Provide support for GetFieldMapping request

src/main/java/org/springframework/data/elasticsearch/client/reactive/DefaultReactiveElasticsearchClient.java

@@ -22,6 +22,8 @@
 import io.netty.handler.ssl.JdkSslContext;
 import io.netty.handler.timeout.ReadTimeoutHandler;
 import io.netty.handler.timeout.WriteTimeoutHandler;
+import org.elasticsearch.client.indices.GetFieldMappingsRequest;
+import org.elasticsearch.client.indices.GetFieldMappingsResponse;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.netty.http.client.HttpClient;
@@ -139,6 +141,7 @@
  * @author Russell Parry
  * @author Thomas Geese
  * @author Brian Clozel
+ * @author Farid Faoudi
  * @since 3.2
  * @see ClientConfiguration
  * @see ReactiveRestClients
@@ -674,6 +677,11 @@ public Mono<GetMappingsResponse> getMapping(HttpHeaders headers, GetMappingsRequ
 		return sendRequest(getMappingsRequest, requestCreator.getMapping(), GetMappingsResponse.class, headers).next();
 	}
 
+	@Override
+	public Mono<GetFieldMappingsResponse> getFieldMapping(HttpHeaders headers, GetFieldMappingsRequest getFieldMappingsRequest) {
+		return sendRequest(getFieldMappingsRequest, requestCreator.getFieldMapping(), GetFieldMappingsResponse.class, headers).next();
+	}
+
 	@Override
 	public Mono<GetSettingsResponse> getSettings(HttpHeaders headers, GetSettingsRequest getSettingsRequest) {
 		return sendRequest(getSettingsRequest, requestCreator.getSettings(), GetSettingsResponse.class, headers).next();

src/main/java/org/springframework/data/elasticsearch/client/reactive/ReactiveElasticsearchClient.java

@@ -15,6 +15,8 @@
  */
 package org.springframework.data.elasticsearch.client.reactive;
 
+import org.elasticsearch.client.indices.GetFieldMappingsRequest;
+import org.elasticsearch.client.indices.GetFieldMappingsResponse;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -77,6 +79,7 @@
  * @author Peter-Josef Meisch
  * @author Henrique Amaral
  * @author Thomas Geese
+ * @author Farid Faoudi
  * @since 3.2
  * @see ClientConfiguration
  * @see ReactiveRestClients
@@ -1162,6 +1165,50 @@ default Mono<GetMappingsResponse> getMapping(GetMappingsRequest getMappingsReque
 		 */
 		Mono<GetMappingsResponse> getMapping(HttpHeaders headers, GetMappingsRequest getMappingsRequest);
 
+		/**
+		 * Execute the given {@link GetFieldMappingsRequest} against the {@literal indices} API.
+		 *
+		 * @param consumer never {@literal null}.
+		 * @return a {@link Mono} signalling operation completion or an {@link Mono#error(Throwable) error} if eg. the index
+		 * 		   does not exist.
+		 * @see <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-get-field-mapping.html"> Indices
+		 *  		 Flush API on elastic.co</a>
+		 * @since 4.2
+		 */
+		default Mono<GetFieldMappingsResponse> getFieldMapping(Consumer<GetFieldMappingsRequest> consumer) {
+
+			GetFieldMappingsRequest request = new GetFieldMappingsRequest();
+			consumer.accept(request);
+			return getFieldMapping(request);
+		}
+
+		/**
+		 * Execute the given {@link GetFieldMappingsRequest} against the {@literal indices} API.
+		 *
+		 * @param getFieldMappingsRequest must not be {@literal null}.
+		 * @return a {@link Mono} signalling operation completion or an {@link Mono#error(Throwable) error} if eg. the index
+		 *         does not exist.
+		 * @see <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-get-field-mapping.html"> Indices
+		 *  		 Flush API on elastic.co</a>
+		 * @since 4.2
+		 */
+		default Mono<GetFieldMappingsResponse> getFieldMapping(GetFieldMappingsRequest getFieldMappingsRequest) {
+			return getFieldMapping(HttpHeaders.EMPTY, getFieldMappingsRequest);
+		}
+
+		/**
+		 * Execute the given {@link GetFieldMappingsRequest} against the {@literal indices} API.
+		 *
+		 * @param headers Use {@link HttpHeaders} to provide eg. authentication data. Must not be {@literal null}.
+		 * @param getFieldMappingsRequest must not be {@literal null}.
+		 * @return a {@link Mono} signalling operation completion or an {@link Mono#error(Throwable) error} if eg. the index
+		 *         does not exist.
+		 * @see <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-get-field-mapping.html"> Indices
+		 * 		 Flush API on elastic.co</a>
+		 * @since 4.2
+		 */
+		Mono<GetFieldMappingsResponse> getFieldMapping(HttpHeaders headers, GetFieldMappingsRequest getFieldMappingsRequest);
+
 		/**
 		 * Execute the given {@link IndicesAliasesRequest} against the {@literal indices} API.
 		 * 

