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Add Get Aliases API to the high-level REST client (#28799)
Given the weirdness of the response returned by the get alias API, we went for a client specific response, which allows us to hold the error message, exception and status returned as part of the response together with aliases. See #30536 . Relates to #27205
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‎client/rest-high-level/src/main/java/org/elasticsearch/client/GetAliasesResponse.java‎

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/*
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* Licensed to Elasticsearch under one or more contributor
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* license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright
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* ownership. Elasticsearch licenses this file to you under
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* the Apache License, Version 2.0 (the "License"); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing,
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* software distributed under the License is distributed on an
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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* KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations
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* under the License.
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*/
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package org.elasticsearch.client;
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import org.elasticsearch.ElasticsearchException;
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import org.elasticsearch.action.ActionResponse;
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import org.elasticsearch.cluster.metadata.AliasMetaData;
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import org.elasticsearch.common.xcontent.StatusToXContentObject;
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import org.elasticsearch.common.xcontent.ToXContent;
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import org.elasticsearch.common.xcontent.XContentBuilder;
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import org.elasticsearch.common.xcontent.XContentParser;
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import org.elasticsearch.common.xcontent.XContentParser.Token;
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import org.elasticsearch.rest.RestStatus;
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import java.io.IOException;
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import java.util.Collections;
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import java.util.HashMap;
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import java.util.HashSet;
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import java.util.Map;
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import java.util.Set;
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import static org.elasticsearch.common.xcontent.XContentParserUtils.ensureExpectedToken;
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/**
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* Response obtained from the get aliases API.
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* The format is pretty horrible as it holds aliases, but at the same time errors can come back through the status and error fields.
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* Such errors are mostly 404 - NOT FOUND for aliases that were specified but not found. In such case the client won't throw exception
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* so it allows to retrieve the returned aliases, while at the same time checking if errors were returned.
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* There's also the case where an exception is returned, like for instance an {@link org.elasticsearch.index.IndexNotFoundException}.
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* We would usually throw such exception, but we configure the client to not throw for 404 to support the case above, hence we also not
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* throw in case an index is not found, although it is a hard error that doesn't come back with aliases.
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*/
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public class GetAliasesResponse extends ActionResponse implements StatusToXContentObject {
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private final RestStatus status;
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private final String error;
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private final ElasticsearchException exception;
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private final Map<String, Set<AliasMetaData>> aliases;
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GetAliasesResponse(RestStatus status, String error, Map<String, Set<AliasMetaData>> aliases) {
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this.status = status;
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this.error = error;
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this.aliases = aliases;
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this.exception = null;
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}
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private GetAliasesResponse(RestStatus status, ElasticsearchException exception) {
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this.status = status;
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this.error = null;
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this.aliases = Collections.emptyMap();
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this.exception = exception;
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}
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@Override
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public RestStatus status() {
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return status;
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}
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/**
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* Return the possibly returned error, null otherwise
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*/
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public String getError() {
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return error;
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}
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/**
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* Return the exception that may have been returned
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*/
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public ElasticsearchException getException() {
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return exception;
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}
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/**
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* Return the requested aliases
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*/
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public Map<String, Set<AliasMetaData>> getAliases() {
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return aliases;
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}
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@Override
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public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
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builder.startObject();
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{
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if (status != RestStatus.OK) {
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builder.field("error", error);
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builder.field("status", status.getStatus());
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}
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for (Map.Entry<String, Set<AliasMetaData>> entry : aliases.entrySet()) {
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builder.startObject(entry.getKey());
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{
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builder.startObject("aliases");
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{
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for (final AliasMetaData alias : entry.getValue()) {
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AliasMetaData.Builder.toXContent(alias, builder, ToXContent.EMPTY_PARAMS);
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}
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}
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builder.endObject();
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}
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builder.endObject();
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}
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}
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builder.endObject();
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return builder;
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}
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/**
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* Parse the get aliases response
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*/
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public static GetAliasesResponse fromXContent(XContentParser parser) throws IOException {
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if (parser.currentToken() == null) {
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parser.nextToken();
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}
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ensureExpectedToken(Token.START_OBJECT, parser.currentToken(), parser::getTokenLocation);
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Map<String, Set<AliasMetaData>> aliases = new HashMap<>();
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String currentFieldName;
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Token token;
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String error = null;
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ElasticsearchException exception = null;
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RestStatus status = RestStatus.OK;
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while (parser.nextToken() != Token.END_OBJECT) {
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if (parser.currentToken() == Token.FIELD_NAME) {
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currentFieldName = parser.currentName();
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if ("status".equals(currentFieldName)) {
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if ((token = parser.nextToken()) != Token.FIELD_NAME) {
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ensureExpectedToken(Token.VALUE_NUMBER, token, parser::getTokenLocation);
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status = RestStatus.fromCode(parser.intValue());
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}
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} else if ("error".equals(currentFieldName)) {
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token = parser.nextToken();
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if (token == Token.VALUE_STRING) {
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error = parser.text();
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} else if (token == Token.START_OBJECT) {
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parser.nextToken();
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exception = ElasticsearchException.innerFromXContent(parser, true);
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} else if (token == Token.START_ARRAY) {
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parser.skipChildren();
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}
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} else {
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String indexName = parser.currentName();
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if (parser.nextToken() == Token.START_OBJECT) {
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Set<AliasMetaData> parseInside = parseAliases(parser);
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aliases.put(indexName, parseInside);
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}
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}
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}
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}
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if (exception != null) {
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assert error == null;
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assert aliases.isEmpty();
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return new GetAliasesResponse(status, exception);
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}
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return new GetAliasesResponse(status, error, aliases);
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}
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private static Set<AliasMetaData> parseAliases(XContentParser parser) throws IOException {
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Set<AliasMetaData> aliases = new HashSet<>();
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Token token;
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String currentFieldName = null;
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while ((token = parser.nextToken()) != Token.END_OBJECT) {
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if (token == Token.FIELD_NAME) {
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currentFieldName = parser.currentName();
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} else if (token == Token.START_OBJECT) {
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if ("aliases".equals(currentFieldName)) {
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while (parser.nextToken() != Token.END_OBJECT) {
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AliasMetaData fromXContent = AliasMetaData.Builder.fromXContent(parser);
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aliases.add(fromXContent);
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}
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} else {
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parser.skipChildren();
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}
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} else if (token == Token.START_ARRAY) {
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parser.skipChildren();
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}
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}
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return aliases;
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}
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}

