Use the new Rest5Client as default, provide the old RestClient as optional.

Original Pull Request: #3125
Closes #3117

Signed-off-by: Peter-Josef Meisch <pj.meisch@sothawo.com>

pom.xml

@@ -132,6 +132,7 @@
 			</exclusions>
 		</dependency>
 
+		<!-- the old RestCLient is an optional dependency for user that still want to use it-->
 		<dependency>
 			<groupId>org.elasticsearch.client</groupId>
 			<artifactId>elasticsearch-rest-client</artifactId>
@@ -142,6 +143,7 @@
 					<artifactId>commons-logging</artifactId>
 				</exclusion>
 			</exclusions>
+			<optional>true</optional>
 		</dependency>
 
 		<dependency>

src/main/antora/modules/ROOT/pages/elasticsearch/clients.adoc

@@ -6,10 +6,10 @@ This chapter illustrates configuration and usage of supported Elasticsearch clie
 Spring Data Elasticsearch operates upon an Elasticsearch client (provided by Elasticsearch client libraries) that is connected to a single Elasticsearch node or a cluster.
 Although the Elasticsearch Client can be used directly to work with the cluster, applications using Spring Data Elasticsearch normally use the higher level abstractions of xref:elasticsearch/template.adoc[Elasticsearch Operations] and xref:elasticsearch/repositories/elasticsearch-repositories.adoc[Elasticsearch Repositories].
 
-[[elasticsearch.clients.restclient]]
+[[elasticsearch.clients.rest5client]]
-== Imperative Rest Client
+== Imperative Rest5Client
 
-To use the imperative (non-reactive) client, a configuration bean must be configured like this:
+To use the imperative (non-reactive) Rest5Client, a configuration bean must be configured like this:
 
 ====
 [source,java]
@@ -31,7 +31,7 @@ public class MyClientConfig extends ElasticsearchConfiguration {
 <.> for a detailed description of the builder methods see xref:elasticsearch/clients.adoc#elasticsearch.clients.configuration[Client Configuration]
 ====
 
-The javadoc:org.springframework.data.elasticsearch.client.elc.ElasticsearchConfiguration[]] class allows further configuration by overriding for example the `jsonpMapper()` or `transportOptions()` methods.
+The javadoc:org.springframework.data.elasticsearch.client.elc.ElasticsearchConfiguration[] class allows further configuration by overriding for example the `jsonpMapper()` or `transportOptions()` methods.
 
 
 The following beans can then be injected in other Spring components:
@@ -46,7 +46,81 @@ ElasticsearchOperations operations;      <.>
 ElasticsearchClient elasticsearchClient; <.>
 
 @Autowired
-RestClient restClient;                   <.>
+Rest5Client rest5Client;                 <.>
+
+@Autowired
+JsonpMapper jsonpMapper;                 <.>
+----
+
+<.> an implementation of javadoc:org.springframework.data.elasticsearch.core.ElasticsearchOperations[]
+<.> the `co.elastic.clients.elasticsearch.ElasticsearchClient` that is used.
+<.> the low level `Rest5Client` from the Elasticsearch libraries
+<.> the `JsonpMapper` user by the Elasticsearch `Transport`
+====
+
+Basically one should just use the javadoc:org.springframework.data.elasticsearch.core.ElasticsearchOperations[] to interact with the Elasticsearch cluster.
+When using repositories, this instance is used under the hood as well.
+
+[[elasticsearch.clients.restclient]]
+== Deprecated Imperative RestClient
+
+To use the imperative (non-reactive) RestClient - deprecated since version 6 - , the following dependency needs to be added, adapt the correct version. The exclusion is needed in a Spring Boot application:
+====
+[source,xml]
+----
+        <dependency>
+            <groupId>org.elasticsearch.client</groupId>
+            <artifactId>elasticsearch-rest-client</artifactId>
+            <version>${elasticsearch-client.version}</version>
+            <exclusions>
+                <exclusion>
+                    <groupId>commons-logging</groupId>
+                    <artifactId>commons-logging</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+
+----
+====
+
+The configuration bean must be configured like this:
+
+====
+[source,java]
+----
+import org.springframework.data.elasticsearch.client.elc.ElasticsearchLegacyRestClientConfiguration;
+
+@Configuration
+public class MyClientConfig extends ElasticsearchLegacyRestClientConfiguration {
+
+	@Override
+	public ClientConfiguration clientConfiguration() {
+		return ClientConfiguration.builder()           <.>
+			.connectedTo("localhost:9200")
+			.build();
+	}
+}
+----
+
+<.> for a detailed description of the builder methods see xref:elasticsearch/clients.adoc#elasticsearch.clients.configuration[Client Configuration]
+====
+
+The javadoc:org.springframework.data.elasticsearch.client.elc.ElasticsearchConfiguration[] class allows further configuration by overriding for example the `jsonpMapper()` or `transportOptions()` methods.
+
+
+The following beans can then be injected in other Spring components:
+
+====
+[source,java]
+----
+import org.springframework.beans.factory.annotation.Autowired;@Autowired
+ElasticsearchOperations operations;      <.>
+
+@Autowired
+ElasticsearchClient elasticsearchClient; <.>
+
+@Autowired
+RestClient restClient;                 <.>
 
 @Autowired
 JsonpMapper jsonpMapper;                 <.>
@@ -61,8 +135,8 @@ JsonpMapper jsonpMapper;                 <.>
 Basically one should just use the javadoc:org.springframework.data.elasticsearch.core.ElasticsearchOperations[] to interact with the Elasticsearch cluster.
 When using repositories, this instance is used under the hood as well.
 
-[[elasticsearch.clients.reactiverestclient]]
+[[elasticsearch.clients.reactiverest5client]]
-== Reactive Rest Client
+== Reactive Rest5Client
 
 When working with the reactive stack, the configuration must be derived from a different class:
 
@@ -99,6 +173,65 @@ ReactiveElasticsearchOperations operations;      <.>
 @Autowired
 ReactiveElasticsearchClient elasticsearchClient; <.>
 
+@Autowired
+Rest5Client rest5Client;                           <.>
+
+@Autowired
+JsonpMapper jsonpMapper;                         <.>
+----
+
+the following can be injected:
+
+<.> an implementation of javadoc:org.springframework.data.elasticsearch.core.ReactiveElasticsearchOperations[]
+<.> the `org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchClient` that is used.
+This is a reactive implementation based on the Elasticsearch client implementation.
+<.> the low level `RestClient` from the Elasticsearch libraries
+<.> the `JsonpMapper` user by the Elasticsearch `Transport`
+====
+
+Basically one should just use the javadoc:org.springframework.data.elasticsearch.core.ReactiveElasticsearchOperations[] to interact with the Elasticsearch cluster.
+When using repositories, this instance is used under the hood as well.
+
+[[elasticsearch.clients.reactiverestclient]]
+== Deprecated Reactive RestClient
+
+See the section above for the imperative code to use the deprecated RestClient for the necessary dependencies to include.
+
+When working with the reactive stack, the configuration must be derived from a different class:
+
+====
+[source,java]
+----
+import org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchLegacyRestClientConfiguration;
+
+@Configuration
+public class MyClientConfig extends ReactiveElasticsearchLegacyRestClientConfiguration {
+
+	@Override
+	public ClientConfiguration clientConfiguration() {
+		return ClientConfiguration.builder()           <.>
+			.connectedTo("localhost:9200")
+			.build();
+	}
+}
+----
+
+<.> for a detailed description of the builder methods see xref:elasticsearch/clients.adoc#elasticsearch.clients.configuration[Client Configuration]
+====
+
+The javadoc:org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchConfiguration[] class allows further configuration by overriding for example the `jsonpMapper()` or `transportOptions()` methods.
+
+The following beans can then be injected in other Spring components:
+
+====
+[source,java]
+----
+@Autowired
+ReactiveElasticsearchOperations operations;      <.>
+
+@Autowired
+ReactiveElasticsearchClient elasticsearchClient; <.>
+
 @Autowired
 RestClient restClient;                           <.>
 
@@ -183,8 +316,8 @@ In the case this is not enough, the user can add callback functions by using the
 
 The following callbacks are provided:
 
-[[elasticsearch.clients.configuration.callbacks.rest]]
+[[elasticsearch.clients.configuration.callbacks.rest5]]
-==== Configuration of the low level Elasticsearch `RestClient`:
+==== Configuration of the low level Elasticsearch `Rest5Client`:
 
 This callback provides a `org.elasticsearch.client.RestClientBuilder` that can be used to configure the Elasticsearch
 `RestClient`:
@@ -193,7 +326,24 @@ This callback provides a `org.elasticsearch.client.RestClientBuilder` that can b
 ----
 ClientConfiguration.builder()
     .connectedTo("localhost:9200", "localhost:9291")
-    .withClientConfigurer(ElasticsearchClients.ElasticsearchRestClientConfigurationCallback.from(restClientBuilder -> {
+    .withClientConfigurer(Rest5Clients.ElasticsearchRest5ClientConfigurationCallback.from(restClientBuilder -> {
+        // configure the Elasticsearch Rest5Client
+        return restClientBuilder;
+    }))
+    .build();
+----
+====
+[[elasticsearch.clients.configuration.callbacks.rest]]
+==== Configuration of the deprecated low level Elasticsearch `RestClient`:
+
+This callback provides a `org.elasticsearch.client.RestClientBuilder` that can be used to configure the Elasticsearch
+`RestClient`:
+====
+[source,java]
+----
+ClientConfiguration.builder()
+    .connectedTo("localhost:9200", "localhost:9291")
+    .withClientConfigurer(RestClients.ElasticsearchRestClientConfigurationCallback.from(restClientBuilder -> {
         // configure the Elasticsearch RestClient
         return restClientBuilder;
     }))
@@ -201,10 +351,29 @@ ClientConfiguration.builder()
 ----
 ====
 
-[[elasticsearch.clients.configurationcallbacks.httpasync]]
+[[elasticsearch.clients.configurationcallbacks.httpasync5]]
-==== Configuration of the HttpAsyncClient used by the low level Elasticsearch `RestClient`:
+==== Configuration of the HttpAsyncClient used by the low level Elasticsearch `Rest5Client`:
 
-This callback provides a `org.apache.http.impl.nio.client.HttpAsyncClientBuilder` to configure the HttpCLient that is
+This callback provides a `org.apache.hc.client5.http.impl.async.HttpAsyncClientBuilder` to configure the HttpClient that is
+used by the `Rest5Client`.
+
+====
+[source,java]
+----
+ClientConfiguration.builder()
+    .connectedTo("localhost:9200", "localhost:9291")
+    .withClientConfigurer(Rest5Clients.ElasticsearchHttpClientConfigurationCallback.from(httpAsyncClientBuilder -> {
+        // configure the HttpAsyncClient
+        return httpAsyncClientBuilder;
+    }))
+    .build();
+----
+====
+
+[[elasticsearch.clients.configurationcallbacks.httpasync]]
+==== Configuration of the HttpAsyncClient used by the deprecated low level Elasticsearch `RestClient`:
+
+This callback provides a `org.apache.http.impl.nio.client.HttpAsyncClientBuilder` to configure the HttpClient that is
 used by the `RestClient`.
 
 ====
@@ -212,7 +381,7 @@ used by the `RestClient`.
 ----
 ClientConfiguration.builder()
     .connectedTo("localhost:9200", "localhost:9291")
-    .withClientConfigurer(ElasticsearchClients.ElasticsearchHttpClientConfigurationCallback.from(httpAsyncClientBuilder -> {
+    .withClientConfigurer(RestClients.ElasticsearchHttpClientConfigurationCallback.from(httpAsyncClientBuilder -> {
         // configure the HttpAsyncClient
         return httpAsyncClientBuilder;
     }))

src/main/antora/modules/ROOT/pages/elasticsearch/elasticsearch-new.adoc

@@ -7,6 +7,7 @@
 * Upgarde to Spring 7
 * Switch to jspecify nullability annotations
 * Upgrade to Elasticsearch 9.0.3
+* Use the new Elasticsearch Rest5Client as default
 
 
 [[new-features.5-5-0]]

src/main/antora/modules/ROOT/pages/migration-guides/migration-guide-5.5-6.0.adoc

@@ -6,9 +6,13 @@ This section describes breaking changes from version 5.5.x to 6.0.x and how remo
 [[elasticsearch-migration-guide-5.5-6.0.breaking-changes]]
 == Breaking Changes
 
+From version 6.0 on, Spring Data Elasticsearch uses the Elasticsearch 9 libraries and as default the new `Rest5Client` provided by these libraries. It is still possible to use the old `RestClient`, check xref:elasticsearch/clients.adoc[Elasticsearch clients] for information. The configuration callbacks for this `RestClient` have been moved from `org.springframework.data.elasticsearch.client.elc.ElasticsearchClients` to the `org.springframework.data.elasticsearch.client.elc.rest_client.RestClients` class.
+
 [[elasticsearch-migration-guide-5.5-6.0.deprecations]]
 == Deprecations
 
+All the code using the old `RestClient` has been moved to the `org.springframework.data.elasticsearch.client.elc.rest_client` package and has been deprecated. Users should switch to the classes from the `org.springframework.data.elasticsearch.client.elc.rest5_client` package.
+
 
