Allow additional tags to be contributed to WebMvc and WebFlux defaults

Closes gh-20175

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

@@ -16,9 +16,12 @@
 
 package org.springframework.boot.actuate.autoconfigure.metrics.web.reactive;
 
+import java.util.stream.Collectors;
+
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.config.MeterFilter;
 
+import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration;
 import org.springframework.boot.actuate.autoconfigure.metrics.MetricsProperties;
 import org.springframework.boot.actuate.autoconfigure.metrics.MetricsProperties.Web.Server.ServerRequest;
@@ -26,6 +29,7 @@ import org.springframework.boot.actuate.autoconfigure.metrics.OnlyOnceLoggingDen
 import org.springframework.boot.actuate.autoconfigure.metrics.export.simple.SimpleMetricsExportAutoConfiguration;
 import org.springframework.boot.actuate.metrics.web.reactive.server.DefaultWebFluxTagsProvider;
 import org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter;
+import org.springframework.boot.actuate.metrics.web.reactive.server.WebFluxTagsContributor;
 import org.springframework.boot.actuate.metrics.web.reactive.server.WebFluxTagsProvider;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -58,9 +62,9 @@ public class WebFluxMetricsAutoConfiguration {
 
 	@Bean
 	@ConditionalOnMissingBean(WebFluxTagsProvider.class)
-	public DefaultWebFluxTagsProvider webfluxTagConfigurer() {
+	public DefaultWebFluxTagsProvider webFluxTagsProvider(ObjectProvider<WebFluxTagsContributor> contributors) {
-		return new DefaultWebFluxTagsProvider(
+		return new DefaultWebFluxTagsProvider(this.properties.getWeb().getServer().getRequest().isIgnoreTrailingSlash(),
-				this.properties.getWeb().getServer().getRequest().isIgnoreTrailingSlash());
+				contributors.orderedStream().collect(Collectors.toList()));
 	}
 
 	@Bean

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

@@ -16,11 +16,14 @@
 
 package org.springframework.boot.actuate.autoconfigure.metrics.web.servlet;
 
+import java.util.stream.Collectors;
+
 import javax.servlet.DispatcherType;
 
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.config.MeterFilter;
 
+import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration;
 import org.springframework.boot.actuate.autoconfigure.metrics.MetricsProperties;
 import org.springframework.boot.actuate.autoconfigure.metrics.MetricsProperties.Web.Server.ServerRequest;
@@ -29,6 +32,7 @@ import org.springframework.boot.actuate.autoconfigure.metrics.export.simple.Simp
 import org.springframework.boot.actuate.metrics.web.servlet.DefaultWebMvcTagsProvider;
 import org.springframework.boot.actuate.metrics.web.servlet.LongTaskTimingHandlerInterceptor;
 import org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter;
+import org.springframework.boot.actuate.metrics.web.servlet.WebMvcTagsContributor;
 import org.springframework.boot.actuate.metrics.web.servlet.WebMvcTagsProvider;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -70,8 +74,9 @@ public class WebMvcMetricsAutoConfiguration {
 
 	@Bean
 	@ConditionalOnMissingBean(WebMvcTagsProvider.class)
-	public DefaultWebMvcTagsProvider webMvcTagsProvider() {
+	public DefaultWebMvcTagsProvider webMvcTagsProvider(ObjectProvider<WebMvcTagsContributor> contributors) {
-		return new DefaultWebMvcTagsProvider(this.properties.getWeb().getServer().getRequest().isIgnoreTrailingSlash());
+		return new DefaultWebMvcTagsProvider(this.properties.getWeb().getServer().getRequest().isIgnoreTrailingSlash(),
+				contributors.orderedStream().collect(Collectors.toList()));
 	}
 
 	@Bean

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

@@ -24,6 +24,7 @@ import org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsRun;
 import org.springframework.boot.actuate.autoconfigure.metrics.web.TestController;
 import org.springframework.boot.actuate.metrics.web.reactive.server.DefaultWebFluxTagsProvider;
 import org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter;
+import org.springframework.boot.actuate.metrics.web.reactive.server.WebFluxTagsContributor;
 import org.springframework.boot.actuate.metrics.web.reactive.server.WebFluxTagsProvider;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration;
@@ -111,6 +112,15 @@ class WebFluxMetricsAutoConfigurationTests {
 				});
 	}
 
