Add URI template support to ProxyExchange for observability

spring-cloud-gateway-mvc/src/main/java/org/springframework/cloud/gateway/mvc/ProxyExchange.java

@@ -32,6 +32,8 @@
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.Vector;
 import java.util.function.Function;
@@ -50,6 +52,7 @@
 import org.springframework.core.Conventions;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.RequestEntity.BodyBuilder;
@@ -147,6 +150,10 @@ public class ProxyExchange<T> {
 
 	private URI uri;
 
+	private String uriTemplate;
+
+	private Map<String, ?> uriVariables;
+
 	private RestTemplate rest;
 
 	private Object body;
@@ -247,6 +254,8 @@ public ProxyExchange<T> excluded(String... names) {
 	 */
 	public ProxyExchange<T> uri(URI uri) {
 		this.uri = uri;
+		this.uriTemplate = null;
+		this.uriVariables = null;
 		return this;
 	}
 
@@ -264,6 +273,21 @@ public ProxyExchange<T> uri(String uri) {
 		}
 	}
 
+	/**
+	 * Sets the uri for the backend call using a URI template with variables. When a
+	 * template is provided, the downstream {@link RestTemplate} call preserves the
+	 * template pattern for observability (e.g. Micrometer URI tags).
+	 * @param uriTemplate the URI template (e.g. {@code "http://service/foos/{id}"})
+	 * @param uriVariables the variables to expand in the template
+	 * @return this for convenience
+	 */
+	public ProxyExchange<T> uri(String uriTemplate, Map<String, ?> uriVariables) {
+		this.uriTemplate = uriTemplate;
+		this.uriVariables = uriVariables;
+		this.uri = rest.getUriTemplateHandler().expand(uriTemplate, uriVariables);
+		return this;
+	}
+
 	public String path() {
 		return (String) this.webRequest.getAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE,
 				WebRequest.SCOPE_REQUEST);
@@ -357,6 +381,11 @@ private ResponseEntity<T> exchange(RequestEntity<?> requestEntity) {
 		if (type instanceof TypeVariable || type instanceof WildcardType) {
 			type = Object.class;
 		}
+		if (this.uriTemplate != null && this.uriVariables != null) {
+			return rest.exchange(this.uriTemplate, Objects.requireNonNull(requestEntity.getMethod()),
+					new HttpEntity<>(requestEntity.getBody(), requestEntity.getHeaders()),
+					ParameterizedTypeReference.forType(type), this.uriVariables);
+		}
 		return rest.exchange(requestEntity, ParameterizedTypeReference.forType(type));
 	}
 

spring-cloud-gateway-mvc/src/test/java/org/springframework/cloud/gateway/mvc/ProductionConfigurationTests.java

@@ -23,6 +23,7 @@
 import java.util.Map;
 
 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import io.micrometer.core.instrument.MeterRegistry;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
@@ -72,6 +73,9 @@ public class ProductionConfigurationTests {
 	@Autowired
 	private TestApplication application;
 
+	@Autowired
+	private MeterRegistry meterRegistry;
+
 	@LocalServerPort
 	private int port;
 
@@ -86,6 +90,17 @@ public void get() {
 		assertThat(rest.getForObject("/proxy/0", Foo.class).getName()).isEqualTo("bye");
 	}
 
+	@Test
+	public void getWithUriTemplate() {
+		assertThat(rest.getForObject("/proxy/template/0", Foo.class).getName()).isEqualTo("bye");
+	}
+
+	@Test
+	public void getWithUriTemplatePreservesUriTagForObservability() {
+		rest.getForObject("/proxy/template/0", Foo.class);
+		assertThat(meterRegistry.find("http.client.requests").tag("uri", "/foos/{id}").timer()).isNotNull();
+	}
+
 	@Test
 	public void path() {
 		assertThat(rest.getForObject("/proxy/path/1", Foo.class).getName()).isEqualTo("foo");
@@ -363,6 +378,11 @@ public ResponseEntity<?> proxyFoos(@PathVariable Integer id, ProxyExchange<?> pr
 				return proxy.uri(home.toString() + "/foos/" + id).get();
 			}
 
+			@GetMapping("/proxy/template/{id}")
+			public ResponseEntity<?> proxyWithTemplate(@PathVariable Integer id, ProxyExchange<?> proxy) {
+				return proxy.uri(home.toString() + "/foos/{id}", Map.of("id", String.valueOf(id))).get();
+			}
+
 			@GetMapping("/proxy/path/**")
 			public ResponseEntity<?> proxyPath(ProxyExchange<?> proxy, UriComponentsBuilder uri) {
 				String path = proxy.path("/proxy/path/");