 === Removals
 

src/main/java/org/springframework/data/elasticsearch/client/ClientConfiguration.java

@@ -127,10 +127,16 @@ public interface ClientConfiguration {
 	Optional<String> getCaFingerprint();
 
 	/**
-	 * Returns the {@link HostnameVerifier} to use. Can be {@link Optional#empty()} if not configured.
+	 * Returns the {@link HostnameVerifier} to use. Must be {@link Optional#empty()} if not configured.
+	 * Cannot be used with the Rest5Client used from Elasticsearch 9 on as the underlying Apache http components 5 does not offer a way
+	 * to set this. Users that need a hostname verifier must integrate this in a SSLContext.
+	 * Returning a value here is ignored in this case
 	 *
 	 * @return the {@link HostnameVerifier} to use. Can be {@link Optional#empty()} if not configured.
+	 * @deprecated since 6.0
 	 */
+	// todo #3117 document this
+	@Deprecated(since = "6.0", forRemoval=true)
 	Optional<HostnameVerifier> getHostNameVerifier();
 
 	/**

src/main/java/org/springframework/data/elasticsearch/client/elc/ElasticsearchClients.java

@@ -15,44 +15,38 @@
  */
 package org.springframework.data.elasticsearch.client.elc;
 
+import static org.springframework.data.elasticsearch.client.elc.rest5_client.Rest5Clients.*;
+import static org.springframework.data.elasticsearch.client.elc.rest_client.RestClients.*;
+
 import co.elastic.clients.elasticsearch.ElasticsearchClient;
 import co.elastic.clients.json.JsonpMapper;
 import co.elastic.clients.json.jackson.JacksonJsonpMapper;
 import co.elastic.clients.transport.ElasticsearchTransport;
 import co.elastic.clients.transport.TransportOptions;
-import co.elastic.clients.transport.TransportUtils;
 import co.elastic.clients.transport.Version;
+import co.elastic.clients.transport.rest5_client.Rest5ClientOptions;
+import co.elastic.clients.transport.rest5_client.Rest5ClientTransport;
+import co.elastic.clients.transport.rest5_client.low_level.RequestOptions;
+import co.elastic.clients.transport.rest5_client.low_level.Rest5Client;
 import co.elastic.clients.transport.rest_client.RestClientOptions;
 import co.elastic.clients.transport.rest_client.RestClientTransport;
 
-import java.net.InetSocketAddress;
-import java.time.Duration;
-import java.util.Arrays;
-import java.util.List;
 import java.util.function.Consumer;
 import java.util.function.Function;
-import java.util.function.Supplier;
-import java.util.stream.Collectors;
 
-import org.apache.http.HttpHost;
-import org.apache.http.HttpRequest;
-import org.apache.http.HttpRequestInterceptor;
-import org.apache.http.client.config.RequestConfig;
 import org.apache.http.entity.ContentType;
 import org.apache.http.impl.nio.client.HttpAsyncClientBuilder;
-import org.apache.http.message.BasicHeader;
 import org.apache.http.message.BasicNameValuePair;
-import org.apache.http.protocol.HttpContext;
-import org.elasticsearch.client.RequestOptions;
 import org.elasticsearch.client.RestClient;
-import org.elasticsearch.client.RestClientBuilder;
 import org.jspecify.annotations.Nullable;
 import org.springframework.data.elasticsearch.client.ClientConfiguration;
-import org.springframework.data.elasticsearch.support.HttpHeaders;
+import org.springframework.data.elasticsearch.support.VersionInfo;
 import org.springframework.util.Assert;
 
 /**
- * Utility class to create the different Elasticsearch clients
+ * Utility class to create the different Elasticsearch clients. The RestClient class is the one used in Elasticsearch
+ * until version 9, it is still available, but it's use is deprecated. The Rest5Client class is the one that should be
+ * used from Elasticsearch 9 on.
  *
  * @author Peter-Josef Meisch
  * @since 4.4
@@ -119,18 +113,32 @@ public final class ElasticsearchClients {
 	 *
 	 * @param restClient the underlying {@link RestClient}
 	 * @return the {@link ReactiveElasticsearchClient}
+	 * @deprecated since 6.0, use the version with a Rest5Client.
 	 */
+	@Deprecated(since = "6.0", forRemoval = true)
 	public static ReactiveElasticsearchClient createReactive(RestClient restClient) {
 		return createReactive(restClient, null, DEFAULT_JSONP_MAPPER);
 	}
 
+	/**
+	 * Creates a new {@link ReactiveElasticsearchClient}.
+	 *
+	 * @param rest5Client the underlying {@link RestClient}
+	 * @return the {@link ReactiveElasticsearchClient}
+	 */
+	public static ReactiveElasticsearchClient createReactive(Rest5Client rest5Client) {
+		return createReactive(rest5Client, null, DEFAULT_JSONP_MAPPER);
+	}
+
 	/**
 	 * Creates a new {@link ReactiveElasticsearchClient}.
 	 *
 	 * @param restClient the underlying {@link RestClient}
 	 * @param transportOptions options to be added to each request.
 	 * @return the {@link ReactiveElasticsearchClient}
+	 * @deprecated since 6.0, use the version with a Rest5Client.
 	 */
+	@Deprecated(since = "6.0", forRemoval = true)
 	public static ReactiveElasticsearchClient createReactive(RestClient restClient,
 			@Nullable TransportOptions transportOptions, JsonpMapper jsonpMapper) {
 
@@ -139,6 +147,21 @@ public final class ElasticsearchClients {
 		var transport = getElasticsearchTransport(restClient, REACTIVE_CLIENT, transportOptions, jsonpMapper);
 		return createReactive(transport);
 	}
+	/**
+	 * Creates a new {@link ReactiveElasticsearchClient}.
+	 *
+	 * @param rest5Client the underlying {@link RestClient}
+	 * @param transportOptions options to be added to each request.
+	 * @return the {@link ReactiveElasticsearchClient}
+	 */
+	public static ReactiveElasticsearchClient createReactive(Rest5Client rest5Client,
+			@Nullable TransportOptions transportOptions, JsonpMapper jsonpMapper) {
+
+		Assert.notNull(rest5Client, "restClient must not be null");
+
+		var transport = getElasticsearchTransport(rest5Client, REACTIVE_CLIENT, transportOptions, jsonpMapper);
+		return createReactive(transport);
+	}
 
 	/**
 	 * Creates a new {@link ReactiveElasticsearchClient} that uses the given {@link ElasticsearchTransport}.
@@ -156,17 +179,21 @@ public final class ElasticsearchClients {
 
 	// region imperative client
 	/**
-	 * Creates a new imperative {@link ElasticsearchClient}
+	 * Creates a new imperative {@link ElasticsearchClient}. This uses a RestClient, if the old RestClient is needed, this
+	 * must be created with the {@link org.springframework.data.elasticsearch.client.elc.rest_client.RestClients} class
+	 * and passed in as parameter.
 	 *
 	 * @param clientConfiguration configuration options, must not be {@literal null}.
 	 * @return the {@link ElasticsearchClient}
 	 */
 	public static ElasticsearchClient createImperative(ClientConfiguration clientConfiguration) {
-		return createImperative(getRestClient(clientConfiguration), null, DEFAULT_JSONP_MAPPER);
+		return createImperative(getRest5Client(clientConfiguration), null, DEFAULT_JSONP_MAPPER);
 	}
 
 	/**
-	 * Creates a new imperative {@link ElasticsearchClient}
+	 * Creates a new imperative {@link ElasticsearchClient}. This uses a RestClient, if the old RestClient is needed, this
+	 * must be created with the {@link org.springframework.data.elasticsearch.client.elc.rest_client.RestClients} class
+	 * and passed in as parameter.
 	 *
 	 * @param clientConfiguration configuration options, must not be {@literal null}.
 	 * @param transportOptions options to be added to each request.
@@ -174,7 +201,7 @@ public final class ElasticsearchClients {
 	 */
 	public static ElasticsearchClient createImperative(ClientConfiguration clientConfiguration,
 			TransportOptions transportOptions) {
-		return createImperative(getRestClient(clientConfiguration), transportOptions, DEFAULT_JSONP_MAPPER);
+		return createImperative(getRest5Client(clientConfiguration), transportOptions, DEFAULT_JSONP_MAPPER);
 	}
 
 	/**
@@ -182,11 +209,23 @@ public final class ElasticsearchClients {
 	 *
 	 * @param restClient the RestClient to use
 	 * @return the {@link ElasticsearchClient}
+	 * @deprecated since 6.0, use the version with a Rest5Client.
 	 */
+	@Deprecated(since = "6.0", forRemoval = true)
 	public static ElasticsearchClient createImperative(RestClient restClient) {
 		return createImperative(restClient, null, DEFAULT_JSONP_MAPPER);
 	}
 
+	/**
+	 * Creates a new imperative {@link ElasticsearchClient}
+	 *
+	 * @param rest5Client the Rest5Client to use
+	 * @return the {@link ElasticsearchClient}
+	 */
+	public static ElasticsearchClient createImperative(Rest5Client rest5Client) {
+		return createImperative(rest5Client, null, DEFAULT_JSONP_MAPPER);
+	}
+
 	/**
 	 * Creates a new imperative {@link ElasticsearchClient}
 	 *
@@ -194,7 +233,9 @@ public final class ElasticsearchClients {
 	 * @param transportOptions options to be added to each request.
 	 * @param jsonpMapper the mapper for the transport to use
 	 * @return the {@link ElasticsearchClient}
+	 * @deprecated since 6.0, use the version with a Rest5Client.
 	 */
+	@Deprecated(since = "6.0", forRemoval = true)
 	public static ElasticsearchClient createImperative(RestClient restClient, @Nullable TransportOptions transportOptions,
 			JsonpMapper jsonpMapper) {
 
@@ -206,6 +247,27 @@ public final class ElasticsearchClients {
 		return createImperative(transport);
 	}
 
+	/**
+	 * Creates a new imperative {@link ElasticsearchClient}
+	 *
+	 * @param rest5Client the Rest5Client to use
+	 * @param transportOptions options to be added to each request.
+	 * @param jsonpMapper the mapper for the transport to use
+	 * @return the {@link ElasticsearchClient}
+	 * @since 6.0
+	 */
+	public static ElasticsearchClient createImperative(Rest5Client rest5Client,
+			@Nullable TransportOptions transportOptions,
+			JsonpMapper jsonpMapper) {
+
+		Assert.notNull(rest5Client, "restClient must not be null");
+
+		ElasticsearchTransport transport = getElasticsearchTransport(rest5Client, IMPERATIVE_CLIENT, transportOptions,
+				jsonpMapper);
+
+		return createImperative(transport);
+	}
+
 	/**
 	 * Creates a new {@link ElasticsearchClient} that uses the given {@link ElasticsearchTransport}.
 	 *
@@ -220,96 +282,6 @@ public final class ElasticsearchClients {
 	}
 	// endregion
 