+	@Test
+	void whenTagContributorsAreDefinedThenTagsProviderUsesThem() {
+		this.contextRunner.withUserConfiguration(TagsContributorsConfiguration.class).run((context) -> {
+			assertThat(context).hasSingleBean(DefaultWebFluxTagsProvider.class);
+			assertThat(context.getBean(DefaultWebFluxTagsProvider.class)).extracting("contributors").asList()
+					.hasSize(2);
+		});
+	}
+
 	private MeterRegistry getInitializedMeterRegistry(AssertableReactiveWebApplicationContext context) {
 		WebTestClient webTestClient = WebTestClient.bindToApplicationContext(context).build();
 		for (int i = 0; i < 3; i++) {
@@ -129,4 +139,19 @@ class WebFluxMetricsAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class TagsContributorsConfiguration {
+
+		@Bean
+		WebFluxTagsContributor tagContributorOne() {
+			return mock(WebFluxTagsContributor.class);
+		}
+
+		@Bean
+		WebFluxTagsContributor tagContributorTwo() {
+			return mock(WebFluxTagsContributor.class);
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/web/servlet/WebMvcMetricsAutoConfigurationTests.java

@@ -39,6 +39,7 @@ import org.springframework.boot.actuate.autoconfigure.metrics.web.TestController
 import org.springframework.boot.actuate.metrics.web.servlet.DefaultWebMvcTagsProvider;
 import org.springframework.boot.actuate.metrics.web.servlet.LongTaskTimingHandlerInterceptor;
 import org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter;
+import org.springframework.boot.actuate.metrics.web.servlet.WebMvcTagsContributor;
 import org.springframework.boot.actuate.metrics.web.servlet.WebMvcTagsProvider;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration;
@@ -56,6 +57,7 @@ import org.springframework.test.web.servlet.setup.MockMvcBuilders;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 /**
@@ -182,6 +184,14 @@ class WebMvcMetricsAutoConfigurationTests {
 						.contains(LongTaskTimingHandlerInterceptor.class));
 	}
 
+	@Test
+	void whenTagContributorsAreDefinedThenTagsProviderUsesThem() {
+		this.contextRunner.withUserConfiguration(TagsContributorsConfiguration.class).run((context) -> {
+			assertThat(context).hasSingleBean(DefaultWebMvcTagsProvider.class);
+			assertThat(context.getBean(DefaultWebMvcTagsProvider.class)).extracting("contributors").asList().hasSize(2);
+		});
+	}
+
 	private MeterRegistry getInitializedMeterRegistry(AssertableWebApplicationContext context) throws Exception {
 		return getInitializedMeterRegistry(context, "/test0", "/test1", "/test2");
 	}
@@ -208,6 +218,21 @@ class WebMvcMetricsAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class TagsContributorsConfiguration {
+
+		@Bean
+		WebMvcTagsContributor tagContributorOne() {
+			return mock(WebMvcTagsContributor.class);
+		}
+
+		@Bean
+		WebMvcTagsContributor tagContributorTwo() {
+			return mock(WebMvcTagsContributor.class);
+		}
+
+	}
+
 	private static final class TestWebMvcTagsProvider implements WebMvcTagsProvider {
 
 		@Override

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

@@ -16,9 +16,11 @@
 
 package org.springframework.boot.actuate.metrics.web.reactive.server;
 
-import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
 
 import io.micrometer.core.instrument.Tag;
+import io.micrometer.core.instrument.Tags;
 
 import org.springframework.web.server.ServerWebExchange;
 
@@ -33,18 +35,47 @@ public class DefaultWebFluxTagsProvider implements WebFluxTagsProvider {
 
 	private final boolean ignoreTrailingSlash;
 
+	private final List<WebFluxTagsContributor> contributors;
+
 	public DefaultWebFluxTagsProvider() {
 		this(false);
 	}
 
