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/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();