-	// region low level RestClient
-	private static RestClientOptions.Builder getRestClientOptionsBuilder(@Nullable TransportOptions transportOptions) {
-
-		if (transportOptions instanceof RestClientOptions restClientOptions) {
-			return restClientOptions.toBuilder();
-		}
-
-		var builder = new RestClientOptions.Builder(RequestOptions.DEFAULT.toBuilder());
-
-		if (transportOptions != null) {
-			transportOptions.headers().forEach(header -> builder.addHeader(header.getKey(), header.getValue()));
-			transportOptions.queryParameters().forEach(builder::setParameter);
-			builder.onWarnings(transportOptions.onWarnings());
-		}
-
-		return builder;
-	}
-
-	/**
-	 * Creates a low level {@link RestClient} for the given configuration.
-	 *
-	 * @param clientConfiguration must not be {@literal null}
-	 * @return the {@link RestClient}
-	 */
-	public static RestClient getRestClient(ClientConfiguration clientConfiguration) {
-		return getRestClientBuilder(clientConfiguration).build();
-	}
-
-	private static RestClientBuilder getRestClientBuilder(ClientConfiguration clientConfiguration) {
-		HttpHost[] httpHosts = formattedHosts(clientConfiguration.getEndpoints(), clientConfiguration.useSsl()).stream()
-				.map(HttpHost::create).toArray(HttpHost[]::new);
-		RestClientBuilder builder = RestClient.builder(httpHosts);
-
-		if (clientConfiguration.getPathPrefix() != null) {
-			builder.setPathPrefix(clientConfiguration.getPathPrefix());
-		}
-
-		HttpHeaders headers = clientConfiguration.getDefaultHeaders();
-
-		if (!headers.isEmpty()) {
-			builder.setDefaultHeaders(toHeaderArray(headers));
-		}
-
-		builder.setHttpClientConfigCallback(clientBuilder -> {
-			if (clientConfiguration.getCaFingerprint().isPresent()) {
-				clientBuilder
-						.setSSLContext(TransportUtils.sslContextFromCaFingerprint(clientConfiguration.getCaFingerprint().get()));
-			}
-			clientConfiguration.getSslContext().ifPresent(clientBuilder::setSSLContext);
-			clientConfiguration.getHostNameVerifier().ifPresent(clientBuilder::setSSLHostnameVerifier);
-			clientBuilder.addInterceptorLast(new CustomHeaderInjector(clientConfiguration.getHeadersSupplier()));
-
-			RequestConfig.Builder requestConfigBuilder = RequestConfig.custom();
-			Duration connectTimeout = clientConfiguration.getConnectTimeout();
-
-			if (!connectTimeout.isNegative()) {
-				requestConfigBuilder.setConnectTimeout(Math.toIntExact(connectTimeout.toMillis()));
-			}
-
-			Duration socketTimeout = clientConfiguration.getSocketTimeout();
-
-			if (!socketTimeout.isNegative()) {
-				requestConfigBuilder.setSocketTimeout(Math.toIntExact(socketTimeout.toMillis()));
-				requestConfigBuilder.setConnectionRequestTimeout(Math.toIntExact(socketTimeout.toMillis()));
-			}
-
-			clientBuilder.setDefaultRequestConfig(requestConfigBuilder.build());
-
-			clientConfiguration.getProxy().map(HttpHost::create).ifPresent(clientBuilder::setProxy);
-
-			for (ClientConfiguration.ClientConfigurationCallback<?> clientConfigurer : clientConfiguration
-					.getClientConfigurers()) {
-				if (clientConfigurer instanceof ElasticsearchHttpClientConfigurationCallback restClientConfigurationCallback) {
-					clientBuilder = restClientConfigurationCallback.configure(clientBuilder);
-				}
-			}
-
-			return clientBuilder;
-		});
-
-		for (ClientConfiguration.ClientConfigurationCallback<?> clientConfigurationCallback : clientConfiguration
-				.getClientConfigurers()) {
-			if (clientConfigurationCallback instanceof ElasticsearchRestClientConfigurationCallback configurationCallback) {
-				builder = configurationCallback.configure(builder);
-			}
-		}
-		return builder;
-	}
-	// endregion
-
 	// region Elasticsearch transport
 	/**
 	 * Creates an {@link ElasticsearchTransport} that will use the given client that additionally is customized with a
@@ -320,7 +292,9 @@ public final class ElasticsearchClients {
 	 * @param transportOptions options for the transport
 	 * @param jsonpMapper mapper for the transport
 	 * @return ElasticsearchTransport
+	 * @deprecated since 6.0, use the version taking a Rest5Client
 	 */
+	@Deprecated(since = "6.0", forRemoval = true)
 	public static ElasticsearchTransport getElasticsearchTransport(RestClient restClient, String clientType,
 			@Nullable TransportOptions transportOptions, JsonpMapper jsonpMapper) {
 
@@ -329,7 +303,7 @@ public final class ElasticsearchClients {
 		Assert.notNull(jsonpMapper, "jsonpMapper must not be null");
 
 		TransportOptions.Builder transportOptionsBuilder = transportOptions != null ? transportOptions.toBuilder()
-				: new RestClientOptions(RequestOptions.DEFAULT, false).toBuilder();
+				: new RestClientOptions(org.elasticsearch.client.RequestOptions.DEFAULT, false).toBuilder();
 
 		RestClientOptions.Builder restClientOptionsBuilder = getRestClientOptionsBuilder(transportOptions);
 
@@ -353,70 +327,35 @@ public final class ElasticsearchClients {
 
 		return new RestClientTransport(restClient, jsonpMapper, restClientOptionsBuilder.build());
 	}
+
+	/**
+	 * Creates an {@link ElasticsearchTransport} that will use the given client that additionally is customized with a
+	 * header to contain the clientType
+	 *
+	 * @param rest5Client the client to use
+	 * @param clientType the client type to pass in each request as header
+	 * @param transportOptions options for the transport
+	 * @param jsonpMapper mapper for the transport
+	 * @return ElasticsearchTransport
+	 */
+	public static ElasticsearchTransport getElasticsearchTransport(Rest5Client rest5Client, String clientType,
+			@Nullable TransportOptions transportOptions, JsonpMapper jsonpMapper) {
+
+		Assert.notNull(rest5Client, "restClient must not be null");
+		Assert.notNull(clientType, "clientType must not be null");
+		Assert.notNull(jsonpMapper, "jsonpMapper must not be null");
+
+		TransportOptions.Builder transportOptionsBuilder = transportOptions != null ? transportOptions.toBuilder()
+				: new Rest5ClientOptions(RequestOptions.DEFAULT, false).toBuilder();
+
+		Rest5ClientOptions.Builder rest5ClientOptionsBuilder = getRest5ClientOptionsBuilder(transportOptions);
+
+		rest5ClientOptionsBuilder.addHeader(X_SPRING_DATA_ELASTICSEARCH_CLIENT,
+				VersionInfo.clientVersions() + " / " + clientType);
+
+		return new Rest5ClientTransport(rest5Client, jsonpMapper, rest5ClientOptionsBuilder.build());
+	}
 	// endregion
 
-	private static List<String> formattedHosts(List<InetSocketAddress> hosts, boolean useSsl) {
+	// todo #3117 remove and document that ElasticsearchHttpClientConfigurationCallback has been move to RestClients.
-		return hosts.stream().map(it -> (useSsl ? "https" : "http") + "://" + it.getHostString() + ':' + it.getPort())
-				.collect(Collectors.toList());
-	}
-
-	private static org.apache.http.Header[] toHeaderArray(HttpHeaders headers) {
-		return headers.entrySet().stream() //
-				.flatMap(entry -> entry.getValue().stream() //
-						.map(value -> new BasicHeader(entry.getKey(), value))) //
-				.toArray(org.apache.http.Header[]::new);
-	}
-
-	/**
-	 * Interceptor to inject custom supplied headers.
-	 *
-	 * @since 4.4
-	 */
-	private record CustomHeaderInjector(Supplier<HttpHeaders> headersSupplier) implements HttpRequestInterceptor {
-
-		@Override
-		public void process(HttpRequest request, HttpContext context) {
-			HttpHeaders httpHeaders = headersSupplier.get();
-
-			if (httpHeaders != null && !httpHeaders.isEmpty()) {
-				Arrays.stream(toHeaderArray(httpHeaders)).forEach(request::addHeader);
-			}
-		}
-	}
-
-	/**
-	 * {@link org.springframework.data.elasticsearch.client.ClientConfiguration.ClientConfigurationCallback} to configure
-	 * the Elasticsearch RestClient's Http client with a {@link HttpAsyncClientBuilder}
-	 *
-	 * @since 4.4
-	 */
-	public interface ElasticsearchHttpClientConfigurationCallback
-			extends ClientConfiguration.ClientConfigurationCallback<HttpAsyncClientBuilder> {
-
-		static ElasticsearchHttpClientConfigurationCallback from(
-				Function<HttpAsyncClientBuilder, HttpAsyncClientBuilder> httpClientBuilderCallback) {
-
-			Assert.notNull(httpClientBuilderCallback, "httpClientBuilderCallback must not be null");
-
-			return httpClientBuilderCallback::apply;
-		}
-	}
-
-	/**
-	 * {@link org.springframework.data.elasticsearch.client.ClientConfiguration.ClientConfigurationCallback} to configure
-	 * the RestClient client with a {@link RestClientBuilder}
-	 *
-	 * @since 5.0
-	 */
-	public interface ElasticsearchRestClientConfigurationCallback
-			extends ClientConfiguration.ClientConfigurationCallback<RestClientBuilder> {
-
-		static ElasticsearchRestClientConfigurationCallback from(
-				Function<RestClientBuilder, RestClientBuilder> restClientBuilderCallback) {
-
-			Assert.notNull(restClientBuilderCallback, "restClientBuilderCallback must not be null");
-
-			return restClientBuilderCallback::apply;
-		}
-	}
 }

src/main/java/org/springframework/data/elasticsearch/client/elc/ElasticsearchConfiguration.java

@@ -20,12 +20,13 @@ import co.elastic.clients.json.JsonpMapper;
 import co.elastic.clients.json.jackson.JacksonJsonpMapper;
 import co.elastic.clients.transport.ElasticsearchTransport;
 import co.elastic.clients.transport.TransportOptions;
-import co.elastic.clients.transport.rest_client.RestClientOptions;
+import co.elastic.clients.transport.rest5_client.Rest5ClientOptions;
+import co.elastic.clients.transport.rest5_client.low_level.RequestOptions;
+import co.elastic.clients.transport.rest5_client.low_level.Rest5Client;
 
-import org.elasticsearch.client.RequestOptions;
-import org.elasticsearch.client.RestClient;
 import org.springframework.context.annotation.Bean;
 import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.rest5_client.Rest5Clients;
 import org.springframework.data.elasticsearch.config.ElasticsearchConfigurationSupport;
 import org.springframework.data.elasticsearch.core.ElasticsearchOperations;
 import org.springframework.data.elasticsearch.core.convert.ElasticsearchConverter;
@@ -38,7 +39,9 @@ import com.fasterxml.jackson.databind.SerializationFeature;
 /**
  * Base class for a @{@link org.springframework.context.annotation.Configuration} class to set up the Elasticsearch
  * connection using the Elasticsearch Client. This class exposes different parts of the setup as Spring beans. Deriving
- * classes must provide the {@link ClientConfiguration} to use.
+ * classes must provide the {@link ClientConfiguration} to use. From Version 6.0 on, this class uses the new Rest5Client
+ * from Elasticsearch 9. The old implementation using the RestClient is still available under the name
+ * {@link ElasticsearchLegacyRestClientConfiguration}.
  *
  * @author Peter-Josef Meisch
  * @since 4.4
@@ -60,27 +63,27 @@ public abstract class ElasticsearchConfiguration extends ElasticsearchConfigurat
 	 * @return RestClient
 	 */
 	@Bean
-	public RestClient elasticsearchRestClient(ClientConfiguration clientConfiguration) {
+	public Rest5Client elasticsearchRest5Client(ClientConfiguration clientConfiguration) {
 
 		Assert.notNull(clientConfiguration, "clientConfiguration must not be null");
 
-		return ElasticsearchClients.getRestClient(clientConfiguration);
+		return Rest5Clients.getRest5Client(clientConfiguration);
 	}
 
 	/**
-	 * Provides the Elasticsearch transport to be used. The default implementation uses the {@link RestClient} bean and
+	 * Provides the Elasticsearch transport to be used. The default implementation uses the {@link Rest5Client} bean and
 	 * the {@link JsonpMapper} bean provided in this class.
 	 *
 	 * @return the {@link ElasticsearchTransport}
 	 * @since 5.2
 	 */
 	@Bean
-	public ElasticsearchTransport elasticsearchTransport(RestClient restClient, JsonpMapper jsonpMapper) {
+	public ElasticsearchTransport elasticsearchTransport(Rest5Client rest5Client, JsonpMapper jsonpMapper) {
 
-		Assert.notNull(restClient, "restClient must not be null");
+		Assert.notNull(rest5Client, "restClient must not be null");
 		Assert.notNull(jsonpMapper, "jsonpMapper must not be null");
 
-		return ElasticsearchClients.getElasticsearchTransport(restClient, ElasticsearchClients.IMPERATIVE_CLIENT,
+		return ElasticsearchClients.getElasticsearchTransport(rest5Client, ElasticsearchClients.IMPERATIVE_CLIENT,
 				transportOptions(), jsonpMapper);
 	}
 
@@ -115,7 +118,7 @@ public abstract class ElasticsearchConfiguration extends ElasticsearchConfigurat
 	}
 
 	/**
-	 * Provides the JsonpMapper bean that is used in the {@link #elasticsearchTransport(RestClient, JsonpMapper)} method.
+	 * Provides the JsonpMapper bean that is used in the {@link #elasticsearchTransport(Rest5Client, JsonpMapper)} method.
 	 *
 	 * @return the {@link JsonpMapper} to use
 	 * @since 5.2
@@ -135,6 +138,6 @@ public abstract class ElasticsearchConfiguration extends ElasticsearchConfigurat
 	 * @return the options that should be added to every request. Must not be {@literal null}
 	 */
 	public TransportOptions transportOptions() {
-		return new RestClientOptions(RequestOptions.DEFAULT, false);
+		return new Rest5ClientOptions(RequestOptions.DEFAULT, false);
 	}
 }

src/main/java/org/springframework/data/elasticsearch/client/elc/ElasticsearchExceptionTranslator.java

@@ -119,14 +119,19 @@ public class ElasticsearchExceptionTranslator implements PersistenceExceptionTra
 		String message = null;
 
 		if (exception instanceof ResponseException responseException) {
+			// this code is for the old RestClient
 			status = responseException.getResponse().getStatusLine().getStatusCode();
 			message = responseException.getMessage();
+		} else if (exception instanceof ElasticsearchException elasticsearchException) {
+			// using the RestClient throws this
+			status = elasticsearchException.status();
+			message = elasticsearchException.getMessage();
 		} else if (exception.getCause() != null) {
 			checkForConflictException(exception.getCause());
 		}
 
 		if (status != null && message != null) {
-			if (status == 409 && message.contains("type\":\"version_conflict_engine_exception"))
+			if (status == 409 && message.contains("version_conflict_engine_exception"))
 				if (message.contains("version conflict, required seqNo")) {
 					throw new OptimisticLockingFailureException("Cannot index a document due to seq_no+primary_term conflict",
 							exception);

src/main/java/org/springframework/data/elasticsearch/client/elc/ElasticsearchLegacyRestClientConfiguration.java

