Add typless client side GetIndexRequest calls and response class (#37778)

The HLRC client currently uses `org.elasticsearch.action.admin.indices.get.GetIndexRequest`
and `org.elasticsearch.action.admin.indices.get.GetIndexResponse` in its get index calls. Both request and
response are designed for the typed APIs, including some return types e.g. for `getMappings()` which in
the maps it returns still use a level including the type name.
In order to change this without breaking existing users of the HLRC API, this PR introduces two new request
and response objects in the `org.elasticsearch.client.indices` client package. These are used by the
IndicesClient#get and IndicesClient#exists calls now by default and support the type-less API. The old request
and response objects are still kept for use in similarly named, but deprecated methods.

The newly introduced client side classes are simplified versions of the server side request/response classes since
they don't need to support wire serialization, and only the response needs fromXContent parsing (but no
xContent-serialization, since this is the responsibility of the server-side class).
Also changing the return type of `GetIndexResponse#getMapping` to
`Map<String, MappingMetaData> getMappings()`, while it previously was returning another map
keyed by the type-name. Similar getters return simple Maps instead of the ImmutableOpenMaps that the 
server side response objects return.

Author: Christoph Büscher

client/rest-high-level/src/main/java/org/elasticsearch/client/IndicesClient.java

@@ -33,10 +33,6 @@
 import org.elasticsearch.action.admin.indices.flush.SyncedFlushRequest;
 import org.elasticsearch.action.admin.indices.forcemerge.ForceMergeRequest;
 import org.elasticsearch.action.admin.indices.forcemerge.ForceMergeResponse;
-import org.elasticsearch.action.admin.indices.get.GetIndexRequest;
-import org.elasticsearch.action.admin.indices.get.GetIndexResponse;
-import org.elasticsearch.client.indices.GetFieldMappingsRequest;
-import org.elasticsearch.client.indices.GetFieldMappingsResponse;
 import org.elasticsearch.action.admin.indices.open.OpenIndexRequest;
 import org.elasticsearch.action.admin.indices.open.OpenIndexResponse;
 import org.elasticsearch.action.admin.indices.refresh.RefreshRequest;
@@ -54,10 +50,14 @@
 import org.elasticsearch.client.indices.CreateIndexRequest;
 import org.elasticsearch.client.indices.CreateIndexResponse;
 import org.elasticsearch.client.indices.FreezeIndexRequest;
+import org.elasticsearch.client.indices.GetFieldMappingsRequest;
+import org.elasticsearch.client.indices.GetFieldMappingsResponse;
+import org.elasticsearch.client.indices.GetIndexRequest;
+import org.elasticsearch.client.indices.GetIndexResponse;
 import org.elasticsearch.client.indices.GetIndexTemplatesRequest;
+import org.elasticsearch.client.indices.GetIndexTemplatesResponse;
 import org.elasticsearch.client.indices.GetMappingsRequest;
 import org.elasticsearch.client.indices.GetMappingsResponse;
-import org.elasticsearch.client.indices.GetIndexTemplatesResponse;
 import org.elasticsearch.client.indices.IndexTemplatesExistRequest;
 import org.elasticsearch.client.indices.PutIndexTemplateRequest;
 import org.elasticsearch.client.indices.PutMappingRequest;
@@ -649,6 +649,41 @@ public void getAsync(GetIndexRequest getIndexRequest, RequestOptions options,
             GetIndexResponse::fromXContent, listener, emptySet());
     }
 
+    /**
+     * Retrieve information about one or more indexes
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-get-index.html">
+     * Indices Get Index API on elastic.co</a>
+     * @param getIndexRequest the request
+     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
+     * @return the response
+     * @throws IOException in case there is a problem sending the request or parsing back the response
+     * @deprecated This method uses an old request object which still refers to types, a deprecated feature. The method
+     * {@link #get(GetIndexRequest, RequestOptions)} should be used instead, which accepts a new request object.
+     */
+    @Deprecated
+    public org.elasticsearch.action.admin.indices.get.GetIndexResponse get(
+            org.elasticsearch.action.admin.indices.get.GetIndexRequest getIndexRequest, RequestOptions options) throws IOException {
+        return restHighLevelClient.performRequestAndParseEntity(getIndexRequest, IndicesRequestConverters::getIndex, options,
+                org.elasticsearch.action.admin.indices.get.GetIndexResponse::fromXContent, emptySet());
+    }
+
+    /**
+     * Retrieve information about one or more indexes
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-get-index.html">
+     * Indices Get Index API on elastic.co</a>
+     * @param getIndexRequest the request
+     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
+     * @param listener the listener to be notified upon request completion
+     * @deprecated This method uses an old request object which still refers to types, a deprecated feature. The method
+     * {@link #getAsync(GetIndexRequest, RequestOptions, ActionListener)} should be used instead, which accepts a new request object.
+     */
+    @Deprecated
+    public void getAsync(org.elasticsearch.action.admin.indices.get.GetIndexRequest getIndexRequest, RequestOptions options,
+            ActionListener<org.elasticsearch.action.admin.indices.get.GetIndexResponse> listener) {
+        restHighLevelClient.performRequestAsyncAndParseEntity(getIndexRequest, IndicesRequestConverters::getIndex, options,
+                org.elasticsearch.action.admin.indices.get.GetIndexResponse::fromXContent, listener, emptySet());
+    }
+
     /**
      * Force merge one or more indices using the Force Merge API.
      * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-forcemerge.html">
@@ -772,6 +807,51 @@ public void existsAsync(GetIndexRequest request, RequestOptions options, ActionL
         );
     }
 
