Use List convenience methods in rest actions (#52286)

This commit replaces usages of older collection utility methods with
the JDK 9 convenience method `List.of()`.

Relates #51950

client/client-benchmark-noop-api-plugin/src/main/java/org/elasticsearch/plugin/noop/action/bulk/RestNoopBulkAction.java

@@ -39,8 +39,6 @@ import org.elasticsearch.rest.action.RestBuilderListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 import static org.elasticsearch.rest.RestStatus.OK;
@@ -49,11 +47,11 @@ public class RestNoopBulkAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_noop_bulk"),
             new Route(PUT, "/_noop_bulk"),
             new Route(POST, "/{index}/_noop_bulk"),
-            new Route(PUT, "/{index}/_noop_bulk")));
+            new Route(PUT, "/{index}/_noop_bulk"));
     }
 
     @Override

client/client-benchmark-noop-api-plugin/src/main/java/org/elasticsearch/plugin/noop/action/search/RestNoopSearchAction.java

@@ -26,8 +26,6 @@ import org.elasticsearch.rest.action.RestStatusToXContentListener;
 
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -35,11 +33,11 @@ public class RestNoopSearchAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_noop_search"),
             new Route(POST, "/_noop_search"),
             new Route(GET, "/{index}/_noop_search"),
-            new Route(POST, "/{index}/_noop_search")));
+            new Route(POST, "/{index}/_noop_search"));
     }
 
     @Override

modules/ingest-common/src/main/java/org/elasticsearch/ingest/common/GrokProcessorGetAction.java

@@ -41,7 +41,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Map;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.ingest.common.IngestCommonPlugin.GROK_PATTERNS;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
@@ -120,7 +119,7 @@ public class GrokProcessorGetAction extends ActionType<GrokProcessorGetAction.Re
 
         @Override
         public List<Route> routes() {
-            return singletonList(new Route(GET, "/_ingest/processor/grok"));
+            return List.of(new Route(GET, "/_ingest/processor/grok"));
         }
 
         @Override

modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/RestMultiSearchTemplateAction.java

@@ -34,7 +34,6 @@ import java.util.List;
 import java.util.Set;
 
 import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -58,11 +57,11 @@ public class RestMultiSearchTemplateAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_msearch/template"),
             new Route(POST, "/_msearch/template"),
             new Route(GET, "/{index}/_msearch/template"),
-            new Route(POST, "/{index}/_msearch/template")));
+            new Route(POST, "/{index}/_msearch/template"));
     }
 
     @Override

modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/RestRenderSearchTemplateAction.java

@@ -29,8 +29,6 @@ import org.elasticsearch.script.ScriptType;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -38,11 +36,11 @@ public class RestRenderSearchTemplateAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_render/template"),
             new Route(POST, "/_render/template"),
             new Route(GET, "/_render/template/{id}"),
-            new Route(POST, "/_render/template/{id}")));
+            new Route(POST, "/_render/template/{id}"));
     }
 
     @Override

modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/RestSearchTemplateAction.java

@@ -34,8 +34,6 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -50,11 +48,11 @@ public class RestSearchTemplateAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_search/template"),
             new Route(POST, "/_search/template"),
             new Route(GET, "/{index}/_search/template"),
-            new Route(POST, "/{index}/_search/template")));
+            new Route(POST, "/{index}/_search/template"));
     }
 
     @Override

modules/lang-painless/src/main/java/org/elasticsearch/painless/action/PainlessContextAction.java

@@ -51,7 +51,6 @@ import java.util.Map;
 import java.util.Objects;
 import java.util.stream.Collectors;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 /**
@@ -196,7 +195,7 @@ public class PainlessContextAction extends ActionType<PainlessContextAction.Resp
 
         @Override
         public List<Route> routes() {
-            return singletonList(new Route(GET, "/_scripts/painless/_context"));
+            return List.of(new Route(GET, "/_scripts/painless/_context"));
         }
 
         @Override

modules/lang-painless/src/main/java/org/elasticsearch/painless/action/PainlessExecuteAction.java

@@ -84,8 +84,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.action.ValidateActions.addValidationError;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
@@ -568,9 +566,9 @@ public class PainlessExecuteAction extends ActionType<PainlessExecuteAction.Resp
 
         @Override
         public List<Route> routes() {
-            return unmodifiableList(asList(
+            return List.of(
                 new Route(GET, "/_scripts/painless/_execute"),
-                new Route(POST, "/_scripts/painless/_execute")));
+                new Route(POST, "/_scripts/painless/_execute"));
         }
 
         @Override

modules/rank-eval/src/main/java/org/elasticsearch/index/rankeval/RestRankEvalAction.java

@@ -31,8 +31,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -94,11 +92,11 @@ public class RestRankEvalAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/" + ENDPOINT),
             new Route(POST, "/" + ENDPOINT),
             new Route(GET, "/{index}/" + ENDPOINT),
-            new Route(POST, "/{index}/" + ENDPOINT)));
+            new Route(POST, "/{index}/" + ENDPOINT));
     }
 