@@ -0,0 +1,144 @@
+/*
+ * Copyright 2021-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.elasticsearch.client.elc;
+
+import co.elastic.clients.elasticsearch.ElasticsearchClient;
+import co.elastic.clients.json.JsonpMapper;
+import co.elastic.clients.json.jackson.JacksonJsonpMapper;
+import co.elastic.clients.transport.ElasticsearchTransport;
+import co.elastic.clients.transport.TransportOptions;
+import co.elastic.clients.transport.rest_client.RestClientOptions;
+
+import org.elasticsearch.client.RequestOptions;
+import org.elasticsearch.client.RestClient;
+import org.springframework.context.annotation.Bean;
+import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.rest_client.RestClients;
+import org.springframework.data.elasticsearch.config.ElasticsearchConfigurationSupport;
+import org.springframework.data.elasticsearch.core.ElasticsearchOperations;
+import org.springframework.data.elasticsearch.core.convert.ElasticsearchConverter;
+import org.springframework.util.Assert;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+
+/**
+ * Base class for a @{@link org.springframework.context.annotation.Configuration} class to set up the Elasticsearch
+ * connection using the Elasticsearch Client. This class exposes different parts of the setup as Spring beans. Deriving
+ * classes must provide the {@link ClientConfiguration} to use. <br/>
+ * This class uses the Elasticsearch RestClient which was replaced by the Rest5Client in Elasticsearch 9. It is still
+ * available here but deprecated.
+ *
+ * @author Peter-Josef Meisch
+ * @since 4.4
+ * @deprecated since 6.0, use {@link ElasticsearchConfiguration}
+ */
+@Deprecated(since = "6.0", forRemoval=true)
+public abstract class ElasticsearchLegacyRestClientConfiguration extends ElasticsearchConfigurationSupport {
+
+	/**
+	 * Must be implemented by deriving classes to provide the {@link ClientConfiguration}.
+	 *
+	 * @return configuration, must not be {@literal null}
+	 */
+	@Bean(name = "elasticsearchClientConfiguration")
+	public abstract ClientConfiguration clientConfiguration();
+
+	/**
+	 * Provides the underlying low level Elasticsearch RestClient.
+	 *
+	 * @param clientConfiguration configuration for the client, must not be {@literal null}
+	 * @return RestClient
+	 */
+	@Bean
+	public RestClient elasticsearchRestClient(ClientConfiguration clientConfiguration) {
+
+		Assert.notNull(clientConfiguration, "clientConfiguration must not be null");
+
+		return RestClients.getRestClient(clientConfiguration);
+	}
+
+	/**
+	 * Provides the Elasticsearch transport to be used. The default implementation uses the {@link RestClient} bean and
+	 * the {@link JsonpMapper} bean provided in this class.
+	 *
+	 * @return the {@link ElasticsearchTransport}
+	 * @since 5.2
+	 */
+	@Bean
+	public ElasticsearchTransport elasticsearchTransport(RestClient restClient, JsonpMapper jsonpMapper) {
+
+		Assert.notNull(restClient, "restClient must not be null");
+		Assert.notNull(jsonpMapper, "jsonpMapper must not be null");
+
+		return ElasticsearchClients.getElasticsearchTransport(restClient, ElasticsearchClients.IMPERATIVE_CLIENT,
+				transportOptions(), jsonpMapper);
+	}
+
+	/**
+	 * Provides the {@link ElasticsearchClient} to be used.
+	 *
+	 * @param transport the {@link ElasticsearchTransport} to use
+	 * @return ElasticsearchClient instance
+	 */
+	@Bean
+	public ElasticsearchClient elasticsearchClient(ElasticsearchTransport transport) {
+
+		Assert.notNull(transport, "transport must not be null");
+
+		return ElasticsearchClients.createImperative(transport);
+	}
+
+	/**
+	 * Creates a {@link ElasticsearchOperations} implementation using an {@link ElasticsearchClient}.
+	 *
+	 * @return never {@literal null}.
+	 */
+	@Bean(name = { "elasticsearchOperations", "elasticsearchTemplate" })
+	public ElasticsearchOperations elasticsearchOperations(ElasticsearchConverter elasticsearchConverter,
+			ElasticsearchClient elasticsearchClient) {
+
+		ElasticsearchTemplate template = new ElasticsearchTemplate(elasticsearchClient, elasticsearchConverter);
+		template.setRefreshPolicy(refreshPolicy());
+
+		return template;
+	}
+
+	/**
+	 * Provides the JsonpMapper bean that is used in the {@link #elasticsearchTransport(RestClient, JsonpMapper)} method.
+	 *
+	 * @return the {@link JsonpMapper} to use
+	 * @since 5.2
+	 */
+	@Bean
+	public JsonpMapper jsonpMapper() {
+		// we need to create our own objectMapper that keeps null values in order to provide the storeNullValue
+		// functionality. The one Elasticsearch would provide removes the nulls. We remove unwanted nulls before they get
+		// into this mapper, so we can safely keep them here.
+		var objectMapper = (new ObjectMapper())
+				.configure(SerializationFeature.INDENT_OUTPUT, false)
+				.setSerializationInclusion(JsonInclude.Include.ALWAYS);
+		return new JacksonJsonpMapper(objectMapper);
+	}
+
+	/**
+	 * @return the options that should be added to every request. Must not be {@literal null}
+	 */
+	public TransportOptions transportOptions() {
+		return new RestClientOptions(RequestOptions.DEFAULT, false);
+	}
+}

src/main/java/org/springframework/data/elasticsearch/client/elc/ReactiveElasticsearchConfiguration.java

@@ -19,12 +19,18 @@ import co.elastic.clients.json.JsonpMapper;
 import co.elastic.clients.json.jackson.JacksonJsonpMapper;
 import co.elastic.clients.transport.ElasticsearchTransport;
 import co.elastic.clients.transport.TransportOptions;
+import co.elastic.clients.transport.rest5_client.Rest5ClientOptions;
+import co.elastic.clients.transport.rest5_client.low_level.RequestOptions;
+import co.elastic.clients.transport.rest5_client.low_level.Rest5Client;
 import co.elastic.clients.transport.rest_client.RestClientOptions;
 
-import org.elasticsearch.client.RequestOptions;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
 import org.elasticsearch.client.RestClient;
 import org.springframework.context.annotation.Bean;
 import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.rest5_client.Rest5Clients;
 import org.springframework.data.elasticsearch.config.ElasticsearchConfigurationSupport;
 import org.springframework.data.elasticsearch.core.ReactiveElasticsearchOperations;
 import org.springframework.data.elasticsearch.core.convert.ElasticsearchConverter;
@@ -55,11 +61,11 @@ public abstract class ReactiveElasticsearchConfiguration extends ElasticsearchCo
 	 * @return RestClient
 	 */
 	@Bean
-	public RestClient elasticsearchRestClient(ClientConfiguration clientConfiguration) {
+	public Rest5Client elasticsearchRestClient(ClientConfiguration clientConfiguration) {
 
 		Assert.notNull(clientConfiguration, "clientConfiguration must not be null");
 
-		return ElasticsearchClients.getRestClient(clientConfiguration);
+		return Rest5Clients.getRest5Client(clientConfiguration);
 	}
 
 	/**
@@ -70,12 +76,12 @@ public abstract class ReactiveElasticsearchConfiguration extends ElasticsearchCo
 	 * @since 5.2
 	 */
 	@Bean
-	public ElasticsearchTransport elasticsearchTransport(RestClient restClient, JsonpMapper jsonpMapper) {
+	public ElasticsearchTransport elasticsearchTransport(Rest5Client rest5Client, JsonpMapper jsonpMapper) {
 
-		Assert.notNull(restClient, "restClient must not be null");
+		Assert.notNull(rest5Client, "restClient must not be null");
 		Assert.notNull(jsonpMapper, "jsonpMapper must not be null");
 
-		return ElasticsearchClients.getElasticsearchTransport(restClient, ElasticsearchClients.REACTIVE_CLIENT,
+		return ElasticsearchClients.getElasticsearchTransport(rest5Client, ElasticsearchClients.REACTIVE_CLIENT,
 				transportOptions(), jsonpMapper);
 	}
 
@@ -110,7 +116,7 @@ public abstract class ReactiveElasticsearchConfiguration extends ElasticsearchCo
 	}
 
 	/**
-	 * Provides the JsonpMapper that is used in the {@link #elasticsearchTransport(RestClient, JsonpMapper)} method and
+	 * Provides the JsonpMapper that is used in the {@link #elasticsearchTransport(Rest5Client, JsonpMapper)} method and
 	 * exposes it as a bean.
 	 *
 	 * @return the {@link JsonpMapper} to use
@@ -118,13 +124,19 @@ public abstract class ReactiveElasticsearchConfiguration extends ElasticsearchCo
 	 */
 	@Bean
 	public JsonpMapper jsonpMapper() {
-		return new JacksonJsonpMapper();
+		// we need to create our own objectMapper that keeps null values in order to provide the storeNullValue
+		// functionality. The one Elasticsearch would provide removes the nulls. We remove unwanted nulls before they get
+		// into this mapper, so we can safely keep them here.
+		var objectMapper = (new ObjectMapper())
+				.configure(SerializationFeature.INDENT_OUTPUT, false)
+				.setSerializationInclusion(JsonInclude.Include.ALWAYS);
+		return new JacksonJsonpMapper(objectMapper);
 	}
 
 	/**
 	 * @return the options that should be added to every request. Must not be {@literal null}
 	 */
 	public TransportOptions transportOptions() {
-		return new RestClientOptions(RequestOptions.DEFAULT, false).toBuilder().build();
+		return new Rest5ClientOptions(RequestOptions.DEFAULT, false);
 	}
 }

src/main/java/org/springframework/data/elasticsearch/client/elc/ReactiveElasticsearchLegacyRestClientConfiguration.java

@@ -0,0 +1,144 @@
+/*
+ * Copyright 2021-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.elasticsearch.client.elc;
+
+import co.elastic.clients.json.JsonpMapper;
+import co.elastic.clients.json.jackson.JacksonJsonpMapper;
+import co.elastic.clients.transport.ElasticsearchTransport;
+import co.elastic.clients.transport.TransportOptions;
+import co.elastic.clients.transport.rest_client.RestClientOptions;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import org.elasticsearch.client.RequestOptions;
+import org.elasticsearch.client.RestClient;
+import org.springframework.context.annotation.Bean;
+import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.rest_client.RestClients;
+import org.springframework.data.elasticsearch.config.ElasticsearchConfigurationSupport;
+import org.springframework.data.elasticsearch.core.ReactiveElasticsearchOperations;
+import org.springframework.data.elasticsearch.core.convert.ElasticsearchConverter;
+import org.springframework.util.Assert;
+
+/**
+ * Base class for a @{@link org.springframework.context.annotation.Configuration} class to set up the Elasticsearch
+ * connection using the {@link ReactiveElasticsearchClient}. This class exposes different parts of the setup as Spring
+ * beans. Deriving * classes must provide the {@link ClientConfiguration} to use. <br/>
+ * This class uses the Elasticsearch RestClient which was replaced b y the Rest5Client in Elasticsearch 9. It is still
+ * available here but deprecated. *
+ *
+ * @author Peter-Josef Meisch
+ * @since 4.4
+ * @deprecated since 6.0 use {@link ReactiveElasticsearchConfiguration}
+ */
+@Deprecated(since = "6.0", forRemoval=true)
+public abstract class ReactiveElasticsearchLegacyRestClientConfiguration extends ElasticsearchConfigurationSupport {
+
+	/**
+	 * Must be implemented by deriving classes to provide the {@link ClientConfiguration}.
+	 *
+	 * @return configuration, must not be {@literal null}
+	 */
+	@Bean(name = "elasticsearchClientConfiguration")
+	public abstract ClientConfiguration clientConfiguration();
+
+	/**
+	 * Provides the underlying low level RestClient.
+	 *
+	 * @param clientConfiguration configuration for the client, must not be {@literal null}
+	 * @return RestClient
+	 */
+	@Bean
+	public RestClient elasticsearchRestClient(ClientConfiguration clientConfiguration) {
+
+		Assert.notNull(clientConfiguration, "clientConfiguration must not be null");
+
+		return RestClients.getRestClient(clientConfiguration);
+	}
+
+	/**
+	 * Provides the Elasticsearch transport to be used. The default implementation uses the {@link RestClient} bean and
+	 * the {@link JsonpMapper} bean provided in this class.
+	 *
+	 * @return the {@link ElasticsearchTransport}
+	 * @since 5.2
+	 */
+	@Bean
+	public ElasticsearchTransport elasticsearchTransport(RestClient restClient, JsonpMapper jsonpMapper) {
+
+		Assert.notNull(restClient, "restClient must not be null");
+		Assert.notNull(jsonpMapper, "jsonpMapper must not be null");
+
+		return ElasticsearchClients.getElasticsearchTransport(restClient, ElasticsearchClients.REACTIVE_CLIENT,
+				transportOptions(), jsonpMapper);
+	}
+
+	/**
+	 * Provides the {@link ReactiveElasticsearchClient} instance used.
+	 *
+	 * @param transport the ElasticsearchTransport to use
+	 * @return ReactiveElasticsearchClient instance.
+	 */
+	@Bean
+	public ReactiveElasticsearchClient reactiveElasticsearchClient(ElasticsearchTransport transport) {
+
+		Assert.notNull(transport, "transport must not be null");
+
+		return ElasticsearchClients.createReactive(transport);
+	}
+
+	/**
+	 * Creates {@link ReactiveElasticsearchOperations}.
+	 *
+	 * @return never {@literal null}.
+	 */
+	@Bean(name = { "reactiveElasticsearchOperations", "reactiveElasticsearchTemplate" })
+	public ReactiveElasticsearchOperations reactiveElasticsearchOperations(ElasticsearchConverter elasticsearchConverter,
+			ReactiveElasticsearchClient reactiveElasticsearchClient) {
+
+		ReactiveElasticsearchTemplate template = new ReactiveElasticsearchTemplate(reactiveElasticsearchClient,
+				elasticsearchConverter);
+		template.setRefreshPolicy(refreshPolicy());
+
+		return template;
+	}
+
+	/**
+	 * Provides the JsonpMapper that is used in the {@link #elasticsearchTransport(RestClient, JsonpMapper)} method and
+	 * exposes it as a bean.
+	 *
+	 * @return the {@link JsonpMapper} to use
+	 * @since 5.2
+	 */
+	@Bean
+	public JsonpMapper jsonpMapper() {
+		// we need to create our own objectMapper that keeps null values in order to provide the storeNullValue
+		// functionality. The one Elasticsearch would provide removes the nulls. We remove unwanted nulls before they get
+		// into this mapper, so we can safely keep them here.
+		var objectMapper = (new ObjectMapper())
+				.configure(SerializationFeature.INDENT_OUTPUT, false)
+				.setSerializationInclusion(JsonInclude.Include.ALWAYS);
+		return new JacksonJsonpMapper(objectMapper);
+	}
+
+	/**
+	 * @return the options that should be added to every request. Must not be {@literal null}
+	 */
+	public TransportOptions transportOptions() {
+		return new RestClientOptions(RequestOptions.DEFAULT, false).toBuilder().build();
+	}
+}

