From 34f259778e23265c6f5c5a31cde02de3e69fcc67 Mon Sep 17 00:00:00 2001
From: rstoyanchev <rossen.stoyanchev@broadcom.com>
Date: Tue, 29 Jul 2025 19:07:16 +0100
Subject: [PATCH] Further alignment of RestTestClient and WebTestClient

See gh-34428
---
 .../web/reactive/server/CookieAssertions.java |   4 +-
 .../reactive/server/DefaultWebTestClient.java |  16 +--
 .../web/reactive/server/HeaderAssertions.java |   2 +
 .../reactive/server/JsonPathAssertions.java   |   5 +-
 .../web/reactive/server/StatusAssertions.java |   2 +
 .../web/reactive/server/WebTestClient.java    |  50 +++----
 .../web/servlet/client/CookieAssertions.java  |   4 +-
 .../servlet/client/DefaultRestTestClient.java | 101 +++++++-------
 .../client/DefaultRestTestClientBuilder.java  |  45 ++++---
 .../web/servlet/client/ExchangeResult.java    |  78 ++++++-----
 .../web/servlet/client/HeaderAssertions.java  |   2 +-
 .../servlet/client/JsonPathAssertions.java    |   8 +-
 .../web/servlet/client/RestTestClient.java    | 124 +++++++++++-------
 .../web/servlet/client/StatusAssertions.java  |   4 +-
 .../web/servlet/client/XpathAssertions.java   |   8 +-
 .../client/samples/RestTestClientTests.java   |   2 +-
 16 files changed, 264 insertions(+), 191 deletions(-)

diff --git a/spring-test/src/main/java/org/springframework/test/web/reactive/server/CookieAssertions.java b/spring-test/src/main/java/org/springframework/test/web/reactive/server/CookieAssertions.java
index 6deca1e015b..dd47cec18bb 100644
--- a/spring-test/src/main/java/org/springframework/test/web/reactive/server/CookieAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/reactive/server/CookieAssertions.java
@@ -29,10 +29,12 @@ import org.springframework.util.MultiValueMap;
  */
 public class CookieAssertions extends AbstractCookieAssertions<ExchangeResult, WebTestClient.ResponseSpec> {
 
-	public CookieAssertions(ExchangeResult exchangeResult, WebTestClient.ResponseSpec responseSpec) {
+
+	CookieAssertions(ExchangeResult exchangeResult, WebTestClient.ResponseSpec responseSpec) {
 		super(exchangeResult, responseSpec);
 	}
 
+
 	@Override
 	protected void assertWithDiagnostics(Runnable assertion) {
 		exchangeResult.assertWithDiagnostics(assertion);
diff --git a/spring-test/src/main/java/org/springframework/test/web/reactive/server/DefaultWebTestClient.java b/spring-test/src/main/java/org/springframework/test/web/reactive/server/DefaultWebTestClient.java
index 0659241cae2..78e287b4248 100644
--- a/spring-test/src/main/java/org/springframework/test/web/reactive/server/DefaultWebTestClient.java
+++ b/spring-test/src/main/java/org/springframework/test/web/reactive/server/DefaultWebTestClient.java
@@ -438,12 +438,12 @@ class DefaultWebTestClient implements WebTestClient {
 
 
 		DefaultResponseSpec(
-				ExchangeResult exchangeResult, ClientResponse response,
+				ExchangeResult result, ClientResponse response,
 				@Nullable JsonEncoderDecoder jsonEncoderDecoder,
 				Consumer<EntityExchangeResult<?>> entityResultConsumer,
 				Duration timeout) {
 
-			this.exchangeResult = exchangeResult;
+			this.exchangeResult = result;
 			this.response = response;
 			this.jsonEncoderDecoder = jsonEncoderDecoder;
 			this.entityResultConsumer = entityResultConsumer;
@@ -468,15 +468,15 @@ class DefaultWebTestClient implements WebTestClient {
 		@Override
 		public <B> BodySpec<B, ?> expectBody(Class<B> bodyType) {
 			B body = this.response.bodyToMono(bodyType).block(this.timeout);
-			EntityExchangeResult<B> entityResult = initEntityExchangeResult(body);
-			return new DefaultBodySpec<>(entityResult);
+			EntityExchangeResult<B> result = initEntityExchangeResult(body);
+			return new DefaultBodySpec<>(result);
 		}
 
 		@Override
 		public <B> BodySpec<B, ?> expectBody(ParameterizedTypeReference<B> bodyType) {
 			B body = this.response.bodyToMono(bodyType).block(this.timeout);
-			EntityExchangeResult<B> entityResult = initEntityExchangeResult(body);
-			return new DefaultBodySpec<>(entityResult);
+			EntityExchangeResult<B> result = initEntityExchangeResult(body);
+			return new DefaultBodySpec<>(result);
 		}
 
 		@Override
@@ -500,8 +500,8 @@ class DefaultWebTestClient implements WebTestClient {
 		public BodyContentSpec expectBody() {
 			ByteArrayResource resource = this.response.bodyToMono(ByteArrayResource.class).block(this.timeout);
 			byte[] body = (resource != null ? resource.getByteArray() : null);
-			EntityExchangeResult<byte[]> entityResult = initEntityExchangeResult(body);
-			return new DefaultBodyContentSpec(entityResult, this.jsonEncoderDecoder);
+			EntityExchangeResult<byte[]> result = initEntityExchangeResult(body);
+			return new DefaultBodyContentSpec(result, this.jsonEncoderDecoder);
 		}
 
 		private <B> EntityExchangeResult<B> initEntityExchangeResult(@Nullable B body) {
diff --git a/spring-test/src/main/java/org/springframework/test/web/reactive/server/HeaderAssertions.java b/spring-test/src/main/java/org/springframework/test/web/reactive/server/HeaderAssertions.java
index 5cf42730b57..d8ca7dadab9 100644
--- a/spring-test/src/main/java/org/springframework/test/web/reactive/server/HeaderAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/reactive/server/HeaderAssertions.java
@@ -31,10 +31,12 @@ import org.springframework.test.web.support.AbstractHeaderAssertions;
  */
 public class HeaderAssertions extends AbstractHeaderAssertions<ExchangeResult, WebTestClient.ResponseSpec> {
 
+
 	HeaderAssertions(ExchangeResult result, WebTestClient.ResponseSpec spec) {
 		super(result, spec);
 	}
 
+
 	@Override
 	protected void assertWithDiagnostics(Runnable assertion) {
 		exchangeResult.assertWithDiagnostics(assertion);
diff --git a/spring-test/src/main/java/org/springframework/test/web/reactive/server/JsonPathAssertions.java b/spring-test/src/main/java/org/springframework/test/web/reactive/server/JsonPathAssertions.java
index 5e5e5da7899..44602c185a9 100644
--- a/spring-test/src/main/java/org/springframework/test/web/reactive/server/JsonPathAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/reactive/server/JsonPathAssertions.java
@@ -34,8 +34,11 @@ import org.springframework.test.web.support.AbstractJsonPathAssertions;
  */
 public class JsonPathAssertions extends AbstractJsonPathAssertions<WebTestClient.BodyContentSpec> {
 
