Resolve URI to baseUrl in RestClient

Closes gh-32679

spring-web/src/main/java/org/springframework/web/client/DefaultRestClient.java

@@ -341,7 +341,13 @@ final class DefaultRestClient implements RestClient {
 
 		@Override
 		public RequestBodySpec uri(URI uri) {
-			this.uri = uri;
+			if (uri.isAbsolute()) {
+				this.uri = uri;
+			}
+			else {
+				URI baseUri = DefaultRestClient.this.uriBuilderFactory.expand("");
+				this.uri = baseUri.resolve(uri);
+			}
 			return this;
 		}
 

spring-web/src/main/java/org/springframework/web/client/DefaultRestClientBuilder.java

@@ -16,6 +16,7 @@
 
 package org.springframework.web.client;
 
+import java.net.URI;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.LinkedHashMap;
@@ -245,6 +246,12 @@ final class DefaultRestClientBuilder implements RestClient.Builder {
 		return this;
 	}
 
+	@Override
+	public RestClient.Builder baseUrl(URI baseUrl) {
+		this.baseUrl = baseUrl.toString();
+		return this;
+	}
+
 	@Override
 	public RestClient.Builder defaultUriVariables(Map<String, ?> defaultUriVariables) {
 		this.defaultUriVariables = defaultUriVariables;

spring-web/src/main/java/org/springframework/web/client/RestClient.java

@@ -154,6 +154,17 @@ public interface RestClient {
 		return new DefaultRestClientBuilder().baseUrl(baseUrl).build();
 	}
 
+	/**
+	 * Variant of {@link #create()} that accepts a default base {@code URI}. For more
+	 * details see {@link Builder#baseUrl(URI) Builder.baseUrl(URI)}.
+	 * @param baseUrl the base URI for all requests
+	 * @since 6.2
+	 * @see #builder()
+	 */
+	static RestClient create(URI baseUrl) {
+		return new DefaultRestClientBuilder().baseUrl(baseUrl).build();
+	}
+
 	/**
 	 * Create a new {@code RestClient} based on the configuration of the given
 	 * {@code RestTemplate}.
@@ -230,6 +241,26 @@ public interface RestClient {
 		 */
 		Builder baseUrl(String baseUrl);
 
+		/**
+		 * Configure a base {@code URI} for requests. Effectively a shortcut for:
+		 * <pre class="code">
+		 * URI baseUrl = URI.create("https://abc.go.com/v1");
+		 * DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory(baseUrl.toString());
+		 * RestClient client = RestClient.builder().uriBuilderFactory(factory).build();
+		 * </pre>
+		 * <p>The {@code DefaultUriBuilderFactory} is used to prepare the URL
+		 * for every request with the given base URL, unless the URL request
+		 * for a given URL is absolute in which case the base URL is ignored.
+		 * <p><strong>Note:</strong> this method is mutually exclusive with
+		 * {@link #uriBuilderFactory(UriBuilderFactory)}. If both are used, the
+		 * {@code baseUrl} value provided here will be ignored.
+		 * @return this builder
+		 * @since 6.2
+		 * @see DefaultUriBuilderFactory#DefaultUriBuilderFactory(String)
+		 * @see #uriBuilderFactory(UriBuilderFactory)
+		 */
+		Builder baseUrl(URI baseUrl);
+
 		/**
 		 * Configure default URL variable values to use when expanding URI
 		 * templates with a {@link Map}. Effectively a shortcut for:
@@ -414,7 +445,11 @@ public interface RestClient {
 	interface UriSpec<S extends RequestHeadersSpec<?>> {
 
 		/**
-		 * Specify the URI using an absolute, fully constructed {@link URI}.
+		 * Specify the URI using a fully constructed {@link URI}.
+		 * <p>If the given URI is absolute, it is used as given. If it is
+		 * a relative URI, the {@link UriBuilderFactory} configured for
+		 * the client (e.g. with a base URI) will be used to
+		 * {@linkplain URI#resolve(URI) resolve} the given URI against.
 		 */
 		S uri(URI uri);
 

spring-web/src/test/java/org/springframework/web/client/RestClientBuilderTests.java

@@ -17,6 +17,7 @@
 package org.springframework.web.client;
 
 import java.lang.reflect.Field;
+import java.net.URI;
 import java.util.List;
 
 import org.junit.jupiter.api.Test;
@@ -90,6 +91,18 @@ public class RestClientBuilderTests {
 		assertThat(fieldValue("uriBuilderFactory", defaultBuilder)).isNull();
 	}
 
+	@Test
+	void defaultUri() {
+		URI baseUrl = URI.create("https://example.org");
+		RestClient.Builder builder = RestClient.builder();
+		builder.baseUrl(baseUrl);
+
+		assertThat(builder).isInstanceOf(DefaultRestClientBuilder.class);
+		DefaultRestClientBuilder defaultBuilder = (DefaultRestClientBuilder) builder;
+
+		assertThat(fieldValue("baseUrl", defaultBuilder)).isEqualTo(baseUrl.toString());
+	}
+
 	@Nullable
 	private static Object fieldValue(String name, DefaultRestClientBuilder instance) {
 		try {

spring-web/src/test/java/org/springframework/web/client/RestClientIntegrationTests.java

@@ -21,6 +21,8 @@ import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
+import java.net.URI;
+import java.net.URISyntaxException;
 import java.nio.charset.StandardCharsets;
 import java.util.List;
 import java.util.Map;
@@ -923,6 +925,28 @@ class RestClientIntegrationTests {
 		expectRequest(request -> assertThat(request.getHeader("Accept")).isEqualTo(MediaType.TEXT_PLAIN_VALUE));
 	}
 
+	@ParameterizedRestClientTest
+	void relativeUri(ClientHttpRequestFactory requestFactory) throws URISyntaxException {
+		startServer(requestFactory);
+
+		prepareResponse(response -> response.setHeader("Content-Type", "text/plain")
+				.setBody("Hello Spring!"));
+
+		URI uri = new URI(null, null, "/foo bar", null);
+
+		String result = this.restClient
+				.get()
+				.uri(uri)
+				.accept(MediaType.TEXT_PLAIN)
+				.retrieve()
+				.body(String.class);
+
+		assertThat(result).isEqualTo("Hello Spring!");
+
+		expectRequestCount(1);
+		expectRequest(request -> assertThat(request.getPath()).isEqualTo("/foo%20bar"));
+	}
+
 
 	private void prepareResponse(Consumer<MockResponse> consumer) {
 		MockResponse response = new MockResponse();