Update contribution

- deprecate sync method on ApiVersionResolver
- add SyncApiVersionResolver
- refactor resolverParseAndValidateApiVersion method

See gh-36084

spring-webflux/src/main/java/org/springframework/web/reactive/accept/ApiVersionResolver.java

@@ -29,8 +29,7 @@ import org.springframework.web.server.ServerWebExchange;
  * @since 7.0
  */
 @FunctionalInterface
-public
-interface ApiVersionResolver {
+public interface ApiVersionResolver {
 
 	/**
 	 * Resolve the version for the given exchange.
@@ -40,15 +39,17 @@ interface ApiVersionResolver {
 	 * @return {@code Mono} emitting the version value, or an empty {@code Mono}
 	 * @since 7.0.3
 	 */
-	default Mono<String> resolveApiVersion(ServerWebExchange exchange){
-		return Mono.justOrEmpty(this.resolveVersion(exchange));
-	}
+	Mono<String> resolveApiVersion(ServerWebExchange exchange);
 
 	/**
 	 * Resolve the version for the given exchange.
 	 * @param exchange the current exchange
 	 * @return the version value, or {@code null} if not found
+	 * @deprecated in favor of {@link #resolveApiVersion(ServerWebExchange)}
 	 */
-	@Nullable String resolveVersion(ServerWebExchange exchange);
+	@Deprecated(since = "7.0.3", forRemoval = true)
+	default @Nullable String resolveVersion(ServerWebExchange exchange) {
+		return null;
+	}
 
 }

spring-webflux/src/main/java/org/springframework/web/reactive/accept/ApiVersionStrategy.java

@@ -88,40 +88,31 @@ public interface ApiVersionStrategy {
 	 * or an empty {@code Mono} if there is no version
 	 * @since 7.0.3
 	 */
-	@SuppressWarnings("Convert2MethodRef")
 	default Mono<Comparable<?>> resolveParseAndValidateApiVersion(ServerWebExchange exchange) {
-		return this.resolveApiVersion(exchange)
-				.switchIfEmpty(Mono.justOrEmpty(this.getDefaultVersion())
-						.mapNotNull(comparable -> comparable.toString()))
-				.<Comparable<?>>handle((version, sink) -> {
+
+		Mono<Comparable<?>> result = resolveApiVersion(exchange)
+				.map(value -> {
+					Comparable<?> version;
 					try {
-						sink.next(this.parseVersion(version));
+						version = parseVersion(value);
 					}
 					catch (Exception ex) {
-						sink.error(new InvalidApiVersionException(version, null, ex));
+						throw new InvalidApiVersionException(value, null, ex);
 					}
-				})
-				.flatMap(version -> this.validateVersionAsync(version, exchange))
-				.switchIfEmpty(this.validateVersionAsync(null, exchange));
-	}
+					validateVersion(version, exchange);
+					return version;
+				});
 
-	/**
-	 * Validates the provided request version against the requirements and constraints
-	 * of the API. If the validation succeeds, the version is returned, otherwise an
-	 * error is emitted.
-	 * @param requestVersion the version to validate, which may be null
-	 * @param exchange the current server exchange representing the HTTP request and response
-	 * @return a {@code Mono} emitting the validated request version as a {@code Comparable<?>},
-	 *         or an error if validation fails
-	 */
-	default Mono<Comparable<?>> validateVersionAsync(@Nullable Comparable<?> requestVersion, ServerWebExchange exchange) {
-		try {
-			this.validateVersion(requestVersion, exchange);
-			return Mono.justOrEmpty(requestVersion);
-		}
-		catch (MissingApiVersionException | InvalidApiVersionException ex) {
-			return Mono.error(ex);
-		}
+		return result.switchIfEmpty(Mono.fromSupplier(() -> {
+			Comparable<?> defaultVersion = getDefaultVersion();
+			if (defaultVersion != null) {
+				return defaultVersion;
+			}
+			else {
+				validateVersion(null, exchange);
+				return null;
+			}
+		}));
 	}
 
 	/**

spring-webflux/src/main/java/org/springframework/web/reactive/accept/HeaderApiVersionResolver.java

@@ -26,7 +26,7 @@ import org.springframework.web.server.ServerWebExchange;
  * @author Rossen Stoyanchev
  * @since 7.0
  */
-public class HeaderApiVersionResolver implements ApiVersionResolver {
+public class HeaderApiVersionResolver implements SyncApiVersionResolver {
 
 	private final String headerName;
 
@@ -37,7 +37,7 @@ public class HeaderApiVersionResolver implements ApiVersionResolver {
 
 
 	@Override
-	public @Nullable String resolveVersion(ServerWebExchange exchange) {
+	public @Nullable String resolveVersionValue(ServerWebExchange exchange) {
 		return exchange.getRequest().getHeaders().getFirst(this.headerName);
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/accept/MediaTypeParamApiVersionResolver.java

@@ -29,7 +29,7 @@ import org.springframework.web.server.ServerWebExchange;
  * @author Rossen Stoyanchev
  * @since 7.0
  */
-public class MediaTypeParamApiVersionResolver implements ApiVersionResolver {
+public class MediaTypeParamApiVersionResolver implements SyncApiVersionResolver {
 
 	private final MediaType compatibleMediaType;
 
@@ -49,7 +49,7 @@ public class MediaTypeParamApiVersionResolver implements ApiVersionResolver {
 
