Fix reactive blocking calls.

src/main/java/org/springframework/data/elasticsearch/core/AbstractElasticsearchTemplate.java

@@ -101,7 +101,10 @@ protected void initialize(ElasticsearchConverter elasticsearchConverter) {
 		this.routingResolver = new DefaultRoutingResolver((SimpleElasticsearchMappingContext) mappingContext);
 
 		requestFactory = new RequestFactory(elasticsearchConverter);
-		VersionInfo.logVersions(getClusterVersion());
+
+		// initialize the VersionInfo class in the initialization phase
+		// noinspection ResultOfMethodCallIgnored
+		VersionInfo.versionProperties();
 	}
 
 	/**
@@ -166,6 +169,16 @@ public void setRefreshPolicy(@Nullable RefreshPolicy refreshPolicy) {
 	public RefreshPolicy getRefreshPolicy() {
 		return refreshPolicy;
 	}
+
+	/**
+	 * logs the versions of the different Elasticsearch components.
+	 *
+	 * @since 4.3
+	 */
+	public void logVersions() {
+		VersionInfo.logVersions(getClusterVersion());
+	}
+
 	// endregion
 
 	// region DocumentOperations

src/main/java/org/springframework/data/elasticsearch/core/DefaultReactiveIndexOperations.java

@@ -49,8 +49,8 @@
 import org.springframework.data.elasticsearch.core.index.DeleteTemplateRequest;
 import org.springframework.data.elasticsearch.core.index.ExistsTemplateRequest;
 import org.springframework.data.elasticsearch.core.index.GetTemplateRequest;
-import org.springframework.data.elasticsearch.core.index.MappingBuilder;
 import org.springframework.data.elasticsearch.core.index.PutTemplateRequest;
+import org.springframework.data.elasticsearch.core.index.ReactiveMappingBuilder;
 import org.springframework.data.elasticsearch.core.index.Settings;
 import org.springframework.data.elasticsearch.core.index.TemplateData;
 import org.springframework.data.elasticsearch.core.mapping.ElasticsearchPersistentEntity;
@@ -190,8 +190,7 @@ public Mono<Document> createMapping(Class<?> clazz) {
 			}
 		}
 
-		String mapping = new MappingBuilder(converter).buildPropertyMapping(clazz);
-		return Mono.just(Document.parse(mapping));
+		return new ReactiveMappingBuilder(converter).buildReactivePropertyMapping(clazz).map(Document::parse);
 	}
 
 	@Override

src/main/java/org/springframework/data/elasticsearch/core/ReactiveElasticsearchTemplate.java

@@ -142,7 +142,9 @@ public ReactiveElasticsearchTemplate(ReactiveElasticsearchClient client, Elastic
 		this.operations = new EntityOperations(this.mappingContext);
 		this.requestFactory = new RequestFactory(converter);
 
-		logVersions();
+		// initialize the VersionInfo class in the initialization phase
+		// noinspection ResultOfMethodCallIgnored
+		VersionInfo.versionProperties();
 	}
 
 	private ReactiveElasticsearchTemplate copy() {
@@ -155,11 +157,14 @@ private ReactiveElasticsearchTemplate copy() {
 		return copy;
 	}
 
-	private void logVersions() {
-		getClusterVersion() //
-				.doOnSuccess(VersionInfo::logVersions) //
-				.doOnError(e -> VersionInfo.logVersions(null)) //
-				.subscribe();
+	/**
+	 * logs the versions of the different Elasticsearch components.
+	 *
+	 * @return a Mono signalling finished execution
+	 * @since 4.3
+	 */
+	public Mono<Void> logVersions() {
+		return getClusterVersion().doOnNext(VersionInfo::logVersions).then();
 	}
 
 	@Override

src/main/java/org/springframework/data/elasticsearch/core/ReactiveResourceUtil.java

