Improve WebReactiveConfigurerComposite

spring-web-reactive/src/main/java/org/springframework/web/reactive/config/WebReactiveConfigurerComposite.java

@@ -3,6 +3,8 @@ package org.springframework.web.reactive.config;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
+import java.util.function.Function;
+import java.util.stream.Collectors;
 
 import org.springframework.format.FormatterRegistry;
 import org.springframework.http.codec.HttpMessageReader;
@@ -19,32 +21,25 @@ import org.springframework.web.reactive.result.method.annotation.RequestMappingH
  * A {@link WebReactiveConfigurer} that delegates to one or more others.
  *
  * @author Brian Clozel
+ * @author Rossen Stoyanchev
  * @since 5.0
  */
 public class WebReactiveConfigurerComposite implements WebReactiveConfigurer {
 
 	private final List<WebReactiveConfigurer> delegates = new ArrayList<>();
 
+
 	public void addWebReactiveConfigurers(List<WebReactiveConfigurer> configurers) {
 		if (!CollectionUtils.isEmpty(configurers)) {
 			this.delegates.addAll(configurers);
 		}
 	}
 
+
 	@Override
 	public Optional<RequestMappingHandlerMapping> createRequestMappingHandlerMapping() {
-		Optional<RequestMappingHandlerMapping> selected = Optional.empty();
-		for (WebReactiveConfigurer configurer : this.delegates) {
-			Optional<RequestMappingHandlerMapping> handlerMapping = configurer.createRequestMappingHandlerMapping();
-			if (handlerMapping.isPresent()) {
-				if (selected != null) {
-					throw new IllegalStateException("No unique RequestMappingHandlerMapping found: {" +
-							selected.get() + ", " + handlerMapping.get() + "}");
-				}
-				selected = handlerMapping;
-			}
-		}
-		return selected;
+		return createSingleBean(WebReactiveConfigurer::createRequestMappingHandlerMapping,
+				RequestMappingHandlerMapping.class);
 	}
 
 	@Override
@@ -69,18 +64,8 @@ public class WebReactiveConfigurerComposite implements WebReactiveConfigurer {
 
 	@Override
 	public Optional<RequestMappingHandlerAdapter> createRequestMappingHandlerAdapter() {
-		Optional<RequestMappingHandlerAdapter> selected = Optional.empty();
-		for (WebReactiveConfigurer configurer : this.delegates) {
-			Optional<RequestMappingHandlerAdapter> handlerAdapter = configurer.createRequestMappingHandlerAdapter();
-			if (handlerAdapter.isPresent()) {
-				if (selected != null) {
-					throw new IllegalStateException("No unique RequestMappingHandlerAdapter found: {" +
-							selected.get() + ", " + handlerAdapter.get() + "}");
-				}
-				selected = handlerAdapter;
-			}
-		}
-		return selected;
+		return createSingleBean(WebReactiveConfigurer::createRequestMappingHandlerAdapter,
+				RequestMappingHandlerAdapter.class);
 	}
 
 	@Override
@@ -105,34 +90,12 @@ public class WebReactiveConfigurerComposite implements WebReactiveConfigurer {
 
 	@Override
 	public Optional<Validator> getValidator() {
-		Optional<Validator> selected = Optional.empty();
-		for (WebReactiveConfigurer configurer : this.delegates) {
-			Optional<Validator> validator = configurer.getValidator();
-			if (validator.isPresent()) {
-				if (selected != null) {
-					throw new IllegalStateException("No unique Validator found: {" +
-							selected.get() + ", " + validator.get() + "}");
-				}
-				selected = validator;
-			}
-		}
-		return selected;
+		return createSingleBean(WebReactiveConfigurer::getValidator, Validator.class);
 	}
 
 	@Override
 	public Optional<MessageCodesResolver> getMessageCodesResolver() {
-		Optional<MessageCodesResolver> selected = Optional.empty();
-		for (WebReactiveConfigurer configurer : this.delegates) {
-			Optional<MessageCodesResolver> messageCodesResolver = configurer.getMessageCodesResolver();
-			if (messageCodesResolver.isPresent()) {
-				if (selected != null) {
-					throw new IllegalStateException("No unique MessageCodesResolver found: {" +
-							selected.get() + ", " + messageCodesResolver.get() + "}");
-				}
-				selected = messageCodesResolver;
-			}
-		}
-		return selected;
+		return createSingleBean(WebReactiveConfigurer::getMessageCodesResolver, MessageCodesResolver.class);
 	}
 
 	@Override
@@ -149,4 +112,23 @@ public class WebReactiveConfigurerComposite implements WebReactiveConfigurer {
 	public void configureViewResolvers(ViewResolverRegistry registry) {
 		this.delegates.stream().forEach(delegate -> delegate.configureViewResolvers(registry));
 	}
+
+	private <T> Optional<T> createSingleBean(Function<WebReactiveConfigurer, Optional<T>> factory,
+			Class<T> beanType) {
+
+		List<Optional<T>> result = this.delegates.stream()
+				.map(factory).filter(Optional::isPresent).collect(Collectors.toList());
+
+		if (result.isEmpty()) {
+			return Optional.empty();
+		}
+		else if (result.size() == 1) {
+			return result.get(1);
+		}
+		else {
+			throw new IllegalStateException("More than one WebReactiveConfigurer implements " +
+					beanType.getSimpleName() + " factory method.");
+		}
+	}
+
 }