Make ServerHttpMessageReader/Writer more powerful and flexible

This commit makes it possible, in addition to provide hints, to
perform additional operations with the request and the response
at ServerHttpMessageReader/Writer level.

AbstractServerHttpMessageReader/Writer now provide
convenient beforeRead/beforeWrite abstract methods for such need.

Issue: SPR-14557

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

@@ -18,7 +18,6 @@ package org.springframework.web.reactive.result.method.annotation;
 import java.lang.annotation.Annotation;
 import java.util.Collections;
 import java.util.List;
-import java.util.Map;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
@@ -35,6 +34,7 @@ import org.springframework.http.MediaType;
 import org.springframework.http.codec.HttpMessageReader;
 import org.springframework.http.codec.ServerHttpMessageReader;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.validation.BeanPropertyBindingResult;
@@ -126,6 +126,7 @@ public abstract class AbstractMessageReaderArgumentResolver {
 		}
 
 		ServerHttpRequest request = exchange.getRequest();
+		ServerHttpResponse response = exchange.getResponse();
 		MediaType mediaType = request.getHeaders().getContentType();
 		if (mediaType == null) {
 			mediaType = MediaType.APPLICATION_OCTET_STREAM;
@@ -133,15 +134,14 @@ public abstract class AbstractMessageReaderArgumentResolver {
 
 		for (HttpMessageReader<?> reader : getMessageReaders()) {
 
-			Map<String, Object> hints = (reader instanceof ServerHttpMessageReader ?
-						((ServerHttpMessageReader<?>)reader).resolveReadHints(bodyType, elementType,
-								mediaType, exchange.getRequest()) : Collections.emptyMap());
-
-			if (reader.canRead(elementType, mediaType, hints)) {
+			if (reader.canRead(elementType, mediaType)) {
 
 				if (adapter != null && adapter.getDescriptor().isMultiValue()) {
-					Flux<?> flux = reader.read(elementType, request, hints)
-							.onErrorResumeWith(ex -> Flux.error(getReadError(ex, bodyParameter)));
+					Flux<?> flux = (reader instanceof ServerHttpMessageReader ?
+							((ServerHttpMessageReader<?>)reader).read(bodyType, elementType,
+									request, response, Collections.emptyMap()) :
+							reader.read(elementType, request, Collections.emptyMap())
+							.onErrorResumeWith(ex -> Flux.error(getReadError(ex, bodyParameter))));
 					if (checkRequired(adapter, isBodyRequired)) {
 						flux = flux.switchIfEmpty(Flux.error(getRequiredBodyError(bodyParameter)));
 					}
@@ -151,8 +151,11 @@ public abstract class AbstractMessageReaderArgumentResolver {
 					return Mono.just(adapter.fromPublisher(flux));
 				}
 				else {
-					Mono<?> mono = reader.readMono(elementType, request, hints)
-							.otherwise(ex -> Mono.error(getReadError(ex, bodyParameter)));
+					Mono<?> mono = (reader instanceof ServerHttpMessageReader ?
+							((ServerHttpMessageReader<?>)reader).readMono(bodyType, elementType,
+									request, response, Collections.emptyMap()) :
+							reader.readMono(elementType, request, Collections.emptyMap())
+							.otherwise(ex -> Mono.error(getReadError(ex, bodyParameter))));
 					if (checkRequired(adapter, isBodyRequired)) {
 						mono = mono.otherwiseIfEmpty(Mono.error(getRequiredBodyError(bodyParameter)));
 					}

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

@@ -17,7 +17,6 @@ package org.springframework.web.reactive.result.method.annotation;
 
 import java.util.Collections;
 import java.util.List;
-import java.util.Map;
 import java.util.stream.Collectors;
 
 import org.reactivestreams.Publisher;
@@ -30,6 +29,7 @@ import org.springframework.core.ResolvableType;
 import org.springframework.http.MediaType;
 import org.springframework.http.codec.HttpMessageWriter;
 import org.springframework.http.codec.ServerHttpMessageWriter;
+import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.util.Assert;
 import org.springframework.web.reactive.accept.RequestedContentTypeResolver;
@@ -119,18 +119,17 @@ public abstract class AbstractMessageWriterResultHandler extends ContentNegotiat
 					"No converter for return value type: " + elementType));
 		}
 