-	JsonPathAssertions(WebTestClient.BodyContentSpec spec, String content, String expression,
+
+	JsonPathAssertions(
+			WebTestClient.BodyContentSpec spec, String content, String expression,
 			@Nullable Configuration configuration) {
+
 		super(spec, content, expression, configuration);
 	}
 }
diff --git a/spring-test/src/main/java/org/springframework/test/web/reactive/server/StatusAssertions.java b/spring-test/src/main/java/org/springframework/test/web/reactive/server/StatusAssertions.java
index 0c0d87e82fa..91fa59ee527 100644
--- a/spring-test/src/main/java/org/springframework/test/web/reactive/server/StatusAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/reactive/server/StatusAssertions.java
@@ -29,10 +29,12 @@ import org.springframework.test.web.support.AbstractStatusAssertions;
  */
 public class StatusAssertions extends AbstractStatusAssertions<ExchangeResult, WebTestClient.ResponseSpec> {
 
+
 	StatusAssertions(ExchangeResult result, WebTestClient.ResponseSpec spec) {
 		super(result, spec);
 	}
 
+
 	@Override
 	protected void assertWithDiagnostics(Runnable assertion) {
 		exchangeResult.assertWithDiagnostics(assertion);
diff --git a/spring-test/src/main/java/org/springframework/test/web/reactive/server/WebTestClient.java b/spring-test/src/main/java/org/springframework/test/web/reactive/server/WebTestClient.java
index 4d9c30fbc1b..2ffaa16168f 100644
--- a/spring-test/src/main/java/org/springframework/test/web/reactive/server/WebTestClient.java
+++ b/spring-test/src/main/java/org/springframework/test/web/reactive/server/WebTestClient.java
@@ -73,7 +73,7 @@ import org.springframework.web.util.UriBuilderFactory;
  * Client for testing web servers that uses {@link WebClient} internally to
  * perform requests while also providing a fluent API to verify responses.
  * This client can connect to any server over HTTP, or to a WebFlux application
- * via mock request and response objects.
+ * with a mock request and response.
  *
  * <p>Use one of the bindToXxx methods to create an instance. For example:
  * <ul>
@@ -89,9 +89,6 @@ import org.springframework.web.util.UriBuilderFactory;
  * @author Sam Brannen
  * @author Michał Rowicki
  * @since 5.0
- * @see StatusAssertions
- * @see HeaderAssertions
- * @see JsonPathAssertions
  */
 public interface WebTestClient {
 
@@ -172,12 +169,10 @@ public interface WebTestClient {
 
 
 	/**
-	 * Use this server setup to test one {@code @Controller} at a time.
-	 * This option loads the default configuration of
-	 * {@link org.springframework.web.reactive.config.EnableWebFlux @EnableWebFlux}.
-	 * There are builder methods to customize the Java config. The resulting
-	 * WebFlux application will be tested without an HTTP server using a mock
-	 * request and response.
+	 * Begin creating a {@link WebTestClient} with a mock server setup that
+	 * tests one {@code @Controller} at a time with
+	 * {@link org.springframework.web.reactive.config.EnableWebFlux @EnableWebFlux}
+	 * equivalent configuration.
 	 * @param controllers one or more controller instances to test
 	 * (specified {@code Class} will be turned into instance)
 	 * @return chained API to customize server and client config; use
@@ -188,10 +183,10 @@ public interface WebTestClient {
 	}
 
 	/**
-	 * Use this option to set up a server from a {@link RouterFunction}.
-	 * Internally the provided configuration is passed to
-	 * {@code RouterFunctions#toWebHandler}. The resulting WebFlux application
-	 * will be tested without an HTTP server using a mock request and response.
+	 * Begin creating a {@link WebTestClient} with a mock server setup that
+	 * tests one {@code RouterFunction} at a time with
+	 * {@link org.springframework.web.reactive.config.EnableWebFlux @EnableWebFlux}
+	 * equivalent configuration.
 	 * @param routerFunction the RouterFunction to test
 	 * @return chained API to customize server and client config; use
 	 * {@link MockServerSpec#configureClient()} to transition to client config
@@ -229,8 +224,7 @@ public interface WebTestClient {
 	}
 
 	/**
-	 * This server setup option allows you to connect to a live server through
-	 * a Reactor Netty client connector.
+	 * This server setup option allows you to connect to a live server.
 	 * <p><pre class="code">
 	 * WebTestClient client = WebTestClient.bindToServer()
 	 *         .baseUrl("http://localhost:8080")
@@ -389,17 +383,12 @@ public interface WebTestClient {
 
 
 	/**
-	 * Steps for customizing the {@link WebClient} used to test with,
-	 * internally delegating to a
-	 * {@link org.springframework.web.reactive.function.client.WebClient.Builder
-	 * WebClient.Builder}.
+	 * Steps to customize the underlying {@link WebClient} via {@link WebClient.Builder}.
 	 */
 	interface Builder {
 
 		/**
-		 * Configure a base URI as described in
-		 * {@link org.springframework.web.reactive.function.client.WebClient#create(String)
-		 * WebClient.create(String)}.
+		 * Configure a base URI as described in {@link WebClient#create(String)}.
 		 */
 		Builder baseUrl(String baseUrl);
 
@@ -428,7 +417,7 @@ public interface WebTestClient {
 		Builder defaultHeaders(Consumer<HttpHeaders> headersConsumer);
 
 		/**
-		 * Add the given header to all requests that haven't added it.
+		 * Add the given cookie to all requests that haven't already added it.
 		 * @param cookieName the cookie name
 		 * @param cookieValues the cookie values
 		 */
@@ -718,6 +707,7 @@ public interface WebTestClient {
 	 * Specification for providing body of a request.
 	 */
 	interface RequestBodySpec extends RequestHeadersSpec<RequestBodySpec> {
+
 		/**
 		 * Set the length of the body in bytes, as specified by the
 		 * {@code Content-Length} header.
@@ -738,7 +728,7 @@ public interface WebTestClient {
 
 		/**
 		 * Set the body to the given {@code Object} value. This method invokes the
-		 * {@link org.springframework.web.reactive.function.client.WebClient.RequestBodySpec#bodyValue(Object)
+		 * {@link WebClient.RequestBodySpec#bodyValue(Object)
 		 * bodyValue} method on the underlying {@code WebClient}.
 		 * @param body the value to write to the request body
 		 * @return spec for further declaration of the request
@@ -773,7 +763,7 @@ public interface WebTestClient {
 
 		/**
 		 * Set the body from the given producer. This method invokes the
-		 * {@link org.springframework.web.reactive.function.client.WebClient.RequestBodySpec#body(Object, Class)
+		 * {@link WebClient.RequestBodySpec#body(Object, Class)
 		 * body(Object, Class)} method on the underlying {@code WebClient}.
 		 * @param producer the producer to write to the request. This must be a
 		 * {@link Publisher} or another producer adaptable to a
@@ -786,7 +776,7 @@ public interface WebTestClient {
 