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

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import org.elasticsearch.action.admin.indices.template.get.GetIndexTemplatesResponse;
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import org.elasticsearch.action.admin.indices.template.put.PutIndexTemplateRequest;
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import org.elasticsearch.action.admin.indices.template.put.PutIndexTemplateResponse;
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import org.elasticsearch.rest.RestStatus;
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import java.io.IOException;
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import java.util.Collections;
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import static java.util.Collections.emptySet;
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import static java.util.Collections.singleton;
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/**
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* A wrapper for the {@link RestHighLevelClient} that provides methods for accessing the Indices API.
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listener, emptySet(), headers);
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}
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/**
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* Gets one or more aliases using the Get Index Aliases API.
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* See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-aliases.html"> Indices Aliases API on
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* elastic.co</a>
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* @param getAliasesRequest the request
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* @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
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* @return the response
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* @throws IOException in case there is a problem sending the request or parsing back the response
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*/
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public GetAliasesResponse getAlias(GetAliasesRequest getAliasesRequest, RequestOptions options) throws IOException {
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return restHighLevelClient.performRequestAndParseEntity(getAliasesRequest, RequestConverters::getAlias, options,
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GetAliasesResponse::fromXContent, singleton(RestStatus.NOT_FOUND.getStatus()));
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}
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/**
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* Asynchronously gets one or more aliases using the Get Index Aliases API.
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* See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-aliases.html"> Indices Aliases API on
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* elastic.co</a>
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* @param getAliasesRequest the request
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* @param options the request options (e.g. headers), use {@link RequestOptions#DEFAULT} if nothing needs to be customized
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* @param listener the listener to be notified upon request completion
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*/
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public void getAliasAsync(GetAliasesRequest getAliasesRequest, RequestOptions options, ActionListener<GetAliasesResponse> listener) {
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restHighLevelClient.performRequestAsyncAndParseEntity(getAliasesRequest, RequestConverters::getAlias, options,
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GetAliasesResponse::fromXContent, listener, singleton(RestStatus.NOT_FOUND.getStatus()));
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}
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/**
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* Updates specific index level settings using the Update Indices Settings API.
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* See <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-update-settings.html"> Update Indices Settings

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

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return request;
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}
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static Request getAlias(GetAliasesRequest getAliasesRequest) {
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String[] indices = getAliasesRequest.indices() == null ? Strings.EMPTY_ARRAY : getAliasesRequest.indices();
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String[] aliases = getAliasesRequest.aliases() == null ? Strings.EMPTY_ARRAY : getAliasesRequest.aliases();
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String endpoint = endpoint(indices, "_alias", aliases);
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Request request = new Request(HttpGet.METHOD_NAME, endpoint);
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Params params = new Params(request);
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params.withIndicesOptions(getAliasesRequest.indicesOptions());
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params.withLocal(getAliasesRequest.local());
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return request;
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}
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private static HttpEntity createEntity(ToXContent toXContent, XContentType xContentType) throws IOException {
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BytesRef source = XContentHelper.toXContent(toXContent, xContentType, false).toBytesRef();
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return new ByteArrayEntity(source.bytes, source.offset, source.length, createContentType(xContentType));

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

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try {
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return responseConverter.apply(e.getResponse());
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} catch (Exception innerException) {
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//the exception is ignored as we now try to parse the response as an error.
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//this covers cases like get where 404 can either be a valid document not found response,
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//or an error for which parsing is completely different. We try to consider the 404 response as a valid one
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//first. If parsing of the response breaks, we fall back to parsing it as an error.
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// the exception is ignored as we now try to parse the response as an error.
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// this covers cases like get where 404 can either be a valid document not found response,
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// or an error for which parsing is completely different. We try to consider the 404 response as a valid one
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// first. If parsing of the response breaks, we fall back to parsing it as an error.
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throw parseResponseException(e);
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}
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}
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try {
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actionListener.onResponse(responseConverter.apply(response));
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} catch (Exception innerException) {
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//the exception is ignored as we now try to parse the response as an error.
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//this covers cases like get where 404 can either be a valid document not found response,
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//or an error for which parsing is completely different. We try to consider the 404 response as a valid one
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//first. If parsing of the response breaks, we fall back to parsing it as an error.
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// the exception is ignored as we now try to parse the response as an error.
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// this covers cases like get where 404 can either be a valid document not found response,
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// or an error for which parsing is completely different. We try to consider the 404 response as a valid one
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// first. If parsing of the response breaks, we fall back to parsing it as an error.
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actionListener.onFailure(parseResponseException(responseException));
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}
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} else {

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