     @Override

modules/reindex/src/main/java/org/elasticsearch/index/reindex/RestDeleteByQueryAction.java

@@ -28,7 +28,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.function.Consumer;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestDeleteByQueryAction extends AbstractBulkByQueryRestHandler<DeleteByQueryRequest, DeleteByQueryAction> {
@@ -39,7 +38,7 @@ public class RestDeleteByQueryAction extends AbstractBulkByQueryRestHandler<Dele
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/{index}/_delete_by_query"));
+        return List.of(new Route(POST, "/{index}/_delete_by_query"));
     }
 
     @Override

modules/reindex/src/main/java/org/elasticsearch/index/reindex/RestReindexAction.java

@@ -26,7 +26,6 @@ import org.elasticsearch.rest.RestRequest;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.common.unit.TimeValue.parseTimeValue;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -41,7 +40,7 @@ public class RestReindexAction extends AbstractBaseReindexRestHandler<ReindexReq
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/_reindex"));
+        return List.of(new Route(POST, "/_reindex"));
     }
 
     @Override

modules/reindex/src/main/java/org/elasticsearch/index/reindex/RestRethrottleAction.java

@@ -28,8 +28,6 @@ import org.elasticsearch.tasks.TaskId;
 import java.util.List;
 import java.util.function.Supplier;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.action.admin.cluster.RestListTasksAction.listTasksResponseListener;
 
@@ -42,10 +40,10 @@ public class RestRethrottleAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_update_by_query/{taskId}/_rethrottle"),
             new Route(POST, "/_delete_by_query/{taskId}/_rethrottle"),
-            new Route(POST, "/_reindex/{taskId}/_rethrottle")));
+            new Route(POST, "/_reindex/{taskId}/_rethrottle"));
     }
 
     @Override

modules/reindex/src/main/java/org/elasticsearch/index/reindex/RestUpdateByQueryAction.java

@@ -34,7 +34,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.function.Consumer;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.script.Script.DEFAULT_SCRIPT_LANG;
 
@@ -46,7 +45,7 @@ public class RestUpdateByQueryAction extends AbstractBulkByQueryRestHandler<Upda
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/{index}/_update_by_query"));
+        return List.of(new Route(POST, "/{index}/_update_by_query"));
     }
 
     @Override

plugins/examples/rest-handler/src/main/java/org/elasticsearch/example/resthandler/ExampleCatAction.java

@@ -27,8 +27,6 @@ import org.elasticsearch.rest.action.cat.RestTable;
 
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -39,9 +37,9 @@ public class ExampleCatAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cat/example"),
-            new Route(POST, "/_cat/example")));
+            new Route(POST, "/_cat/example"));
     }
 
     @Override

qa/die-with-dignity/src/main/java/org/elasticsearch/RestDieWithDignityAction.java

@@ -25,7 +25,6 @@ import org.elasticsearch.rest.RestRequest;
 
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestDieWithDignityAction extends BaseRestHandler {
@@ -34,7 +33,7 @@ public class RestDieWithDignityAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_die_with_dignity"));
+        return List.of(new Route(GET, "/_die_with_dignity"));
     }
 
     @Override

qa/smoke-test-http/src/test/java/org/elasticsearch/http/TestResponseHeaderRestAction.java

@@ -27,14 +27,13 @@ import org.elasticsearch.rest.RestStatus;
 
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class TestResponseHeaderRestAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_protected"));
+        return List.of(new Route(GET, "/_protected"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/RestFieldCapabilitiesAction.java

@@ -29,8 +29,6 @@ import org.elasticsearch.rest.RestRequest;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -38,11 +36,11 @@ public class RestFieldCapabilitiesAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_field_caps"),
             new Route(POST, "/_field_caps"),
             new Route(GET, "/{index}/_field_caps"),
-            new Route(POST, "/{index}/_field_caps")));
+            new Route(POST, "/{index}/_field_caps"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/RestMainAction.java

@@ -33,8 +33,6 @@ import org.elasticsearch.rest.RestStatus;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.HEAD;
 
@@ -42,9 +40,9 @@ public class RestMainAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/"),
-            new Route(HEAD, "/")));
+            new Route(HEAD, "/"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestAddVotingConfigExclusionAction.java

@@ -31,7 +31,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestAddVotingConfigExclusionAction extends BaseRestHandler {
@@ -45,7 +44,7 @@ public class RestAddVotingConfigExclusionAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/_cluster/voting_config_exclusions/{node_name}"));
+        return List.of(new Route(POST, "/_cluster/voting_config_exclusions/{node_name}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestCancelTasksAction.java

@@ -31,8 +31,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.function.Supplier;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.action.admin.cluster.RestListTasksAction.listTasksResponseListener;
 
@@ -51,8 +49,8 @@ public class RestCancelTasksAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(new Route(POST, "/_tasks/_cancel"),
+        return List.of(new Route(POST, "/_tasks/_cancel"),
-            new Route(POST, "/_tasks/{task_id}/_cancel")));
+            new Route(POST, "/_tasks/{task_id}/_cancel"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestCleanupRepositoryAction.java

@@ -28,7 +28,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.client.Requests.cleanupRepositoryRequest;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -39,7 +38,7 @@ public class RestCleanupRepositoryAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/_snapshot/{repository}/_cleanup"));
+        return List.of(new Route(POST, "/_snapshot/{repository}/_cleanup"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClearVotingConfigExclusionsAction.java

@@ -29,14 +29,13 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.DELETE;
 
 public class RestClearVotingConfigExclusionsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(DELETE, "/_cluster/voting_config_exclusions"));
+        return List.of(new Route(DELETE, "/_cluster/voting_config_exclusions"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterAllocationExplainAction.java

@@ -35,8 +35,6 @@ import org.elasticsearch.rest.action.RestBuilderListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -47,9 +45,9 @@ public class RestClusterAllocationExplainAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cluster/allocation/explain"),
-            new Route(POST, "/_cluster/allocation/explain")));
+            new Route(POST, "/_cluster/allocation/explain"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterGetSettingsAction.java

@@ -41,7 +41,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestClusterGetSettingsAction extends BaseRestHandler {
@@ -58,7 +57,7 @@ public class RestClusterGetSettingsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cluster/settings"));
+        return List.of(new Route(GET, "/_cluster/settings"));
     }
     @Override
     public String getName() {

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterHealthAction.java

@@ -36,8 +36,6 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.client.Requests.clusterHealthRequest;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
@@ -45,8 +43,8 @@ public class RestClusterHealthAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(new Route(GET, "/_cluster/health"),
+        return List.of(new Route(GET, "/_cluster/health"),
-            new Route(GET, "/_cluster/health/{index}")));
+            new Route(GET, "/_cluster/health/{index}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterRerouteAction.java

@@ -41,7 +41,6 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestClusterRerouteAction extends BaseRestHandler {
@@ -63,7 +62,7 @@ public class RestClusterRerouteAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/_cluster/reroute"));
+        return List.of(new Route(POST, "/_cluster/reroute"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterSearchShardsAction.java

@@ -31,8 +31,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -40,11 +38,11 @@ public class RestClusterSearchShardsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_search_shards"),
             new Route(POST, "/_search_shards"),
             new Route(GET, "/{index}/_search_shards"),
-            new Route(POST, "/{index}/_search_shards")));
+            new Route(POST, "/{index}/_search_shards"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterStateAction.java

@@ -43,8 +43,6 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestClusterStateAction extends BaseRestHandler {
@@ -62,10 +60,10 @@ public class RestClusterStateAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cluster/state"),
             new Route(GET, "/_cluster/state/{metric}"),
-            new Route(GET, "/_cluster/state/{metric}/{indices}")));
+            new Route(GET, "/_cluster/state/{metric}/{indices}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterStatsAction.java

@@ -28,17 +28,15 @@ import org.elasticsearch.rest.action.RestActions.NodesResponseRestListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestClusterStatsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cluster/stats"),
-            new Route(GET, "/_cluster/stats/nodes/{nodeId}")));
+            new Route(GET, "/_cluster/stats/nodes/{nodeId}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestClusterUpdateSettingsAction.java

@@ -33,7 +33,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 
 public class RestClusterUpdateSettingsAction extends BaseRestHandler {
@@ -43,7 +42,7 @@ public class RestClusterUpdateSettingsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(PUT, "/_cluster/settings"));
+        return List.of(new Route(PUT, "/_cluster/settings"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestCreateSnapshotAction.java

@@ -28,8 +28,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.client.Requests.createSnapshotRequest;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
@@ -41,9 +39,9 @@ public class RestCreateSnapshotAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(PUT, "/_snapshot/{repository}/{snapshot}"),
-            new Route(POST, "/_snapshot/{repository}/{snapshot}")));
+            new Route(POST, "/_snapshot/{repository}/{snapshot}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestDeleteRepositoryAction.java

@@ -28,7 +28,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.client.Requests.deleteRepositoryRequest;
 import static org.elasticsearch.rest.RestRequest.Method.DELETE;
 
@@ -39,7 +38,7 @@ public class RestDeleteRepositoryAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(DELETE, "/_snapshot/{repository}"));
+        return List.of(new Route(DELETE, "/_snapshot/{repository}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestDeleteSnapshotAction.java

@@ -28,7 +28,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.client.Requests.deleteSnapshotRequest;
 import static org.elasticsearch.rest.RestRequest.Method.DELETE;
 
@@ -39,7 +38,7 @@ public class RestDeleteSnapshotAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(DELETE, "/_snapshot/{repository}/{snapshot}"));
+        return List.of(new Route(DELETE, "/_snapshot/{repository}/{snapshot}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestDeleteStoredScriptAction.java

@@ -27,14 +27,13 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.DELETE;
 
 public class RestDeleteStoredScriptAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(DELETE, "/_scripts/{id}"));
+        return List.of(new Route(DELETE, "/_scripts/{id}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestGetRepositoriesAction.java

@@ -32,8 +32,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.client.Requests.getRepositoryRequest;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
@@ -55,9 +53,9 @@ public class RestGetRepositoriesAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_snapshot"),
-            new Route(GET, "/_snapshot/{repository}")));
+            new Route(GET, "/_snapshot/{repository}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestGetScriptContextAction.java