 		/**
 		 * Set the body from the given producer. This method invokes the
-		 * {@link org.springframework.web.reactive.function.client.WebClient.RequestBodySpec#body(Object, ParameterizedTypeReference)
+		 * {@link WebClient.RequestBodySpec#body(Object, ParameterizedTypeReference)
 		 * body(Object, ParameterizedTypeReference)} method on the underlying {@code WebClient}.
 		 * @param producer the producer to write to the request. This must be a
 		 * {@link Publisher} or another producer adaptable to a
@@ -800,7 +790,7 @@ public interface WebTestClient {
 		/**
 		 * Set the body of the request to the given {@code BodyInserter}.
 		 * This method invokes the
-		 * {@link org.springframework.web.reactive.function.client.WebClient.RequestBodySpec#body(BodyInserter)
+		 * {@link WebClient.RequestBodySpec#body(BodyInserter)
 		 * body(BodyInserter)} method on the underlying {@code WebClient}.
 		 * @param inserter the body inserter to use
 		 * @return spec for further declaration of the request
@@ -908,8 +898,8 @@ public interface WebTestClient {
 		BodyContentSpec expectBody();
 
 		/**
-		 * Exit the chained flow in order to consume the response body
-		 * externally, for example, via {@link reactor.test.StepVerifier}.
+		 * Exit the chained flow in order to consume the response body externally,
+		 * for example, via {@link reactor.test.StepVerifier}.
 		 * <p>Note that when {@code Void.class} is passed in, the response body
 		 * is consumed and released. If no content is expected, then consider
 		 * using {@code .expectBody().isEmpty()} instead which asserts that
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/CookieAssertions.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/CookieAssertions.java
index b4f8cced077..e5a033f8252 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/CookieAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/CookieAssertions.java
@@ -28,10 +28,12 @@ import org.springframework.util.MultiValueMap;
  */
 public class CookieAssertions extends AbstractCookieAssertions<ExchangeResult, RestTestClient.ResponseSpec> {
 
-	public CookieAssertions(ExchangeResult exchangeResult, RestTestClient.ResponseSpec responseSpec) {
+
+	CookieAssertions(ExchangeResult exchangeResult, RestTestClient.ResponseSpec responseSpec) {
 		super(exchangeResult, responseSpec);
 	}
 
+
 	@Override
 	protected void assertWithDiagnostics(Runnable assertion) {
 		exchangeResult.assertWithDiagnostics(assertion);
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/DefaultRestTestClient.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/DefaultRestTestClient.java
index d831a68af03..4e69ffdc134 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/DefaultRestTestClient.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/DefaultRestTestClient.java
@@ -21,7 +21,6 @@ import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.time.ZonedDateTime;
 import java.util.Map;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.Consumer;
@@ -59,12 +58,9 @@ class DefaultRestTestClient implements RestTestClient {
 
 	private final AtomicLong requestIndex = new AtomicLong();
 
-	private final RestClient.Builder restClientBuilder;
 
-
-	DefaultRestTestClient(RestClient.Builder restClientBuilder) {
-		this.restClient = restClientBuilder.build();
-		this.restClientBuilder = restClientBuilder;
+	DefaultRestTestClient(RestClient.Builder builder) {
+		this.restClient = builder.build();
 	}
 
 
@@ -104,8 +100,8 @@ class DefaultRestTestClient implements RestTestClient {
 	}
 
 	@Override
-	public RequestBodyUriSpec method(HttpMethod method) {
-		return methodInternal(method);
+	public RequestBodyUriSpec method(HttpMethod httpMethod) {
+		return methodInternal(httpMethod);
 	}
 
 	private RequestBodyUriSpec methodInternal(HttpMethod httpMethod) {
@@ -114,7 +110,7 @@ class DefaultRestTestClient implements RestTestClient {
 
 	@Override
 	public <B extends Builder<B>> Builder<B> mutate() {
-		return new DefaultRestTestClientBuilder<>(this.restClientBuilder);
+		return new DefaultRestTestClientBuilder<>(this.restClient.mutate());
 	}
 
 
@@ -122,103 +118,105 @@ class DefaultRestTestClient implements RestTestClient {
 
 		private final RestClient.RequestBodyUriSpec requestHeadersUriSpec;
 
-		private RestClient.RequestBodySpec requestBodySpec;
-
-		private final String requestId;
-
 		DefaultRequestBodyUriSpec(RestClient.RequestBodyUriSpec spec) {
 			this.requestHeadersUriSpec = spec;
-			this.requestBodySpec = spec;
-			this.requestId = String.valueOf(requestIndex.incrementAndGet());
+			String requestId = String.valueOf(requestIndex.incrementAndGet());
+			this.requestHeadersUriSpec.header(RESTTESTCLIENT_REQUEST_ID, requestId);
 		}
 
 		@Override
-		public RequestBodySpec uri(String uriTemplate, Object... uriVariables) {
-			this.requestBodySpec = this.requestHeadersUriSpec.uri(uriTemplate, uriVariables);
+		public RequestBodySpec uri(String uriTemplate, @Nullable Object... uriVariables) {
+			this.requestHeadersUriSpec.uri(uriTemplate, uriVariables);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec uri(String uri, Map<String, ?> uriVariables) {
-			this.requestBodySpec = this.requestHeadersUriSpec.uri(uri, uriVariables);
+			this.requestHeadersUriSpec.uri(uri, uriVariables);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec uri(Function<UriBuilder, URI> uriFunction) {
-			this.requestBodySpec = this.requestHeadersUriSpec.uri(uriFunction);
+			this.requestHeadersUriSpec.uri(uriFunction);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec uri(URI uri) {
-			this.requestBodySpec = this.requestHeadersUriSpec.uri(uri);
+			this.requestHeadersUriSpec.uri(uri);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec header(String headerName, String... headerValues) {
-			this.requestBodySpec = this.requestHeadersUriSpec.header(headerName, headerValues);
+			this.requestHeadersUriSpec.header(headerName, headerValues);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec headers(Consumer<HttpHeaders> headersConsumer) {
-			this.requestBodySpec = this.requestHeadersUriSpec.headers(headersConsumer);
+			this.requestHeadersUriSpec.headers(headersConsumer);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec accept(MediaType... acceptableMediaTypes) {
-			this.requestBodySpec = this.requestHeadersUriSpec.accept(acceptableMediaTypes);
+			this.requestHeadersUriSpec.accept(acceptableMediaTypes);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec acceptCharset(Charset... acceptableCharsets) {
-			this.requestBodySpec = this.requestHeadersUriSpec.acceptCharset(acceptableCharsets);
+			this.requestHeadersUriSpec.acceptCharset(acceptableCharsets);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec contentType(MediaType contentType) {
-			this.requestBodySpec = this.requestHeadersUriSpec.contentType(contentType);
+			this.requestHeadersUriSpec.contentType(contentType);
+			return this;
+		}
+
+		@Override
+		public RequestBodySpec contentLength(long contentLength) {
+			this.requestHeadersUriSpec.contentLength(contentLength);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec cookie(String name, String value) {
-			this.requestBodySpec = this.requestHeadersUriSpec.cookie(name, value);
+			this.requestHeadersUriSpec.cookie(name, value);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec cookies(Consumer<MultiValueMap<String, String>> cookiesConsumer) {
-			this.requestBodySpec = this.requestHeadersUriSpec.cookies(cookiesConsumer);
+			this.requestHeadersUriSpec.cookies(cookiesConsumer);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec ifModifiedSince(ZonedDateTime ifModifiedSince) {
-			this.requestBodySpec = this.requestHeadersUriSpec.ifModifiedSince(ifModifiedSince);
+			this.requestHeadersUriSpec.ifModifiedSince(ifModifiedSince);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec ifNoneMatch(String... ifNoneMatches) {
-			this.requestBodySpec = this.requestHeadersUriSpec.ifNoneMatch(ifNoneMatches);
+			this.requestHeadersUriSpec.ifNoneMatch(ifNoneMatches);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec attribute(String name, Object value) {
-			this.requestBodySpec = this.requestHeadersUriSpec.attribute(name, value);
+			this.requestHeadersUriSpec.attribute(name, value);
 			return this;
 		}
 