+		ServerHttpRequest request = exchange.getRequest();
+		ServerHttpResponse response = exchange.getResponse();
 		MediaType bestMediaType = selectMediaType(exchange, producibleTypes);
-
 		if (bestMediaType != null) {
 			for (HttpMessageWriter<?> messageWriter : getMessageWriters()) {
-				Map<String, Object> hints = (messageWriter instanceof ServerHttpMessageWriter ?
-						((ServerHttpMessageWriter<?>)messageWriter).resolveWriteHints(bodyType, elementType,
-								bestMediaType, exchange.getRequest()) : Collections.emptyMap());
-				if (messageWriter.canWrite(elementType, bestMediaType, hints)) {
-
-					ServerHttpResponse response = exchange.getResponse();
-					return messageWriter.write((Publisher) publisher, elementType,
-							bestMediaType, response, hints);
+				if (messageWriter.canWrite(elementType, bestMediaType)) {
+					return (messageWriter instanceof ServerHttpMessageWriter ?
+							((ServerHttpMessageWriter<?>)messageWriter).write((Publisher) publisher,
+									bodyType, elementType, bestMediaType, request, response, Collections.emptyMap()) :
+							messageWriter.write((Publisher) publisher, elementType,
+									bestMediaType, response, Collections.emptyMap()));
 				}
 			}
 		}
@@ -140,7 +139,7 @@ public abstract class AbstractMessageWriterResultHandler extends ContentNegotiat
 
 	private List<MediaType> getProducibleMediaTypes(ResolvableType elementType) {
 		return getMessageWriters().stream()
-				.filter(converter -> converter.canWrite(elementType, null, Collections.emptyMap()))
+				.filter(converter -> converter.canWrite(elementType, null))
 				.flatMap(converter -> converter.getWritableMediaTypes().stream())
 				.collect(Collectors.toList());
 	}

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

@@ -28,6 +28,7 @@ import org.springframework.core.ResolvableType;
 import org.springframework.http.MediaType;
 import org.springframework.http.ReactiveHttpInputMessage;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 
 /**
  * {@link HttpMessageReader} wrapper that implements {@link ServerHttpMessageReader} in order
@@ -46,8 +47,8 @@ public abstract class AbstractServerHttpMessageReader<T> implements ServerHttpMe
 	}
 
 	@Override
-	public boolean canRead(ResolvableType elementType, MediaType mediaType, Map<String, Object> hints) {
-		return this.reader.canRead(elementType, mediaType, hints);
+	public boolean canRead(ResolvableType elementType, MediaType mediaType) {
+		return this.reader.canRead(elementType, mediaType);
 	}
 
 	@Override
@@ -66,29 +67,42 @@ public abstract class AbstractServerHttpMessageReader<T> implements ServerHttpMe
 	}
 
 	@Override
-	public final Map<String, Object> resolveReadHints(ResolvableType streamType,
-			ResolvableType elementType, MediaType mediaType, ServerHttpRequest request) {
-
-		Map<String, Object> hints = new HashMap<>();
-		if (this.reader instanceof ServerHttpMessageReader) {
-			hints.putAll(((ServerHttpMessageReader<T>)this.reader).resolveReadHints(streamType, elementType, mediaType, request));
-		}
-		hints.putAll(resolveReadHintsInternal(streamType, elementType, mediaType, request));
-		return hints;
+	public Flux<T> read(ResolvableType streamType, ResolvableType elementType,
+			ServerHttpRequest request, ServerHttpResponse response, Map<String, Object> hints) {
+
+		Map<String, Object> mergedHints = new HashMap<>(hints);
+		mergedHints.putAll(beforeRead(streamType, elementType, request, response));
+
+		return (this.reader instanceof ServerHttpMessageReader ?
+				((ServerHttpMessageReader<T>)this.reader).read(streamType, elementType, request, response, mergedHints) :
+				this.read(elementType, request, mergedHints));
+	}
+
+	@Override
+	public Mono<T> readMono(ResolvableType streamType, ResolvableType elementType,
+			ServerHttpRequest request, ServerHttpResponse response, Map<String, Object> hints) {
+
+		Map<String, Object> mergedHints = new HashMap<>(hints);
+		mergedHints.putAll(beforeRead(streamType, elementType, request, response));
+
+		return (this.reader instanceof ServerHttpMessageReader ?
+				((ServerHttpMessageReader<T>)this.reader).readMono(streamType, elementType, request, response, mergedHints) :
+				this.readMono(elementType, request, mergedHints));
 	}
 
