add java reference as well

docs/source/java/index.rst

@@ -28,4 +28,4 @@ on the Arrow format and other language bindings see the :doc:`parent documentati
    vector_schema_root
    ipc
    algorithm
-   Reference (javadoc) <https://arrow.apache.org/docs/java/reference/>
+   Reference (javadoc) <reference/index>

docs/source/java/reference/index.rst

@@ -0,0 +1,21 @@
+.. Licensed to the Apache Software Foundation (ASF) under one
+.. or more contributor license agreements.  See the NOTICE file
+.. distributed with this work for additional information
+.. regarding copyright ownership.  The ASF licenses this file
+.. to you under the Apache License, Version 2.0 (the
+.. "License"); you may not use this file except in compliance
+.. with the License.  You may obtain a copy of the License at
+
+..   http://www.apache.org/licenses/LICENSE-2.0
+
+.. Unless required by applicable law or agreed to in writing,
+.. software distributed under the License is distributed on an
+.. "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+.. KIND, either express or implied.  See the License for the
+.. specific language governing permissions and limitations
+.. under the License.
+
+Java Reference (javadoc)
+========================
+
+Stub page for the Java reference docs; actual source is located in the java/ directory.