@@ -29,14 +29,13 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestGetScriptContextAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_script_context"));
+        return List.of(new Route(GET, "/_script_context"));
     }
 
     @Override public String getName() {

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestGetScriptLanguageAction.java

@@ -29,14 +29,13 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestGetScriptLanguageAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_script_language"));
+        return List.of(new Route(GET, "/_script_language"));
     }
 
     @Override public String getName() {

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestGetSnapshotsAction.java

@@ -29,7 +29,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.client.Requests.getSnapshotsRequest;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
@@ -40,7 +39,7 @@ public class RestGetSnapshotsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_snapshot/{repository}/{snapshot}"));
+        return List.of(new Route(GET, "/_snapshot/{repository}/{snapshot}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestGetStoredScriptAction.java

@@ -27,14 +27,13 @@ import org.elasticsearch.rest.action.RestStatusToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestGetStoredScriptAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_scripts/{id}"));
+        return List.of(new Route(GET, "/_scripts/{id}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestGetTaskAction.java

@@ -30,14 +30,13 @@ import org.elasticsearch.tasks.TaskId;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestGetTaskAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_tasks/{task_id}"));
+        return List.of(new Route(GET, "/_tasks/{task_id}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestListTasksAction.java

@@ -41,7 +41,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.function.Supplier;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 
@@ -55,7 +54,7 @@ public class RestListTasksAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_tasks"));
+        return List.of(new Route(GET, "/_tasks"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestNodesHotThreadsAction.java

@@ -35,8 +35,6 @@ import org.elasticsearch.rest.action.RestResponseListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 
@@ -44,7 +42,7 @@ public class RestNodesHotThreadsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cluster/nodes/hotthreads"),
             new Route(GET, "/_cluster/nodes/hot_threads"),
             new Route(GET, "/_cluster/nodes/{nodeId}/hotthreads"),
@@ -52,7 +50,7 @@ public class RestNodesHotThreadsAction extends BaseRestHandler {
             new Route(GET, "/_nodes/hotthreads"),
             new Route(GET, "/_nodes/hot_threads"),
             new Route(GET, "/_nodes/{nodeId}/hotthreads"),
-            new Route(GET, "/_nodes/{nodeId}/hot_threads")));
+            new Route(GET, "/_nodes/{nodeId}/hot_threads"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestNodesInfoAction.java

@@ -33,8 +33,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestNodesInfoAction extends BaseRestHandler {
@@ -58,13 +56,13 @@ public class RestNodesInfoAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_nodes"),
             // this endpoint is used for metrics, not for node IDs, like /_nodes/fs
             new Route(GET, "/_nodes/{nodeId}"),
             new Route(GET, "/_nodes/{nodeId}/{metrics}"),
             // added this endpoint to be aligned with stats
-            new Route(GET, "/_nodes/{nodeId}/info/{metrics}")));
+            new Route(GET, "/_nodes/{nodeId}/info/{metrics}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestNodesStatsAction.java

@@ -38,8 +38,6 @@ import java.util.Set;
 import java.util.TreeSet;
 import java.util.function.Consumer;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static java.util.Map.entry;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
@@ -47,13 +45,13 @@ public class RestNodesStatsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_nodes/stats"),
             new Route(GET, "/_nodes/{nodeId}/stats"),
             new Route(GET, "/_nodes/stats/{metric}"),
             new Route(GET, "/_nodes/{nodeId}/stats/{metric}"),
             new Route(GET, "/_nodes/stats/{metric}/{index_metric}"),
-            new Route(GET, "/_nodes/{nodeId}/stats/{metric}/{index_metric}")));
+            new Route(GET, "/_nodes/{nodeId}/stats/{metric}/{index_metric}"));
     }
 
     static final Map<String, Consumer<NodesStatsRequest>> METRICS = Map.ofEntries(

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestNodesUsageAction.java

@@ -37,19 +37,17 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestNodesUsageAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_nodes/usage"),
             new Route(GET, "/_nodes/{nodeId}/usage"),
             new Route(GET, "/_nodes/usage/{metric}"),
-            new Route(GET, "/_nodes/{nodeId}/usage/{metric}")));
+            new Route(GET, "/_nodes/{nodeId}/usage/{metric}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestPendingClusterTasksAction.java

@@ -28,14 +28,13 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestPendingClusterTasksAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cluster/pending_tasks"));
+        return List.of(new Route(GET, "/_cluster/pending_tasks"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestPutRepositoryAction.java

@@ -29,8 +29,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.client.Requests.putRepositoryRequest;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
@@ -42,9 +40,9 @@ public class RestPutRepositoryAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_snapshot/{repository}"),
-            new Route(PUT, "/_snapshot/{repository}")));
+            new Route(PUT, "/_snapshot/{repository}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestPutStoredScriptAction.java

