Avoid required uri when using WebClient w/ base url

This commit makes the `uri` step of the WebClient optional, so that
users who have specified a base URL during WebClient config do not need
to provide an empty one (i.e. `url("")`).

The basic idea of this fix is that the HTTP method methods in WebClient
(`get`, `post`, etc.) should be able to "bypass" the uri stage, and skip
straight to defining headers, or even doing an exchange or retrieve
(i.e. call methods on `RequestHeaderSpec` or `RequestBodySpec`).

I have accomplished this by adding two new composed interfaces:
`RequestHeadersUriSpec` and `RequestBodyUriSpec`.
`RequestHeadersUriSpec` extends from the existing `UriSpec` and
`RequestHeaderSpec`, while `RequestBodyUriSpec` extends from `UriSpec`
and `RequestBodySpec`. These types are returned from the HTTP methods
(`get`, `post` etc). The `uri` methods on these types return a plain
`RequestHeaderSpec` and `RequestBodySpec` (i.e. types without the `uri`
methods), so that you can call `uri` once only.

Issue: SPR-15695

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

@@ -86,48 +86,48 @@ class DefaultWebClient implements WebClient {
 
 
 	@Override
-	public UriSpec<RequestHeadersSpec<?>> get() {
+	public RequestHeadersUriSpec<?> get() {
 		return methodInternal(HttpMethod.GET);
 	}
 
 	@Override
-	public UriSpec<RequestHeadersSpec<?>> head() {
+	public RequestHeadersUriSpec<?> head() {
 		return methodInternal(HttpMethod.HEAD);
 	}
 
 	@Override
-	public UriSpec<RequestBodySpec> post() {
+	public RequestBodyUriSpec post() {
 		return methodInternal(HttpMethod.POST);
 	}
 
 	@Override
-	public UriSpec<RequestBodySpec> put() {
+	public RequestBodyUriSpec put() {
 		return methodInternal(HttpMethod.PUT);
 	}
 
 	@Override
-	public UriSpec<RequestBodySpec> patch() {
+	public RequestBodyUriSpec patch() {
 		return methodInternal(HttpMethod.PATCH);
 	}
 
 	@Override
-	public UriSpec<RequestHeadersSpec<?>> delete() {
+	public RequestHeadersUriSpec<?> delete() {
 		return methodInternal(HttpMethod.DELETE);
 	}
 
 	@Override
-	public UriSpec<RequestHeadersSpec<?>> options() {
+	public RequestHeadersUriSpec<?> options() {
 		return methodInternal(HttpMethod.OPTIONS);
 	}
 
 	@Override
-	public UriSpec<RequestBodySpec> method(HttpMethod httpMethod) {
+	public RequestBodyUriSpec method(HttpMethod httpMethod) {
 		return methodInternal(httpMethod);
 	}
 
 	@SuppressWarnings("unchecked")
-	private <S extends RequestHeadersSpec<?>> UriSpec<S> methodInternal(HttpMethod httpMethod) {
-		return new DefaultUriSpec<>(httpMethod);
+	private RequestBodyUriSpec methodInternal(HttpMethod httpMethod) {
+		return new DefaultRequestBodyUriSpec(httpMethod);
 	}
 
 	@Override
@@ -135,59 +135,49 @@ class DefaultWebClient implements WebClient {
 		return this.builder;
 	}
 
-	private class DefaultUriSpec<S extends RequestHeadersSpec<?>> implements UriSpec<S> {
+
+	private class DefaultRequestBodyUriSpec implements RequestBodyUriSpec {
 
 		private final HttpMethod httpMethod;
 
+		@Nullable
+		private URI uri;
+
+		@Nullable
+		private HttpHeaders headers;
+
+		@Nullable
+		private MultiValueMap<String, String> cookies;
+
+		@Nullable
+		private BodyInserter<?, ? super ClientHttpRequest> inserter;
+
+		@Nullable
+		private Map<String, Object> attributes;
 
-		DefaultUriSpec(HttpMethod httpMethod) {
+		DefaultRequestBodyUriSpec(HttpMethod httpMethod) {
 			this.httpMethod = httpMethod;
 		}
 