 		@Override
 		public RequestBodySpec attributes(Consumer<Map<String, Object>> attributesConsumer) {
-			this.requestBodySpec = this.requestHeadersUriSpec.attributes(attributesConsumer);
+			this.requestHeadersUriSpec.attributes(attributesConsumer);
 			return this;
 		}
 
@@ -230,11 +228,9 @@ class DefaultRestTestClient implements RestTestClient {
 
 		@Override
 		public ResponseSpec exchange() {
-			this.requestBodySpec = this.requestBodySpec.header(RESTTESTCLIENT_REQUEST_ID, this.requestId);
-			ExchangeResult exchangeResult = this.requestBodySpec.exchange(
-					(clientRequest, clientResponse) -> new ExchangeResult(clientResponse),
-					false);
-			return new DefaultResponseSpec(Objects.requireNonNull(exchangeResult));
+			return new DefaultResponseSpec(
+					this.requestHeadersUriSpec.exchangeForRequiredValue(
+							(request, response) -> new ExchangeResult(response), false));
 		}
 	}
 
@@ -243,8 +239,8 @@ class DefaultRestTestClient implements RestTestClient {
 
 		private final ExchangeResult exchangeResult;
 
-		DefaultResponseSpec(ExchangeResult exchangeResult) {
-			this.exchangeResult = exchangeResult;
+		DefaultResponseSpec(ExchangeResult result) {
+			this.exchangeResult = result;
 		}
 
 		@Override
@@ -265,19 +261,22 @@ class DefaultRestTestClient implements RestTestClient {
 		@Override
 		public <B> BodySpec<B, ?> expectBody(Class<B> bodyType) {
 			B body = this.exchangeResult.getBody(bodyType);
-			return new DefaultBodySpec<>(new EntityExchangeResult<>(this.exchangeResult, body));
+			EntityExchangeResult<B> result = new EntityExchangeResult<>(this.exchangeResult, body);
+			return new DefaultBodySpec<>(result);
 		}
 
 		@Override
 		public <B> BodySpec<B, ?> expectBody(ParameterizedTypeReference<B> bodyType) {
 			B body = this.exchangeResult.getBody(bodyType);
-			return new DefaultBodySpec<>(new EntityExchangeResult<>(this.exchangeResult, body));
+			EntityExchangeResult<B> result = new EntityExchangeResult<>(this.exchangeResult, body);
+			return new DefaultBodySpec<>(result);
 		}
 
 		@Override
 		public BodyContentSpec expectBody() {
 			byte[] body = this.exchangeResult.getBody(byte[].class);
-			return new DefaultBodyContentSpec( new EntityExchangeResult<>(this.exchangeResult, body));
+			EntityExchangeResult<byte[]> result = new EntityExchangeResult<>(this.exchangeResult, body);
+			return new DefaultBodyContentSpec(result);
 		}
 
 		@Override
@@ -318,20 +317,26 @@ class DefaultRestTestClient implements RestTestClient {
 
 		private final EntityExchangeResult<B> result;
 
-		DefaultBodySpec(@Nullable EntityExchangeResult<B> result) {
-			this.result = Objects.requireNonNull(result, "exchangeResult must be non-null");
+		DefaultBodySpec(EntityExchangeResult<B> result) {
+			this.result = result;
 		}
 
 		@Override
-		public <T extends S> T isEqualTo(B expected) {
+		public <T extends S> T isEqualTo(@Nullable B expected) {
 			this.result.assertWithDiagnostics(() ->
 					AssertionErrors.assertEquals("Response body", expected, this.result.getResponseBody()));
 			return self();
 		}
 
+		@Override
+		public <T extends S> T value(Matcher<? super @Nullable B> matcher) {
+			this.result.assertWithDiagnostics(() -> MatcherAssert.assertThat(this.result.getResponseBody(), matcher));
+			return self();
+		}
+
 		@Override
 		@SuppressWarnings("NullAway") // https://github.com/uber/NullAway/issues/1129
-		public <T extends S, R> T value(Function<B, R> bodyMapper, Matcher<? super R> matcher) {
+		public <T extends S, R> T value(Function<@Nullable B, @Nullable R> bodyMapper, Matcher<? super @Nullable R> matcher) {
 			this.result.assertWithDiagnostics(() -> {
 				B body = this.result.getResponseBody();
 				MatcherAssert.assertThat(bodyMapper.apply(body), matcher);
@@ -340,7 +345,8 @@ class DefaultRestTestClient implements RestTestClient {
 		}
 
 		@Override
-		public <T extends S> T value(Consumer<B> consumer) {
+		@SuppressWarnings("NullAway") // https://github.com/uber/NullAway/issues/1129
+		public <T extends S> T value(Consumer<@Nullable B> consumer) {
 			this.result.assertWithDiagnostics(() -> consumer.accept(this.result.getResponseBody()));
 			return self();
 		}
@@ -374,8 +380,7 @@ class DefaultRestTestClient implements RestTestClient {
 		@Override
 		public EntityExchangeResult<Void> isEmpty() {
 			this.result.assertWithDiagnostics(() ->
-					AssertionErrors.assertTrue("Expected empty body",
-							this.result.getBody(byte[].class) == null));
+					AssertionErrors.assertTrue("Expected empty body", this.result.getBody(byte[].class) == null));
 			return new EntityExchangeResult<>(this.result, null);
 		}
 
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/DefaultRestTestClientBuilder.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/DefaultRestTestClientBuilder.java
index 48c1d255b07..748deb67aaf 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/DefaultRestTestClientBuilder.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/DefaultRestTestClientBuilder.java
@@ -18,12 +18,14 @@ package org.springframework.test.web.servlet.client;
 
 import java.util.function.Consumer;
 
