Merge branch '2.2.x'

Closes gh-21560

Author: snicoll

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/reactive/server/WebFluxTags.java

@@ -110,6 +110,9 @@ public static Tag uri(ServerWebExchange exchange, boolean ignoreTrailingSlash) {
 			if (ignoreTrailingSlash && patternString.length() > 1) {
 				patternString = TRAILING_SLASH_PATTERN.matcher(patternString).replaceAll("");
 			}
+			if (patternString.isEmpty()) {
+				return URI_ROOT;
+			}
 			return Tag.of("uri", patternString);
 		}
 		HttpStatus status = exchange.getResponse().getStatusCode();

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/web/servlet/WebMvcTags.java

@@ -115,6 +115,9 @@ public static Tag uri(HttpServletRequest request, HttpServletResponse response,
 				if (ignoreTrailingSlash && pattern.length() > 1) {
 					pattern = TRAILING_SLASH_PATTERN.matcher(pattern).replaceAll("");
 				}
+				if (pattern.isEmpty()) {
+					return URI_ROOT;
+				}
 				return Tag.of("uri", pattern);
 			}
 			if (response != null) {

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/servlet/WebMvcTagsTests.java

@@ -58,6 +58,14 @@ void uriTagValueIsBestMatchingPatternWhenAvailable() {
 		assertThat(tag.getValue()).isEqualTo("/spring/");
 	}
 
+	@Test
+	void uriTagValueIsRootWhenBestMatchingPatternIsEmpty() {
+		this.request.setAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, "");
+		this.response.setStatus(301);
+		Tag tag = WebMvcTags.uri(this.request, this.response);
+		assertThat(tag.getValue()).isEqualTo("root");
+	}
+
 	@Test
 	void uriTagValueWithBestMatchingPatternAndIgnoreTrailingSlashRemoveTrailingSlash() {
 		this.request.setAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, "/spring/");

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/web/reactive/server/WebFluxTagsTests.java

@@ -61,6 +61,14 @@ void uriTagValueIsBestMatchingPatternWhenAvailable() {
 		assertThat(tag.getValue()).isEqualTo("/spring/");
 	}
 
+	@Test
+	void uriTagValueIsRootWhenBestMatchingPatternIsEmpty() {
+		this.exchange.getAttributes().put(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE, this.parser.parse(""));
+		this.exchange.getResponse().setStatusCode(HttpStatus.MOVED_PERMANENTLY);
+		Tag tag = WebFluxTags.uri(this.exchange);
+		assertThat(tag.getValue()).isEqualTo("root");
+	}
+
 	@Test
 	void uriTagValueWithBestMatchingPatternAndIgnoreTrailingSlashRemoveTrailingSlash() {
 		this.exchange.getAttributes().put(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE,