WebClientResponseException supports decoding empty content

Closes gh-31179

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -50,6 +50,7 @@ import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.MimeType;
 import org.springframework.util.MultiValueMap;
+import org.springframework.util.ObjectUtils;
 import org.springframework.web.reactive.function.BodyExtractor;
 import org.springframework.web.reactive.function.BodyExtractors;
 
@@ -233,6 +234,9 @@ class DefaultClientResponse implements ClientResponse {
 
 	private Function<ResolvableType, ?> initDecodeFunction(byte[] body, @Nullable MediaType contentType) {
 		return targetType -> {
+			if (ObjectUtils.isEmpty(body)) {
+				return null;
+			}
 			Decoder<?> decoder = null;
 			for (HttpMessageReader<?> reader : strategies().messageReaders()) {
 				if (reader.canRead(targetType, contentType)) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -233,22 +233,21 @@ public class WebClientResponseException extends WebClientException {
 	 */
 	@Nullable
 	public <E> E getResponseBodyAs(Class<E> targetType) {
-		return getResponseBodyAs(ResolvableType.forClass(targetType));
+		return decodeBody(ResolvableType.forClass(targetType));
 	}
 
 	/**
-	 * Variant of {@link #getResponseBodyAs(Class)} with
-	 * {@link ParameterizedTypeReference}.
+	 * Variant of {@link #getResponseBodyAs(Class)} with {@link ParameterizedTypeReference}.
 	 * @since 6.0
 	 */
 	@Nullable
 	public <E> E getResponseBodyAs(ParameterizedTypeReference<E> targetType) {
-		return getResponseBodyAs(ResolvableType.forType(targetType.getType()));
+		return decodeBody(ResolvableType.forType(targetType.getType()));
 	}
 
 	@SuppressWarnings("unchecked")
 	@Nullable
-	private <E> E getResponseBodyAs(ResolvableType targetType) {
+	private <E> E decodeBody(ResolvableType targetType) {
 		Assert.state(this.bodyDecodeFunction != null, "Decoder function not set");
 		return (E) this.bodyDecodeFunction.apply(targetType);
 	}

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

@@ -21,6 +21,7 @@ import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 import java.util.OptionalLong;
 
 import org.junit.jupiter.api.BeforeEach;
@@ -45,6 +46,7 @@ import org.springframework.http.ResponseEntity;
 import org.springframework.http.client.reactive.ClientHttpResponse;
 import org.springframework.http.codec.DecoderHttpMessageReader;
 import org.springframework.http.codec.HttpMessageReader;
+import org.springframework.http.codec.json.Jackson2JsonDecoder;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 
@@ -346,6 +348,40 @@ class DefaultClientResponseTests {
 		assertThat(exception.getResponseBodyAsByteArray()).isEqualTo(bytes);
 	}
 
+	@Test
+	void createExceptionAndDecodeContent() {
+		byte[] bytes = "{\"name\":\"Jason\"}".getBytes(StandardCharsets.UTF_8);
+		DataBuffer buffer = DefaultDataBufferFactory.sharedInstance.wrap(bytes);
+
+		httpHeaders.setContentType(MediaType.APPLICATION_JSON);
+		given(mockResponse.getStatusCode()).willReturn(HttpStatus.NOT_FOUND);
+		given(mockResponse.getBody()).willReturn(Flux.just(buffer));
+
+		given(mockExchangeStrategies.messageReaders()).willReturn(List.of(
+				new DecoderHttpMessageReader<>(new ByteArrayDecoder()),
+				new DecoderHttpMessageReader<>(new Jackson2JsonDecoder())));
+
+		WebClientResponseException ex = defaultClientResponse.createException().block();
+		assertThat(ex.getResponseBodyAs(Map.class)).hasSize(1).containsEntry("name", "Jason");
+	}
+
+	@Test
+	void createExceptionAndDecodeWithoutContent() {
+		byte[] bytes = new byte[0];
+		DataBuffer buffer = DefaultDataBufferFactory.sharedInstance.wrap(bytes);
+
+		httpHeaders.setContentType(MediaType.APPLICATION_JSON);
+		given(mockResponse.getStatusCode()).willReturn(HttpStatus.NOT_FOUND);
+		given(mockResponse.getBody()).willReturn(Flux.just(buffer));
+
+		given(mockExchangeStrategies.messageReaders()).willReturn(List.of(
+				new DecoderHttpMessageReader<>(new ByteArrayDecoder()),
+				new DecoderHttpMessageReader<>(new Jackson2JsonDecoder())));
+
+		WebClientResponseException ex = defaultClientResponse.createException().block();
+		assertThat(ex.getResponseBodyAs(Map.class)).isNull();
+	}
+
 	@Test
 	@SuppressWarnings("deprecation")
 	void createError() {