-import org.jspecify.annotations.Nullable;
-
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.MockMvcBuilder;
+import org.springframework.test.web.servlet.client.RestTestClient.MockMvcSetupBuilder;
+import org.springframework.test.web.servlet.client.RestTestClient.RouterFunctionSetupBuilder;
+import org.springframework.test.web.servlet.client.RestTestClient.StandaloneSetupBuilder;
+import org.springframework.test.web.servlet.client.RestTestClient.WebAppContextSetupBuilder;
 import org.springframework.test.web.servlet.setup.DefaultMockMvcBuilder;
 import org.springframework.test.web.servlet.setup.MockMvcBuilders;
 import org.springframework.test.web.servlet.setup.RouterFunctionMockMvcBuilder;
@@ -39,8 +41,8 @@ import org.springframework.web.util.UriBuilderFactory;
  *
  * @author Rob Worsnop
  * @author Rossen Stoyanchev
- * @param <B> the type of the builder
  * @since 7.0
+ * @param <B> the type of the builder
  */
 class DefaultRestTestClientBuilder<B extends RestTestClient.Builder<B>> implements RestTestClient.Builder<B> {
 
@@ -92,12 +94,6 @@ class DefaultRestTestClientBuilder<B extends RestTestClient.Builder<B>> implemen
 		return self();
 	}
 
-	@Override
-	public <T extends B> T apply(Consumer<RestTestClient.Builder<B>> builderConsumer) {
-		builderConsumer.accept(this);
-		return self();
-	}
-
 	@SuppressWarnings("unchecked")
 	protected <T extends B> T self() {
 		return (T) this;
@@ -113,8 +109,13 @@ class DefaultRestTestClientBuilder<B extends RestTestClient.Builder<B>> implemen
 	}
 
 
+	/**
+	 * Base class for implementations for {@link MockMvcSetupBuilder}.
+	 * @param <S> the "self" type of the builder
+	 * @param <M> the type of {@link MockMvc} builder
+	 */
 	static class AbstractMockMvcSetupBuilder<S extends RestTestClient.Builder<S>, M extends MockMvcBuilder>
-			extends DefaultRestTestClientBuilder<S> implements RestTestClient.MockMvcSetupBuilder<S, M> {
+			extends DefaultRestTestClientBuilder<S> implements MockMvcSetupBuilder<S, M> {
 
 		private final M mockMvcBuilder;
 
@@ -136,8 +137,12 @@ class DefaultRestTestClientBuilder<B extends RestTestClient.Builder<B>> implemen
 	}
 
 
-	static class DefaultStandaloneSetupBuilder extends AbstractMockMvcSetupBuilder<RestTestClient.StandaloneSetupBuilder, StandaloneMockMvcBuilder>
-			implements RestTestClient.StandaloneSetupBuilder {
+	/**
+	 * Default implementation of {@link StandaloneSetupBuilder}.
+	 */
+	static class DefaultStandaloneSetupBuilder
+			extends AbstractMockMvcSetupBuilder<StandaloneSetupBuilder, StandaloneMockMvcBuilder>
+			implements StandaloneSetupBuilder {
 
 		DefaultStandaloneSetupBuilder(Object... controllers) {
 			super(MockMvcBuilders.standaloneSetup(controllers));
@@ -145,8 +150,12 @@ class DefaultRestTestClientBuilder<B extends RestTestClient.Builder<B>> implemen
 	}
 
 
-	static class DefaultRouterFunctionSetupBuilder extends AbstractMockMvcSetupBuilder<RestTestClient.RouterFunctionSetupBuilder, RouterFunctionMockMvcBuilder>
-			implements RestTestClient.RouterFunctionSetupBuilder {
+	/**
+	 * Default implementation of {@link RouterFunctionSetupBuilder}.
+	 */
+	static class DefaultRouterFunctionSetupBuilder
+			extends AbstractMockMvcSetupBuilder<RouterFunctionSetupBuilder, RouterFunctionMockMvcBuilder>
+			implements RouterFunctionSetupBuilder {
 
 		DefaultRouterFunctionSetupBuilder(RouterFunction<?>... routerFunctions) {
 			super(MockMvcBuilders.routerFunctions(routerFunctions));
@@ -155,8 +164,12 @@ class DefaultRestTestClientBuilder<B extends RestTestClient.Builder<B>> implemen
 	}
 
 
-	static class DefaultWebAppContextSetupBuilder extends AbstractMockMvcSetupBuilder<RestTestClient.WebAppContextSetupBuilder, DefaultMockMvcBuilder>
-			implements RestTestClient.WebAppContextSetupBuilder {
+	/**
+	 * Default implementation of {@link WebAppContextSetupBuilder}.
+	 */
+	static class DefaultWebAppContextSetupBuilder
+			extends AbstractMockMvcSetupBuilder<WebAppContextSetupBuilder, DefaultMockMvcBuilder>
+			implements WebAppContextSetupBuilder {
 
 		DefaultWebAppContextSetupBuilder(WebApplicationContext context) {
 			super(MockMvcBuilders.webAppContextSetup(context));
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/ExchangeResult.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/ExchangeResult.java
index bb899d2a8b0..a440f016d45 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/ExchangeResult.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/ExchangeResult.java
@@ -19,7 +19,6 @@ package org.springframework.test.web.servlet.client;
 import java.io.IOException;
 import java.net.HttpCookie;
 import java.util.List;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -32,6 +31,7 @@ import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatusCode;
 import org.springframework.http.ResponseCookie;
+import org.springframework.util.Assert;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.client.RestClient.RequestHeadersSpec.ConvertibleClientHttpResponse;
@@ -41,21 +41,28 @@ import org.springframework.web.client.RestClient.RequestHeadersSpec.ConvertibleC
  * {@link RestTestClient}.
  *
  * @author Rob Worsnop
+ * @author Rossen Stoyanchev
+ * @since 7.0
  */
 public class ExchangeResult {
+
 	private static final Pattern SAME_SITE_PATTERN = Pattern.compile("(?i).*SameSite=(Strict|Lax|None).*");
+
 	private static final Pattern PARTITIONED_PATTERN = Pattern.compile("(?i).*;\\s*Partitioned(\\s*;.*|\\s*)$");
 
 
 	private static final Log logger = LogFactory.getLog(ExchangeResult.class);
 
+
+	private final ConvertibleClientHttpResponse clientResponse;
+
 	/** Ensure single logging; for example, for expectAll. */
 	private boolean diagnosticsLogged;
 
-	private final ConvertibleClientHttpResponse clientResponse;
 
-	ExchangeResult(@Nullable ConvertibleClientHttpResponse clientResponse) {
-		this.clientResponse = Objects.requireNonNull(clientResponse, "clientResponse must be non-null");
+	ExchangeResult(@Nullable ConvertibleClientHttpResponse response) {
+		Assert.notNull(response, "Response must not be null");
+		this.clientResponse = response;
 	}
 
 	ExchangeResult(ExchangeResult result) {
@@ -63,6 +70,10 @@ public class ExchangeResult {
 		this.diagnosticsLogged = result.diagnosticsLogged;
 	}
 
