Upgrade to Reactor Core 3.1

Issue: SPR-15318

build.gradle

@@ -79,7 +79,7 @@ configure(allprojects) { project ->
 	ext.poiVersion             = "3.15"
 	ext.protobufVersion        = "3.2.0"
 	ext.quartzVersion          = "2.2.3"
-	ext.reactorVersion         = "Aluminium-BUILD-SNAPSHOT"
+	ext.reactorVersion         = "Bismuth-BUILD-SNAPSHOT"
 	ext.romeVersion            = "1.7.1"
 	ext.rxjavaVersion          = '1.2.9'
 	ext.rxjavaAdapterVersion   = '1.2.1'

spring-core/src/main/java/org/springframework/core/codec/ResourceRegionEncoder.java

@@ -85,7 +85,7 @@ public class ResourceRegionEncoder extends AbstractEncoder<ResourceRegion> {
 
 		if (inputStream instanceof Mono) {
 			return ((Mono<? extends ResourceRegion>) inputStream)
-					.flatMap(region -> writeResourceRegion(region, bufferFactory));
+					.flatMapMany(region -> writeResourceRegion(region, bufferFactory));
 		}
 		else {
 			Assert.notNull(hints, "'hints' must not be null");

spring-core/src/main/java/org/springframework/core/io/buffer/DataBufferUtils.java

@@ -114,7 +114,7 @@ public abstract class DataBufferUtils {
 		ByteBuffer byteBuffer = ByteBuffer.allocate(bufferSize);
 
 		return Flux.create(emitter -> {
-			emitter.setCancellation(() -> closeChannel(channel));
+			emitter.onDispose(() -> closeChannel(channel));
 			AsynchronousFileChannelCompletionHandler completionHandler =
 					new AsynchronousFileChannelCompletionHandler(emitter, position,
 							dataBufferFactory, byteBuffer);

spring-messaging/src/main/java/org/springframework/messaging/tcp/reactor/ReactorNettyTcpClient.java

@@ -146,7 +146,7 @@ public class ReactorNettyTcpClient<P> implements TcpOperations<P> {
 				.doOnNext(updateConnectMono(connectMono))
 				.doOnError(updateConnectMono(connectMono))
 				.doOnError(handler::afterConnectFailure)    // report all connect failures to the handler
-				.then(NettyContext::onClose)                // post-connect issues
+				.flatMap(NettyContext::onClose)                // post-connect issues
 				.retryWhen(reconnectFunction(strategy))
 				.repeatWhen(reconnectFunction(strategy))
 				.subscribe();

spring-web/src/main/java/org/springframework/http/codec/FormHttpMessageWriter.java

@@ -97,7 +97,7 @@ public class FormHttpMessageWriter implements HttpMessageWriter<MultiValueMap<St
 				.from(inputStream)
 				.single()
 				.map(form -> generateForm(form, charset))
-				.then(value -> {
+				.flatMap(value -> {
 					ByteBuffer byteBuffer = charset.encode(value);
 					DataBuffer buffer = message.bufferFactory().wrap(byteBuffer);
 					message.getHeaders().setContentLength(byteBuffer.remaining());

spring-web/src/main/java/org/springframework/http/codec/ResourceHttpMessageWriter.java

@@ -108,7 +108,7 @@ public class ResourceHttpMessageWriter implements HttpMessageWriter<Resource> {
 	public Mono<Void> write(Publisher<? extends Resource> inputStream, ResolvableType elementType,
 			MediaType mediaType, ReactiveHttpOutputMessage message, Map<String, Object> hints) {
 
-		return Mono.from(inputStream).then(resource ->
+		return Mono.from(inputStream).flatMap(resource ->
 				writeResource(resource, elementType, mediaType, message, hints));
 	}
 
@@ -191,7 +191,7 @@ public class ResourceHttpMessageWriter implements HttpMessageWriter<Resource> {
 			return response.setComplete();
 		}
 
-		return Mono.from(inputStream).then(resource -> {
+		return Mono.from(inputStream).flatMap(resource -> {
 
 			if (ranges.isEmpty()) {
 				return writeResource(resource, elementType, mediaType, response, hints);

spring-web/src/main/java/org/springframework/http/codec/xml/XmlEventDecoder.java

@@ -99,7 +99,7 @@ public class XmlEventDecoder extends AbstractDecoder<XMLEvent> {
 		else {
 			Mono<DataBuffer> singleBuffer = flux.reduce(DataBuffer::write);
 			return singleBuffer.
-					flatMap(dataBuffer -> {
+					flatMapMany(dataBuffer -> {
 						try {
 							InputStream is = dataBuffer.asInputStream();
 							XMLEventReader eventReader = inputFactory.createXMLEventReader(is);

spring-web/src/main/java/org/springframework/http/server/reactive/ChannelSendOperator.java

@@ -21,6 +21,7 @@ import java.util.function.Function;
 import org.reactivestreams.Publisher;
 import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;
+import reactor.core.Exceptions;
 import reactor.core.publisher.MonoSource;
 import reactor.core.publisher.Operators;
 
@@ -56,7 +57,7 @@ public class ChannelSendOperator<T> extends MonoSource<T, Void> {
 
 
 	@SuppressWarnings("deprecation")
-	private class WriteWithBarrier extends Operators.SubscriberAdapter<T, Void> implements Publisher<T> {
+	private class WriteWithBarrier extends SubscriberAdapter<T, Void> implements Publisher<T> {
 
 		/**
 		 * We've at at least one emission, we've called the write function, the write
@@ -210,6 +211,134 @@ public class ChannelSendOperator<T> extends MonoSource<T, Void> {
 		}
 	}
 
+	// TODO Remove this copy of Reactor 3.0.x Operators.SubscriberAdapter
+	private static class SubscriberAdapter<I, O> implements Subscriber<I>, Subscription {
+
+		protected final Subscriber<? super O> subscriber;
+
+		protected Subscription subscription;
+
+		public SubscriberAdapter(Subscriber<? super O> subscriber) {
+			this.subscriber = subscriber;
+		}
+
+		public Subscriber<? super O> downstream() {
+			return subscriber;
+		}
+
+		@Override
+		public final void cancel() {
+			try {
+				doCancel();
+			} catch (Throwable throwable) {
+				doOnSubscriberError(Operators.onOperatorError(subscription, throwable));
+			}
+		}
+
+		@Override
+		public final void onComplete() {
+			try {
+				doComplete();
+			} catch (Throwable throwable) {
+				doOnSubscriberError(Operators.onOperatorError(throwable));
+			}
+		}
+
+		@Override
+		public final void onError(Throwable t) {
+			if (t == null) {
+				throw Exceptions.argumentIsNullException();
+			}
+			doError(t);
+		}
+
+		@Override
+		public final void onNext(I i) {
+			if (i == null) {
+				throw Exceptions.argumentIsNullException();
+			}
+			try {
+				doNext(i);
+			}
+			catch (Throwable throwable) {
+				doOnSubscriberError(Operators.onOperatorError(subscription, throwable, i));
+			}
+		}
+
+		@Override
+		public final void onSubscribe(Subscription s) {
+			if (Operators.validate(subscription, s)) {
+				try {
+					subscription = s;
+					doOnSubscribe(s);
+				}
+				catch (Throwable throwable) {
+					doOnSubscriberError(Operators.onOperatorError(s, throwable));
+				}
+			}
+		}
+
+		@Override
+		public final void request(long n) {
+			try {
+				Operators.checkRequest(n);
+				doRequest(n);
+			} catch (Throwable throwable) {
+				doCancel();
+				doOnSubscriberError(Operators.onOperatorError(throwable));
+			}
+		}
+
+		@Override
+		public String toString() {
+			return getClass().getSimpleName();
+		}
+
+		/**
+		 * Hook for further processing of onSubscribe's Subscription.
+		 * @param subscription the subscription to optionally process
+		 */
+		protected void doOnSubscribe(Subscription subscription) {
+			subscriber.onSubscribe(this);
+		}
+
+		public Subscription upstream() {
+			return subscription;
+		}
+
+		@SuppressWarnings("unchecked")
+		protected void doNext(I i) {
+			subscriber.onNext((O) i);
+		}
+
+		protected void doError(Throwable throwable) {
+			subscriber.onError(throwable);
+		}
+
+		protected void doOnSubscriberError(Throwable throwable){
+			subscriber.onError(throwable);
+		}
+
+		protected void doComplete() {
+			subscriber.onComplete();
+		}
+
+		protected void doRequest(long n) {
+			Subscription s = this.subscription;
+			if (s != null) {
+				s.request(n);
+			}
+		}
+
+		protected void doCancel() {
+			Subscription s = this.subscription;
+			if (s != null) {
+				this.subscription = null;
+				s.cancel();
+			}
+		}
+	}
+
 
 	private class DownstreamBridge implements Subscriber<Void> {
 

spring-web/src/main/java/org/springframework/web/bind/support/WebExchangeDataBinder.java

@@ -72,7 +72,7 @@ public class WebExchangeDataBinder extends WebDataBinder {
 				.map(this::getParamsToBind)
 				.doOnNext(values -> values.putAll(getMultipartFiles(exchange)))
 				.doOnNext(values -> values.putAll(getExtraValuesToBind(exchange)))
-				.then(values -> {
+				.flatMap(values -> {
 					doBind(new MutablePropertyValues(values));
 					return Mono.empty();
 				});

spring-web/src/main/java/org/springframework/web/filter/reactive/HiddenHttpMethodFilter.java

@@ -81,7 +81,7 @@ public class HiddenHttpMethodFilter implements WebFilter {
 					String method = formData.getFirst(this.methodParamName);
 					return StringUtils.hasLength(method) ? mapExchange(exchange, method) : exchange;
 				})
-				.then((exchange1) -> chain.filter(exchange1));
+				.flatMap((exchange1) -> chain.filter(exchange1));
 	}
 
 	private ServerWebExchange mapExchange(ServerWebExchange exchange, String methodParamValue) {

spring-web/src/main/java/org/springframework/web/server/session/DefaultWebSessionManager.java