+	/**
+	 * Creates a new {@link DefaultWebFluxTagsProvider} that will provide tags from the
+	 * given {@code contributors} in addition to its own.
+	 * @param contributors the contributors that will provide additional tags
+	 * @since 2.3.0
+	 */
+	public DefaultWebFluxTagsProvider(List<WebFluxTagsContributor> contributors) {
+		this(false, contributors);
+	}
+
 	public DefaultWebFluxTagsProvider(boolean ignoreTrailingSlash) {
+		this(ignoreTrailingSlash, Collections.emptyList());
+	}
+
+	/**
+	 * Creates a new {@link DefaultWebFluxTagsProvider} that will provide tags from the
+	 * given {@code contributors} in addition to its own.
+	 * @param ignoreTrailingSlash wither trailing slashes should be ignored when
+	 * determining the {@code uri} tag.
+	 * @param contributors the contributors that will provide additional tags
+	 * @since 2.3.0
+	 */
+	public DefaultWebFluxTagsProvider(boolean ignoreTrailingSlash, List<WebFluxTagsContributor> contributors) {
 		this.ignoreTrailingSlash = ignoreTrailingSlash;
+		this.contributors = contributors;
 	}
 
 	@Override
 	public Iterable<Tag> httpRequestTags(ServerWebExchange exchange, Throwable exception) {
-		return Arrays.asList(WebFluxTags.method(exchange), WebFluxTags.uri(exchange, this.ignoreTrailingSlash),
+		Tags tags = Tags.of(WebFluxTags.method(exchange), WebFluxTags.uri(exchange, this.ignoreTrailingSlash),
 				WebFluxTags.exception(exception), WebFluxTags.status(exchange), WebFluxTags.outcome(exchange));
+		for (WebFluxTagsContributor contributor : this.contributors) {
+			tags = tags.and(contributor.httpRequestTags(exchange, exception));
+		}
+		return tags;
 	}
 
 }

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

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2012-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.metrics.web.reactive.server;
+
+import io.micrometer.core.instrument.Tag;
+
+import org.springframework.web.server.ServerWebExchange;
+
+/**
+ * A contributor of {@link Tag Tags} for WebFlux-based request handling. Typically used by
+ * a {@link WebFluxTagsProvider} to provide tags in addition to its defaults.
+ *
+ * @author Andy Wilkinson
+ * @since 2.3.0
+ */
+@FunctionalInterface
+public interface WebFluxTagsContributor {
+
+	/**
+	 * Provides tags to be associated with metrics for the given {@code exchange}.
+	 * @param exchange the exchange
+	 * @param ex the current exception (may be {@code null})
+	 * @return tags to associate with metrics for the request and response exchange
+	 */
+	Iterable<Tag> httpRequestTags(ServerWebExchange exchange, Throwable ex);
+
+}

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

@@ -16,6 +16,9 @@
 
 package org.springframework.boot.actuate.metrics.web.servlet;
 
+import java.util.Collections;
+import java.util.List;
+
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
@@ -32,24 +35,57 @@ public class DefaultWebMvcTagsProvider implements WebMvcTagsProvider {
 
 	private final boolean ignoreTrailingSlash;
 
+	private final List<WebMvcTagsContributor> contributors;
+
 	public DefaultWebMvcTagsProvider() {
 		this(false);
 	}
 
+	/**
+	 * Creates a new {@link DefaultWebMvcTagsProvider} that will provide tags from the
+	 * given {@code contributors} in addition to its own.
+	 * @param contributors the contributors that will provide additional tags
+	 * @since 2.3.0
+	 */
+	public DefaultWebMvcTagsProvider(List<WebMvcTagsContributor> contributors) {
+		this(false, contributors);
+	}
+
 	public DefaultWebMvcTagsProvider(boolean ignoreTrailingSlash) {
+		this(ignoreTrailingSlash, Collections.emptyList());
+	}
+
+	/**
+	 * Creates a new {@link DefaultWebMvcTagsProvider} that will provide tags from the
+	 * given {@code contributors} in addition to its own.
+	 * @param ignoreTrailingSlash whether trailing slashes should be ignored when
+	 * determining the {@code uri} tag.
+	 * @param contributors the contributors that will provide additional tags
+	 * @since 2.3.0
+	 */
+	public DefaultWebMvcTagsProvider(boolean ignoreTrailingSlash, List<WebMvcTagsContributor> contributors) {
 		this.ignoreTrailingSlash = ignoreTrailingSlash;
+		this.contributors = contributors;
 	}
 
 	@Override
 	public Iterable<Tag> getTags(HttpServletRequest request, HttpServletResponse response, Object handler,
 			Throwable exception) {
-		return Tags.of(WebMvcTags.method(request), WebMvcTags.uri(request, response, this.ignoreTrailingSlash),
+		Tags tags = Tags.of(WebMvcTags.method(request), WebMvcTags.uri(request, response, this.ignoreTrailingSlash),
 				WebMvcTags.exception(exception), WebMvcTags.status(response), WebMvcTags.outcome(response));
+		for (WebMvcTagsContributor contributor : this.contributors) {
+			tags = tags.and(contributor.getTags(request, response, handler, exception));
+		}
+		return tags;
 	}
 