src/main/java/org/springframework/data/elasticsearch/client/elc/rest5_client/Rest5Clients.java

@@ -0,0 +1,274 @@
+package org.springframework.data.elasticsearch.client.elc.rest5_client;
+
+import co.elastic.clients.transport.TransportOptions;
+import co.elastic.clients.transport.TransportUtils;
+import co.elastic.clients.transport.rest5_client.Rest5ClientOptions;
+import co.elastic.clients.transport.rest5_client.low_level.RequestOptions;
+import co.elastic.clients.transport.rest5_client.low_level.Rest5Client;
+import co.elastic.clients.transport.rest5_client.low_level.Rest5ClientBuilder;
+
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.security.NoSuchAlgorithmException;
+import java.time.Duration;
+import java.util.List;
+import java.util.Locale;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.Function;
+
+import javax.net.ssl.SSLContext;
+
+import org.apache.hc.client5.http.config.ConnectionConfig;
+import org.apache.hc.client5.http.config.RequestConfig;
+import org.apache.hc.client5.http.impl.DefaultAuthenticationStrategy;
+import org.apache.hc.client5.http.impl.async.CloseableHttpAsyncClient;
+import org.apache.hc.client5.http.impl.async.HttpAsyncClientBuilder;
+import org.apache.hc.client5.http.impl.nio.PoolingAsyncClientConnectionManager;
+import org.apache.hc.client5.http.impl.nio.PoolingAsyncClientConnectionManagerBuilder;
+import org.apache.hc.client5.http.impl.routing.DefaultProxyRoutePlanner;
+import org.apache.hc.core5.http.Header;
+import org.apache.hc.core5.http.HttpHost;
+import org.apache.hc.core5.http.message.BasicHeader;
+import org.apache.hc.core5.http.nio.ssl.BasicClientTlsStrategy;
+import org.apache.hc.core5.util.Timeout;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
+import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.support.HttpHeaders;
+import org.springframework.data.elasticsearch.support.VersionInfo;
+import org.springframework.util.Assert;
+
+/**
+ * Utility class containing the functions to create the Elasticsearch Rest5Client used from Elasticsearch 9 on.
+ *
+ * @since 6.0
+ */
+public final class Rest5Clients {
+
+	// values copied from Rest5ClientBuilder
+	public static final int DEFAULT_CONNECT_TIMEOUT_MILLIS = 1000;
+	public static final int DEFAULT_SOCKET_TIMEOUT_MILLIS = 30000;
+	public static final int DEFAULT_RESPONSE_TIMEOUT_MILLIS = 0; // meaning infinite
+	public static final int DEFAULT_MAX_CONN_PER_ROUTE = 10;
+	public static final int DEFAULT_MAX_CONN_TOTAL = 30;
+
+	private Rest5Clients() {}
+
+	/**
+	 * Creates a low level {@link Rest5Client} for the given configuration.
+	 *
+	 * @param clientConfiguration must not be {@literal null}
+	 * @return the {@link Rest5Client}
+	 */
+	public static Rest5Client getRest5Client(ClientConfiguration clientConfiguration) {
+		return getRest5ClientBuilder(clientConfiguration).build();
+	}
+
+	private static Rest5ClientBuilder getRest5ClientBuilder(ClientConfiguration clientConfiguration) {
+
+		HttpHost[] httpHosts = getHttpHosts(clientConfiguration);
+		Rest5ClientBuilder builder = Rest5Client.builder(httpHosts);
+
+		if (clientConfiguration.getPathPrefix() != null) {
+			builder.setPathPrefix(clientConfiguration.getPathPrefix());
+		}
+
+		HttpHeaders headers = clientConfiguration.getDefaultHeaders();
+
+		if (!headers.isEmpty()) {
+			builder.setDefaultHeaders(toHeaderArray(headers));
+		}
+
+		// we need to provide our own HttpClient, as the Rest5ClientBuilder
+		// does not provide a callback for configuration the http client as the old RestClientBuilder.
+		var httpClient = createHttpClient(clientConfiguration);
+		builder.setHttpClient(httpClient);
+
+		for (ClientConfiguration.ClientConfigurationCallback<?> clientConfigurationCallback : clientConfiguration
+				.getClientConfigurers()) {
+			if (clientConfigurationCallback instanceof ElasticsearchRest5ClientConfigurationCallback configurationCallback) {
+				builder = configurationCallback.configure(builder);
+			}
+		}
+
+		return builder;
+	}
+
+	private static HttpHost @NonNull [] getHttpHosts(ClientConfiguration clientConfiguration) {
+		List<InetSocketAddress> hosts = clientConfiguration.getEndpoints();
+		boolean useSsl = clientConfiguration.useSsl();
+		return hosts.stream()
+				.map(it -> (useSsl ? "https" : "http") + "://" + it.getHostString() + ':' + it.getPort())
+				.map(URI::create)
+				.map(HttpHost::create)
+				.toArray(HttpHost[]::new);
+	}
+
+	private static Header[] toHeaderArray(HttpHeaders headers) {
+		return headers.entrySet().stream() //
+				.flatMap(entry -> entry.getValue().stream() //
+						.map(value -> new BasicHeader(entry.getKey(), value))) //
+				.toList().toArray(new Header[0]);
+	}
+
+	// the basic logic to create the http client is copied from the Rest5ClientBuilder class, this is taken from the
+	// Elasticsearch code, as there is no public usable instance in that
+	private static CloseableHttpAsyncClient createHttpClient(ClientConfiguration clientConfiguration) {
+
+		var requestConfigBuilder = RequestConfig.custom();
+		var connectionConfigBuilder = ConnectionConfig.custom();
+
+		Duration connectTimeout = clientConfiguration.getConnectTimeout();
+
+		if (!connectTimeout.isNegative()) {
+			connectionConfigBuilder.setConnectTimeout(
+					Timeout.of(Math.toIntExact(connectTimeout.toMillis()), TimeUnit.MILLISECONDS));
+		}
+
+		Duration socketTimeout = clientConfiguration.getSocketTimeout();
+
+		if (!socketTimeout.isNegative()) {
+			var soTimeout = Timeout.of(Math.toIntExact(socketTimeout.toMillis()), TimeUnit.MILLISECONDS);
+			connectionConfigBuilder.setSocketTimeout(soTimeout);
+			requestConfigBuilder.setConnectionRequestTimeout(soTimeout);
+		} else {
+			connectionConfigBuilder.setSocketTimeout(Timeout.of(DEFAULT_SOCKET_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS));
+			requestConfigBuilder
+					.setConnectionRequestTimeout(Timeout.of(DEFAULT_RESPONSE_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS));
+		}
+
+		try {
+			SSLContext sslContext = clientConfiguration.getCaFingerprint().isPresent()
+					? TransportUtils.sslContextFromCaFingerprint(clientConfiguration.getCaFingerprint().get())
+					: (clientConfiguration.getSslContext().isPresent()
+							? clientConfiguration.getSslContext().get()
+							: SSLContext.getDefault());
+
+			ConnectionConfig connectionConfig = connectionConfigBuilder.build();
+
+			PoolingAsyncClientConnectionManager defaultConnectionManager = PoolingAsyncClientConnectionManagerBuilder.create()
+					.setDefaultConnectionConfig(connectionConfig)
+					.setMaxConnPerRoute(DEFAULT_MAX_CONN_PER_ROUTE)
+					.setMaxConnTotal(DEFAULT_MAX_CONN_TOTAL)
+					.setTlsStrategy(new BasicClientTlsStrategy(sslContext))
+					.build();
+
+			var requestConfig = requestConfigBuilder.build();
+
+            var immutableRefToHttpClientBuilder = new Object() {
+                HttpAsyncClientBuilder httpClientBuilder = HttpAsyncClientBuilder.create()
+                        .setDefaultRequestConfig(requestConfig)
+                        .setConnectionManager(defaultConnectionManager)
+                        .setUserAgent(VersionInfo.clientVersions())
+                        .setTargetAuthenticationStrategy(new DefaultAuthenticationStrategy())
+                        .setThreadFactory(new RestClientThreadFactory());
+            };
+
+			clientConfiguration.getProxy().ifPresent(proxy -> {
+				try {
+					var proxyRoutePlanner = new DefaultProxyRoutePlanner(HttpHost.create(proxy));
+					immutableRefToHttpClientBuilder.httpClientBuilder.setRoutePlanner(proxyRoutePlanner);
+				} catch (URISyntaxException e) {
+					throw new RuntimeException(e);
+				}
+			});
+
+			immutableRefToHttpClientBuilder.httpClientBuilder.addRequestInterceptorFirst((request, entity, context) -> {
+				clientConfiguration.getHeadersSupplier().get().forEach((header, values) -> {
+					// The accept and content-type headers are already put on the request, despite this being the first
+					// interceptor.
+					if ("Accept".equalsIgnoreCase(header) || " Content-Type".equalsIgnoreCase(header)) {
+						request.removeHeaders(header);
+					}
+					values.forEach(value -> request.addHeader(header, value));
+				});
+			});
+
+			for (ClientConfiguration.ClientConfigurationCallback<?> clientConfigurer : clientConfiguration
+					.getClientConfigurers()) {
+				if (clientConfigurer instanceof ElasticsearchHttpClientConfigurationCallback httpClientConfigurer) {
+					immutableRefToHttpClientBuilder.httpClientBuilder = httpClientConfigurer.configure(immutableRefToHttpClientBuilder.httpClientBuilder);
+				}
+			}
+
+			return immutableRefToHttpClientBuilder.httpClientBuilder.build();
+		} catch (NoSuchAlgorithmException e) {
+			throw new IllegalStateException("could not create the default ssl context", e);
+		}
+	}
+
+	/*
+	 * Copied from the Elasticsearch code as this class is not public there.
+	 */
+	private static class RestClientThreadFactory implements ThreadFactory {
+		private static final AtomicLong CLIENT_THREAD_POOL_ID_GENERATOR = new AtomicLong();
+		private final long clientThreadPoolId;
+		private final AtomicLong clientThreadId;
+
+		private RestClientThreadFactory() {
+			this.clientThreadPoolId = CLIENT_THREAD_POOL_ID_GENERATOR.getAndIncrement();
+			this.clientThreadId = new AtomicLong();
+		}
+
+		public Thread newThread(Runnable runnable) {
+			return new Thread(runnable, String.format(Locale.ROOT, "elasticsearch-rest-client-%d-thread-%d",
+					this.clientThreadPoolId, this.clientThreadId.incrementAndGet()));
+		}
+	}
+
+	/**
+	 * {@link org.springframework.data.elasticsearch.client.ClientConfiguration.ClientConfigurationCallback} to configure
+	 * the Elasticsearch Rest5Client's Http client with a {@link HttpAsyncClientBuilder}
+	 *
+	 * @since 6.0
+	 */
+	public interface ElasticsearchHttpClientConfigurationCallback
+			extends ClientConfiguration.ClientConfigurationCallback<HttpAsyncClientBuilder> {
+
+		static Rest5Clients.ElasticsearchHttpClientConfigurationCallback from(
+				Function<HttpAsyncClientBuilder, HttpAsyncClientBuilder> httpClientBuilderCallback) {
+
+			Assert.notNull(httpClientBuilderCallback, "httpClientBuilderCallback must not be null");
+
+			return httpClientBuilderCallback::apply;
+		}
+	}
+
+	/**
+	 * {@link ClientConfiguration.ClientConfigurationCallback} to configure the Rest5Client client with a
+	 * {@link Rest5ClientBuilder}
+	 *
+	 * @since 6.0
+	 */
+	public interface ElasticsearchRest5ClientConfigurationCallback
+			extends ClientConfiguration.ClientConfigurationCallback<Rest5ClientBuilder> {
+
+		static ElasticsearchRest5ClientConfigurationCallback from(
+				Function<Rest5ClientBuilder, Rest5ClientBuilder> rest5ClientBuilderCallback) {
+
+			Assert.notNull(rest5ClientBuilderCallback, "rest5ClientBuilderCallback must not be null");
+
+			return rest5ClientBuilderCallback::apply;
+		}
+	}
+
+	public static Rest5ClientOptions.Builder getRest5ClientOptionsBuilder(@Nullable TransportOptions transportOptions) {
+
+		if (transportOptions instanceof Rest5ClientOptions rest5ClientOptions) {
+			return rest5ClientOptions.toBuilder();
+		}
+
+		var builder = new Rest5ClientOptions.Builder(RequestOptions.DEFAULT.toBuilder());
+
+		if (transportOptions != null) {
+			transportOptions.headers().forEach(header -> builder.addHeader(header.getKey(), header.getValue()));
+			transportOptions.queryParameters().forEach(builder::setParameter);
+			builder.onWarnings(transportOptions.onWarnings());
+		}
+
+		return builder;
+	}
+}

