Resolve URI to baseUrl in RestClient

Closes gh-32679

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();