Support dynamic default uri variables for RestClient

spring-web/src/main/java/org/springframework/web/util/UriComponents.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,8 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Function;
+import java.util.function.Supplier;
 import java.util.function.UnaryOperator;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -42,6 +44,7 @@
  * @author Arjen Poutsma
  * @author Juergen Hoeller
  * @author Rossen Stoyanchev
+ * @author Yanming Zhou
  * @since 3.1
  * @see UriComponentsBuilder
  */
@@ -144,7 +147,9 @@ public final UriComponents encode() {
 	/**
 	 * Replace all URI template variables with the values from a given map.
 	 * <p>The given map keys represent variable names; the corresponding values
-	 * represent variable values. The order of variables is not significant.
+	 * represent variable values, if the variable value is {@link Supplier} or
+	 * {@link Function}, then the value to use is applied base on the variable name.
+	 * The order of variables is not significant.
 	 * @param uriVariables the map of URI variables
 	 * @return the expanded URI components
 	 */
@@ -233,6 +238,7 @@ public final String toString() {
 		return expandUriComponent(source, uriVariables, null);
 	}
 
+	@SuppressWarnings({"unchecked", "rawtypes"})
 	static @Nullable String expandUriComponent(@Nullable String source, UriTemplateVariables uriVariables,
 			@Nullable UnaryOperator<String> encoder) {
 
@@ -254,6 +260,12 @@ public final String toString() {
 			if (UriTemplateVariables.SKIP_VALUE.equals(varValue)) {
 				continue;
 			}
+			if (varValue instanceof Supplier supplier) {
+				varValue = supplier.get();
+			}
+			else if (varValue instanceof Function function) {
+				varValue = function.apply(varName);
+			}
 			String formatted = getVariableValueAsString(varValue);
 			formatted = encoder != null ? encoder.apply(formatted) : Matcher.quoteReplacement(formatted);
 			matcher.appendReplacement(sb, formatted);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,8 +20,10 @@
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Function;
 
 import org.assertj.core.api.InstanceOfAssertFactories;
 import org.jspecify.annotations.Nullable;
@@ -44,6 +46,7 @@
  * @author Arjen Poutsma
  * @author Sebastien Deleuze
  * @author Nicklas Wiegandt
+ * @author Yanming Zhou
  */
 public class RestClientBuilderTests {
 
@@ -110,6 +113,23 @@ void defaultUri() {
 		assertThat(fieldValue("baseUrl", defaultBuilder)).isEqualTo(baseUrl.toString());
 	}
 
+	@Test
+	void baseUriWithDynamicDefaultUriVariables() {
+		String key = "partition";
+		String baseUrl = "http://{" + key + "}.example.com";
+		Map<String, String> holder = new HashMap<>();
+		RestClient restClient = RestClient.builder().baseUrl(baseUrl)
+			.defaultUriVariables(Map.of(key, (Function<String, String>) holder::get)).build();
+
+		holder.put(key, "p0");
+		assertThat(fieldValue("uri", restClient.get().uri("/{foo}.html", Map.of("foo", "index")))
+			.toString()).isEqualTo("http://p0.example.com/index.html");
+
+		holder.put(key, "p1");
+		assertThat(fieldValue("uri", restClient.get().uri("/{bar}.html", Map.of("bar", "index")))
+			.toString()).isEqualTo("http://p1.example.com/index.html");
+	}
+
 	@Test
 	void messageConvertersList() {
 		StringHttpMessageConverter stringConverter = new StringHttpMessageConverter();
@@ -281,4 +301,17 @@ void buildCopiesDefaultCookiesImmutable() {
 			return null;
 		}
 	}
+
+	private static @Nullable Object fieldValue(String name, Object instance) {
+		try {
+			Field field = instance.getClass().getDeclaredField(name);
+			field.setAccessible(true);
+
+			return field.get(instance);
+		}
+		catch (NoSuchFieldException | IllegalAccessException ex) {
+			fail(ex.getMessage(), ex);
+			return null;
+		}
+	}
 }

spring-web/src/test/java/org/springframework/web/util/UriComponentsTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,9 @@
 import java.net.URI;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.function.Supplier;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -42,6 +45,7 @@
  * @author Arjen Poutsma
  * @author Phillip Webb
  * @author Rossen Stoyanchev
+ * @author Yanming Zhou
  */
 class UriComponentsTests {
 
@@ -266,4 +270,24 @@ void equalsOpaqueUriComponents(ParserType parserType) {
 		assertThat(uric1).isNotEqualTo(uric3);
 	}
 
+	@Test
+	void expandSupplier() {
+		String key = "partition";
+		Map<String, String> holder = Map.of(key, "p0");
+		UriComponents uri = UriComponentsBuilder.fromUriString("http://{" + key + "}.example.com")
+			.uriVariables(Map.of(key, (Supplier<String>) () -> holder.get(key))).build();
+
+		assertThat(uri.toString()).isEqualTo("http://p0.example.com");
+	}
+
+	@Test
+	void expandFunction() {
+		String key = "partition";
+		Map<String, String> holder = Map.of(key, "p0");
+		UriComponents uri = UriComponentsBuilder.fromUriString("http://{" + key + "}.example.com")
+			.uriVariables(Map.of(key, (Function<String, String>) holder::get)).build();
+
+		assertThat(uri.toString()).isEqualTo("http://p0.example.com");
+	}
+
 }