@@ -63,7 +63,7 @@ public static Mono<String> readFileFromClasspath(String url) {
 
 						String line;
 						while ((line = br.readLine()) != null) {
-							sb.append(line);
+							sb.append(line).append('\n');
 						}
 
 						sink.next(sb.toString());

src/main/java/org/springframework/data/elasticsearch/core/index/MappingBuilder.java

@@ -97,7 +97,7 @@ public class MappingBuilder {
 	private static final String DYNAMIC_DATE_FORMATS = "dynamic_date_formats";
 	private static final String RUNTIME = "runtime";
 
-	private final ElasticsearchConverter elasticsearchConverter;
+	protected final ElasticsearchConverter elasticsearchConverter;
 
 	private boolean writeTypeHints = true;
 
@@ -113,9 +113,16 @@ public MappingBuilder(ElasticsearchConverter elasticsearchConverter) {
 	 */
 	public String buildPropertyMapping(Class<?> clazz) throws MappingException {
 
+		ElasticsearchPersistentEntity<?> entity = elasticsearchConverter.getMappingContext()
+				.getRequiredPersistentEntity(clazz);
+
+		return buildPropertyMapping(entity, getRuntimeFields(entity));
+	}
+
+	protected String buildPropertyMapping(ElasticsearchPersistentEntity<?> entity,
+			@Nullable org.springframework.data.elasticsearch.core.document.Document runtimeFields) {
+
 		try {
-			ElasticsearchPersistentEntity<?> entity = elasticsearchConverter.getMappingContext()
-					.getRequiredPersistentEntity(clazz);
 
 			writeTypeHints = entity.writeTypeHints();
 
@@ -124,7 +131,8 @@ public String buildPropertyMapping(Class<?> clazz) throws MappingException {
 			// Dynamic templates
 			addDynamicTemplatesMapping(builder, entity);
 
-			mapEntity(builder, entity, true, "", false, FieldType.Auto, null, entity.findAnnotation(DynamicMapping.class));
+			mapEntity(builder, entity, true, "", false, FieldType.Auto, null, entity.findAnnotation(DynamicMapping.class),
+					runtimeFields);
 
 			builder.endObject() // root object
 					.close();
@@ -148,7 +156,8 @@ private void writeTypeHintMapping(XContentBuilder builder) throws IOException {
 
 	private void mapEntity(XContentBuilder builder, @Nullable ElasticsearchPersistentEntity<?> entity,
 			boolean isRootObject, String nestedObjectFieldName, boolean nestedOrObjectField, FieldType fieldType,
-			@Nullable Field parentFieldAnnotation, @Nullable DynamicMapping dynamicMapping) throws IOException {
+			@Nullable Field parentFieldAnnotation, @Nullable DynamicMapping dynamicMapping,
+			@Nullable org.springframework.data.elasticsearch.core.document.Document runtimeFields) throws IOException {
 
 		if (entity != null && entity.isAnnotationPresent(Mapping.class)) {
 			Mapping mappingAnnotation = entity.getRequiredAnnotation(Mapping.class);
@@ -170,8 +179,8 @@ private void mapEntity(XContentBuilder builder, @Nullable ElasticsearchPersisten
 				builder.field(DYNAMIC_DATE_FORMATS, mappingAnnotation.dynamicDateFormats());
 			}
 
-			if (StringUtils.hasText(mappingAnnotation.runtimeFieldsPath())) {
-				addRuntimeFields(builder, mappingAnnotation.runtimeFieldsPath());
+			if (runtimeFields != null) {
+				builder.field(RUNTIME, runtimeFields);
 			}
 		}
 
@@ -227,13 +236,22 @@ private void mapEntity(XContentBuilder builder, @Nullable ElasticsearchPersisten
 
 	}
 
-	private void addRuntimeFields(XContentBuilder builder, String runtimeFieldsPath) throws IOException {
+	@Nullable
+	private org.springframework.data.elasticsearch.core.document.Document getRuntimeFields(
+			@Nullable ElasticsearchPersistentEntity<?> entity) {
 