 	/**
-	 * Abstract method that returns hints which can be used to customize how the body should be read.
-	 * Invoked from {@link #resolveReadHints}.
-	 * @param streamType the original type used in the method parameter. For annotation
+	 * Invoked before reading the request by
+	 * {@link #read(ResolvableType, ResolvableType, ServerHttpRequest, ServerHttpResponse, Map)}
+	 *
+	 * @param streamType the original type used for the method return value. For annotation
 	 * based controllers, the {@link MethodParameter} is available via {@link ResolvableType#getSource()}.
-	 * @param elementType the stream element type to return
-	 * @param mediaType the media type to read, can be {@code null} if not specified.
-	 * Typically the value of a {@code Content-Type} header.
-	 * @param request the current HTTP request
-	 * @return Additional information about how to read the body
+	 * Can be {@code null}.
+	 * @param elementType the stream element type to process
+	 * @param request the current HTTP request, can be {@code null}
+	 * @param response the current HTTP response, can be {@code null}
+	 * @return Additional information about how to write the body
 	 */
-	protected abstract Map<String, Object> resolveReadHintsInternal(ResolvableType streamType,
-			ResolvableType elementType, MediaType mediaType, ServerHttpRequest request);
+	protected abstract Map<String, Object> beforeRead(ResolvableType streamType,
+			ResolvableType elementType, ServerHttpRequest request, ServerHttpResponse response);
 
 }

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

@@ -28,10 +28,13 @@ import org.springframework.core.ResolvableType;
 import org.springframework.http.MediaType;
 import org.springframework.http.ReactiveHttpOutputMessage;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 
 /**
  * {@link HttpMessageWriter} wrapper that implements {@link ServerHttpMessageWriter} in order
- * to allow providing hints.
+ * to allow providing hints to the nested {@code writer} or setting the response status, for
+ * example, by implementing {@link #beforeWrite(ResolvableType, ResolvableType, MediaType, ServerHttpRequest, ServerHttpResponse)}
+ *
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -46,15 +49,8 @@ public abstract class AbstractServerHttpMessageWriter<T> implements ServerHttpMe
 	}
 
 	@Override
-	public boolean canWrite(ResolvableType elementType, MediaType mediaType, Map<String, Object> hints) {
-		return this.writer.canWrite(elementType, mediaType, hints);
-	}
-
-	@Override
-	public Mono<Void> write(Publisher<? extends T> inputStream, ResolvableType elementType,
-			MediaType mediaType, ReactiveHttpOutputMessage outputMessage, Map<String, Object> hints) {
-
-		return this.writer.write(inputStream, elementType, mediaType, outputMessage, hints);
+	public boolean canWrite(ResolvableType elementType, MediaType mediaType) {
+		return this.writer.canWrite(elementType, mediaType);
 	}
 
 	@Override
@@ -63,29 +59,37 @@ public abstract class AbstractServerHttpMessageWriter<T> implements ServerHttpMe
 	}
 
 	@Override
-	public final Map<String, Object> resolveWriteHints(ResolvableType streamType,
-			ResolvableType elementType, MediaType mediaType, ServerHttpRequest request) {
+	public Mono<Void> write(Publisher<? extends T> inputStream, ResolvableType elementType,
+			MediaType mediaType, ReactiveHttpOutputMessage outputMessage, Map<String, Object> hints) {
+		return this.writer.write(inputStream, elementType, mediaType, outputMessage, hints);
+	}
 
-		Map<String, Object> hints = new HashMap<>();
-		if (this.writer instanceof ServerHttpMessageWriter) {
-			hints.putAll(((ServerHttpMessageWriter<T>)this.writer).resolveWriteHints(streamType, elementType, mediaType, request));
-		}
-		hints.putAll(resolveWriteHintsInternal(streamType, elementType, mediaType, request));
-		return hints;
+	@Override
+	public Mono<Void> write(Publisher<? extends T> inputStream, ResolvableType streamType, ResolvableType elementType,
+			MediaType mediaType, ServerHttpRequest request, ServerHttpResponse response, Map<String, Object> hints) {
+
+		Map<String, Object> mergedHints = new HashMap<>(hints);
+		mergedHints.putAll(beforeWrite(streamType, elementType, mediaType, request, response));
+		return (this.writer instanceof ServerHttpMessageWriter ?
+				((ServerHttpMessageWriter<T>)this.writer).write(inputStream, streamType, elementType, mediaType, request, response, mergedHints) :
+				this.writer.write(inputStream, elementType, mediaType, response, mergedHints));
 	}
 