src/main/java/org/springframework/data/elasticsearch/client/elc/rest5_client/package-info.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * This package contains related to the new (from Elasticsearch 9 on) Rest5Client. There are also classes copied over from Elasticsearch in order to have a Rest5ClientBuilder that allows to configure the http client.
+ */
+@org.jspecify.annotations.NullMarked
+package org.springframework.data.elasticsearch.client.elc.rest5_client;

src/main/java/org/springframework/data/elasticsearch/client/elc/rest_client/RestClients.java

@@ -0,0 +1,195 @@
+package org.springframework.data.elasticsearch.client.elc.rest_client;
+
+import co.elastic.clients.transport.TransportOptions;
+import co.elastic.clients.transport.TransportUtils;
+import co.elastic.clients.transport.rest_client.RestClientOptions;
+
+import java.net.InetSocketAddress;
+import java.time.Duration;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+import org.apache.http.HttpHost;
+import org.apache.http.HttpRequest;
+import org.apache.http.HttpRequestInterceptor;
+import org.apache.http.client.config.RequestConfig;
+import org.apache.http.impl.nio.client.HttpAsyncClientBuilder;
+import org.apache.http.message.BasicHeader;
+import org.apache.http.protocol.HttpContext;
+import org.elasticsearch.client.RequestOptions;
+import org.elasticsearch.client.RestClient;
+import org.elasticsearch.client.RestClientBuilder;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
+import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.ElasticsearchClients;
+import org.springframework.data.elasticsearch.support.HttpHeaders;
+import org.springframework.util.Assert;
+
+/**
+ * Utility class containing the functions to create the Elasticsearch RestClient used up to Elasticsearch 9.
+ *
+ * @since 6.0
+ * @deprecated since 6.0, use the new Rest5Client the code for that is in the package ../rest_client.
+ */
+@Deprecated(since = "6.0", forRemoval = true)
+public final class RestClients {
+
+	/**
+	 * Creates a low level {@link RestClient} for the given configuration.
+	 *
+	 * @param clientConfiguration must not be {@literal null}
+	 * @return the {@link RestClient}
+	 */
+	public static RestClient getRestClient(ClientConfiguration clientConfiguration) {
+		return getRestClientBuilder(clientConfiguration).build();
+	}
+
+	private static RestClientBuilder getRestClientBuilder(ClientConfiguration clientConfiguration) {
+		HttpHost[] httpHosts = getHttpHosts(clientConfiguration);
+		RestClientBuilder builder = RestClient.builder(httpHosts);
+
+		if (clientConfiguration.getPathPrefix() != null) {
+			builder.setPathPrefix(clientConfiguration.getPathPrefix());
+		}
+
+		HttpHeaders headers = clientConfiguration.getDefaultHeaders();
+
+		if (!headers.isEmpty()) {
+			builder.setDefaultHeaders(toHeaderArray(headers));
+		}
+
+		builder.setHttpClientConfigCallback(clientBuilder -> {
+			if (clientConfiguration.getCaFingerprint().isPresent()) {
+				clientBuilder
+						.setSSLContext(TransportUtils.sslContextFromCaFingerprint(clientConfiguration.getCaFingerprint().get()));
+			}
+			clientConfiguration.getSslContext().ifPresent(clientBuilder::setSSLContext);
+			clientConfiguration.getHostNameVerifier().ifPresent(clientBuilder::setSSLHostnameVerifier);
+			clientBuilder.addInterceptorLast(new CustomHeaderInjector(clientConfiguration.getHeadersSupplier()));
+
+			RequestConfig.Builder requestConfigBuilder = RequestConfig.custom();
+			Duration connectTimeout = clientConfiguration.getConnectTimeout();
+
+			if (!connectTimeout.isNegative()) {
+				requestConfigBuilder.setConnectTimeout(Math.toIntExact(connectTimeout.toMillis()));
+			}
+
+			Duration socketTimeout = clientConfiguration.getSocketTimeout();
+
+			if (!socketTimeout.isNegative()) {
+				requestConfigBuilder.setSocketTimeout(Math.toIntExact(socketTimeout.toMillis()));
+				requestConfigBuilder.setConnectionRequestTimeout(Math.toIntExact(socketTimeout.toMillis()));
+			}
+
+			clientBuilder.setDefaultRequestConfig(requestConfigBuilder.build());
+
+			clientConfiguration.getProxy().map(HttpHost::create).ifPresent(clientBuilder::setProxy);
+
+			for (ClientConfiguration.ClientConfigurationCallback<?> clientConfigurer : clientConfiguration
+					.getClientConfigurers()) {
+				if (clientConfigurer instanceof RestClients.ElasticsearchHttpClientConfigurationCallback restClientConfigurationCallback) {
+					clientBuilder = restClientConfigurationCallback.configure(clientBuilder);
+				}
+			}
+
+			return clientBuilder;
+		});
+
+		for (ClientConfiguration.ClientConfigurationCallback<?> clientConfigurationCallback : clientConfiguration
+				.getClientConfigurers()) {
+			if (clientConfigurationCallback instanceof ElasticsearchRestClientConfigurationCallback configurationCallback) {
+				builder = configurationCallback.configure(builder);
+			}
+		}
+		return builder;
+	}
+
+	private static HttpHost @NonNull [] getHttpHosts(ClientConfiguration clientConfiguration) {
+		List<InetSocketAddress> hosts = clientConfiguration.getEndpoints();
+		boolean useSsl = clientConfiguration.useSsl();
+		return hosts.stream()
+				.map(it -> (useSsl ? "https" : "http") + "://" + it.getHostString() + ':' + it.getPort())
+				.map(HttpHost::create).toArray(HttpHost[]::new);
+	}
+
+	private static org.apache.http.Header[] toHeaderArray(HttpHeaders headers) {
+		return headers.entrySet().stream() //
+				.flatMap(entry -> entry.getValue().stream() //
+						.map(value -> new BasicHeader(entry.getKey(), value))) //
+				.toArray(org.apache.http.Header[]::new);
+	}
+
+	/**
+	 * Interceptor to inject custom supplied headers.
+	 *
+	 * @since 4.4
+	 */
+	record CustomHeaderInjector(Supplier<HttpHeaders> headersSupplier) implements HttpRequestInterceptor {
+
+		@Override
+		public void process(HttpRequest request, HttpContext context) {
+			HttpHeaders httpHeaders = headersSupplier.get();
+
+			if (httpHeaders != null && !httpHeaders.isEmpty()) {
+				Arrays.stream(toHeaderArray(httpHeaders)).forEach(request::addHeader);
+			}
+		}
+	}
+
+	/**
+	 * {@link org.springframework.data.elasticsearch.client.ClientConfiguration.ClientConfigurationCallback} to configure
+	 * the Elasticsearch RestClient's Http client with a {@link HttpAsyncClientBuilder}
+	 *
+	 * @since 4.4
+	 */
+	public interface ElasticsearchHttpClientConfigurationCallback
+			extends ClientConfiguration.ClientConfigurationCallback<HttpAsyncClientBuilder> {
+
+		static RestClients.ElasticsearchHttpClientConfigurationCallback from(
+				Function<HttpAsyncClientBuilder, HttpAsyncClientBuilder> httpClientBuilderCallback) {
+
+			Assert.notNull(httpClientBuilderCallback, "httpClientBuilderCallback must not be null");
+
+			return httpClientBuilderCallback::apply;
+		}
+	}
+
+	/**
+	 * {@link org.springframework.data.elasticsearch.client.ClientConfiguration.ClientConfigurationCallback} to configure
+	 * the RestClient client with a {@link RestClientBuilder}
+	 *
+	 * @since 5.0
+	 */
+	public interface ElasticsearchRestClientConfigurationCallback
+			extends ClientConfiguration.ClientConfigurationCallback<RestClientBuilder> {
+
+		static ElasticsearchRestClientConfigurationCallback from(
+				Function<RestClientBuilder, RestClientBuilder> restClientBuilderCallback) {
+
+			Assert.notNull(restClientBuilderCallback, "restClientBuilderCallback must not be null");
+
+			return restClientBuilderCallback::apply;
+		}
+	}
+
+	public static RestClientOptions.Builder getRestClientOptionsBuilder(@Nullable TransportOptions transportOptions) {
+
+		if (transportOptions instanceof RestClientOptions restClientOptions) {
+			return restClientOptions.toBuilder();
+		}
+
+		var builder = new RestClientOptions.Builder(RequestOptions.DEFAULT.toBuilder());
+
+		if (transportOptions != null) {
+			transportOptions.headers().forEach(header -> builder.addHeader(header.getKey(), header.getValue()));
+			transportOptions.queryParameters().forEach(builder::setParameter);
+			builder.onWarnings(transportOptions.onWarnings());
+		}
+
+		return builder;
+	}
+
+}

src/main/java/org/springframework/data/elasticsearch/client/elc/rest_client/package-info.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2022-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * This package contains related to the old (up to Elasticsearch 9) RestClient.
+ */
+@Deprecated(since = "6.0", forRemoval=true)
+@org.jspecify.annotations.NullMarked
+package org.springframework.data.elasticsearch.client.elc.rest_client;

src/main/java/org/springframework/data/elasticsearch/support/VersionInfo.java

@@ -92,6 +92,17 @@ public final class VersionInfo {
 		}
 	}
 
+	/**
+	 * @return a String to use in a header, containing the versions of Spring Data Elasticsearch and the Elasticsearch
+	 *         library
+	 * @since 6.0
+	 */
+	public static String clientVersions() {
+		return String.format("spring-data-elasticsearch %s / elasticsearch client %s",
+				versionProperties.getProperty(VERSION_SPRING_DATA_ELASTICSEARCH),
+				versionProperties.getProperty(VERSION_ELASTICSEARCH_CLIENT));
+	}
+
 	/**
 	 * gets the version properties from the classpath resource.
 	 *

src/test/java/org/springframework/data/elasticsearch/client/RestClientsTest.java

@@ -1,21 +1,22 @@
 /*
- * Copyright 2019-2025 the original author or authors.
+* Copyright 2019-2025 the original author or authors.
- *
+*
- * Licensed under the Apache License, Version 2.0 (the "License");
+* Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
+* you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
+* You may obtain a copy of the License at
- *
+*
- *      https://www.apache.org/licenses/LICENSE-2.0
+*      https://www.apache.org/licenses/LICENSE-2.0
- *
+*
- * Unless required by applicable law or agreed to in writing, software
+* Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
+* distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
+* See the License for the specific language governing permissions and
- * limitations under the License.
+* limitations under the License.
- */
+*/
 package org.springframework.data.elasticsearch.client;
 
 import static com.github.tomakehurst.wiremock.client.WireMock.*;
+import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.*;
 import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.options;
 import static io.specto.hoverfly.junit.dsl.HoverflyDsl.*;
 import static io.specto.hoverfly.junit.verification.HoverflyVerifications.*;
@@ -40,10 +41,13 @@ import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 import org.springframework.data.elasticsearch.client.elc.ElasticsearchClients;
 import org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchClient;
+import org.springframework.data.elasticsearch.client.elc.rest5_client.Rest5Clients;
+import org.springframework.data.elasticsearch.client.elc.rest_client.RestClients;
 import org.springframework.data.elasticsearch.support.HttpHeaders;
 
 import com.github.tomakehurst.wiremock.WireMockServer;
 import com.github.tomakehurst.wiremock.client.WireMock;
+import com.github.tomakehurst.wiremock.common.ConsoleNotifier;
 import com.github.tomakehurst.wiremock.matching.AnythingPattern;
 import com.github.tomakehurst.wiremock.matching.EqualToPattern;
 import com.github.tomakehurst.wiremock.stubbing.StubMapping;
@@ -115,25 +119,38 @@ public class RestClientsTest {
 						return httpHeaders;
 					});
 