@@ -104,7 +104,7 @@ public class DefaultWebSessionManager implements WebSessionManager {
 				Flux.fromIterable(getSessionIdResolver().resolveSessionIds(exchange))
 						.concatMap(this.sessionStore::retrieveSession)
 						.next()
-						.then(session -> validateSession(exchange, session))
+						.flatMap(session -> validateSession(exchange, session))
 						.otherwiseIfEmpty(createSession(exchange))
 						.map(session -> extendSession(exchange, session)));
 	}

spring-web/src/test/java/org/springframework/http/server/reactive/ChannelSendOperatorTests.java

@@ -29,7 +29,6 @@ import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
-import reactor.core.publisher.Operators;
 import reactor.core.publisher.Signal;
 
 import static org.junit.Assert.assertEquals;
@@ -142,37 +141,41 @@ public class ChannelSendOperatorTests {
 
 
 		public Publisher<Void> send(Publisher<String> publisher) {
-			return subscriber -> {
-				Executors.newSingleThreadScheduledExecutor().schedule(() -> publisher.subscribe(new WriteSubscriber(subscriber)),
-						50, TimeUnit.MILLISECONDS);
-			};
+			return subscriber -> Executors.newSingleThreadScheduledExecutor().schedule(() ->
+							publisher.subscribe(new WriteSubscriber(subscriber)),50, TimeUnit.MILLISECONDS);
 		}
 
-		private class WriteSubscriber extends Operators.SubscriberAdapter<String, Void> {
+
+		private class WriteSubscriber implements Subscriber<String> {
+
+			private Subscription subscription;
+
+			private final Subscriber<? super Void> subscriber;
 
 			public WriteSubscriber(Subscriber<? super Void> subscriber) {
-				super(subscriber);
+				this.subscriber = subscriber;
 			}
 
 			@Override
-			protected void doOnSubscribe(Subscription subscription) {
-				subscription.request(1);
+			public void onSubscribe(Subscription subscription) {
+				this.subscription = subscription;
+				this.subscription.request(1);
 			}
 
 			@Override
-			public void doNext(String item) {
+			public void onNext(String item) {
 				items.add(item);
 				this.subscription.request(1);
 			}
 
 			@Override
-			public void doError(Throwable ex) {
+			public void onError(Throwable ex) {
 				error = ex;
 				this.subscriber.onError(ex);
 			}
 
 			@Override
-			public void doComplete() {
+			public void onComplete() {
 				completed = true;
 				this.subscriber.onComplete();
 			}

spring-web/src/test/java/org/springframework/web/server/handler/FilteringWebHandlerTests.java

@@ -163,7 +163,7 @@ public class FilteringWebHandlerTests {
 
 		@Override
 		public Mono<Void> doFilter(ServerWebExchange exchange, WebFilterChain chain) {
-			return doAsyncWork().then(asyncResult -> {
+			return doAsyncWork().flatMap(asyncResult -> {
 				logger.debug("Async result: " + asyncResult);
 				return chain.filter(exchange);
 			});

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

@@ -126,8 +126,8 @@ public class DispatcherHandler implements WebHandler, ApplicationContextAware {
 				.concatMap(mapping -> mapping.getHandler(exchange))
 				.next()
 				.otherwiseIfEmpty(Mono.error(HANDLER_NOT_FOUND_EXCEPTION))
-				.then(handler -> invokeHandler(exchange, handler))
-				.then(result -> handleResult(exchange, result));
+				.flatMap(handler -> invokeHandler(exchange, handler))
+				.flatMap(result -> handleResult(exchange, result));
 	}
 
 	private Mono<HandlerResult> invokeHandler(ServerWebExchange exchange, Object handler) {
@@ -141,7 +141,7 @@ public class DispatcherHandler implements WebHandler, ApplicationContextAware {
 
 	private Mono<Void> handleResult(ServerWebExchange exchange, HandlerResult result) {
 		return getResultHandler(result).handleResult(exchange, result)
-				.otherwise(ex -> result.applyExceptionHandler(ex).then(exceptionResult ->
+				.otherwise(ex -> result.applyExceptionHandler(ex).flatMap(exceptionResult ->
 						getResultHandler(exceptionResult).handleResult(exchange, exceptionResult)));
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultWebClient.java

@@ -346,17 +346,17 @@ class DefaultWebClient implements WebClient {
 
 		@Override
 		public <T> Mono<T> bodyToMono(Class<T> bodyType) {
-			return this.responseMono.then(clientResponse -> clientResponse.bodyToMono(bodyType));
+			return this.responseMono.flatMap(clientResponse -> clientResponse.bodyToMono(bodyType));
 		}
 
