT OR
+ * CONSEQUENTIAL DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
+ * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+ * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
+ * OF THE DATA FILES OR SOFTWARE.
+ *
+ * Except as contained in this notice, the name of a copyright holder shall not
+ * be used in advertising or otherwise to promote the sale, use or other
+ * dealings in these Data Files or Software without prior written authorization
+ * of the copyright holder.
+ */
+
+package sun.text.resources.ext;
+
+import sun.util.resources.ParallelListResourceBundle;
+
+public class FormatData_ja extends ParallelListResourceBundle {
+    /**
+     * Overrides ParallelListResourceBundle
+     */
+    @Override
+    protected final Object[][] getContents() {
+        return new Object[][] {
+            { "japanese.FirstYear",
+                new String[] {  // first year name
+                    "\u5143",   // "Gan"-nen
+                }
+            },
+        };
+    }
+}