+
+	/**
+	 * Return the HTTP status code as an {@link HttpStatusCode} value.
+	 */
 	public HttpStatusCode getStatus() {
 		try {
 			return this.clientResponse.getStatusCode();
@@ -72,10 +83,41 @@ public class ExchangeResult {
 		}
 	}
 
+	/**
+	 * Return the response headers received from the server.
+	 */
 	public HttpHeaders getResponseHeaders() {
 		return this.clientResponse.getHeaders();
 	}
 
+	/**
+	 * Return response cookies received from the server.
+	 */
+	public MultiValueMap<String, ResponseCookie> getResponseCookies() {
+		return Optional.ofNullable(this.clientResponse.getHeaders().get(HttpHeaders.SET_COOKIE)).orElse(List.of()).stream()
+				.flatMap(header -> {
+					Matcher matcher = SAME_SITE_PATTERN.matcher(header);
+					String sameSite = (matcher.matches() ? matcher.group(1) : null);
+					boolean partitioned = PARTITIONED_PATTERN.matcher(header).matches();
+					return HttpCookie.parse(header).stream().map(cookie -> toResponseCookie(cookie, sameSite, partitioned));
+				})
+				.collect(LinkedMultiValueMap::new,
+						(cookies, cookie) -> cookies.add(cookie.getName(), cookie),
+						LinkedMultiValueMap::addAll);
+	}
+
+	private static ResponseCookie toResponseCookie(HttpCookie cookie, @Nullable String sameSite, boolean partitioned) {
+		return ResponseCookie.from(cookie.getName(), cookie.getValue())
+				.domain(cookie.getDomain())
+				.httpOnly(cookie.isHttpOnly())
+				.maxAge(cookie.getMaxAge())
+				.path(cookie.getPath())
+				.secure(cookie.getSecure())
+				.sameSite(sameSite)
+				.partitioned(partitioned)
+				.build();
+	}
+
 	@Nullable
 	public <T> T getBody(Class<T> bodyType) {
 		return this.clientResponse.bodyTo(bodyType);
@@ -86,7 +128,6 @@ public class ExchangeResult {
 		return this.clientResponse.bodyTo(bodyType);
 	}
 
-
 	/**
 	 * Execute the given Runnable, catch any {@link AssertionError}, log details
 	 * about the request and response at ERROR level under the class log
@@ -105,31 +146,4 @@ public class ExchangeResult {
 		}
 	}
 
-	/**
-	 * Return response cookies received from the server.
-	 */
-	public MultiValueMap<String, ResponseCookie> getResponseCookies() {
-		return Optional.ofNullable(this.clientResponse.getHeaders().get(HttpHeaders.SET_COOKIE)).orElse(List.of()).stream()
-				.flatMap(header -> {
-					Matcher matcher = SAME_SITE_PATTERN.matcher(header);
-					String sameSite = (matcher.matches() ? matcher.group(1) : null);
-					boolean partitioned = PARTITIONED_PATTERN.matcher(header).matches();
-					return HttpCookie.parse(header).stream().map(cookie -> toResponseCookie(cookie, sameSite, partitioned));
-				})
-				.collect(LinkedMultiValueMap::new,
-						(cookies, cookie) -> cookies.add(cookie.getName(), cookie),
-						LinkedMultiValueMap::addAll);
-	}
-
-	private static ResponseCookie toResponseCookie(HttpCookie cookie, @Nullable String sameSite, boolean partitioned) {
-		return ResponseCookie.from(cookie.getName(), cookie.getValue())
-				.domain(cookie.getDomain())
-				.httpOnly(cookie.isHttpOnly())
-				.maxAge(cookie.getMaxAge())
-				.path(cookie.getPath())
-				.secure(cookie.getSecure())
-				.sameSite(sameSite)
-				.partitioned(partitioned)
-				.build();
-	}
 }
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/HeaderAssertions.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/HeaderAssertions.java
index 89e557b93e5..777097e67d6 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/HeaderAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/HeaderAssertions.java
@@ -29,7 +29,7 @@ import org.springframework.test.web.support.AbstractHeaderAssertions;
 public class HeaderAssertions extends AbstractHeaderAssertions<ExchangeResult, RestTestClient.ResponseSpec> {
 
 
-	public HeaderAssertions(ExchangeResult exchangeResult, RestTestClient.ResponseSpec responseSpec) {
+	HeaderAssertions(ExchangeResult exchangeResult, RestTestClient.ResponseSpec responseSpec) {
 		super(exchangeResult, responseSpec);
 	}
 
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/JsonPathAssertions.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/JsonPathAssertions.java
index b5eda5ba59a..efe57d0b3d2 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/JsonPathAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/JsonPathAssertions.java
@@ -26,13 +26,19 @@ import org.springframework.test.web.support.AbstractJsonPathAssertions;
  * <a href="https://github.com/jayway/JsonPath">JsonPath</a> assertions.
  *
  * @author Rob Worsnop
+ * @author Rossen Stoyanchev
  * @since 7.0
  * @see <a href="https://github.com/jayway/JsonPath">https://github.com/jayway/JsonPath</a>
  * @see JsonPathExpectationsHelper
  */
 public class JsonPathAssertions extends AbstractJsonPathAssertions<RestTestClient.BodyContentSpec> {
 
-	JsonPathAssertions(RestTestClient.BodyContentSpec spec, String content, String expression, @Nullable Configuration configuration) {
+
+	JsonPathAssertions(
+			RestTestClient.BodyContentSpec spec, String content, String expression,
+			@Nullable Configuration configuration) {
+
 		super(spec, content, expression, configuration);
 	}
+
 }
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/RestTestClient.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/RestTestClient.java
index 32bbed7535a..2394060227a 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/RestTestClient.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/RestTestClient.java
@@ -37,6 +37,7 @@ import org.springframework.test.json.JsonComparison;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.MockMvcBuilder;
 import org.springframework.test.web.servlet.setup.DefaultMockMvcBuilder;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
 import org.springframework.test.web.servlet.setup.RouterFunctionMockMvcBuilder;
 import org.springframework.test.web.servlet.setup.StandaloneMockMvcBuilder;
 import org.springframework.util.MultiValueMap;
@@ -47,7 +48,19 @@ import org.springframework.web.util.UriBuilder;
 import org.springframework.web.util.UriBuilderFactory;
 
 /**
- * Client for testing web servers.
+ * Client for testing web servers that uses {@link RestClient} internally to
+ * perform requests while also providing a fluent API to verify responses.
+ * This client can connect to any server over HTTP or to a {@link MockMvc} server
+ * with a mock request and response.
+ *
+ * <p>Use one of the bindToXxx methods to create an instance. For example:
+ * <ul>
+ * <li>{@link #bindToController(Object...)}
+ * <li>{@link #bindToRouterFunction(RouterFunction[])}
+ * <li>{@link #bindToApplicationContext(WebApplicationContext)}
+ * <li>{@link #bindToServer()}
+ * <li>...
+ * </ul>
  *
  * @author Rob Worsnop
  * @author Rossen Stoyanchev
@@ -121,34 +134,24 @@ public interface RestTestClient {
 
