Improve Tags generation for methods names

This commit optimizes the `Tag` generation for method names by only
allocating new `Tag` instances for well-known method names. Others will
be marked as "UNKNOWN".

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 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 +24,7 @@
 import io.micrometer.core.instrument.Tag;
 
 import org.springframework.boot.actuate.metrics.http.Outcome;
+import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.util.StringUtils;
@@ -53,6 +54,8 @@ public final class WebFluxTags {
 
 	private static final Tag EXCEPTION_NONE = Tag.of("exception", "None");
 
+	private static final Tag METHOD_UNKNOWN = Tag.of("method", "UNKNOWN");
+
 	private static final Pattern FORWARD_SLASHES_PATTERN = Pattern.compile("//+");
 
 	private static final Set<String> DISCONNECTED_CLIENT_EXCEPTIONS = new HashSet<>(
@@ -70,7 +73,11 @@ private WebFluxTags() {
 	 * @return the method tag whose value is a capitalized method (e.g. GET).
 	 */
 	public static Tag method(ServerWebExchange exchange) {
-		return Tag.of("method", exchange.getRequest().getMethodValue());
+		HttpMethod httpMethod = exchange.getRequest().getMethod();
+		if (httpMethod != null) {
+			return Tag.of("method", httpMethod.name());
+		}
+		return METHOD_UNKNOWN;
 	}
 
 	/**

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2023 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 +24,7 @@
 import io.micrometer.core.instrument.Tag;
 
 import org.springframework.boot.actuate.metrics.http.Outcome;
+import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.util.StringUtils;
 import org.springframework.web.servlet.HandlerMapping;
@@ -71,7 +72,13 @@ private WebMvcTags() {
 	 * @return the method tag whose value is a capitalized method (e.g. GET).
 	 */
 	public static Tag method(HttpServletRequest request) {
-		return (request != null) ? Tag.of("method", request.getMethod()) : METHOD_UNKNOWN;
+		if (request != null) {
+			HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
+			if (httpMethod != null) {
+				return Tag.of("method", httpMethod.name());
+			}
+		}
+		return METHOD_UNKNOWN;
 	}
 
 	/**

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -179,4 +179,18 @@ void outcomeTagIsUnknownWhenResponseStatusIsInUnknownSeries() {
 		assertThat(tag.getValue()).isEqualTo("UNKNOWN");
 	}
 
+	@Test
+	void methodTagIsWellKnownHttpMethod() {
+		this.request.setMethod("GET");
+		Tag tag = WebMvcTags.method(this.request);
+		assertThat(tag.getValue()).isEqualTo("GET");
+	}
+
+	@Test
+	void methodTagForUnknownHttpMethods() {
+		this.request.setMethod("TEST");
+		Tag tag = WebMvcTags.method(this.request);
+		assertThat(tag.getValue()).isEqualTo("UNKNOWN");
+	}
+
 }

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

@@ -22,6 +22,7 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.http.server.reactive.ServerHttpResponse;
@@ -130,13 +131,23 @@ void uriTagValueIsUnknownWhenRequestHasNoPatternAndNonRootPathInfo() {
 	}
 
 	@Test
-	void methodTagToleratesNonStandardHttpMethods() {
+	void methodTagValueIsHttpMethod() {
 		ServerWebExchange exchange = mock(ServerWebExchange.class);
 		ServerHttpRequest request = mock(ServerHttpRequest.class);
 		given(exchange.getRequest()).willReturn(request);
-		given(request.getMethodValue()).willReturn("CUSTOM");
+		given(request.getMethod()).willReturn(HttpMethod.GET);
 		Tag tag = WebFluxTags.method(exchange);
-		assertThat(tag.getValue()).isEqualTo("CUSTOM");
+		assertThat(tag.getValue()).isEqualTo("GET");
+	}
+
+	@Test
+	void methodTagMarksNonStandardHttpMethodsAsUnknown() {
+		ServerWebExchange exchange = mock(ServerWebExchange.class);
+		ServerHttpRequest request = mock(ServerHttpRequest.class);
+		given(exchange.getRequest()).willReturn(request);
+		given(request.getMethod()).willReturn(null);
+		Tag tag = WebFluxTags.method(exchange);
+		assertThat(tag.getValue()).isEqualTo("UNKNOWN");
 	}
 
 	@Test