Better support for overriding base URI in WebClient

The base URI is ignored for requests that include a host.

WebClient exposes UriBuilder (rather than UriBuilderFactory) for
per-request URI building based on the base URI. That provides
full control to add or replace components of the base URI.

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

@@ -38,6 +38,7 @@ import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.reactive.function.BodyInserter;
 import org.springframework.web.util.DefaultUriBuilderFactory;
+import org.springframework.web.util.UriBuilder;
 import org.springframework.web.util.UriBuilderFactory;
 
 
@@ -150,8 +151,8 @@ class DefaultWebClient implements WebClient {
 		}
 
 		@Override
-		public HeaderSpec uri(Function<UriBuilderFactory, URI> uriFunction) {
-			return uri(uriFunction.apply(getUriBuilderFactory()));
+		public HeaderSpec uri(Function<UriBuilder, URI> uriFunction) {
+			return uri(uriFunction.apply(getUriBuilderFactory().builder()));
 		}
 
 		@Override

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

@@ -31,6 +31,7 @@ import org.springframework.http.client.reactive.ClientHttpConnector;
 import org.springframework.http.client.reactive.ClientHttpRequest;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.reactive.function.BodyInserter;
+import org.springframework.web.util.UriBuilder;
 import org.springframework.web.util.UriBuilderFactory;
 
 /**
@@ -113,6 +114,7 @@ public interface WebClient {
 	/**
 	 * Create a new {@code WebClient} with no default, shared preferences across
 	 * requests such as base URI, default headers, and others.
+	 * @see #create(String)
 	 */
 	static WebClient create() {
 		return new DefaultWebClientBuilder().build();
@@ -123,33 +125,48 @@ public interface WebClient {
 	 * example to avoid repeating the same host, port, base path, or even
 	 * query parameters with every request.
 	 *
-	 * <p>Given the following initialization:
+	 * <p>For example given this initialization:
 	 * <pre class="code">
 	 * WebClient client = WebClient.create("http://abc.com/v1");
 	 * </pre>
 	 *
-	 * <p>A base URI is applied when using a URI template:
+	 * <p>The base URI is applied to exchanges with a URI template:
 	 * <pre class="code">
-	 *
 	 * // GET http://abc.com/v1/accounts/43
-	 *
 	 * Mono&#060;Account&#062; result = client.get()
 	 *         .uri("/accounts/{id}", 43)
 	 *         .exchange()
-	 *         .then(response -> response.bodyToMono(String.class));
+	 *         .then(response -> response.bodyToMono(Account.class));
 	 * </pre>
 	 *
-	 * <p>It is also applied when using a {@link UriBuilderFactory}:
+	 * <p>The base URI is also applied to exchanges with a {@code UriBuilder}:
 	 * <pre class="code">
-
 	 * // GET http://abc.com/v1/accounts?q=12
-	 *
-	 * Mono&#060;Account&#062; result = client.get()
-	 *         .uri(factory -> factory.uriString("/accounts").queryParam("q", "12").build())
+	 * Flux&#060;Account&#062; result = client.get()
+	 *         .uri(builder -> builder.path("/accounts").queryParam("q", "12").build())
 	 *         .exchange()
-	 *         .then(response -> response.bodyToMono(String.class));
+	 *         .then(response -> response.bodyToFlux(Account.class));
 	 * </pre>
 	 *
+	 * <p>The base URI can be overridden with an absolute URI:
+	 * <pre class="code">
+	 * // GET http://xyz.com/path
+	 * Mono&#060;Account&#062; result = client.get()
+	 *         .uri("http://xyz.com/path")
+	 *         .exchange()
+	 *         .then(response -> response.bodyToMono(Account.class));
+	 * </pre>
+	 *
+	 * <p>The base URI can be partially overridden with a {@code UriBuilder}:
+	 * <pre class="code">
+	 * // GET http://abc.com/v2/accounts?q=12
+	 * Flux&#060;Account&#062; result = client.get()
+	 *         .uri(builder -> builder.replacePath("/v2/accounts").queryParam("q", "12").build())
+	 *         .exchange()
+	 *         .then(response -> response.bodyToFlux(Account.class));
+	 * </pre>
+	 *
+	 *
 	 * @param baseUrl the base URI for all requests
 	 */
 	static WebClient create(String baseUrl) {
@@ -284,7 +301,7 @@ public interface WebClient {
 		 * Build the URI for the request using the {@link UriBuilderFactory}
 		 * configured for this client.
 		 */
-		HeaderSpec uri(Function<UriBuilderFactory, URI> uriFunction);
+		HeaderSpec uri(Function<UriBuilder, URI> uriFunction);
 
 	}
 

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

@@ -64,6 +64,26 @@ public class DefaultWebClientTests {
 		assertEquals(Collections.emptyMap(), request.cookies());
 	}
 
+	@Test
+	public void uriBuilder() throws Exception {
+		WebClient client = builder().build();
+		client.get().uri(builder -> builder.path("/path").queryParam("q", "12").build()).exchange();
+
+		ClientRequest<?> request = verifyExchange();
+		assertEquals("/base/path?q=12", request.url().toString());
+		verifyNoMoreInteractions(this.exchangeFunction);
+	}
+
+	@Test
+	public void uriBuilderWithPathOverride() throws Exception {
+		WebClient client = builder().build();
+		client.get().uri(builder -> builder.replacePath("/path").build()).exchange();
+
+		ClientRequest<?> request = verifyExchange();
+		assertEquals("/path", request.url().toString());
+		verifyNoMoreInteractions(this.exchangeFunction);
+	}
+
 	@Test
 	public void requestHeaderAndCookie() throws Exception {
 		WebClient client = builder().build();