Data binding from pathvars and headers in fn handlers

Closes gh-35800

framework-docs/modules/ROOT/pages/web/webflux-functional.adoc

@@ -296,7 +296,8 @@ allPartsEvents.windowUntil(PartEvent::isLast)
 
 NOTE: The body contents of the `PartEvent` objects must be completely consumed, relayed, or released to avoid memory leaks.
 
-The following shows how to bind request parameters, including an optional `DataBinder` customization:
+The following shows how to bind request parameters, URI variables, or headers via `DataBinder`,
+and also shows how to customize the `DataBinder`:
 
 [tabs]
 ======

framework-docs/modules/ROOT/pages/web/webmvc-functional.adoc

@@ -184,7 +184,8 @@ val map = request.params()
 ----
 ======
 
-The following shows how to bind request parameters, including an optional `DataBinder` customization:
+The following shows how to bind request parameters, URI variables, or headers via `DataBinder`,
+and also shows how to customize the `DataBinder`:
 
 [tabs]
 ======

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

@@ -61,6 +61,7 @@ import org.springframework.web.reactive.accept.ApiVersionStrategy;
 import org.springframework.web.reactive.function.BodyExtractor;
 import org.springframework.web.reactive.function.BodyExtractors;
 import org.springframework.web.reactive.function.UnsupportedMediaTypeException;
+import org.springframework.web.reactive.result.method.annotation.ExtendedWebExchangeDataBinder;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.ServerWebInputException;
 import org.springframework.web.server.UnsupportedMediaTypeStatusException;
@@ -244,7 +245,7 @@ class DefaultServerRequest implements ServerRequest {
 		Assert.notNull(dataBinderCustomizer, "DataBinderCustomizer must not be null");
 
 		return Mono.defer(() -> {
-			WebExchangeDataBinder dataBinder = new WebExchangeDataBinder(null);
+			WebExchangeDataBinder dataBinder = new ExtendedWebExchangeDataBinder(null);
 			dataBinder.setTargetType(ResolvableType.forClass(bindType));
 			dataBinderCustomizer.accept(dataBinder);
 

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

@@ -51,6 +51,17 @@ public class ExtendedWebExchangeDataBinder extends WebExchangeDataBinder {
 	private Predicate<String> headerPredicate = name -> !FILTERED_HEADER_NAMES.contains(name.toLowerCase(Locale.ROOT));
 
 
+	/**
+	 * Create a new instance, with default object name.
+	 * @param target the target object to bind onto (or {@code null} if the
+	 * binder is just used to convert a plain parameter value)
+	 * @since 7.0.2
+	 * @see #DEFAULT_OBJECT_NAME
+	 */
+	public ExtendedWebExchangeDataBinder(@Nullable Object target) {
+		super(target);
+	}
+
 	public ExtendedWebExchangeDataBinder(@Nullable Object target, String objectName) {
 		super(target, objectName);
 	}

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

@@ -30,6 +30,7 @@ import org.springframework.web.testfixture.http.server.reactive.bootstrap.HttpSe
 import static org.springframework.web.reactive.function.server.RouterFunctions.route;
 
 /**
+ * Integration tests with data binding in fn handlers.
  * @author Arjen Poutsma
  */
 class BindingFunctionIntegrationTests extends AbstractRouterFunctionIntegrationTests {
@@ -65,7 +66,8 @@ class BindingFunctionIntegrationTests extends AbstractRouterFunctionIntegrationT
 		startServer(httpServer);
 
 		Mono<String> result = this.webClient.get()
-				.uri("/constructor?foo=FOO&bar=BAR")
+				.uri("/constructor?foo=FOO")
+				.header("bar", "BAR")
 				.retrieve()
 				.bodyToMono(String.class);
 
@@ -80,7 +82,8 @@ class BindingFunctionIntegrationTests extends AbstractRouterFunctionIntegrationT
 		startServer(httpServer);
 
 		Mono<String> result = this.webClient.get()
-				.uri("/property?foo=FOO&bar=BAR")
+				.uri("/property?foo=FOO")
+				.header("bar", "BAR")
 				.retrieve()
 				.bodyToMono(String.class);
 
@@ -95,7 +98,8 @@ class BindingFunctionIntegrationTests extends AbstractRouterFunctionIntegrationT
 			startServer(httpServer);
 
 			Mono<String> result = this.webClient.get()
-					.uri("/mixed?foo=FOO&bar=BAR")
+					.uri("/mixed?foo=FOO")
+					.header("bar", "BAR")
 					.retrieve()
 					.bodyToMono(String.class);
 

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerRequest.java

@@ -76,6 +76,7 @@ import org.springframework.web.bind.ServletRequestDataBinder;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.context.request.ServletWebRequest;
 import org.springframework.web.context.request.WebRequest;
+import org.springframework.web.servlet.mvc.method.annotation.ExtendedServletRequestDataBinder;
 import org.springframework.web.servlet.support.ServletUriComponentsBuilder;
 import org.springframework.web.util.ServletRequestPathUtils;
 import org.springframework.web.util.UriBuilder;
@@ -258,7 +259,7 @@ class DefaultServerRequest implements ServerRequest {
 		Assert.notNull(bindType, "BindType must not be null");
 		Assert.notNull(dataBinderCustomizer, "DataBinderCustomizer must not be null");
 
-		ServletRequestDataBinder dataBinder = new ServletRequestDataBinder(null);
+		ServletRequestDataBinder dataBinder = new ExtendedServletRequestDataBinder(null);
 		dataBinder.setTargetType(ResolvableType.forClass(bindType));
 		dataBinderCustomizer.accept(dataBinder);
 

spring-webmvc/src/test/java/org/springframework/web/servlet/function/DefaultServerRequestTests.java

@@ -64,8 +64,7 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 
 /**
- * Tests for {@link DefaultServerRequest}.
+ * Unit tests for {@link DefaultServerRequest}.
- *
  * @author Arjen Poutsma
  */
 class DefaultServerRequestTests {
@@ -350,7 +349,7 @@ class DefaultServerRequestTests {
 	void bindToConstructor() throws BindException {
 		MockHttpServletRequest servletRequest = PathPatternsTestUtils.initRequest("GET", "/", true);
 		servletRequest.addParameter("foo", "FOO");
-		servletRequest.addParameter("bar", "BAR");
+		servletRequest.addHeader("bar", "BAR");
 
 		DefaultServerRequest request = new DefaultServerRequest(servletRequest, this.messageConverters);
 
@@ -363,7 +362,7 @@ class DefaultServerRequestTests {
 	void bindToProperties() throws BindException {
 		MockHttpServletRequest servletRequest = PathPatternsTestUtils.initRequest("GET", "/", true);
 		servletRequest.addParameter("foo", "FOO");
-		servletRequest.addParameter("bar", "BAR");
+		servletRequest.addHeader("bar", "BAR");
 
 		DefaultServerRequest request = new DefaultServerRequest(servletRequest, this.messageConverters);
 
@@ -376,7 +375,7 @@ class DefaultServerRequestTests {
 	void bindToMixed() throws BindException {
 		MockHttpServletRequest servletRequest = PathPatternsTestUtils.initRequest("GET", "/", true);
 		servletRequest.addParameter("foo", "FOO");
-		servletRequest.addParameter("bar", "BAR");
+		servletRequest.addHeader("bar", "BAR");
 
 		DefaultServerRequest request = new DefaultServerRequest(servletRequest, this.messageConverters);