 		@Override
 		public <T> Flux<T> bodyToFlux(Class<T> elementType) {
-			return this.responseMono.flatMap(clientResponse -> clientResponse.bodyToFlux(elementType));
+			return this.responseMono.flatMapMany(clientResponse -> clientResponse.bodyToFlux(elementType));
 		}
 
 		@Override
 		public <T> Mono<ResponseEntity<T>> bodyToEntity(Class<T> bodyType) {
-			return this.responseMono.then(response ->
+			return this.responseMono.flatMap(response ->
 					response.bodyToMono(bodyType).map(body -> {
 						HttpHeaders headers = response.headers().asHttpHeaders();
 						return new ResponseEntity<>(body, headers, response.statusCode());
@@ -366,7 +366,7 @@ class DefaultWebClient implements WebClient {
 
 		@Override
 		public <T> Mono<ResponseEntity<List<T>>> bodyToEntityList(Class<T> responseType) {
-			return this.responseMono.then(response ->
+			return this.responseMono.flatMap(response ->
 					response.bodyToFlux(responseType).collectList().map(body -> {
 						HttpHeaders headers = response.headers().asHttpHeaders();
 						return new ResponseEntity<>(body, headers, response.statusCode());

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/ExchangeFilterFunction.java

@@ -77,7 +77,7 @@ public interface ExchangeFilterFunction {
 			Mono<ClientRequest>> requestProcessor) {
 
 		Assert.notNull(requestProcessor, "'requestProcessor' must not be null");
-		return (request, next) -> requestProcessor.apply(request).then(next::exchange);
+		return (request, next) -> requestProcessor.apply(request).flatMap(next::exchange);
 	}
 
 	/**
@@ -90,7 +90,7 @@ public interface ExchangeFilterFunction {
 			Mono<ClientResponse>> responseProcessor) {
 
 		Assert.notNull(responseProcessor, "'responseProcessor' must not be null");
-		return (request, next) -> next.exchange(request).then(responseProcessor);
+		return (request, next) -> next.exchange(request).flatMap(responseProcessor);
 	}
 
 }

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultRenderingResponseBuilder.java

@@ -170,7 +170,7 @@ class DefaultRenderingResponseBuilder implements RenderingResponse.Builder {
 					.next()
 					.otherwiseIfEmpty(Mono.error(new IllegalArgumentException("Could not resolve view with name '" +
 							name() +"'")))
-					.then(view -> view.render(model(), contentType, exchange));
+					.flatMap(view -> view.render(model(), contentType, exchange));
 		}
 
 		private Locale resolveLocale(ServerWebExchange exchange, HandlerStrategies strategies) {

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/HandlerFilterFunction.java

@@ -82,7 +82,7 @@ public interface HandlerFilterFunction<T extends ServerResponse, R extends Serve
 			Function<ServerRequest, Mono<ServerRequest>> requestProcessor) {
 
 		Assert.notNull(requestProcessor, "'requestProcessor' must not be null");
-		return (request, next) -> requestProcessor.apply(request).then(next::handle);
+		return (request, next) -> requestProcessor.apply(request).flatMap(next::handle);
 	}
 
 	/**
@@ -95,7 +95,7 @@ public interface HandlerFilterFunction<T extends ServerResponse, R extends Serve
 			Function<T, Mono<R>> responseProcessor) {
 
 		Assert.notNull(responseProcessor, "'responseProcessor' must not be null");
-		return (request, next) -> next.handle(request).then(responseProcessor);
+		return (request, next) -> next.handle(request).flatMap(responseProcessor);
 	}
 
 

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/RouterFunctions.java

@@ -232,8 +232,8 @@ public abstract class RouterFunctions {
 			addAttributes(exchange, request);
 			return routerFunction.route(request)
 					.defaultIfEmpty(notFound())
-					.then(handlerFunction -> wrapException(() -> handlerFunction.handle(request)))
-					.then(response -> wrapException(() -> response.writeTo(exchange, strategies)))
+					.flatMap(handlerFunction -> wrapException(() -> handlerFunction.handle(request)))
+					.flatMap(response -> wrapException(() -> response.writeTo(exchange, strategies)))
 					.otherwise(ResponseStatusException.class,
 							ex -> {
 								exchange.getResponse().setStatusCode(ex.getStatus());

spring-webflux/src/main/java/org/springframework/web/reactive/resource/AppCacheManifestTransformer.java

@@ -106,7 +106,7 @@ public class AppCacheManifestTransformer extends ResourceTransformerSupport {
 			ResourceTransformerChain chain) {
 
 		return chain.transform(exchange, inputResource)
-				.then(resource -> {
+				.flatMap(resource -> {
 					String name = resource.getFilename();
 					if (!this.fileExtension.equals(StringUtils.getFilenameExtension(name))) {
 						return Mono.just(resource);
@@ -124,7 +124,7 @@ public class AppCacheManifestTransformer extends ResourceTransformerSupport {
 					return Flux.generate(new LineGenerator(content))
 							.concatMap(info -> processLine(info, exchange, resource, chain))
 							.collect(() -> new LineAggregator(resource, content), LineAggregator::add)
-							.then(aggregator -> Mono.just(aggregator.createResource()));
+							.flatMap(aggregator -> Mono.just(aggregator.createResource()));
 				});
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/resource/CssLinkResourceTransformer.java