+    /**
+     * Checks if the index (indices) exists or not.
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-exists.html">
+     * Indices Exists API on elastic.co</a>
+     * @param request the request
+     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
+     * @return the response
+     * @throws IOException in case there is a problem sending the request
+     * @deprecated This method uses an old request object which still refers to types, a deprecated feature. The method
+     * {@link #exists(GetIndexRequest, RequestOptions)} should be used instead, which accepts a new request object.
+     */
+    @Deprecated
+    public boolean exists(org.elasticsearch.action.admin.indices.get.GetIndexRequest request, RequestOptions options) throws IOException {
+        return restHighLevelClient.performRequest(
+            request,
+            IndicesRequestConverters::indicesExist,
+            options,
+            RestHighLevelClient::convertExistsResponse,
+            Collections.emptySet()
+        );
+    }
+
+    /**
+     * Asynchronously checks if the index (indices) exists or not.
+     * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-exists.html">
+     * Indices Exists API on elastic.co</a>
+     * @param request the request
+     * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
+     * @param listener the listener to be notified upon request completion
+     * @deprecated This method uses an old request object which still refers to types, a deprecated feature. The method
+     * {@link #existsAsync(GetIndexRequest, RequestOptions, ActionListener)} should be used instead, which accepts a new request object.
+     */
+    @Deprecated
+    public void existsAsync(org.elasticsearch.action.admin.indices.get.GetIndexRequest request, RequestOptions options,
+            ActionListener<Boolean> listener) {
+        restHighLevelClient.performRequestAsync(
+                request,
+                IndicesRequestConverters::indicesExist,
+                options,
+                RestHighLevelClient::convertExistsResponse,
+                listener,
+                Collections.emptySet()
+        );
+    }
+
     /**
      * Shrinks an index using the Shrink Index API.
      * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-shrink-index.html">
@@ -948,7 +1028,7 @@ public void putSettingsAsync(UpdateSettingsRequest updateSettingsRequest, Reques
             AcknowledgedResponse::fromXContent, listener, emptySet());
     }
 
