Normalize micrometer client tag URIs

Update `MetricsClientHttpRequestInterceptor` so that captured URIs
are normalize to always contain a leading slash.

Fixes gh-11798

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/client/MetricsClientHttpRequestInterceptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -97,10 +97,15 @@ class MetricsClientHttpRequestInterceptor implements ClientHttpRequestIntercepto
 
 	private Timer.Builder getTimeBuilder(HttpRequest request,
 			ClientHttpResponse response) {
+		String url = ensureLeadingSlash(urlTemplate.get());
 		return Timer.builder(this.metricName)
-				.tags(this.tagProvider.getTags(urlTemplate.get(), request, response))
+				.tags(this.tagProvider.getTags(url, request, response))
 				.description("Timer of RestTemplate operation")
 				.publishPercentileHistogram(this.recordPercentiles);
 	}
 
+	private String ensureLeadingSlash(String url) {
+		return (url.startsWith("/") ? url : "/" + url);
+	}
+
 }

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/web/client/MetricsRestTemplateCustomizerTests.java

@@ -47,18 +47,23 @@ public class MetricsRestTemplateCustomizerTests {
 
 	private RestTemplate restTemplate;
 
+	private MockRestServiceServer mockServer;
+
+	private MetricsRestTemplateCustomizer customizer;
+
 	@Before
 	public void setup() {
 		this.registry = new SimpleMeterRegistry(SimpleConfig.DEFAULT, new MockClock());
 		this.restTemplate = new RestTemplate();
+		this.mockServer = MockRestServiceServer.createServer(this.restTemplate);
+		this.customizer = new MetricsRestTemplateCustomizer(this.registry,
+				new DefaultRestTemplateExchangeTagsProvider(), "http.client.requests",
+				true);
+		this.customizer.customize(this.restTemplate);
 	}
 
 	@Test
 	public void interceptRestTemplate() {
-		MetricsRestTemplateCustomizer customizer = new MetricsRestTemplateCustomizer(
-				this.registry, new DefaultRestTemplateExchangeTagsProvider(),
-				"http.client.requests", true);
-		customizer.customize(this.restTemplate);
 		MockRestServiceServer mockServer = MockRestServiceServer
 				.createServer(this.restTemplate);
 		mockServer.expect(MockRestRequestMatchers.requestTo("/test/123"))
@@ -79,13 +84,22 @@ public class MetricsRestTemplateCustomizerTests {
 
 	@Test
 	public void avoidDuplicateRegistration() {
-		MetricsRestTemplateCustomizer customizer = new MetricsRestTemplateCustomizer(
-				this.registry, new DefaultRestTemplateExchangeTagsProvider(),
-				"http.client.requests", true);
-		customizer.customize(this.restTemplate);
+		this.customizer.customize(this.restTemplate);
 		assertThat(this.restTemplate.getInterceptors()).hasSize(1);
-		customizer.customize(this.restTemplate);
+		this.customizer.customize(this.restTemplate);
 		assertThat(this.restTemplate.getInterceptors()).hasSize(1);
 	}
 
+	@Test
+	public void normalizeUriToContainLeadingSlash() {
+		this.mockServer.expect(MockRestRequestMatchers.requestTo("/test/123"))
+				.andExpect(MockRestRequestMatchers.method(HttpMethod.GET))
+				.andRespond(MockRestResponseCreators.withSuccess("OK",
+						MediaType.APPLICATION_JSON));
+		String result = this.restTemplate.getForObject("test/{id}", String.class, 123);
+		this.registry.get("http.client.requests").tags("uri", "/test/{id}").timer();
+		assertThat(result).isEqualTo("OK");
+		this.mockServer.verify();
+	}
+
 }