@@ -71,7 +71,7 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 			ResourceTransformerChain transformerChain) {
 
 		return transformerChain.transform(exchange, resource)
-				.then(newResource -> {
+				.flatMap(newResource -> {
 					String filename = newResource.getFilename();
 					if (!"css".equals(StringUtils.getFilenameExtension(filename)) ||
 							resource instanceof GzipResourceResolver.GzippedResource) {
@@ -115,7 +115,7 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 								writer.write(chunk);
 								return writer;
 							})
-							.then(writer -> {
+							.flatMap(writer -> {
 								byte[] newContent = writer.toString().getBytes(DEFAULT_CHARSET);
 								return Mono.just(new TransformedResource(resource, newContent));
 							});

spring-webflux/src/main/java/org/springframework/web/reactive/resource/ResourceWebHandler.java

@@ -281,7 +281,7 @@ public class ResourceWebHandler
 					exchange.getResponse().setStatusCode(HttpStatus.NOT_FOUND);
 					return Mono.empty();
 				}))
-				.then(resource -> {
+				.flatMap(resource -> {
 					try {
 						if (HttpMethod.OPTIONS.equals(exchange.getRequest().getMethod())) {
 							exchange.getResponse().getHeaders().add("Allow", "GET,HEAD,OPTIONS");
@@ -378,7 +378,7 @@ public class ResourceWebHandler
 
 		ResourceResolverChain resolveChain = createResolverChain();
 		return resolveChain.resolveResource(exchange, path, getLocations())
-				.then(resource -> {
+				.flatMap(resource -> {
 					ResourceTransformerChain transformerChain = createTransformerChain(resolveChain);
 					return transformerChain.transform(exchange, resource);
 				});

spring-webflux/src/main/java/org/springframework/web/reactive/resource/VersionResourceResolver.java

@@ -185,7 +185,7 @@ public class VersionResourceResolver extends AbstractResourceResolver {
 		}
 
 		return chain.resolveResource(exchange, simplePath, locations)
-				.then(baseResource -> {
+				.flatMap(baseResource -> {
 					String actualVersion = versionStrategy.getResourceVersion(baseResource);
 					if (candidateVersion.equals(actualVersion)) {
 						if (logger.isTraceEnabled()) {
@@ -208,7 +208,7 @@ public class VersionResourceResolver extends AbstractResourceResolver {
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 
 		return chain.resolveUrlPath(resourceUrlPath, locations)
-				.then(baseUrl -> {
+				.flatMap(baseUrl -> {
 					if (StringUtils.hasText(baseUrl)) {
 						VersionStrategy versionStrategy = getStrategyForPath(resourceUrlPath);
 						if (versionStrategy == null) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/SimpleHandlerAdapter.java

@@ -60,7 +60,7 @@ public class SimpleHandlerAdapter implements HandlerAdapter {
 	public Mono<HandlerResult> handle(ServerWebExchange exchange, Object handler) {
 		WebHandler webHandler = (WebHandler) handler;
 		Mono<Void> mono = webHandler.handle(exchange);
-		return mono.then(aVoid -> Mono.empty());
+		return mono.then(Mono.empty());
 	}
 
 }

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java

@@ -113,7 +113,7 @@ public class InvocableHandlerMethod extends HandlerMethod {
 	public Mono<HandlerResult> invoke(ServerWebExchange exchange, BindingContext bindingContext,
 			Object... providedArgs) {
 
-		return resolveArguments(exchange, bindingContext, providedArgs).then(args -> {
+		return resolveArguments(exchange, bindingContext, providedArgs).flatMap(args -> {
 			try {
 				Object value = doInvoke(args);
 				HandlerResult result = new HandlerResult(this, value, getReturnType(), bindingContext);

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ModelAttributeMethodArgumentResolver.java

@@ -117,7 +117,7 @@ public class ModelAttributeMethodArgumentResolver extends HandlerMethodArgumentR
 		MonoProcessor<BindingResult> bindingResultMono = MonoProcessor.create();
 		model.put(BindingResult.MODEL_KEY_PREFIX + name, bindingResultMono);
 
-		return valueMono.then(value -> {
+		return valueMono.flatMap(value -> {
 			WebExchangeDataBinder binder = context.createDataBinder(exchange, value, name);
 			return binder.bind(exchange)
 					.doOnError(bindingResultMono::onError)
@@ -188,7 +188,7 @@ public class ModelAttributeMethodArgumentResolver extends HandlerMethodArgumentR
 		}
 