-    
+
     /**
      * Puts an index template using the Index Templates API.
      * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-templates.html"> Index Templates API
@@ -957,7 +1037,7 @@ public void putSettingsAsync(UpdateSettingsRequest updateSettingsRequest, Reques
      * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
      * @return the response
      * @throws IOException in case there is a problem sending the request or parsing back the response
-     * @deprecated This old form of request allows types in mappings. Use {@link #putTemplate(PutIndexTemplateRequest, RequestOptions)} 
+     * @deprecated This old form of request allows types in mappings. Use {@link #putTemplate(PutIndexTemplateRequest, RequestOptions)}
      * instead which introduces a new request object without types.
      */
     @Deprecated
@@ -975,18 +1055,18 @@ public AcknowledgedResponse putTemplate(
      * @param putIndexTemplateRequest the request
      * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
      * @param listener the listener to be notified upon request completion
-     * @deprecated This old form of request allows types in mappings. 
-     * Use {@link #putTemplateAsync(PutIndexTemplateRequest, RequestOptions, ActionListener)} 
+     * @deprecated This old form of request allows types in mappings.
+     * Use {@link #putTemplateAsync(PutIndexTemplateRequest, RequestOptions, ActionListener)}
      * instead which introduces a new request object without types.
      */
     @Deprecated
-    public void putTemplateAsync(org.elasticsearch.action.admin.indices.template.put.PutIndexTemplateRequest putIndexTemplateRequest, 
+    public void putTemplateAsync(org.elasticsearch.action.admin.indices.template.put.PutIndexTemplateRequest putIndexTemplateRequest,
             RequestOptions options, ActionListener<AcknowledgedResponse> listener) {
         restHighLevelClient.performRequestAsyncAndParseEntity(putIndexTemplateRequest, IndicesRequestConverters::putTemplate, options,
             AcknowledgedResponse::fromXContent, listener, emptySet());
     }
-    
-    
+
+
     /**
      * Puts an index template using the Index Templates API.
      * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-templates.html"> Index Templates API
@@ -1011,7 +1091,7 @@ public AcknowledgedResponse putTemplate(
      * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
      * @param listener the listener to be notified upon request completion
      */
-    public void putTemplateAsync(PutIndexTemplateRequest putIndexTemplateRequest, 
+    public void putTemplateAsync(PutIndexTemplateRequest putIndexTemplateRequest,
             RequestOptions options, ActionListener<AcknowledgedResponse> listener) {
         restHighLevelClient.performRequestAsyncAndParseEntity(putIndexTemplateRequest, IndicesRequestConverters::putTemplate, options,
             AcknowledgedResponse::fromXContent, listener, emptySet());
@@ -1056,7 +1136,7 @@ public void validateQueryAsync(ValidateQueryRequest validateQueryRequest, Reques
      * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
      * @return the response
      * @throws IOException in case there is a problem sending the request or parsing back the response
-     * @deprecated This method uses an old response object which still refers to types, a deprecated feature. Use 
+     * @deprecated This method uses an old response object which still refers to types, a deprecated feature. Use
      * {@link #getIndexTemplate(GetIndexTemplatesRequest, RequestOptions)} instead which returns a new response object
      */
     @Deprecated
@@ -1066,7 +1146,7 @@ public org.elasticsearch.action.admin.indices.template.get.GetIndexTemplatesResp
             IndicesRequestConverters::getTemplatesWithDocumentTypes,
             options, org.elasticsearch.action.admin.indices.template.get.GetIndexTemplatesResponse::fromXContent, emptySet());
     }
-    
+
     /**
      * Gets index templates using the Index Templates API
      * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-templates.html"> Index Templates API
@@ -1081,17 +1161,17 @@ public GetIndexTemplatesResponse getIndexTemplate(GetIndexTemplatesRequest getIn
         return restHighLevelClient.performRequestAndParseEntity(getIndexTemplatesRequest,
             IndicesRequestConverters::getTemplates,
             options, GetIndexTemplatesResponse::fromXContent, emptySet());
-    }    
+    }
 
     /**
-     * Asynchronously gets index templates using the Index Templates API. The mappings will be returned in a legacy deprecated format, 
+     * Asynchronously gets index templates using the Index Templates API. The mappings will be returned in a legacy deprecated format,
      * where the mapping definition is nested under the type name.
      * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-templates.html"> Index Templates API
      * on elastic.co</a>
      * @param getIndexTemplatesRequest the request
      * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
      * @param listener the listener to be notified upon request completion
-     * @deprecated This method uses an old response object which still refers to types, a deprecated feature. Use 
+     * @deprecated This method uses an old response object which still refers to types, a deprecated feature. Use
      * {@link #getIndexTemplateAsync(GetIndexTemplatesRequest, RequestOptions, ActionListener)} instead which returns a new response object
      */
     @Deprecated
@@ -1101,7 +1181,7 @@ public void getTemplateAsync(GetIndexTemplatesRequest getIndexTemplatesRequest,
             IndicesRequestConverters::getTemplatesWithDocumentTypes,
             options, org.elasticsearch.action.admin.indices.template.get.GetIndexTemplatesResponse::fromXContent, listener, emptySet());
     }
-    
+
     /**
      * Asynchronously gets index templates using the Index Templates API
      * See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-templates.html"> Index Templates API
@@ -1110,12 +1190,12 @@ public void getTemplateAsync(GetIndexTemplatesRequest getIndexTemplatesRequest,
      * @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
      * @param listener the listener to be notified upon request completion
      */
-    public void getIndexTemplateAsync(GetIndexTemplatesRequest getIndexTemplatesRequest, RequestOptions options, 
+    public void getIndexTemplateAsync(GetIndexTemplatesRequest getIndexTemplatesRequest, RequestOptions options,
                                  ActionListener<GetIndexTemplatesResponse> listener) {
         restHighLevelClient.performRequestAsyncAndParseEntity(getIndexTemplatesRequest,
             IndicesRequestConverters::getTemplates,
             options, GetIndexTemplatesResponse::fromXContent, listener, emptySet());
-    }    
+    }
 
     /**
      * Uses the Index Templates API to determine if index templates exist