@@ -30,8 +30,6 @@ import org.elasticsearch.script.StoredScriptSource;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 
@@ -39,11 +37,11 @@ public class RestPutStoredScriptAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_scripts/{id}"),
             new Route(PUT, "/_scripts/{id}"),
             new Route(POST, "/_scripts/{id}/{context}"),
-            new Route(PUT, "/_scripts/{id}/{context}")));
+            new Route(PUT, "/_scripts/{id}/{context}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestReloadSecureSettingsAction.java

@@ -39,8 +39,6 @@ import org.elasticsearch.rest.action.RestBuilderListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public final class RestReloadSecureSettingsAction extends BaseRestHandler {
@@ -60,9 +58,9 @@ public final class RestReloadSecureSettingsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_nodes/reload_secure_settings"),
-            new Route(POST, "/_nodes/{nodeId}/reload_secure_settings")));
+            new Route(POST, "/_nodes/{nodeId}/reload_secure_settings"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestRemoteClusterInfoAction.java

@@ -28,14 +28,13 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public final class RestRemoteClusterInfoAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "_remote/info"));
+        return List.of(new Route(GET, "_remote/info"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestRestoreSnapshotAction.java

@@ -28,7 +28,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.client.Requests.restoreSnapshotRequest;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -39,7 +38,7 @@ public class RestRestoreSnapshotAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/_snapshot/{repository}/{snapshot}/_restore"));
+        return List.of(new Route(POST, "/_snapshot/{repository}/{snapshot}/_restore"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestSnapshotsStatusAction.java

@@ -29,8 +29,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.client.Requests.snapshotsStatusRequest;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
@@ -41,10 +39,10 @@ public class RestSnapshotsStatusAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_snapshot/{repository}/{snapshot}/_status"),
             new Route(GET, "/_snapshot/{repository}/_status"),
-            new Route(GET, "/_snapshot/_status")));
+            new Route(GET, "/_snapshot/_status"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestVerifyRepositoryAction.java

@@ -28,7 +28,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.client.Requests.verifyRepositoryRequest;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -36,7 +35,7 @@ public class RestVerifyRepositoryAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/_snapshot/{repository}/_verify"));
+        return List.of(new Route(POST, "/_snapshot/{repository}/_verify"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestAnalyzeAction.java

@@ -29,8 +29,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -50,11 +48,11 @@ public class RestAnalyzeAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_analyze"),
             new Route(POST, "/_analyze"),
             new Route(GET, "/{index}/_analyze"),
-            new Route(POST, "/{index}/_analyze")));
+            new Route(POST, "/{index}/_analyze"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestClearIndicesCacheAction.java

@@ -30,17 +30,15 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestClearIndicesCacheAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_cache/clear"),
-            new Route(POST, "/{index}/_cache/clear")));
+            new Route(POST, "/{index}/_cache/clear"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestCloseIndexAction.java

@@ -31,17 +31,15 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestCloseIndexAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_close"),
-            new Route(POST, "/{index}/_close")));
+            new Route(POST, "/{index}/_close"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestCreateIndexAction.java

@@ -34,7 +34,6 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
-import static java.util.Collections.singletonList;
 import static java.util.Collections.singletonMap;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 
@@ -42,7 +41,7 @@ public class RestCreateIndexAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(PUT, "/{index}"));
+        return List.of(new Route(PUT, "/{index}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestDeleteIndexAction.java

@@ -30,17 +30,15 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.DELETE;
 
 public class RestDeleteIndexAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(DELETE, "/"),
-            new Route(DELETE, "/{index}")));
+            new Route(DELETE, "/{index}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestDeleteIndexTemplateAction.java

@@ -27,14 +27,13 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.DELETE;
 
 public class RestDeleteIndexTemplateAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(DELETE, "/_template/{name}"));
+        return List.of(new Route(DELETE, "/_template/{name}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestFlushAction.java

@@ -30,8 +30,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -39,11 +37,11 @@ public class RestFlushAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_flush"),
             new Route(POST, "/_flush"),
             new Route(GET, "/{index}/_flush"),
-            new Route(POST, "/{index}/_flush")));
+            new Route(POST, "/{index}/_flush"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestForceMergeAction.java

@@ -30,17 +30,15 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestForceMergeAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_forcemerge"),
-            new Route(POST, "/{index}/_forcemerge")));
+            new Route(POST, "/{index}/_forcemerge"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetAliasesAction.java

@@ -46,8 +46,6 @@ import java.util.Set;
 import java.util.SortedSet;
 import java.util.TreeSet;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.HEAD;
 
@@ -58,7 +56,7 @@ public class RestGetAliasesAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_alias"),
             new Route(GET, "/_aliases"),
             new Route(GET, "/_alias/{name}"),
@@ -66,7 +64,7 @@ public class RestGetAliasesAction extends BaseRestHandler {
             new Route(GET, "/{index}/_alias"),
             new Route(HEAD, "/{index}/_alias"),
             new Route(GET, "/{index}/_alias/{name}"),
-            new Route(HEAD, "/{index}/_alias/{name}")));
+            new Route(HEAD, "/{index}/_alias/{name}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetFieldMappingAction.java