 
 	/**
-	 * Begin creating a {@link RestTestClient} by providing the {@code @Controller}
-	 * instance(s) to handle requests with.
-	 * <p>Internally this is delegated to and equivalent to using
-	 * {@link org.springframework.test.web.servlet.setup.MockMvcBuilders#standaloneSetup(Object...)}
-	 * to initialize {@link MockMvc}.
+	 * Begin creating a {@link RestTestClient} with a {@link MockMvcBuilders#standaloneSetup
+	 * Standalone MockMvc setup}.
 	 */
 	static StandaloneSetupBuilder bindToController(Object... controllers) {
 		return new DefaultRestTestClientBuilder.DefaultStandaloneSetupBuilder(controllers);
 	}
 
 	/**
-	 * Begin creating a {@link RestTestClient} by providing the {@link RouterFunction}
-	 * instance(s) to handle requests with.
-	 * <p>Internally this is delegated to and equivalent to using
-	 * {@link org.springframework.test.web.servlet.setup.MockMvcBuilders#routerFunctions(RouterFunction[])}
-	 * to initialize {@link MockMvc}.
+	 * Begin creating a {@link RestTestClient} with a {@link MockMvcBuilders#routerFunctions}
+	 * RouterFunction's MockMvc setup}.
 	 */
 	static RouterFunctionSetupBuilder bindToRouterFunction(RouterFunction<?>... routerFunctions) {
 		return new DefaultRestTestClientBuilder.DefaultRouterFunctionSetupBuilder(routerFunctions);
 	}
 
 	/**
-	 * Begin creating a {@link RestTestClient} by providing a
-	 * {@link WebApplicationContext} with Spring MVC infrastructure and
-	 * controllers.
-	 * <p>Internally this is delegated to and equivalent to using
-	 * {@link org.springframework.test.web.servlet.setup.MockMvcBuilders#webAppContextSetup(WebApplicationContext)}
-	 * to initialize {@code MockMvc}.
+	 * Begin creating a {@link RestTestClient} with a {@link MockMvcBuilders#webAppContextSetup}
+	 * WebAppContext MockMvc setup}.
 	 */
 	static WebAppContextSetupBuilder bindToApplicationContext(WebApplicationContext context) {
 		return new DefaultRestTestClientBuilder.DefaultWebAppContextSetupBuilder(context);
@@ -164,8 +167,7 @@ public interface RestTestClient {
 	}
 
 	/**
-	 * This server setup option allows you to connect to a live server through
-	 * a client connector.
+	 * This server setup option allows you to connect to a live server.
 	 * <p><pre class="code">
 	 * RestTestClient client = RestTestClient.bindToServer()
 	 *         .baseUrl("http://localhost:8080")
@@ -186,12 +188,14 @@ public interface RestTestClient {
 	}
 
 
+	/**
+	 * Steps to customize the underlying {@link RestClient} via {@link RestClient.Builder}.
+	 * @param <B> the type of builder
+	 */
 	interface Builder<B extends Builder<B>> {
 
 		/**
-		 * Configure a base URI as described in
-		 * {@link RestClient#create(String)
-		 * WebClient.create(String)}.
+		 * Configure a base URI as described in {@link RestClient#create(String)}.
 		 */
 		<T extends B> T baseUrl(String baseUrl);
 
@@ -203,7 +207,7 @@ public interface RestTestClient {
 
 		/**
 		 * Add the given header to all requests that haven't added it.
-		 * @param headerName   the header name
+		 * @param headerName the header name
 		 * @param headerValues the header values
 		 */
 		<T extends B> T defaultHeader(String headerName, String... headerValues);
@@ -220,8 +224,8 @@ public interface RestTestClient {
 		<T extends B> T defaultHeaders(Consumer<HttpHeaders> headersConsumer);
 
 		/**
-		 * Add the given cookie to all requests.
-		 * @param cookieName   the cookie name
+		 * Add the given cookie to all requests that haven't already added it.
+		 * @param cookieName the cookie name
 		 * @param cookieValues the cookie values
 		 */
 		<T extends B> T defaultCookie(String cookieName, String... cookieValues);
@@ -237,39 +241,48 @@ public interface RestTestClient {
 		 */
 		<T extends B> T defaultCookies(Consumer<MultiValueMap<String, String>> cookiesConsumer);
 
-		/**
-		 * Apply the given {@code Consumer} to this builder instance.
-		 * <p>This can be useful for applying pre-packaged customizations.
-		 * @param builderConsumer the consumer to apply
-		 */
-		<T extends B> T apply(Consumer<Builder<B>> builderConsumer);
-
 		/**
 		 * Build the {@link RestTestClient} instance.
 		 */
 		RestTestClient build();
- 	}
+	}
 
 
-	interface MockMvcSetupBuilder<B extends Builder<B>, M extends MockMvcBuilder> extends Builder<B> {
+	/**
+	 * Extension of {@link Builder} for tests against a MockMvc server.
+	 * @param <S> the builder type
+	 * @param <M> the type of {@link MockMvc} setup
+	 */
+	interface MockMvcSetupBuilder<S extends Builder<S>, M extends MockMvcBuilder> extends Builder<S> {
 
-		<T extends B> T configureServer(Consumer<M> consumer);
+		<T extends S> T configureServer(Consumer<M> consumer);
 	}
 
 
+	/**
+	 * Extension of {@link Builder} for tests витх а
+	 * {@link MockMvcBuilders#standaloneSetup(Object...) standalone MockMvc setup}.
+	 */
 	interface StandaloneSetupBuilder extends MockMvcSetupBuilder<StandaloneSetupBuilder, StandaloneMockMvcBuilder> {
 	}
 
 
+	/**
+	 * Extension of {@link Builder} for tests витх а
+	 * {@link MockMvcBuilders#routerFunctions(RouterFunction[]) RouterFunction MockMvc setup}.
+	 */
 	interface RouterFunctionSetupBuilder extends MockMvcSetupBuilder<RouterFunctionSetupBuilder, RouterFunctionMockMvcBuilder> {
 	}
 
 
+	/**
+	 * Extension of {@link Builder} for tests витх а
+	 * {@link MockMvcBuilders#webAppContextSetup(WebApplicationContext) WebAppContext MockMvc setup}.
+	 */
 	interface WebAppContextSetupBuilder extends MockMvcSetupBuilder<WebAppContextSetupBuilder, DefaultMockMvcBuilder> {
 	}
 
 
-
 	/**
 	 * Specification for providing the URI of a request.
 	 *
@@ -294,7 +307,7 @@ public interface RestTestClient {
 		 * with a base URI) it will be used to expand the URI template.
 		 * @return spec to add headers or perform the exchange
 		 */
-		S uri(String uri, Object... uriVariables);
+		S uri(String uri, @Nullable Object... uriVariables);
 