 	@Override
 	public Iterable<Tag> getLongRequestTags(HttpServletRequest request, Object handler) {
-		return Tags.of(WebMvcTags.method(request), WebMvcTags.uri(request, null, this.ignoreTrailingSlash));
+		Tags tags = Tags.of(WebMvcTags.method(request), WebMvcTags.uri(request, null, this.ignoreTrailingSlash));
+		for (WebMvcTagsContributor contributor : this.contributors) {
+			tags = tags.and(contributor.getLongRequestTags(request, handler));
+		}
+		return tags;
 	}
 
 }

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

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2012-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.metrics.web.servlet;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import io.micrometer.core.instrument.LongTaskTimer;
+import io.micrometer.core.instrument.Tag;
+
+/**
+ * A contributor of {@link Tag Tags} for Spring MVC-based request handling. Typically used
+ * by a {@link WebMvcTagsProvider} to provide tags in addition to its defaults.
+ *
+ * @author Andy Wilkinson
+ * @since 2.3.0
+ */
+public interface WebMvcTagsContributor {
+
+	/**
+	 * Provides tags to be associated with metrics for the given {@code request} and
+	 * {@code response} exchange.
+	 * @param request the request
+	 * @param response the response
+	 * @param handler the handler for the request or {@code null} if the handler is
+	 * unknown
+	 * @param exception the current exception, if any
+	 * @return tags to associate with metrics for the request and response exchange
+	 */
+	Iterable<Tag> getTags(HttpServletRequest request, HttpServletResponse response, Object handler,
+			Throwable exception);
+
+	/**
+	 * Provides tags to be used by {@link LongTaskTimer long task timers}.
+	 * @param request the HTTP request
+	 * @param handler the handler for the request or {@code null} if the handler is
+	 * unknown
+	 * @return tags to associate with metrics recorded for the request
+	 */
+	Iterable<Tag> getLongRequestTags(HttpServletRequest request, Object handler);
+
+}

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

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2012-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.endpoint.web.servlet;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.StreamSupport;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import com.datastax.oss.driver.shaded.guava.common.base.Functions;
+import io.micrometer.core.instrument.Tag;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.actuate.metrics.web.servlet.DefaultWebMvcTagsProvider;
+import org.springframework.boot.actuate.metrics.web.servlet.WebMvcTagsContributor;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DefaultWebMvcTagsProvider}.
+ *
+ * @author Andy Wilkinson
+ */
+public class DefaultWebMvcTagsProviderTests {
+
+	@Test
+	void whenTagsAreProvidedThenDefaultTagsArePresent() {
+		Map<String, Tag> tags = asMap(new DefaultWebMvcTagsProvider().getTags(null, null, null, null));
+		assertThat(tags).containsOnlyKeys("exception", "method", "outcome", "status", "uri");
+	}
+
+	@Test
+	void givenSomeContributorsWhenTagsAreProvidedThenDefaultTagsAndContributedTagsArePresent() {
+		Map<String, Tag> tags = asMap(
+				new DefaultWebMvcTagsProvider(Arrays.asList(new TestWebMvcTagsContributor("alpha"),
+						new TestWebMvcTagsContributor("bravo", "charlie"))).getTags(null, null, null, null));
+		assertThat(tags).containsOnlyKeys("exception", "method", "outcome", "status", "uri", "alpha", "bravo",
+				"charlie");
+	}
+
+	@Test
+	void whenLongRequestTagsAreProvidedThenDefaultTagsArePresent() {
+		Map<String, Tag> tags = asMap(new DefaultWebMvcTagsProvider().getLongRequestTags(null, null));
+		assertThat(tags).containsOnlyKeys("method", "uri");
+	}
+
+	@Test
+	void givenSomeContributorsWhenLongRequestTagsAreProvidedThenDefaultTagsAndContributedTagsArePresent() {
+		Map<String, Tag> tags = asMap(
+				new DefaultWebMvcTagsProvider(Arrays.asList(new TestWebMvcTagsContributor("alpha"),
+						new TestWebMvcTagsContributor("bravo", "charlie"))).getLongRequestTags(null, null));
+		assertThat(tags).containsOnlyKeys("method", "uri", "alpha", "bravo", "charlie");
+	}
+
+	private Map<String, Tag> asMap(Iterable<Tag> tags) {
+		return StreamSupport.stream(tags.spliterator(), false)
+				.collect(Collectors.toMap(Tag::getKey, Functions.identity()));
+	}
+
+	private static final class TestWebMvcTagsContributor implements WebMvcTagsContributor {
+
+		private final List<String> tagNames;
+
+		private TestWebMvcTagsContributor(String... tagNames) {
+			this.tagNames = Arrays.asList(tagNames);
+		}
+
+		@Override
+		public Iterable<Tag> getTags(HttpServletRequest request, HttpServletResponse response, Object handler,
+				Throwable exception) {
+			return this.tagNames.stream().map((name) -> Tag.of(name, "value")).collect(Collectors.toList());
+		}
+
+		@Override
+		public Iterable<Tag> getLongRequestTags(HttpServletRequest request, Object handler) {
+			return this.tagNames.stream().map((name) -> Tag.of(name, "value")).collect(Collectors.toList());
+		}
+
+	}
+
+}