 	/**
-	 * Abstract method that returns hints which can be used to customize how the body should be written.
-	 * Invoked from {@link #resolveWriteHints}.
+	 * Invoked before writing the response by
+	 * {@link #write(Publisher, ResolvableType, ResolvableType, MediaType, ServerHttpRequest, ServerHttpResponse, Map)}.
+	 *
 	 * @param streamType the original type used for the method return value. For annotation
 	 * based controllers, the {@link MethodParameter} is available via {@link ResolvableType#getSource()}.
+	 * Can be {@code null}.
 	 * @param elementType the stream element type to process
 	 * @param mediaType the content type to use when writing. May be {@code null} to
 	 * indicate that the default content type of the converter must be used.
-	 * @param request the current HTTP request
+	 * @param request the current HTTP request, can be {@code null}
+	 * @param response the current HTTP response, can be {@code null}
 	 * @return Additional information about how to write the body
 	 */
-	protected abstract Map<String, Object> resolveWriteHintsInternal(ResolvableType streamType,
-			ResolvableType elementType, MediaType mediaType, ServerHttpRequest request);
+	protected abstract Map<String, Object> beforeWrite(ResolvableType streamType, ResolvableType elementType,
+			MediaType mediaType, ServerHttpRequest request, ServerHttpResponse response);
 
 }

spring-web/src/main/java/org/springframework/http/codec/Jackson2ServerHttpMessageReader.java

@@ -23,9 +23,9 @@ import com.fasterxml.jackson.annotation.JsonView;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ResolvableType;
-import org.springframework.http.MediaType;
 import org.springframework.http.codec.json.AbstractJackson2Codec;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 
 /**
  * {@link ServerHttpMessageReader} that resolves those annotation or request based Jackson 2 hints:
@@ -44,8 +44,8 @@ public class Jackson2ServerHttpMessageReader extends AbstractServerHttpMessageRe
 	}
 
 	@Override
-	protected Map<String, Object> resolveReadHintsInternal(ResolvableType streamType,
-			ResolvableType elementType, MediaType mediaType, ServerHttpRequest request) {
+	protected Map<String, Object> beforeRead(ResolvableType streamType,
+			ResolvableType elementType, ServerHttpRequest request, ServerHttpResponse response) {
 
 		Object source = streamType.getSource();
 		MethodParameter parameter = (source instanceof MethodParameter ? (MethodParameter)source : null);

spring-web/src/main/java/org/springframework/http/codec/Jackson2ServerHttpMessageWriter.java

@@ -16,16 +16,20 @@
 
 package org.springframework.http.codec;
 
-import java.util.Collections;
+
+import java.util.HashMap;
 import java.util.Map;
 
 import com.fasterxml.jackson.annotation.JsonView;
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Mono;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ResolvableType;
 import org.springframework.http.MediaType;
 import org.springframework.http.codec.json.AbstractJackson2Codec;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 
 /**
  * {@link ServerHttpMessageWriter} that resolves those annotation or request based Jackson 2 hints:
@@ -44,9 +48,10 @@ public class Jackson2ServerHttpMessageWriter extends AbstractServerHttpMessageWr
 	}
 
 	@Override
-	protected Map<String, Object> resolveWriteHintsInternal(ResolvableType streamType,
-			ResolvableType elementType, MediaType mediaType, ServerHttpRequest request) {
+	protected Map<String, Object> beforeWrite(ResolvableType streamType, ResolvableType elementType,
+			MediaType mediaType, ServerHttpRequest request, ServerHttpResponse response) {
 
+		Map<String, Object> hints = new HashMap<>();
 		Object source = streamType.getSource();
 		MethodParameter returnValue = (source instanceof MethodParameter ? (MethodParameter)source : null);
 		if (returnValue != null) {
@@ -57,10 +62,10 @@ public class Jackson2ServerHttpMessageWriter extends AbstractServerHttpMessageWr
 					throw new IllegalArgumentException(
 							"@JsonView only supported for write hints with exactly 1 class argument: " + returnValue);
 				}
-				return Collections.singletonMap(AbstractJackson2Codec.JSON_VIEW_HINT, classes[0]);
+				hints.put(AbstractJackson2Codec.JSON_VIEW_HINT, classes[0]);
 			}
 		}
-		return Collections.emptyMap();
+		return hints;
 	}
 
 }

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

@@ -18,14 +18,17 @@ package org.springframework.http.codec;
 
 import java.util.Map;
 