 		// A single data class constructor -> resolve constructor arguments from request parameters.
-		return exchange.getRequestParams().then(requestParams -> {
+		return exchange.getRequestParams().flatMap(requestParams -> {
 			ConstructorProperties cp = ctor.getAnnotation(ConstructorProperties.class);
 			String[] paramNames = (cp != null ? cp.value() : parameterNameDiscoverer.getParameterNames(ctor));
 			Assert.state(paramNames != null, () -> "Cannot resolve parameter names for constructor " + ctor);

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ModelInitializer.java

@@ -86,7 +86,7 @@ class ModelInitializer {
 					.map(object -> (HandlerResult) object)
 					.map(handlerResult -> handleResult(handlerResult, bindingContext))
 					.collect(Collectors.toList());
-		}).then(completionList -> Mono.when(completionList));
+		}).flatMap(completionList -> Mono.when(completionList));
 	}
 
 	private Mono<Void> handleResult(HandlerResult handlerResult, BindingContext bindingContext) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ResponseEntityResultHandler.java

@@ -110,7 +110,7 @@ public class ResponseEntityResultHandler extends AbstractMessageWriterResultHand
 			bodyParameter = result.getReturnTypeSource().nested();
 		}
 
-		return returnValueMono.then(returnValue -> {
+		return returnValueMono.flatMap(returnValue -> {
 			Assert.isInstanceOf(HttpEntity.class, returnValue, "HttpEntity expected");
 			HttpEntity<?> httpEntity = (HttpEntity<?>) returnValue;
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/AbstractView.java

@@ -155,7 +155,7 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 			exchange.getResponse().getHeaders().setContentType(contentType);
 		}
 
-		return getModelAttributes(model, exchange).then(mergedModel -> {
+		return getModelAttributes(model, exchange).flatMap(mergedModel -> {
 			// Expose RequestContext?
 			if (this.requestContextAttribute != null) {
 				mergedModel.put(this.requestContextAttribute, createRequestContext(exchange, mergedModel));

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/ViewResolutionResultHandler.java

@@ -194,7 +194,7 @@ public class ViewResolutionResultHandler extends HandlerResultHandlerSupport
 
 		return valueMono
 				.otherwiseIfEmpty(exchange.isNotModified() ? Mono.empty() : NO_VALUE_MONO)
-				.then(returnValue -> {
+				.flatMap(returnValue -> {
 
 					Mono<List<View>> viewsMono;
 					Model model = result.getModel();
@@ -242,7 +242,7 @@ public class ViewResolutionResultHandler extends HandlerResultHandlerSupport
 
 					updateBindingContext(result.getBindingContext(), exchange);
 
-					return viewsMono.then(views -> render(views, model.asMap(), exchange));
+					return viewsMono.flatMap(views -> render(views, model.asMap(), exchange));
 				});
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/socket/client/ReactorNettyWebSocketClient.java

@@ -81,7 +81,7 @@ public class ReactorNettyWebSocketClient extends WebSocketClientSupport implemen
 				.ws(url.toString(),
 						nettyHeaders -> setNettyHeaders(headers, nettyHeaders),
 						StringUtils.arrayToCommaDelimitedString(protocols))
-				.then(response -> {
+				.flatMap(response -> {
 					HandshakeInfo info = afterHandshake(url, toHttpHeaders(response));
 					ByteBufAllocator allocator = response.channel().alloc();
 					NettyDataBufferFactory factory = new NettyDataBufferFactory(allocator);

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

@@ -63,7 +63,7 @@ public class FlushingIntegrationTests extends AbstractHttpHandlerIntegrationTest
 		Mono<String> result = this.webClient.get()
 				.uri("/write-and-flush")
 				.exchange()
-				.flatMap(response -> response.body(BodyExtractors.toFlux(String.class)))
+				.flatMapMany(response -> response.body(BodyExtractors.toFlux(String.class)))
 				.takeUntil(s -> s.endsWith("data1"))
 				.reduce((s1, s2) -> s1 + s2);
 
@@ -78,7 +78,7 @@ public class FlushingIntegrationTests extends AbstractHttpHandlerIntegrationTest
 		Mono<String> result = this.webClient.get()
 				.uri("/write-and-complete")
 				.exchange()
-				.flatMap(response -> response.bodyToFlux(String.class))
+				.flatMapMany(response -> response.bodyToFlux(String.class))
 				.reduce((s1, s2) -> s1 + s2);
 
 		StepVerifier.create(result)
@@ -92,7 +92,7 @@ public class FlushingIntegrationTests extends AbstractHttpHandlerIntegrationTest
 		Flux<String> result = this.webClient.get()
 				.uri("/write-and-never-complete")
 				.exchange()
-				.flatMap(response -> response.bodyToFlux(String.class));
+				.flatMapMany(response -> response.bodyToFlux(String.class));
 
 		StepVerifier.create(result)
 				.expectNextMatches(s -> s.startsWith("0123456789"))

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/WebClientIntegrationTests.java

@@ -99,7 +99,7 @@ public class WebClientIntegrationTests {
 				.uri("/greeting?name=Spring")
 				.header("X-Test-Header", "testvalue")
 				.exchange()
-				.then(response -> response.bodyToMono(String.class));
+				.flatMap(response -> response.bodyToMono(String.class));
 
 		StepVerifier.create(result)
 				.expectNext("Hello Spring!")
@@ -123,7 +123,7 @@ public class WebClientIntegrationTests {
 				.uri("/json")
 				.accept(MediaType.APPLICATION_JSON)
 				.exchange()
-				.then(response -> response.bodyToMono(String.class));
+				.flatMap(response -> response.bodyToMono(String.class));
 
 		StepVerifier.create(result)
 				.expectNext(content)
@@ -248,7 +248,7 @@ public class WebClientIntegrationTests {
 				.uri("/pojo")
 				.accept(MediaType.APPLICATION_JSON)
 				.exchange()
-				.then(response -> response.bodyToMono(Pojo.class));
+				.flatMap(response -> response.bodyToMono(Pojo.class));
 
 		StepVerifier.create(result)
 				.consumeNextWith(p -> assertEquals("barbar", p.getBar()))
@@ -270,7 +270,7 @@ public class WebClientIntegrationTests {
 				.uri("/pojos")
 				.accept(MediaType.APPLICATION_JSON)
 				.exchange()
-				.flatMap(response -> response.bodyToFlux(Pojo.class));
+				.flatMapMany(response -> response.bodyToFlux(Pojo.class));
 
 		StepVerifier.create(result)
 				.consumeNextWith(p -> assertThat(p.getBar(), Matchers.is("bar1")))
@@ -296,7 +296,7 @@ public class WebClientIntegrationTests {
 				.contentType(MediaType.APPLICATION_JSON)
 				.body(new Pojo("foofoo", "barbar"))
 				.exchange()
-				.then(response -> response.bodyToMono(Pojo.class));
+				.flatMap(response -> response.bodyToMono(Pojo.class));
 
 		StepVerifier.create(result)
 				.consumeNextWith(p -> assertEquals("BARBAR", p.getBar()))
@@ -321,7 +321,7 @@ public class WebClientIntegrationTests {
 				.uri("/test")
 				.cookie("testkey", "testvalue")
 				.exchange()
-				.then(response -> response.bodyToMono(String.class));
+				.flatMap(response -> response.bodyToMono(String.class));
 
 		StepVerifier.create(result)
 				.expectNext("test")
@@ -365,7 +365,7 @@ public class WebClientIntegrationTests {
 		Mono<String> result = filteredClient.get()
 				.uri("/greeting?name=Spring")
 				.exchange()
-				.then(response -> response.bodyToMono(String.class));
+				.flatMap(response -> response.bodyToMono(String.class));
 
 		StepVerifier.create(result)
 				.expectNext("Hello Spring!")
@@ -390,7 +390,7 @@ public class WebClientIntegrationTests {
 		Mono<String> result = filteredClient.get()
 				.uri("/greeting?name=Spring")
 				.exchange()
-				.then(response -> response.bodyToMono(String.class));
+				.flatMap(response -> response.bodyToMono(String.class));
 
 		StepVerifier.create(result)
 				.expectNext("Hello Spring!")

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

@@ -273,7 +273,7 @@ public class DefaultServerResponseBuilderTests {
 		when(exchange.getResponse()).thenReturn(response);
 		HandlerStrategies strategies = mock(HandlerStrategies.class);
 
-		result.then(res -> res.writeTo(exchange, strategies)).block();
+		result.flatMap(res -> res.writeTo(exchange, strategies)).block();
 
 		assertEquals(HttpStatus.CREATED, response.getStatusCode());
 		assertEquals("MyValue", response.getHeaders().getFirst("MyKey"));
@@ -290,7 +290,7 @@ public class DefaultServerResponseBuilderTests {
 		when(exchange.getResponse()).thenReturn(response);
 		HandlerStrategies strategies = mock(HandlerStrategies.class);
 
-		result.then(res -> res.writeTo(exchange, strategies)).block();
+		result.flatMap(res -> res.writeTo(exchange, strategies)).block();
 
 		StepVerifier.create(response.getBody()).expectComplete().verify();
 	}

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

@@ -55,7 +55,7 @@ public class ResourceHandlerFunctionTests {
 
 		Mono<ServerResponse> responseMono = this.handlerFunction.handle(request);
 
-		Mono<Void> result = responseMono.then(response -> {
+		Mono<Void> result = responseMono.flatMap(response -> {
 					assertEquals(HttpStatus.OK, response.statusCode());
 					/*
 					TODO: enable when ServerEntityResponse is reintroduced
@@ -94,7 +94,7 @@ public class ResourceHandlerFunctionTests {
 
 		Mono<ServerResponse> response = this.handlerFunction.handle(request);
 
-		Mono<Void> result = response.then(res -> {
+		Mono<Void> result = response.flatMap(res -> {
 			assertEquals(HttpStatus.OK, res.statusCode());
 			return res.writeTo(exchange, HandlerStrategies.withDefaults());
 		});
@@ -114,7 +114,7 @@ public class ResourceHandlerFunctionTests {
 		ServerRequest request = new DefaultServerRequest(exchange, HandlerStrategies.withDefaults());
 
 		Mono<ServerResponse> responseMono = this.handlerFunction.handle(request);
-		Mono<Void> result = responseMono.then(response -> {
+		Mono<Void> result = responseMono.flatMap(response -> {
 			assertEquals(HttpStatus.OK, response.statusCode());
 			assertEquals(EnumSet.of(HttpMethod.GET, HttpMethod.HEAD, HttpMethod.OPTIONS),
 					response.headers().getAllow());

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

@@ -91,7 +91,7 @@ public class RouterFunctionTests {
 		RouterFunction<EntityResponse<Mono<String>>> routerFunction = request -> Mono.just(handlerFunction);
 
 		HandlerFilterFunction<EntityResponse<Mono<String>>, EntityResponse<Mono<Integer>>> filterFunction =
-				(request, next) -> next.handle(request).then(
+				(request, next) -> next.handle(request).flatMap(
 						response -> {
 							Mono<Integer> intMono = response.entity()
 									.map(Integer::parseInt);
@@ -102,7 +102,7 @@ public class RouterFunctionTests {
 
 		MockServerRequest request = MockServerRequest.builder().build();
 		Mono<EntityResponse<Mono<Integer>>> responseMono =
-				result.route(request).then(hf -> hf.handle(request));
+				result.route(request).flatMap(hf -> hf.handle(request));
 
 		StepVerifier.create(responseMono)
 				.consumeNextWith(

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

@@ -63,7 +63,7 @@ public class SseHandlerFunctionIntegrationTests extends AbstractRouterFunctionIn
 				.uri("/string")
 				.accept(TEXT_EVENT_STREAM)
 				.exchange()
-				.flatMap(response -> response.body(toFlux(String.class)));
+				.flatMapMany(response -> response.body(toFlux(String.class)));
 
 		StepVerifier.create(result)
 				.expectNext("foo 0")
@@ -78,7 +78,7 @@ public class SseHandlerFunctionIntegrationTests extends AbstractRouterFunctionIn
 				.uri("/person")
 				.accept(TEXT_EVENT_STREAM)
 				.exchange()
-				.flatMap(response -> response.body(toFlux(Person.class)));
+				.flatMapMany(response -> response.body(toFlux(Person.class)));
 
 		StepVerifier.create(result)
 				.expectNext(new Person("foo 0"))
@@ -93,7 +93,7 @@ public class SseHandlerFunctionIntegrationTests extends AbstractRouterFunctionIn
 				.uri("/event")
 				.accept(TEXT_EVENT_STREAM)
 				.exchange()
-				.flatMap(response -> response.body(toFlux(
+				.flatMapMany(response -> response.body(toFlux(
 						forClassWithGenerics(ServerSentEvent.class, String.class))));
 
 		StepVerifier.create(result)

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/JsonStreamingIntegrationTests.java

@@ -71,7 +71,7 @@ public class JsonStreamingIntegrationTests extends AbstractHttpHandlerIntegratio
 				.uri("/stream")
 				.accept(APPLICATION_STREAM_JSON)
 				.exchange()
-				.flatMap(response -> response.bodyToFlux(Person.class));
+				.flatMapMany(response -> response.bodyToFlux(Person.class));
 
 		StepVerifier.create(result)
 				.expectNext(new Person("foo 0"))

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/SseIntegrationTests.java

@@ -77,7 +77,7 @@ public class SseIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 				.uri("/string")
 				.accept(TEXT_EVENT_STREAM)
 				.exchange()
-				.flatMap(response -> response.bodyToFlux(String.class));
+				.flatMapMany(response -> response.bodyToFlux(String.class));
 
 		StepVerifier.create(result)
 				.expectNext("foo 0")
@@ -92,7 +92,7 @@ public class SseIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 				.uri("/person")
 				.accept(TEXT_EVENT_STREAM)
 				.exchange()
-				.flatMap(response -> response.bodyToFlux(Person.class));
+				.flatMapMany(response -> response.bodyToFlux(Person.class));
 
 		StepVerifier.create(result)
 				.expectNext(new Person("foo 0"))
@@ -108,7 +108,7 @@ public class SseIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 				.uri("/event")
 				.accept(TEXT_EVENT_STREAM)
 				.exchange()
-				.flatMap(response -> response.body(toFlux(type)));
+				.flatMapMany(response -> response.body(toFlux(type)));
 
 		StepVerifier.create(result)
 				.consumeNextWith( event -> {
@@ -135,7 +135,7 @@ public class SseIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 				.uri("/event")
 				.accept(TEXT_EVENT_STREAM)
 				.exchange()
-				.flatMap(response -> response.body(toFlux(
+				.flatMapMany(response -> response.body(toFlux(
 						forClassWithGenerics(ServerSentEvent.class, String.class))));
 
 		StepVerifier.create(result)