src/main/java/org/springframework/data/elasticsearch/client/reactive/RequestCreator.java

@@ -28,6 +28,7 @@
 import org.elasticsearch.action.update.UpdateRequest;
 import org.elasticsearch.client.Request;
 import org.elasticsearch.client.core.CountRequest;
+import org.elasticsearch.client.indices.GetFieldMappingsRequest;
 import org.elasticsearch.client.indices.GetIndexTemplatesRequest;
 import org.elasticsearch.client.indices.IndexTemplatesExistRequest;
 import org.elasticsearch.client.indices.PutIndexTemplateRequest;
@@ -37,6 +38,7 @@
 
 /**
  * @author Roman Puchkovskiy
+ * @author Farid Faoudi
  * @since 4.0
  */
 public interface RequestCreator {
@@ -194,4 +196,11 @@ default Function<IndexTemplatesExistRequest, Request> templatesExist() {
 	default Function<DeleteIndexTemplateRequest, Request> deleteTemplate() {
 		return RequestConverters::deleteTemplate;
 	}
+
+	/**
+	 * @since 4.2
+	 */
+	default Function<GetFieldMappingsRequest, Request> getFieldMapping() {
+		return RequestConverters::getFieldMapping;
+	}
 }

src/main/java/org/springframework/data/elasticsearch/client/util/RequestConverters.java

@@ -71,6 +71,7 @@
 import org.elasticsearch.client.RethrottleRequest;
 import org.elasticsearch.client.core.CountRequest;
 import org.elasticsearch.client.indices.AnalyzeRequest;
+import org.elasticsearch.client.indices.GetFieldMappingsRequest;
 import org.elasticsearch.client.indices.GetIndexTemplatesRequest;
 import org.elasticsearch.client.indices.IndexTemplatesExistRequest;
 import org.elasticsearch.client.indices.PutIndexTemplateRequest;
@@ -115,6 +116,7 @@
  *
  * @author Christoph Strobl
  * @author Peter-Josef Meisch
+ * @author Farid Faoudi
  * @since 3.2
  */
 @SuppressWarnings("JavadocReference")
@@ -891,6 +893,24 @@ public static Request deleteTemplate(DeleteIndexTemplateRequest deleteIndexTempl
 		return request;
 	}
 
+	public static Request getFieldMapping(GetFieldMappingsRequest getFieldMappingsRequest) {
+		String[] indices = getFieldMappingsRequest.indices() == null ? Strings.EMPTY_ARRAY : getFieldMappingsRequest.indices();
+		String[] fields = getFieldMappingsRequest.fields() == null ? Strings.EMPTY_ARRAY : getFieldMappingsRequest.fields();
+
+		final String endpoint = new EndpointBuilder().addCommaSeparatedPathParts(indices)
+				.addPathPartAsIs("_mapping").addPathPartAsIs("field")
+				.addCommaSeparatedPathParts(fields)
+				.build();
+
+		Request request = new Request(HttpMethod.GET.name(), endpoint);
+
+		RequestConverters.Params parameters = new Params(request);
+		parameters.withIndicesOptions(getFieldMappingsRequest.indicesOptions());
+		parameters.withIncludeDefaults(getFieldMappingsRequest.includeDefaults());
+		parameters.withIncludeTypeName(false);
+		return request;
+	}
+
 	static HttpEntity createEntity(ToXContent toXContent, XContentType xContentType) {
 