-			if (clientUnderTestFactory instanceof ELCUnderTestFactory) {
+			if (clientUnderTestFactory instanceof ELCRest5ClientUnderTestFactory) {
 				configurationBuilder.withClientConfigurer(
-						ElasticsearchClients.ElasticsearchHttpClientConfigurationCallback.from(httpClientBuilder -> {
+						Rest5Clients.ElasticsearchHttpClientConfigurationCallback.from(httpClientBuilder -> {
 							httpClientConfigurerCount.incrementAndGet();
 							return httpClientBuilder;
 						}));
 				configurationBuilder.withClientConfigurer(
-						ElasticsearchClients.ElasticsearchRestClientConfigurationCallback.from(restClientBuilder -> {
+						Rest5Clients.ElasticsearchRest5ClientConfigurationCallback.from(rest5ClientBuilder -> {
+							restClientConfigurerCount.incrementAndGet();
+							return rest5ClientBuilder;
+						}));
+
+			} else if (clientUnderTestFactory instanceof ELCRestClientUnderTestFactory) {
+				configurationBuilder.withClientConfigurer(
+						RestClients.ElasticsearchHttpClientConfigurationCallback.from(httpClientBuilder -> {
+							httpClientConfigurerCount.incrementAndGet();
+							return httpClientBuilder;
+						}));
+				configurationBuilder.withClientConfigurer(
+						RestClients.ElasticsearchRestClientConfigurationCallback.from(restClientBuilder -> {
 							restClientConfigurerCount.incrementAndGet();
 							return restClientBuilder;
 						}));
+
 			} else if (clientUnderTestFactory instanceof ReactiveELCUnderTestFactory) {
 				configurationBuilder
-						.withClientConfigurer(ElasticsearchClients.ElasticsearchHttpClientConfigurationCallback.from(webClient -> {
+						.withClientConfigurer(RestClients.ElasticsearchHttpClientConfigurationCallback.from(webClient -> {
 							httpClientConfigurerCount.incrementAndGet();
 							return webClient;
 						}));
 				configurationBuilder.withClientConfigurer(
-						ElasticsearchClients.ElasticsearchRestClientConfigurationCallback.from(restClientBuilder -> {
+						RestClients.ElasticsearchRestClientConfigurationCallback.from(restClientBuilder -> {
 							restClientConfigurerCount.incrementAndGet();
 							return restClientBuilder;
 						}));
@@ -155,8 +172,9 @@ public class RestClientsTest {
 						.withHeader("def2", new EqualToPattern("def2-1")) //
 						.withHeader("supplied", new EqualToPattern("val0")) //
 						// on the first call Elasticsearch does the version check and thus already increments the counter
-						.withHeader("supplied", new EqualToPattern("val" + (i))) //
+						.withHeader("supplied", new EqualToPattern("val" + i)) //
-				);
+						.withHeader("supplied", including("val0", "val" + i)));
+				;
 			}
 
 			assertThat(httpClientConfigurerCount).hasValue(1);
@@ -166,8 +184,8 @@ public class RestClientsTest {
 
 	@ParameterizedTest // #2088
 	@MethodSource("clientUnderTestFactorySource")
-	@DisplayName("should set compatibility headers")
+	@DisplayName("should set explicit compatibility headers")
-	void shouldSetCompatibilityHeaders(ClientUnderTestFactory clientUnderTestFactory) {
+	void shouldSetExplicitCompatibilityHeaders(ClientUnderTestFactory clientUnderTestFactory) {
 
 		wireMockServer(server -> {
 
@@ -190,7 +208,8 @@ public class RestClientsTest {
 							}
 							""" //
 							, 201) //
-							.withHeader("Content-Type", "application/vnd.elasticsearch+json;compatible-with=7") //
+							.withHeader("Content-Type",
+									"application/vnd.elasticsearch+json;compatible-with=7") //
 							.withHeader("X-Elastic-Product", "Elasticsearch")));
 
 			ClientConfigurationBuilder configurationBuilder = new ClientConfigurationBuilder();
@@ -198,8 +217,8 @@ public class RestClientsTest {
 					.connectedTo("localhost:" + server.port()) //
 					.withHeaders(() -> {
 						HttpHeaders defaultCompatibilityHeaders = new HttpHeaders();
-						defaultCompatibilityHeaders.add("Accept", "application/vnd.elasticsearch+json;compatible-with=7");
+						defaultCompatibilityHeaders.add("Accept", "application/vnd.elasticsearch+json; compatible-with=7");
-						defaultCompatibilityHeaders.add("Content-Type", "application/vnd.elasticsearch+json;compatible-with=7");
+						defaultCompatibilityHeaders.add("Content-Type", "application/vnd.elasticsearch+json; compatible-with=7");
 						return defaultCompatibilityHeaders;
 					});
 
@@ -214,11 +233,66 @@ public class RestClientsTest {
 				}
 			}
 
-            clientUnderTest.index(new Foo("42"));
+			clientUnderTest.index(new Foo("42"));
 
 			verify(putRequestedFor(urlMatching(urlPattern)) //
-					.withHeader("Accept", new EqualToPattern("application/vnd.elasticsearch+json;compatible-with=7")) //
+					.withHeader("Accept", new EqualToPattern("application/vnd.elasticsearch+json; compatible-with=7"))
-					.withHeader("Content-Type", new EqualToPattern("application/vnd.elasticsearch+json;compatible-with=7")) //
+					.withHeader("Content-Type", new EqualToPattern("application/vnd.elasticsearch+json; compatible-with=7")));
+		});
+	}
+
+	@ParameterizedTest
+	@MethodSource("clientUnderTestFactorySource")
+	@DisplayName("should set implicit compatibility headers")
+	void shouldSetImplicitCompatibilityHeaders(ClientUnderTestFactory clientUnderTestFactory) {
+
+		wireMockServer(server -> {
+
+			String urlPattern = "^/index/_doc/42(\\?.*)?$";
+			var elasticsearchMajorVersion = clientUnderTestFactory.getElasticsearchMajorVersion();
+			stubFor(put(urlMatching(urlPattern)) //
+					.willReturn(jsonResponse("""
+							{
+							  "_id": "42",
+							  "_index": "test",
+							  "_primary_term": 1,
+							  "_seq_no": 0,
+							  "_shards": {
+							    "failed": 0,
+							    "successful": 1,
+							    "total": 2
+							  },
+							  "_type": "_doc",
+							  "_version": 1,
+							  "result": "created"
+							}
+							""" //
+							, 201) //
+							.withHeader("Content-Type",
+									"application/vnd.elasticsearch+json; compatible-with=" + elasticsearchMajorVersion) //
+							.withHeader("X-Elastic-Product", "Elasticsearch")));
+
+			ClientConfigurationBuilder configurationBuilder = new ClientConfigurationBuilder();
+			configurationBuilder.connectedTo("localhost:" + server.port());
+
+			ClientConfiguration clientConfiguration = configurationBuilder.build();
+			ClientUnderTest clientUnderTest = clientUnderTestFactory.create(clientConfiguration);
+
+			class Foo {
+				public final String id;
+
+				Foo(String id) {
+					this.id = id;
+				}
+			}
+
+			clientUnderTest.index(new Foo("42"));
+
+			verify(putRequestedFor(urlMatching(urlPattern)) //
+					.withHeader("Accept",
+							new EqualToPattern("application/vnd.elasticsearch+json; compatible-with=" + elasticsearchMajorVersion)) //
+					.withHeader("Content-Type",
+							new EqualToPattern("application/vnd.elasticsearch+json; compatible-with=" + elasticsearchMajorVersion)) //
 			);
 		});
 	}
@@ -280,6 +354,7 @@ public class RestClientsTest {
 	private void wireMockServer(WiremockConsumer consumer) {
 		WireMockServer wireMockServer = new WireMockServer(options() //
 				.dynamicPort() //
+				// .notifier(new ConsoleNotifier(true)) // for debugging output
 				.usingFilesUnderDirectory("src/test/resources/wiremock-mappings")); // needed, otherwise Wiremock goes to
 		// test/resources/mappings
 		try {
@@ -295,7 +370,7 @@ public class RestClientsTest {
 	}
 
 	/**
-	 * The client to be tested. Abstraction to be able to test reactive and non-reactive clients.
+	 * The client to be tested. Abstraction to be able to test reactive and non-reactive clients in different versions.
 	 */
 	interface ClientUnderTest {
 		/**
@@ -332,16 +407,19 @@ public class RestClientsTest {
 		protected Integer getExpectedRestClientConfigCalls() {
 			return 0;
 		}
+
+		protected abstract int getElasticsearchMajorVersion();
 	}
 
 	/**
-	 * {@link ClientUnderTestFactory} implementation for the {@link co.elastic.clients.elasticsearch.ElasticsearchClient}.
+	 * {@link ClientUnderTestFactory} implementation for the {@link co.elastic.clients.elasticsearch.ElasticsearchClient}
+	 * using the Rest5_Client.
 	 */
-	static class ELCUnderTestFactory extends ClientUnderTestFactory {
+	static class ELCRest5ClientUnderTestFactory extends ClientUnderTestFactory {
 
 		@Override
 		protected String getDisplayName() {
-			return "ElasticsearchClient";
+			return "ElasticsearchRest5Client";
 		}
 
 		@Override
@@ -349,6 +427,11 @@ public class RestClientsTest {
 			return 1;
 		}
 
+		@Override
+		protected int getElasticsearchMajorVersion() {
+			return 9;
+		}
+
 		@Override
 		ClientUnderTest create(ClientConfiguration clientConfiguration) {
 
@@ -372,6 +455,51 @@ public class RestClientsTest {
 		}
 	}
 
+	/**
+	 * {@link ClientUnderTestFactory} implementation for the {@link co.elastic.clients.elasticsearch.ElasticsearchClient}
+	 * using the old Rest_Client.
+	 */
+	static class ELCRestClientUnderTestFactory extends ClientUnderTestFactory {
+
+		@Override
+		protected String getDisplayName() {
+			return "ElasticsearchRestClient";
+		}
+
+		@Override
+		protected Integer getExpectedRestClientConfigCalls() {
+			return 1;
+		}
+
+		@Override
+		protected int getElasticsearchMajorVersion() {
+			return 9;
+		}
+
+		@Override
+		ClientUnderTest create(ClientConfiguration clientConfiguration) {
+
+			var restClient = RestClients.getRestClient(clientConfiguration);
+			ElasticsearchClient client = ElasticsearchClients.createImperative(restClient);
+			return new ClientUnderTest() {
+				@Override
+				public boolean ping() throws Exception {
+					return client.ping().value();
+				}
+
+				@Override
+				public boolean usesInitialRequest() {
+					return false;
+				}
+
+				@Override
+				public <T> void index(T entity) throws IOException {
+					client.index(ir -> ir.index("index").id("42").document(entity));
+				}
+			};
+		}
+	}
+
 	/**
 	 * {@link ClientUnderTestFactory} implementation for the {@link ReactiveElasticsearchClient}.
 	 */
@@ -387,6 +515,11 @@ public class RestClientsTest {
 			return 1;
 		}
 
+		@Override
+		protected int getElasticsearchMajorVersion() {
+			return 9;
+		}
+
 		@Override
 		ClientUnderTest create(ClientConfiguration clientConfiguration) {
 
@@ -416,8 +549,9 @@ public class RestClientsTest {
 	 * @return stream of factories
 	 */
 	static Stream<ClientUnderTestFactory> clientUnderTestFactorySource() {
-		return Stream.of( //
+		return Stream.of(
-				new ELCUnderTestFactory(), //
+				new ELCRestClientUnderTestFactory(),
+				new ELCRest5ClientUnderTestFactory(),
 				new ReactiveELCUnderTestFactory());
 	}
 }

src/test/java/org/springframework/data/elasticsearch/client/elc/DevTests.java

@@ -37,6 +37,9 @@ import co.elastic.clients.json.jackson.JacksonJsonpMapper;
 import co.elastic.clients.transport.ElasticsearchTransport;
 import co.elastic.clients.transport.TransportOptions;
 import co.elastic.clients.transport.rest_client.RestClientOptions;
+import org.elasticsearch.client.RestClient;
+import org.springframework.data.elasticsearch.client.elc.rest5_client.Rest5Clients;
+import org.springframework.data.elasticsearch.client.elc.rest_client.RestClients;
 import reactor.core.publisher.Mono;
 
 import java.io.IOException;
@@ -85,7 +88,7 @@ public class DevTests {
 	private final ReactiveElasticsearchClient reactiveElasticsearchClient = ElasticsearchClients
 			.createReactive(clientConfiguration(), transportOptions);
 	private final ElasticsearchClient imperativeElasticsearchClient = ElasticsearchClients
-			.createImperative(ElasticsearchClients.getRestClient(clientConfiguration()), transportOptions, jsonpMapper);
+			.createImperative(Rest5Clients.getRest5Client(clientConfiguration()), transportOptions, jsonpMapper);
 