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ResolvableType;
-import org.springframework.http.MediaType;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 
 /**
- * Server and annotation based controller specific {@link HttpMessageReader} that allows to
- * resolve hints using annotations or request based information.
+ * Server oriented {@link HttpMessageReader} that allows to resolve hints using annotations or
+ * perform additional operation using {@link ServerHttpRequest} or {@link ServerHttpResponse}.
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -33,16 +36,37 @@ import org.springframework.http.server.reactive.ServerHttpRequest;
 public interface ServerHttpMessageReader<T> extends HttpMessageReader<T> {
 
 	/**
+	 * Read a {@link Flux} of the given type form the given input message with additional server related
+	 * parameters which could be used to create some hints or set the response status for example.
+	 *
+	 * Return hints that can be used to customize how the body should be read
+	 * @param streamType the original type used in the method parameter. For annotation
+	 * based controllers, the {@link MethodParameter} is available via {@link ResolvableType#getSource()}.
+	 * @param elementType the stream element type to return
+	 * Typically the value of a {@code Content-Type} header.
+	 * @param request the current HTTP request
+	 * @param response the current HTTP response
+	 * @param hints additional information about how to read the body
+	 * @return the converted {@link Flux} of elements
+	 */
+	Flux<T> read(ResolvableType streamType, ResolvableType elementType, ServerHttpRequest request,
+			ServerHttpResponse response, Map<String, Object> hints);
+
+	/**
+	 * Read a {@link Mono} of the given type form the given input message with additional server related
+	 * parameters which could be used to create some hints or set the response status for example.
+	 *
 	 * Return hints that can be used to customize how the body should be read
 	 * @param streamType the original type used in the method parameter. For annotation
 	 * based controllers, the {@link MethodParameter} is available via {@link ResolvableType#getSource()}.
 	 * @param elementType the stream element type to return
-	 * @param mediaType the media type to read, can be {@code null} if not specified.
 	 * Typically the value of a {@code Content-Type} header.
 	 * @param request the current HTTP request
-	 * @return Additional information about how to read the body
+	 * @param response the current HTTP response
+	 * @param hints additional information about how to read the body
+	 * @return the converted {@link Mono} of object
 	 */
-	Map<String, Object> resolveReadHints(ResolvableType streamType, ResolvableType elementType,
-			MediaType mediaType, ServerHttpRequest request);
+	Mono<T> readMono(ResolvableType streamType, ResolvableType elementType, ServerHttpRequest request,
+			ServerHttpResponse response, Map<String, Object> hints);
 
 }

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

@@ -18,14 +18,18 @@ package org.springframework.http.codec;
 
 import java.util.Map;
 
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Mono;
+
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ResolvableType;
 import org.springframework.http.MediaType;
 import org.springframework.http.server.reactive.ServerHttpRequest;
+import org.springframework.http.server.reactive.ServerHttpResponse;
 
 /**
  * Server oriented {@link HttpMessageWriter} that allows to resolve hints using annotations or
- * request based information.
+ * perform additional operation using {@link ServerHttpRequest} or {@link ServerHttpResponse}.
  *
  * @author Sebastien Deleuze
  * @since 5.0
@@ -33,16 +37,21 @@ import org.springframework.http.server.reactive.ServerHttpRequest;
 public interface ServerHttpMessageWriter<T> extends HttpMessageWriter<T> {
 
 	/**
-	 * Return hints that can be used to customize how the body should be written
+	 * Write a given object to the given output message with additional server related
+	 * parameters which could be used to create some hints or set the response status for example.
+	 *
 	 * @param streamType the original type used for the method return value. For annotation
 	 * based controllers, the {@link MethodParameter} is available via {@link ResolvableType#getSource()}.
+	 * Can be {@code null}.
 	 * @param elementType the stream element type to process
 	 * @param mediaType the content type to use when writing. May be {@code null} to
 	 * indicate that the default content type of the converter must be used.
-	 * @param request the current HTTP request
-	 * @return Additional information about how to write the body
+	 * @param request the current HTTP request, can be {@code null}
+	 * @param response the current HTTP response, can be {@code null}
+	 * @return a {@link Mono} that indicates completion or error
 	 */
-	Map<String, Object> resolveWriteHints(ResolvableType streamType, ResolvableType elementType,
-			MediaType mediaType, ServerHttpRequest request);
+	Mono<Void> write(Publisher<? extends T> inputStream, ResolvableType streamType,
+			ResolvableType elementType, MediaType mediaType, ServerHttpRequest request,
+			ServerHttpResponse response, Map<String, Object> hints);
 
 }