 		try {

src/test/java/org/springframework/data/elasticsearch/client/reactive/ReactiveElasticsearchClientIntegrationTests.java

@@ -18,12 +18,14 @@
 import static org.assertj.core.api.Assertions.*;
 
 import lombok.SneakyThrows;
+import org.elasticsearch.action.admin.indices.mapping.put.PutMappingRequest;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
 import java.time.Duration;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.UUID;
@@ -73,6 +75,7 @@
  * @author Henrique Amaral
  * @author Russell Parry
  * @author Thomas Geese
+ * @author Farid Faoudi
  */
 @SpringIntegrationTest
 @ContextConfiguration(classes = { ReactiveElasticsearchClientIntegrationTests.Config.class })
@@ -721,6 +724,61 @@ public void suggestReturnsSuggestionResults() {
 				.verifyComplete();
 	}
 
+	@Test // #1640
+	void getFieldMapping() {
+
+		operations.indexOps(IndexCoordinates.of(INDEX_I)).create().block();
+
+		Map<String, Object> properties = new HashMap<>();
+		properties.put("message1", Collections.singletonMap("type", "text"));
+		properties.put("message2", Collections.singletonMap("type", "keyword"));
+
+		Map<String, Object> jsonMap = Collections.singletonMap("properties", properties);
+
+		final PutMappingRequest putMappingRequest = new PutMappingRequest(INDEX_I)
+				.source(jsonMap);
+
+		client.indices().putMapping(putMappingRequest).block();
+
+		client.indices().getFieldMapping(request -> request.indices(INDEX_I).fields("message1", "message2"))
+				.as(StepVerifier::create)
+				.consumeNextWith(it -> {
+					assertThat(it.mappings().get(INDEX_I).keySet().size()).isEqualTo(2);
+					assertThat(it.mappings().get(INDEX_I).get("message1").sourceAsMap()).isEqualTo(Collections.singletonMap("message1", Collections.singletonMap("type", "text")));
+					assertThat(it.mappings().get(INDEX_I).get("message2").sourceAsMap()).isEqualTo(Collections.singletonMap("message2", Collections.singletonMap("type", "keyword")));
+				})
+				.verifyComplete();
+	}
+
+	@Test // #1640
+	void getFieldMappingNonExistingField() {
+
+		operations.indexOps(IndexCoordinates.of(INDEX_I)).create().block();
+
+		Map<String, Object> jsonMap = Collections.singletonMap("properties",
+				Collections.singletonMap("message", Collections.singletonMap("type", "text")));
+
+		final PutMappingRequest putMappingRequest = new PutMappingRequest(INDEX_I)
+				.source(jsonMap);
+
+		client.indices().putMapping(putMappingRequest).block();
+
+		client.indices().getFieldMapping(request -> request.indices(INDEX_I).fields("message1"))
+				.as(StepVerifier::create)
+				.consumeNextWith(it -> {
+					assertThat(it.mappings().get(INDEX_I).keySet().size()).isZero();
+				})
+				.verifyComplete();
+	}
+
+	@Test // #1640
+	void getFieldMappingNonExistingIndex() {
+
+		client.indices().getFieldMapping(request -> request.indices(INDEX_I).fields("message1"))
+				.as(StepVerifier::create)
+				.verifyError(ElasticsearchStatusException.class);
+	}
+
 	@Test // DATAES-796
 	@DisplayName("should return the whole SearchResponse")
 	void shouldReturnTheWholeSearchResponse() {