 	@Test
 	void someTest() throws IOException {

src/test/java/org/springframework/data/elasticsearch/client/elc/rest5_client/ELCRest5ClientWiremockTests.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.springframework.data.elasticsearch.client.elc;
+package org.springframework.data.elasticsearch.client.elc.rest5_client;
 
 import static com.github.tomakehurst.wiremock.client.WireMock.*;
 import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.*;
@@ -29,6 +29,7 @@ import org.springframework.data.annotation.Id;
 import org.springframework.data.elasticsearch.annotations.Document;
 import org.springframework.data.elasticsearch.annotations.Field;
 import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.ElasticsearchConfiguration;
 import org.springframework.data.elasticsearch.core.ElasticsearchOperations;
 import org.springframework.test.context.junit.jupiter.SpringExtension;
 
@@ -41,7 +42,7 @@ import com.github.tomakehurst.wiremock.junit5.WireMockExtension;
  */
 @SuppressWarnings("UastIncorrectHttpHeaderInspection")
 @ExtendWith(SpringExtension.class)
-public class ELCWiremockTests {
+public class ELCRest5ClientWiremockTests {
 
 	@RegisterExtension static WireMockExtension wireMock = WireMockExtension.newInstance()
 			.options(wireMockConfig()
@@ -69,7 +70,7 @@ public class ELCWiremockTests {
 		wireMock.stubFor(put(urlPathEqualTo("/null-fields/_doc/42"))
 				.withRequestBody(equalToJson("""
 						{
-							"_class": "org.springframework.data.elasticsearch.client.elc.ELCWiremockTests$EntityWithNullFields",
+							"_class": "org.springframework.data.elasticsearch.client.elc.rest5_client.ELCRest5ClientWiremockTests$EntityWithNullFields",
 							"id": "42",
 							"field1": null
 							}

src/test/java/org/springframework/data/elasticsearch/client/elc/rest_client/ELCRestClientWiremockTests.java

@@ -0,0 +1,145 @@
+/*
+ * Copyright 2024-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.elasticsearch.client.elc.rest_client;
+
+import static com.github.tomakehurst.wiremock.client.WireMock.*;
+import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.*;
+
+import org.jspecify.annotations.Nullable;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.elasticsearch.annotations.Document;
+import org.springframework.data.elasticsearch.annotations.Field;
+import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.ElasticsearchConfiguration;
+import org.springframework.data.elasticsearch.client.elc.ElasticsearchLegacyRestClientConfiguration;
+import org.springframework.data.elasticsearch.core.ElasticsearchOperations;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import com.github.tomakehurst.wiremock.junit5.WireMockExtension;
+
+/**
+ * Tests that need to check the data produced by the Elasticsearch client
+ *
+ * @author Peter-Josef Meisch
+ */
+@SuppressWarnings("UastIncorrectHttpHeaderInspection")
+@Deprecated(since = "6.0", forRemoval = true)
+@ExtendWith(SpringExtension.class)
+public class ELCRestClientWiremockTests {
+
+	@RegisterExtension static WireMockExtension wireMock = WireMockExtension.newInstance()
+			.options(wireMockConfig()
+					.dynamicPort()
+					// needed, otherwise Wiremock goes to test/resources/mappings
+					.usingFilesUnderDirectory("src/test/resources/wiremock-mappings"))
+			.build();
+
+	@Configuration
+	static class Config extends ElasticsearchLegacyRestClientConfiguration {
+		@Override
+		public ClientConfiguration clientConfiguration() {
+			return ClientConfiguration.builder()
+					.connectedTo("localhost:" + wireMock.getPort())
+					.build();
+		}
+	}
+
+	@Autowired ElasticsearchOperations operations;
+
+	@Test // #2839
+	@DisplayName("should store null values if configured")
+	void shouldStoreNullValuesIfConfigured() {
+
+		wireMock.stubFor(put(urlPathEqualTo("/null-fields/_doc/42"))
+				.withRequestBody(equalToJson("""
+						{
+							"_class": "org.springframework.data.elasticsearch.client.elc.rest_client.ELCRestClientWiremockTests$EntityWithNullFields",
+							"id": "42",
+							"field1": null
+							}
+						"""))
+				.willReturn(
+						aResponse()
+								.withStatus(200)
+								.withHeader("X-elastic-product", "Elasticsearch")
+								.withHeader("content-type", "application/vnd.elasticsearch+json;compatible-with=8")
+								.withBody("""
+										{
+										  "_index": "null-fields",
+										  "_id": "42",
+										  "_version": 1,
+										  "result": "created",
+										  "forced_refresh": true,
+										  "_shards": {
+										    "total": 2,
+										    "successful": 1,
+										    "failed": 0
+										  },
+										  "_seq_no": 1,
+										  "_primary_term": 1
+										}
+										""")));
+
+		var entity = new EntityWithNullFields();
+		entity.setId("42");
+
+		operations.save(entity);
+		// no need to assert anything, if the field1:null is not sent, we run into a 404 error
+	}
+
+	@Document(indexName = "null-fields")
+	static class EntityWithNullFields {
+		@Nullable
+		@Id private String id;
+		@Nullable
+		@Field(storeNullValue = true) private String field1;
+		@Nullable
+		@Field private String field2;
+
+		@Nullable
+		public String getId() {
+			return id;
+		}
+
+		public void setId(@Nullable String id) {
+			this.id = id;
+		}
+
+		@Nullable
+		public String getField1() {
+			return field1;
+		}
+
+		public void setField1(@Nullable String field1) {
+			this.field1 = field1;
+		}
+
+		@Nullable
+		public String getField2() {
+			return field2;
+		}
+
+		public void setField2(@Nullable String field2) {
+			this.field2 = field2;
+		}
+	}
+}

src/test/java/org/springframework/data/elasticsearch/client/elc/rest_client/package-info.java

@@ -0,0 +1,2 @@
+@Deprecated(since = "6.0", forRemoval=true)
+package org.springframework.data.elasticsearch.client.elc.rest_client;

src/test/java/org/springframework/data/elasticsearch/config/configuration/ElasticsearchConfigurationELCTests.java

@@ -19,7 +19,8 @@ import static org.assertj.core.api.Assertions.*;
 
 import co.elastic.clients.elasticsearch.ElasticsearchClient;
 
-import org.elasticsearch.client.RestClient;
+import co.elastic.clients.transport.rest5_client.low_level.Rest5Client;
+import org.jspecify.annotations.NonNull;
 import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -50,7 +51,7 @@ public class ElasticsearchConfigurationELCTests {
 			considerNestedRepositories = true)
 	static class Config extends ElasticsearchConfiguration {
 		@Override
-		public ClientConfiguration clientConfiguration() {
+		public @NonNull ClientConfiguration clientConfiguration() {
 			return ClientConfiguration.builder() //
 					.connectedTo("localhost:9200") //
 					.build();
@@ -61,7 +62,7 @@ public class ElasticsearchConfigurationELCTests {
 	 * using a repository with an entity that is set to createIndex = false as we have no elastic running for this test
 	 * and just check that all the necessary beans are created.
 	 */
-	@Autowired private RestClient restClient;
+	@Autowired private Rest5Client rest5Client;
 	@Autowired private ElasticsearchClient elasticsearchClient;
 	@Autowired private ElasticsearchOperations elasticsearchOperations;
 
@@ -69,7 +70,7 @@ public class ElasticsearchConfigurationELCTests {
 
 	@Test
 	public void providesRequiredBeans() {
-		assertThat(restClient).isNotNull();
+		assertThat(rest5Client).isNotNull();
 		assertThat(elasticsearchClient).isNotNull();
 		assertThat(elasticsearchOperations).isNotNull();
 		assertThat(repository).isNotNull();

src/test/java/org/springframework/data/elasticsearch/config/configuration/ElasticsearchLegacyRestClientConfigurationELCTests.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright 2021-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.elasticsearch.config.configuration;
+
+import static org.assertj.core.api.Assertions.*;
+
+import co.elastic.clients.elasticsearch.ElasticsearchClient;
+
+import org.elasticsearch.client.RestClient;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.elasticsearch.annotations.Document;
+import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.ElasticsearchConfiguration;
+import org.springframework.data.elasticsearch.client.elc.ElasticsearchLegacyRestClientConfiguration;
+import org.springframework.data.elasticsearch.core.ElasticsearchOperations;
+import org.springframework.data.elasticsearch.repository.ElasticsearchRepository;
+import org.springframework.data.elasticsearch.repository.config.EnableElasticsearchRepositories;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+/**
+ * Tests for {@link ElasticsearchConfiguration}.
+ *
+ * @author Peter-Josef Meisch
+ * @since 4.4
+ */
+@ExtendWith(SpringExtension.class)
+@ContextConfiguration
+public class ElasticsearchLegacyRestClientConfigurationELCTests {
+
+	@Configuration
+	@EnableElasticsearchRepositories(basePackages = { "org.springframework.data.elasticsearch.config.configuration" },
+			considerNestedRepositories = true)
+	static class Config extends ElasticsearchLegacyRestClientConfiguration {
+		@Override
+		public @NonNull ClientConfiguration clientConfiguration() {
+			return ClientConfiguration.builder() //
+					.connectedTo("localhost:9200") //
+					.build();
+		}
+	}
+
+	/*
+	 * using a repository with an entity that is set to createIndex = false as we have no elastic running for this test
+	 * and just check that all the necessary beans are created.
+	 */
+	@Autowired private RestClient restClient;
+	@Autowired private ElasticsearchClient elasticsearchClient;
+	@Autowired private ElasticsearchOperations elasticsearchOperations;
+
+	@Autowired private CreateIndexFalseRepository repository;
+
+	@Test
+	public void providesRequiredBeans() {
+		assertThat(restClient).isNotNull();
+		assertThat(elasticsearchClient).isNotNull();
+		assertThat(elasticsearchOperations).isNotNull();
+		assertThat(repository).isNotNull();
+	}
+
+	@Document(indexName = "test-index-config-configuration", createIndex = false)
+	static class CreateIndexFalseEntity {
+
+		@Nullable
+		@Id private String id;
+	}
+
+	interface CreateIndexFalseRepository extends ElasticsearchRepository<CreateIndexFalseEntity, String> {}
+}

src/test/java/org/springframework/data/elasticsearch/config/configuration/ReactiveElasticsearchConfigurationELCTests.java

@@ -66,7 +66,6 @@ public class ReactiveElasticsearchConfigurationELCTests {
 
 	@Test
 	public void providesRequiredBeans() {
-		// assertThat(webClient).isNotNull();
 		assertThat(reactiveElasticsearchClient).isNotNull();
 		assertThat(reactiveElasticsearchOperations).isNotNull();
 		assertThat(repository).isNotNull();

src/test/java/org/springframework/data/elasticsearch/config/configuration/ReactiveElasticsearchLegacyRestClientConfigurationELCTests.java

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2019-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.elasticsearch.config.configuration;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.elasticsearch.annotations.Document;
+import org.springframework.data.elasticsearch.client.ClientConfiguration;
+import org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchClient;
+import org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchConfiguration;
+import org.springframework.data.elasticsearch.client.elc.ReactiveElasticsearchLegacyRestClientConfiguration;
+import org.springframework.data.elasticsearch.core.ReactiveElasticsearchOperations;
+import org.springframework.data.elasticsearch.repository.ReactiveElasticsearchRepository;
+import org.springframework.data.elasticsearch.repository.config.EnableReactiveElasticsearchRepositories;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+/**
+ * @author Peter-Josef Meisch
+ * @since 4.4
+ */
+@SuppressWarnings("SpringJavaInjectionPointsAutowiringInspection")
+@ExtendWith(SpringExtension.class)
+@ContextConfiguration
+public class ReactiveElasticsearchLegacyRestClientConfigurationELCTests {
+
+	@Configuration
+	@EnableReactiveElasticsearchRepositories(
+			basePackages = { "org.springframework.data.elasticsearch.config.configuration" },
+			considerNestedRepositories = true)
+	static class Config extends ReactiveElasticsearchLegacyRestClientConfiguration {
+
+		@Override
+		public @NonNull ClientConfiguration clientConfiguration() {
+			return ClientConfiguration.builder() //
+					.connectedTo("localhost:9200") //
+					.build();
+		}
+	}
+
+	/*
+	 * using a repository with an entity that is set to createIndex = false as we have no elastic running for this test
+	 * and just check that all the necessary beans are created.
+	 */
+	@Autowired private ReactiveElasticsearchClient reactiveElasticsearchClient;
+	@Autowired private ReactiveElasticsearchOperations reactiveElasticsearchOperations;
+	@Autowired private CreateIndexFalseRepository repository;
+
+	@Test
+	public void providesRequiredBeans() {
+		// assertThat(webClient).isNotNull();
+		assertThat(reactiveElasticsearchClient).isNotNull();
+		assertThat(reactiveElasticsearchOperations).isNotNull();
+		assertThat(repository).isNotNull();
+	}
+
+	@Document(indexName = "test-index-config-configuration", createIndex = false)
+	static class CreateIndexFalseEntity {
+
+		@Nullable
+		@Id private String id;
+	}
+
+	interface CreateIndexFalseRepository extends ReactiveElasticsearchRepository<CreateIndexFalseEntity, String> {}
+}