Add apply method to WebClient.Builder

This commit introduces an apply method to `WebClient.Builder`, allowing
users to make multiple changes to the builder in one consumer.

Issue: SPR-15743

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

@@ -256,4 +256,12 @@ class DefaultWebClientBuilder implements WebClient.Builder {
 		return new DefaultWebClientBuilder(this);
 	}
 
+	@Override
+	public WebClient.Builder apply(Consumer<WebClient.Builder> builderConsumer) {
+		Assert.notNull(builderConsumer, "'builderConsumer' must not be null");
+
+		builderConsumer.accept(this);
+		return this;
+	}
+
 }

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

@@ -301,16 +301,22 @@ public interface WebClient {
 		 */
 		Builder exchangeFunction(ExchangeFunction exchangeFunction);
 
-		/**
-		 * Builder the {@link WebClient} instance.
-		 */
-		WebClient build();
-
 		/**
 		 * Clone this {@code WebClient.Builder}
 		 */
 		Builder clone();
 
+		/**
+		 * Shortcut for pre-packaged customizations to WebTest builder.
+		 * @param builderConsumer the consumer to apply
+		 */
+		Builder apply(Consumer<Builder> builderConsumer);
+
+		/**
+		 * Builder the {@link WebClient} instance.
+		 */
+		WebClient build();
+
 	}
 
 

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

@@ -157,6 +157,19 @@ public class DefaultWebClientTests {
 		client.get().uri("/path").attribute("foo", "bar").exchange();
 	}
 
+	@Test
+	public void apply() {
+		WebClient client = builder()
+					.apply(builder -> builder.defaultHeader("Accept", "application/json").defaultCookie("id", "123"))
+				.build();
+		client.get().uri("/path").exchange();
+
+		ClientRequest request = verifyExchange();
+		assertEquals("application/json", request.headers().getFirst("Accept"));
+		assertEquals("123", request.cookies().getFirst("id"));
+		verifyNoMoreInteractions(this.exchangeFunction);
+	}
+
 
 
 	private WebClient.Builder builder() {