 		@Override
-		public S uri(String uriTemplate, Object... uriVariables) {
+		public RequestBodySpec uri(String uriTemplate, Object... uriVariables) {
 			return uri(uriBuilderFactory.expand(uriTemplate, uriVariables));
 		}
 
 		@Override
-		public S uri(String uriTemplate, Map<String, ?> uriVariables) {
+		public RequestBodySpec uri(String uriTemplate, Map<String, ?> uriVariables) {
 			return uri(uriBuilderFactory.expand(uriTemplate, uriVariables));
 		}
 
 		@Override
-		public S uri(Function<UriBuilder, URI> uriFunction) {
+		public RequestBodySpec uri(Function<UriBuilder, URI> uriFunction) {
 			return uri(uriFunction.apply(uriBuilderFactory.builder()));
 		}
 
 		@Override
-		@SuppressWarnings("unchecked")
-		public S uri(URI uri) {
-			return (S) new DefaultRequestBodySpec(this.httpMethod, uri);
-		}
-	}
-
-
-	private class DefaultRequestBodySpec implements RequestBodySpec {
-
-		private final HttpMethod httpMethod;
-
-		private final URI uri;
-
-		@Nullable
-		private HttpHeaders headers;
-
-		@Nullable
-		private MultiValueMap<String, String> cookies;
-
-		@Nullable
-		private BodyInserter<?, ? super ClientHttpRequest> inserter;
-
-		@Nullable
-		private Map<String, Object> attributes;
-
-		DefaultRequestBodySpec(HttpMethod httpMethod, URI uri) {
-			this.httpMethod = httpMethod;
+		public RequestBodySpec uri(URI uri) {
 			this.uri = uri;
+			return this;
 		}
 
 		private HttpHeaders getHeaders() {
@@ -212,7 +202,7 @@ class DefaultWebClient implements WebClient {
 		}
 
 		@Override
-		public DefaultRequestBodySpec header(String headerName, String... headerValues) {
+		public DefaultRequestBodyUriSpec header(String headerName, String... headerValues) {
 			for (String headerValue : headerValues) {
 				getHeaders().add(headerName, headerValue);
 			}
@@ -220,7 +210,7 @@ class DefaultWebClient implements WebClient {
 		}
 
 		@Override
-		public DefaultRequestBodySpec headers(Consumer<HttpHeaders> headersConsumer) {
+		public DefaultRequestBodyUriSpec headers(Consumer<HttpHeaders> headersConsumer) {
 			Assert.notNull(headersConsumer, "'headersConsumer' must not be null");
 			headersConsumer.accept(getHeaders());
 			return this;
@@ -240,37 +230,37 @@ class DefaultWebClient implements WebClient {
 		}
 
 		@Override
-		public DefaultRequestBodySpec accept(MediaType... acceptableMediaTypes) {
+		public DefaultRequestBodyUriSpec accept(MediaType... acceptableMediaTypes) {
 			getHeaders().setAccept(Arrays.asList(acceptableMediaTypes));
 			return this;
 		}
 
 		@Override
-		public DefaultRequestBodySpec acceptCharset(Charset... acceptableCharsets) {
+		public DefaultRequestBodyUriSpec acceptCharset(Charset... acceptableCharsets) {
 			getHeaders().setAcceptCharset(Arrays.asList(acceptableCharsets));
 			return this;
 		}
 
 		@Override
-		public DefaultRequestBodySpec contentType(MediaType contentType) {
+		public DefaultRequestBodyUriSpec contentType(MediaType contentType) {
 			getHeaders().setContentType(contentType);
 			return this;
 		}
 
 		@Override
-		public DefaultRequestBodySpec contentLength(long contentLength) {
+		public DefaultRequestBodyUriSpec contentLength(long contentLength) {
 			getHeaders().setContentLength(contentLength);
 			return this;
 		}
 
 		@Override
-		public DefaultRequestBodySpec cookie(String name, String value) {
+		public DefaultRequestBodyUriSpec cookie(String name, String value) {
 			getCookies().add(name, value);
 			return this;
 		}
 