 		/**
 		 * Specify the URI for the request using a URI template and URI variables.
@@ -302,7 +315,7 @@ public interface RestTestClient {
 		 * with a base URI) it will be used to expand the URI template.
 		 * @return spec to add headers or perform the exchange
 		 */
-		S uri(String uri, Map<String, ?> uriVariables);
+		S uri(String uri, Map<String, ? extends @Nullable Object> uriVariables);
 
 		/**
 		 * Build the URI for the request with a {@link UriBuilder} obtained
@@ -419,6 +432,16 @@ public interface RestTestClient {
 	 * Specification for providing body of a request.
 	 */
 	interface RequestBodySpec extends RequestHeadersSpec<RequestBodySpec> {
+
+		/**
+		 * Set the length of the body in bytes, as specified by the
+		 * {@code Content-Length} header.
+		 * @param contentLength the content length
+		 * @return the same instance
+		 * @see HttpHeaders#setContentLength(long)
+		 */
+		RequestBodySpec contentLength(long contentLength);
+
 		/**
 		 * Set the {@linkplain MediaType media type} of the body, as specified
 		 * by the {@code Content-Type} header.
@@ -430,7 +453,7 @@ public interface RestTestClient {
 
 		/**
 		 * Set the body to the given {@code Object} value. This method invokes the
-		 * {@link org.springframework.web.client.RestClient.RequestBodySpec#body(Object)} (Object)
+		 * {@link RestClient.RequestBodySpec#body(Object)} (Object)
 		 * bodyValue} method on the underlying {@code RestClient}.
 		 * @param body the value to write to the request body
 		 * @return spec for further declaration of the request
@@ -461,8 +484,8 @@ public interface RestTestClient {
 	interface ResponseSpec {
 
 		/**
-		 * Apply multiple assertions to a response with the given
-		 * {@linkplain RestTestClient.ResponseSpec.ResponseSpecConsumer consumers}, with the guarantee that
+s		 * Apply multiple assertions to a response with the given
+		 * {@linkplain ResponseSpecConsumer consumers}, with the guarantee that
 		 * all assertions will be applied even if one or more assertions fails
 		 * with an exception.
 		 * <p>If a single {@link Error} or {@link RuntimeException} is thrown,
@@ -522,8 +545,7 @@ public interface RestTestClient {
 		BodyContentSpec expectBody();
 
 		/**
-		 * Exit the chained flow in order to consume the response body
-		 * externally.
+		 * Exit the chained flow in order to consume the response body externally.
 		 */
 		<T> EntityExchangeResult<T> returnResult(Class<T> elementClass);
 
@@ -534,8 +556,8 @@ public interface RestTestClient {
 		<T> EntityExchangeResult<T> returnResult(ParameterizedTypeReference<T> elementTypeRef);
 
 		/**
-		 * {@link Consumer} of a {@link RestTestClient.ResponseSpec}.
-		 * @see RestTestClient.ResponseSpec#expectAll(RestTestClient.ResponseSpec.ResponseSpecConsumer...)
+		 * {@link Consumer} of a {@link ResponseSpec}.
+		 * @see ResponseSpec#expectAll(ResponseSpecConsumer...)
 		 */
 		@FunctionalInterface
 		interface ResponseSpecConsumer extends Consumer<ResponseSpec> {
@@ -554,18 +576,24 @@ public interface RestTestClient {
 		/**
 		 * Assert the extracted body is equal to the given value.
 		 */
-		<T extends S> T isEqualTo(B expected);
+		<T extends S> T isEqualTo(@Nullable B expected);
+
+		/**
+		 * Assert the extracted body with a {@link Matcher}.
+		 * @since 5.1
+		 */
+		<T extends S> T value(Matcher<? super @Nullable B> matcher);
 
 		/**
 		 * Transform the extracted the body with a function, for example, extracting a
 		 * property, and assert the mapped value with a {@link Matcher}.
 		 */
-		<T extends S, R> T value(Function<B, R> bodyMapper, Matcher<? super R> matcher);
+		<T extends S, R> T value(Function<@Nullable B, @Nullable R> bodyMapper, Matcher<? super @Nullable R> matcher);
 
 		/**
 		 * Assert the extracted body with a {@link Consumer}.
 		 */
-		<T extends S> T value(Consumer<B> consumer);
+		<T extends S> T value(Consumer<@Nullable B> consumer);
 
 		/**
 		 * Assert the exchange result with the given {@link Consumer}.
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/StatusAssertions.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/StatusAssertions.java
index c2f76ef22b0..f29df0975ab 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/StatusAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/StatusAssertions.java
@@ -29,10 +29,12 @@ import org.springframework.test.web.support.AbstractStatusAssertions;
  */
 public class StatusAssertions extends AbstractStatusAssertions<ExchangeResult, RestTestClient.ResponseSpec> {
 
-	public StatusAssertions(ExchangeResult exchangeResult, ResponseSpec responseSpec) {
+
+	StatusAssertions(ExchangeResult exchangeResult, ResponseSpec responseSpec) {
 		super(exchangeResult, responseSpec);
 	}
 
+
 	@Override
 	protected void assertWithDiagnostics(Runnable assertion) {
 		exchangeResult.assertWithDiagnostics(assertion);
diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/client/XpathAssertions.java b/spring-test/src/main/java/org/springframework/test/web/servlet/client/XpathAssertions.java
index cfec64a17ee..253bb0fbc63 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/client/XpathAssertions.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/client/XpathAssertions.java
@@ -33,11 +33,15 @@ import org.springframework.util.Assert;
  */
 public class XpathAssertions extends AbstractXpathAssertions<RestTestClient.BodyContentSpec> {
 
-	XpathAssertions(RestTestClient.BodyContentSpec spec,
-					String expression, @Nullable Map<String, String> namespaces, Object... args) {
+
+	XpathAssertions(
+			RestTestClient.BodyContentSpec spec,
+			String expression, @Nullable Map<String, String> namespaces, Object... args) {
+
 		super(spec, expression, namespaces, args);
 	}
 
+
 	@Override
 	protected Optional<HttpHeaders> getResponseHeaders() {
 		return Optional.of(bodySpec.returnResult())
diff --git a/spring-test/src/test/java/org/springframework/test/web/servlet/client/samples/RestTestClientTests.java b/spring-test/src/test/java/org/springframework/test/web/servlet/client/samples/RestTestClientTests.java
index 381c520ca7f..af1be6b11bc 100644
--- a/spring-test/src/test/java/org/springframework/test/web/servlet/client/samples/RestTestClientTests.java
+++ b/spring-test/src/test/java/org/springframework/test/web/servlet/client/samples/RestTestClientTests.java
@@ -133,7 +133,7 @@ class RestTestClientTests {
 		@Test
 		void test() {
 			RestTestClientTests.this.client.mutate()
-					.apply(builder -> builder.defaultHeader("foo", "bar"))
+					.defaultHeader("foo", "bar")
 					.uriBuilderFactory(new DefaultUriBuilderFactory("/test"))
 					.defaultCookie("foo", "bar")
 					.defaultCookies(cookies -> cookies.add("a", "b"))