 
 	@Override
-	public @Nullable String resolveVersion(ServerWebExchange exchange) {
+	public @Nullable String resolveVersionValue(ServerWebExchange exchange) {
 		HttpHeaders headers = exchange.getRequest().getHeaders();
 		for (MediaType mediaType : headers.getAccept()) {
 			if (this.compatibleMediaType.isCompatibleWith(mediaType)) {

spring-webflux/src/main/java/org/springframework/web/reactive/accept/PathApiVersionResolver.java

@@ -32,7 +32,7 @@ import org.springframework.web.server.ServerWebExchange;
  * @author Rossen Stoyanchev
  * @since 7.0
  */
-public class PathApiVersionResolver implements ApiVersionResolver {
+public class PathApiVersionResolver implements SyncApiVersionResolver {
 
 	private final int pathSegmentIndex;
 
@@ -49,7 +49,7 @@ public class PathApiVersionResolver implements ApiVersionResolver {
 
 
 	@Override
-	public String resolveVersion(ServerWebExchange exchange) {
+	public String resolveVersionValue(ServerWebExchange exchange) {
 		int i = 0;
 		for (PathContainer.Element e : exchange.getRequest().getPath().pathWithinApplication().elements()) {
 			if (e instanceof PathContainer.PathSegment && i++ == this.pathSegmentIndex) {

spring-webflux/src/main/java/org/springframework/web/reactive/accept/QueryApiVersionResolver.java

@@ -26,7 +26,7 @@ import org.springframework.web.server.ServerWebExchange;
  * @author Rossen Stoyanchev
  * @since 7.0
  */
-public class QueryApiVersionResolver implements ApiVersionResolver {
+public class QueryApiVersionResolver implements SyncApiVersionResolver {
 
 	private final String queryParamName;
 
@@ -37,7 +37,7 @@ public class QueryApiVersionResolver implements ApiVersionResolver {
 
 
 	@Override
-	public @Nullable String resolveVersion(ServerWebExchange exchange) {
+	public @Nullable String resolveVersionValue(ServerWebExchange exchange) {
 		return exchange.getRequest().getQueryParams().getFirst(this.queryParamName);
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/accept/SyncApiVersionResolver.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2002-present 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.web.reactive.accept;
+
+import org.jspecify.annotations.Nullable;
+import reactor.core.publisher.Mono;
+
+import org.springframework.web.server.ServerWebExchange;
+
+/**
+ * An extension of {@link ApiVersionResolver}s for implementations that can
+ * resolve the version in an imperative way without blocking.
+ *
+ * @author Rossen Stoyanchev
+ * @since 7.0.3
+ */
+@FunctionalInterface
+public interface SyncApiVersionResolver extends ApiVersionResolver {
+
+	/**
+	 * {@inheritDoc}
+	 * <p>This method delegates to the synchronous
+	 * {@link #resolveVersionValue} and wraps the result as {@code Mono}.
+	 */
+	@Override
+	default Mono<String> resolveApiVersion(ServerWebExchange exchange) {
+		return Mono.justOrEmpty(resolveVersionValue(exchange));
+	}
+
+	/**
+	 * Resolve the version for the given exchange imperatively without blocking.
+	 * @param exchange the current exchange
+	 * @return the version value, or {@code null} if not found
+	 */
+	@Nullable String resolveVersionValue(ServerWebExchange exchange);
+
+	@SuppressWarnings("removal")
+	@Override
+	default @Nullable String resolveVersion(ServerWebExchange exchange) {
+		return resolveVersionValue(exchange);
+	}
+
+}

spring-webflux/src/test/java/org/springframework/web/reactive/accept/DefaultApiVersionStrategiesTests.java

@@ -137,7 +137,7 @@ public class DefaultApiVersionStrategiesTests {
 			@Nullable Predicate<Comparable<?>> supportedVersionPredicate) {
 
 			return new DefaultApiVersionStrategy(
-				List.of(exchange -> exchange.getRequest().getQueryParams().getFirst("api-version")),
+				List.of(new QueryApiVersionResolver("api-version")),
 				parser, null, defaultVersion, detectSupportedVersions, supportedVersionPredicate, null);
 	}
 

spring-webflux/src/test/java/org/springframework/web/reactive/function/server/RequestPredicatesTests.java

@@ -22,6 +22,7 @@ import java.util.List;
 import java.util.function.Function;
 
 import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Mono;
 
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
@@ -380,7 +381,7 @@ class RequestPredicatesTests {
 
 	private static DefaultApiVersionStrategy apiVersionStrategy() {
 		return new DefaultApiVersionStrategy(
-				List.of(exchange -> null), new SemanticApiVersionParser(), true, null, false, null, null);
+				List.of(exchange -> Mono.empty()), new SemanticApiVersionParser(), true, null, false, null, null);
 	}
 
 }

spring-webflux/src/test/java/org/springframework/web/reactive/result/condition/VersionRequestConditionTests.java

@@ -28,6 +28,7 @@ import org.springframework.web.accept.NotAcceptableApiVersionException;
 import org.springframework.web.accept.SemanticApiVersionParser;
 import org.springframework.web.reactive.HandlerMapping;
 import org.springframework.web.reactive.accept.DefaultApiVersionStrategy;
+import org.springframework.web.reactive.accept.QueryApiVersionResolver;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRequest;
 import org.springframework.web.testfixture.server.MockServerWebExchange;
@@ -51,7 +52,7 @@ public class VersionRequestConditionTests {
 
 	private static DefaultApiVersionStrategy initVersionStrategy(@Nullable String defaultVersion) {
 		return new DefaultApiVersionStrategy(
-				List.of(exchange -> exchange.getRequest().getQueryParams().getFirst("api-version")),
+				List.of(new QueryApiVersionResolver("api-version")),
 				new SemanticApiVersionParser(), null, defaultVersion, false, null, null);
 	}