 		@Override
-		public DefaultRequestBodySpec cookies(
+		public DefaultRequestBodyUriSpec cookies(
 				Consumer<MultiValueMap<String, String>> cookiesConsumer) {
 			Assert.notNull(cookiesConsumer, "'cookiesConsumer' must not be null");
 			cookiesConsumer.accept(this.cookies);
@@ -278,7 +268,7 @@ class DefaultWebClient implements WebClient {
 		}
 
 		@Override
-		public DefaultRequestBodySpec ifModifiedSince(ZonedDateTime ifModifiedSince) {
+		public DefaultRequestBodyUriSpec ifModifiedSince(ZonedDateTime ifModifiedSince) {
 			ZonedDateTime gmt = ifModifiedSince.withZoneSameInstant(ZoneId.of("GMT"));
 			String headerValue = DateTimeFormatter.RFC_1123_DATE_TIME.format(gmt);
 			getHeaders().set(HttpHeaders.IF_MODIFIED_SINCE, headerValue);
@@ -286,7 +276,7 @@ class DefaultWebClient implements WebClient {
 		}
 
 		@Override
-		public DefaultRequestBodySpec ifNoneMatch(String... ifNoneMatches) {
+		public DefaultRequestBodyUriSpec ifNoneMatch(String... ifNoneMatches) {
 			getHeaders().setIfNoneMatch(Arrays.asList(ifNoneMatches));
 			return this;
 		}
@@ -320,7 +310,8 @@ class DefaultWebClient implements WebClient {
 		}
 
 		private ClientRequest.Builder initRequestBuilder() {
-			return ClientRequest.method(this.httpMethod, this.uri)
+			URI uri = this.uri != null ? this.uri : uriBuilderFactory.expand("");
+			return ClientRequest.method(this.httpMethod, uri)
 					.headers(headers -> headers.addAll(initHeaders()))
 					.cookies(cookies -> cookies.addAll(initCookies()))
 					.attributes(attributes -> attributes.putAll(getAttributes()));

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

@@ -63,49 +63,49 @@ public interface WebClient {
 	 * Prepare an HTTP GET request.
 	 * @return a spec for specifying the target URL
 	 */
-	UriSpec<RequestHeadersSpec<?>> get();
+	RequestHeadersUriSpec<?> get();
 
 	/**
 	 * Prepare an HTTP HEAD request.
 	 * @return a spec for specifying the target URL
 	 */
-	UriSpec<RequestHeadersSpec<?>> head();
+	RequestHeadersUriSpec<?> head();
 
 	/**
 	 * Prepare an HTTP POST request.
 	 * @return a spec for specifying the target URL
 	 */
-	UriSpec<RequestBodySpec> post();
+	RequestBodyUriSpec post();
 
 	/**
 	 * Prepare an HTTP PUT request.
 	 * @return a spec for specifying the target URL
 	 */
-	UriSpec<RequestBodySpec> put();
+	RequestBodyUriSpec put();
 
 	/**
 	 * Prepare an HTTP PATCH request.
 	 * @return a spec for specifying the target URL
 	 */
-	UriSpec<RequestBodySpec> patch();
+	RequestBodyUriSpec patch();
 
 	/**
 	 * Prepare an HTTP DELETE request.
 	 * @return a spec for specifying the target URL
 	 */
-	UriSpec<RequestHeadersSpec<?>> delete();
+	RequestHeadersUriSpec<?> delete();
 
 	/**
 	 * Prepare an HTTP OPTIONS request.
 	 * @return a spec for specifying the target URL
 	 */
-	UriSpec<RequestHeadersSpec<?>> options();
+	RequestHeadersUriSpec<?> options();
 
 	/**
 	 * Prepare a request for the specified {@code HttpMethod}.
 	 * @return a spec for specifying the target URL
 	 */
-	UriSpec<RequestBodySpec> method(HttpMethod method);
+	RequestBodyUriSpec method(HttpMethod method);
 
 
 	/**
@@ -579,4 +579,14 @@ public interface WebClient {
 
 	}
 
+
+	interface RequestHeadersUriSpec<S extends RequestHeadersSpec<S>>
+			extends UriSpec<S>, RequestHeadersSpec<S> {
+	}
+
+
+	interface RequestBodyUriSpec extends RequestBodySpec, RequestHeadersUriSpec<RequestBodySpec> {
+	}
+
+
 }