-		ClassPathResource runtimeFields = new ClassPathResource(runtimeFieldsPath);
+		if (entity != null) {
+			Mapping mappingAnnotation = entity.findAnnotation(Mapping.class);
+			if (mappingAnnotation != null) {
+				String runtimeFieldsPath = mappingAnnotation.runtimeFieldsPath();
 
-		if (runtimeFields.exists()) {
-			builder.rawField(RUNTIME, runtimeFields.getInputStream(), XContentType.JSON);
+				if (hasText(runtimeFieldsPath)) {
+					String jsonString = ResourceUtil.readFileFromClasspath(runtimeFieldsPath);
+					return org.springframework.data.elasticsearch.core.document.Document.parse(jsonString);
+				}
+			}
 		}
+		return null;
 	}
 
 	private void buildPropertyMapping(XContentBuilder builder, boolean isRootObject,
@@ -291,7 +309,7 @@ private void buildPropertyMapping(XContentBuilder builder, boolean isRootObject,
 						: null;
 
 				mapEntity(builder, persistentEntity, false, property.getFieldName(), true, fieldAnnotation.type(),
-						fieldAnnotation, dynamicMapping);
+						fieldAnnotation, dynamicMapping, null);
 				return;
 			}
 		}

src/main/java/org/springframework/data/elasticsearch/core/index/ReactiveMappingBuilder.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2021 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.core.index;
+
+import static org.springframework.util.StringUtils.*;
+
+import reactor.core.publisher.Mono;
+
+import org.springframework.data.elasticsearch.annotations.Mapping;
+import org.springframework.data.elasticsearch.core.ReactiveResourceUtil;
+import org.springframework.data.elasticsearch.core.convert.ElasticsearchConverter;
+import org.springframework.data.elasticsearch.core.document.Document;
+import org.springframework.data.elasticsearch.core.mapping.ElasticsearchPersistentEntity;
+import org.springframework.data.mapping.MappingException;
+import org.springframework.lang.Nullable;
+
+/**
+ * Subclass of {@link MappingBuilder} with specialized methods TO inhibit blocking CALLS
+ *
+ * @author Peter-Josef Meisch
+ * @since 4.3
+ */
+public class ReactiveMappingBuilder extends MappingBuilder {
+
+	public ReactiveMappingBuilder(ElasticsearchConverter elasticsearchConverter) {
+		super(elasticsearchConverter);
+	}
+
+	@Override
+	public String buildPropertyMapping(Class<?> clazz) throws MappingException {
+		throw new UnsupportedOperationException(
+				"Use ReactiveMappingBuilder.buildReactivePropertyMapping() instead of buildPropertyMapping()");
+	}
+
+	public Mono<String> buildReactivePropertyMapping(Class<?> clazz) throws MappingException {
+		ElasticsearchPersistentEntity<?> entity = elasticsearchConverter.getMappingContext()
+				.getRequiredPersistentEntity(clazz);
+
+		return getRuntimeFields(entity) //
+				.switchIfEmpty(Mono.just(Document.create())) //
+				.map(document -> {
+					if (document.isEmpty()) {
+						return buildPropertyMapping(entity, null);
+					} else {
+						return buildPropertyMapping(entity, document);
+					}
+				});
+	}
+
+	private Mono<Document> getRuntimeFields(@Nullable ElasticsearchPersistentEntity<?> entity) {
+
+		if (entity != null) {
+			Mapping mappingAnnotation = entity.findAnnotation(Mapping.class);
+			if (mappingAnnotation != null) {
+				String runtimeFieldsPath = mappingAnnotation.runtimeFieldsPath();
+
+				if (hasText(runtimeFieldsPath)) {
+					return ReactiveResourceUtil.readFileFromClasspath(runtimeFieldsPath).map(Document::parse);
+				}
+			}
+		}
+
+		return Mono.empty();
+	}
+}