@@ -37,8 +37,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Map;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestStatus.NOT_FOUND;
 import static org.elasticsearch.rest.RestStatus.OK;
@@ -47,9 +45,9 @@ public class RestGetFieldMappingAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_mapping/field/{fields}"),
-            new Route(GET, "/{index}/_mapping/field/{fields}")));
+            new Route(GET, "/{index}/_mapping/field/{fields}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetIndexTemplateAction.java

@@ -33,8 +33,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.HEAD;
 import static org.elasticsearch.rest.RestStatus.NOT_FOUND;
@@ -47,10 +45,10 @@ public class RestGetIndexTemplateAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_template"),
             new Route(GET, "/_template/{name}"),
-            new Route(HEAD, "/_template/{name}")));
+            new Route(HEAD, "/_template/{name}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetIndicesAction.java

@@ -33,8 +33,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.HEAD;
 
@@ -45,9 +43,9 @@ public class RestGetIndicesAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/{index}"),
-            new Route(HEAD, "/{index}")));
+            new Route(HEAD, "/{index}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetMappingAction.java

@@ -35,19 +35,17 @@ import org.elasticsearch.rest.action.RestBuilderListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestGetMappingAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_mapping"),
             new Route(GET, "/_mappings"),
             new Route(GET, "/{index}/_mapping"),
-            new Route(GET, "/{index}/_mappings")));
+            new Route(GET, "/{index}/_mappings"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetSettingsAction.java

@@ -30,20 +30,18 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestGetSettingsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_settings"),
             new Route(GET, "/_settings/{name}"),
             new Route(GET, "/{index}/_settings"),
             new Route(GET, "/{index}/_settings/{name}"),
-            new Route(GET, "/{index}/_setting/{name}")));
+            new Route(GET, "/{index}/_setting/{name}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestIndexDeleteAliasesAction.java

@@ -29,17 +29,15 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.DELETE;
 
 public class RestIndexDeleteAliasesAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(DELETE, "/{index}/_alias/{name}"),
-            new Route(DELETE, "/{index}/_aliases/{name}")));
+            new Route(DELETE, "/{index}/_aliases/{name}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestIndexPutAliasAction.java

@@ -31,8 +31,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Map;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 
@@ -40,7 +38,7 @@ public class RestIndexPutAliasAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/{index}/_alias/{name}"),
             new Route(PUT, "/{index}/_alias/{name}"),
             new Route(POST, "/_alias/{name}"),
@@ -51,7 +49,7 @@ public class RestIndexPutAliasAction extends BaseRestHandler {
             new Route(PUT, "/_aliases/{name}"),
             new Route(PUT, "/{index}/_alias"),
             new Route(PUT, "/{index}/_aliases"),
-            new Route(PUT, "/_alias")));
+            new Route(PUT, "/_alias"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestIndicesAliasesAction.java

@@ -29,7 +29,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestIndicesAliasesAction extends BaseRestHandler {
@@ -41,7 +40,7 @@ public class RestIndicesAliasesAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(POST, "/_aliases"));
+        return List.of(new Route(POST, "/_aliases"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestIndicesSegmentsAction.java

@@ -30,17 +30,15 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestIndicesSegmentsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_segments"),
-            new Route(GET, "/{index}/_segments")));
+            new Route(GET, "/{index}/_segments"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestIndicesShardStoresAction.java

@@ -35,8 +35,6 @@ import org.elasticsearch.rest.action.RestBuilderListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestStatus.OK;
 
@@ -47,9 +45,9 @@ public class RestIndicesShardStoresAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_shard_stores"),
-            new Route(GET, "/{index}/_shard_stores")));
+            new Route(GET, "/{index}/_shard_stores"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestIndicesStatsAction.java

@@ -39,19 +39,17 @@ import java.util.Set;
 import java.util.TreeSet;
 import java.util.function.Consumer;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestIndicesStatsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_stats"),
             new Route(GET, "/_stats/{metric}"),
             new Route(GET, "/{index}/_stats"),
-            new Route(GET, "/{index}/_stats/{metric}")));
+            new Route(GET, "/{index}/_stats/{metric}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestOpenIndexAction.java

@@ -31,17 +31,15 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestOpenIndexAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_open"),
-            new Route(POST, "/{index}/_open")));
+            new Route(POST, "/{index}/_open"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestPutIndexTemplateAction.java

@@ -32,7 +32,6 @@ import java.util.List;
 import java.util.Map;
 
 import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 
@@ -40,9 +39,9 @@ public class RestPutIndexTemplateAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/_template/{name}"),
-            new Route(PUT, "/_template/{name}")));
+            new Route(PUT, "/_template/{name}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestPutMappingAction.java

@@ -33,8 +33,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Map;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.client.Requests.putMappingRequest;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
@@ -43,11 +41,11 @@ public class RestPutMappingAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/{index}/_mapping/"),
             new Route(PUT, "/{index}/_mapping/"),
             new Route(POST, "/{index}/_mappings/"),
-            new Route(PUT, "/{index}/_mappings/")));
+            new Route(PUT, "/{index}/_mappings/"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestRecoveryAction.java