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

@@ -0,0 +1,79 @@
+/*
+ * Copyright 2012-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.metrics.web.reactive.server;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.StreamSupport;
+
+import com.datastax.oss.driver.shaded.guava.common.base.Functions;
+import io.micrometer.core.instrument.Tag;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
+import org.springframework.web.server.ServerWebExchange;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DefaultWebFluxTagsProvider}.
+ *
+ * @author Andy Wilkinson
+ */
+public class DefaultWebFluxTagsProviderTests {
+
+	@Test
+	void whenTagsAreProvidedThenDefaultTagsArePresent() {
+		ServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/test"));
+		Map<String, Tag> tags = asMap(new DefaultWebFluxTagsProvider().httpRequestTags(exchange, null));
+		assertThat(tags).containsOnlyKeys("exception", "method", "outcome", "status", "uri");
+	}
+
+	@Test
+	void givenSomeContributorsWhenTagsAreProvidedThenDefaultTagsAndContributedTagsArePresent() {
+		ServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/test"));
+		Map<String, Tag> tags = asMap(
+				new DefaultWebFluxTagsProvider(Arrays.asList(new TestWebFluxTagsContributor("alpha"),
+						new TestWebFluxTagsContributor("bravo", "charlie"))).httpRequestTags(exchange, null));
+		assertThat(tags).containsOnlyKeys("exception", "method", "outcome", "status", "uri", "alpha", "bravo",
+				"charlie");
+	}
+
+	private Map<String, Tag> asMap(Iterable<Tag> tags) {
+		return StreamSupport.stream(tags.spliterator(), false)
+				.collect(Collectors.toMap(Tag::getKey, Functions.identity()));
+	}
+
+	private static final class TestWebFluxTagsContributor implements WebFluxTagsContributor {
+
+		private final List<String> tagNames;
+
+		private TestWebFluxTagsContributor(String... tagNames) {
+			this.tagNames = Arrays.asList(tagNames);
+		}
+
+		@Override
+		public Iterable<Tag> httpRequestTags(ServerWebExchange exchange, Throwable ex) {
+			return this.tagNames.stream().map((name) -> Tag.of(name, "value")).collect(Collectors.toList());
+		}
+
+	}
+
+}

spring-boot-project/spring-boot-docs/src/docs/asciidoc/production-ready-features.adoc

@@ -1727,7 +1727,8 @@ By default, Spring MVC-related metrics are tagged with the following information
 | Request's URI template prior to variable substitution, if possible (for example, `/api/person/\{id}`)
 |===
 
-To customize the tags, provide a `@Bean` that implements `WebMvcTagsProvider`.
+To add to the default tags, provide one or more `@Bean`s that implement `WebMvcTagsContributor`.
+To replace the default tags, provide a `@Bean` that implements `WebMvcTagsProvider`.
 
 
 
@@ -1760,7 +1761,8 @@ By default, WebFlux-related metrics are tagged with the following information:
 | Request's URI template prior to variable substitution, if possible (for example, `/api/person/\{id}`)
 |===
 
-To customize the tags, provide a `@Bean` that implements `WebFluxTagsProvider`.
+To add to the default tags, provide one or more `@Bean`s that implement `WebFluxTagsContributor`.
+To replace the default tags, provide a `@Bean` that implements `WebFluxTagsProvider`.