@@ -30,8 +30,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 /**
@@ -41,9 +39,9 @@ public class RestRecoveryAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_recovery"),
-            new Route(GET, "/{index}/_recovery")));
+            new Route(GET, "/{index}/_recovery"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestRefreshAction.java

@@ -32,8 +32,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -41,11 +39,11 @@ public class RestRefreshAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_refresh"),
             new Route(POST, "/_refresh"),
             new Route(GET, "/{index}/_refresh"),
-            new Route(POST, "/{index}/_refresh")));
+            new Route(POST, "/{index}/_refresh"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestResizeHandler.java

@@ -30,8 +30,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 
@@ -60,9 +58,9 @@ public abstract class RestResizeHandler extends BaseRestHandler {
 
         @Override
         public List<Route> routes() {
-            return unmodifiableList(asList(
+            return List.of(
                 new Route(POST, "/{index}/_shrink/{target}"),
-                new Route(PUT, "/{index}/_shrink/{target}")));
+                new Route(PUT, "/{index}/_shrink/{target}"));
         }
 
         @Override
@@ -81,9 +79,9 @@ public abstract class RestResizeHandler extends BaseRestHandler {
 
         @Override
         public List<Route> routes() {
-            return unmodifiableList(asList(
+            return List.of(
                 new Route(POST, "/{index}/_split/{target}"),
-                new Route(PUT, "/{index}/_split/{target}")));
+                new Route(PUT, "/{index}/_split/{target}"));
         }
 
         @Override
@@ -102,9 +100,9 @@ public abstract class RestResizeHandler extends BaseRestHandler {
 
         @Override
         public List<Route> routes() {
-            return unmodifiableList(asList(
+            return List.of(
                 new Route(POST, "/{index}/_clone/{target}"),
-                new Route(PUT, "/{index}/_clone/{target}")));
+                new Route(PUT, "/{index}/_clone/{target}"));
         }
 
         @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestRolloverIndexAction.java

@@ -29,17 +29,15 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestRolloverIndexAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(POST, "/{index}/_rollover"),
-            new Route(POST, "/{index}/_rollover/{new_index}")));
+            new Route(POST, "/{index}/_rollover/{new_index}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestSyncedFlushAction.java

@@ -39,8 +39,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
@@ -51,11 +49,11 @@ public class RestSyncedFlushAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_flush/synced"),
             new Route(POST, "/_flush/synced"),
             new Route(GET, "/{index}/_flush/synced"),
-            new Route(POST, "/{index}/_flush/synced")));
+            new Route(POST, "/{index}/_flush/synced"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestUpdateSettingsAction.java

@@ -32,8 +32,6 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Set;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.client.Requests.updateSettingsRequest;
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 
@@ -41,9 +39,9 @@ public class RestUpdateSettingsAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(PUT, "/{index}/_settings"),
-            new Route(PUT, "/_settings")));
+            new Route(PUT, "/_settings"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestUpgradeActionDeprecated.java

@@ -33,8 +33,6 @@ import java.io.IOException;
 import java.util.Collections;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
 public class RestUpgradeActionDeprecated extends BaseRestHandler {
@@ -47,9 +45,9 @@ public class RestUpgradeActionDeprecated extends BaseRestHandler {
 
     @Override
     public List<DeprecatedRoute> deprecatedRoutes() {
-        return unmodifiableList(asList(
+        return List.of(
             new DeprecatedRoute(POST, "/_upgrade", UPGRADE_API_DEPRECATION_MESSAGE),
-            new DeprecatedRoute(POST, "/{index}/_upgrade", UPGRADE_API_DEPRECATION_MESSAGE)));
+            new DeprecatedRoute(POST, "/{index}/_upgrade", UPGRADE_API_DEPRECATION_MESSAGE));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestUpgradeStatusActionDeprecated.java

@@ -33,8 +33,6 @@ import java.io.IOException;
 import java.util.Collections;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.action.admin.indices.RestUpgradeActionDeprecated.UPGRADE_API_DEPRECATION_MESSAGE;
 
@@ -45,9 +43,9 @@ public class RestUpgradeStatusActionDeprecated extends BaseRestHandler {
 
     @Override
     public List<DeprecatedRoute> deprecatedRoutes() {
-        return unmodifiableList(asList(
+        return List.of(
             new DeprecatedRoute(GET, "/_upgrade", UPGRADE_API_DEPRECATION_MESSAGE),
-            new DeprecatedRoute(GET, "/{index}/_upgrade", UPGRADE_API_DEPRECATION_MESSAGE)));
+            new DeprecatedRoute(GET, "/{index}/_upgrade", UPGRADE_API_DEPRECATION_MESSAGE));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestValidateQueryAction.java

@@ -37,8 +37,6 @@ import org.elasticsearch.rest.action.RestToXContentListener;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 import static org.elasticsearch.rest.RestStatus.OK;
@@ -47,11 +45,11 @@ public class RestValidateQueryAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_validate/query"),
             new Route(POST, "/_validate/query"),
             new Route(GET, "/{index}/_validate/query"),
-            new Route(POST, "/{index}/_validate/query")));
+            new Route(POST, "/{index}/_validate/query"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestAliasAction.java

@@ -31,17 +31,15 @@ import org.elasticsearch.rest.action.RestResponseListener;
 
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestAliasAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cat/aliases"),
-            new Route(GET, "/_cat/aliases/{alias}")));
+            new Route(GET, "/_cat/aliases/{alias}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestAllocationAction.java

@@ -39,8 +39,6 @@ import org.elasticsearch.rest.action.RestResponseListener;
 
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 
@@ -48,9 +46,9 @@ public class RestAllocationAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cat/allocation"),
-            new Route(GET, "/_cat/allocation/{nodes}")));
+            new Route(GET, "/_cat/allocation/{nodes}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestCatAction.java

@@ -28,7 +28,6 @@ import org.elasticsearch.rest.RestStatus;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestCatAction extends BaseRestHandler {
@@ -48,7 +47,7 @@ public class RestCatAction extends BaseRestHandler {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat"));
+        return List.of(new Route(GET, "/_cat"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestCatRecoveryAction.java

@@ -40,8 +40,6 @@ import java.util.Comparator;
 import java.util.List;
 import java.util.Locale;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 /**
@@ -53,9 +51,9 @@ public class RestCatRecoveryAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cat/recovery"),
-            new Route(GET, "/_cat/recovery/{index}")));
+            new Route(GET, "/_cat/recovery/{index}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestCountAction.java

@@ -36,17 +36,15 @@ import org.elasticsearch.search.builder.SearchSourceBuilder;
 import java.io.IOException;
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestCountAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cat/count"),
-            new Route(GET, "/_cat/count/{index}")));
+            new Route(GET, "/_cat/count/{index}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestFielddataAction.java

@@ -32,8 +32,6 @@ import org.elasticsearch.rest.action.RestResponseListener;
 
 import java.util.List;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 /**
@@ -43,9 +41,9 @@ public class RestFielddataAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cat/fielddata"),
-            new Route(GET, "/_cat/fielddata/{fields}")));
+            new Route(GET, "/_cat/fielddata/{fields}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestHealthAction.java

@@ -30,14 +30,13 @@ import org.elasticsearch.rest.action.RestResponseListener;
 import java.util.List;
 import java.util.Locale;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestHealthAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat/health"));
+        return List.of(new Route(GET, "/_cat/health"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestIndicesAction.java

@@ -62,7 +62,6 @@ import java.util.stream.Collectors;
 import java.util.stream.StreamSupport;
 
 import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.action.support.master.MasterNodeRequest.DEFAULT_MASTER_NODE_TIMEOUT;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
@@ -72,9 +71,9 @@ public class RestIndicesAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cat/indices"),
-            new Route(GET, "/_cat/indices/{index}")));
+            new Route(GET, "/_cat/indices/{index}"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestMasterAction.java

@@ -31,14 +31,13 @@ import org.elasticsearch.rest.action.RestResponseListener;
 
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestMasterAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat/master"));
+        return List.of(new Route(GET, "/_cat/master"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestNodeAttrsAction.java

@@ -37,14 +37,13 @@ import org.elasticsearch.rest.action.RestResponseListener;
 import java.util.List;
 import java.util.Map;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestNodeAttrsAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat/nodeattrs"));
+        return List.of(new Route(GET, "/_cat/nodeattrs"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestNodesAction.java

@@ -65,14 +65,13 @@ import java.util.List;
 import java.util.Locale;
 import java.util.stream.Collectors;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestNodesAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat/nodes"));
+        return List.of(new Route(GET, "/_cat/nodes"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestPendingClusterTasksAction.java

@@ -30,14 +30,13 @@ import org.elasticsearch.rest.action.RestResponseListener;
 
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestPendingClusterTasksAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat/pending_tasks"));
+        return List.of(new Route(GET, "/_cat/pending_tasks"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestPluginsAction.java

@@ -36,14 +36,13 @@ import org.elasticsearch.rest.action.RestResponseListener;
 
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestPluginsAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat/plugins"));
+        return List.of(new Route(GET, "/_cat/plugins"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestRepositoriesAction.java

@@ -30,7 +30,6 @@ import org.elasticsearch.rest.action.RestResponseListener;
 
 import java.util.List;
 
-import static java.util.Collections.singletonList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 /**
@@ -40,7 +39,7 @@ public class RestRepositoriesAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat/repositories"));
+        return List.of(new Route(GET, "/_cat/repositories"));
     }
 
     @Override

server/src/main/java/org/elasticsearch/rest/action/cat/RestSegmentsAction.java

@@ -39,17 +39,15 @@ import org.elasticsearch.rest.action.RestResponseListener;
 import java.util.List;
 import java.util.Map;
 
-import static java.util.Arrays.asList;
-import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestSegmentsAction extends AbstractCatAction {
 
     @Override
     public List<Route> routes() {
-        return unmodifiableList(asList(
+        return List.of(
             new Route(GET, "/_cat/segments"),
-            new Route(GET, "/_cat/segments/{index}")));
+            new Route(GET, "/_cat/segments/{index}"));
     }
 
     @Override