Protect TomcatMetrics auto-config against early MeterBinder init

Closes gh-11916

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

@@ -19,7 +19,6 @@ package org.springframework.boot.actuate.autoconfigure.metrics.web.tomcat;
 import java.util.Collections;
 
 import io.micrometer.core.instrument.binder.tomcat.TomcatMetrics;
-import org.apache.catalina.Container;
 import org.apache.catalina.Context;
 import org.apache.catalina.Manager;
 
@@ -27,9 +26,10 @@ import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
-import org.springframework.boot.web.context.WebServerApplicationContext;
-import org.springframework.boot.web.embedded.tomcat.TomcatWebServer;
-import org.springframework.boot.web.server.WebServer;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication.Type;
+import org.springframework.boot.web.embedded.tomcat.TomcatReactiveWebServerFactory;
+import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
+import org.springframework.boot.web.server.WebServerFactoryCustomizer;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 
@@ -43,32 +43,29 @@ import org.springframework.context.annotation.Bean;
 @ConditionalOnClass({ TomcatMetrics.class, Manager.class })
 public class TomcatMetricsAutoConfiguration {
 
+	private volatile Context context;
+
 	@Bean
 	@ConditionalOnMissingBean(TomcatMetrics.class)
 	public TomcatMetrics tomcatMetrics(ApplicationContext applicationContext) {
-		Context context = findContext(applicationContext);
-		return new TomcatMetrics(context == null ? null : context.getManager(),
+		return new TomcatMetrics(this.context == null ? null : this.context.getManager(),
 				Collections.emptyList());
 	}
 
-	private Context findContext(ApplicationContext context) {
-		if (!(context instanceof WebServerApplicationContext)) {
-			return null;
-		}
-		WebServer webServer = ((WebServerApplicationContext) context).getWebServer();
-		if (!(webServer instanceof TomcatWebServer)) {
-			return null;
-		}
-		return findContext((TomcatWebServer) webServer);
+	@Bean
+	@ConditionalOnWebApplication(type = Type.SERVLET)
+	public WebServerFactoryCustomizer<TomcatServletWebServerFactory> contextCapturingServletTomcatCustomizer() {
+		return (tomcatFactory) -> tomcatFactory.addContextCustomizers(this::setContext);
 	}
 
-	private Context findContext(TomcatWebServer webServer) {
-		for (Container child : webServer.getTomcat().getHost().findChildren()) {
-			if (child instanceof Context) {
-				return (Context) child;
-			}
-		}
-		return null;
+	@Bean
+	@ConditionalOnWebApplication(type = Type.REACTIVE)
+	public WebServerFactoryCustomizer<TomcatReactiveWebServerFactory> contextCapturingReactiveTomcatCustomizer() {
+		return (tomcatFactory) -> tomcatFactory.addContextCustomizers(this::setContext);
+	}
+
+	private void setContext(Context context) {
+		this.context = context;
 	}
 
 }

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

@@ -18,17 +18,22 @@ package org.springframework.boot.actuate.autoconfigure.metrics.web.tomcat;
 
 import java.util.Collections;
 
+import io.micrometer.core.instrument.binder.MeterBinder;
 import io.micrometer.core.instrument.binder.tomcat.TomcatMetrics;
 import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
 import org.junit.Test;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration;
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
 import org.springframework.boot.web.embedded.tomcat.TomcatReactiveWebServerFactory;
 import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
 import org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext;
+import org.springframework.boot.web.servlet.ServletContextInitializer;
 import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
+import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.http.server.reactive.HttpHandler;
@@ -47,8 +52,9 @@ public class TomcatMetricsAutoConfigurationTests {
 	public void autoConfiguresTomcatMetricsWithEmbeddedServletTomcat() {
 		new WebApplicationContextRunner(
 				AnnotationConfigServletWebServerApplicationContext::new)
-						.withConfiguration(AutoConfigurations
-								.of(TomcatMetricsAutoConfiguration.class))
+						.withConfiguration(AutoConfigurations.of(
+								TomcatMetricsAutoConfiguration.class,
+								ServletWebServerFactoryAutoConfiguration.class))
 						.withUserConfiguration(ServletWebServerConfiguration.class)
 						.run((context) -> {
 							assertThat(context).hasSingleBean(TomcatMetrics.class);
@@ -62,12 +68,34 @@ public class TomcatMetricsAutoConfigurationTests {
 						});
 	}
 
+	@Test
+	public void sessionMetricsAreAvailableWhenEarlyMeterBinderInitializationOccurs() {
+		new WebApplicationContextRunner(
+				AnnotationConfigServletWebServerApplicationContext::new)
+						.withConfiguration(AutoConfigurations.of(
+								TomcatMetricsAutoConfiguration.class,
+								ServletWebServerFactoryAutoConfiguration.class))
+						.withUserConfiguration(ServletWebServerConfiguration.class,
+								EarlyMeterBinderInitializationConfiguration.class)
+						.run((context) -> {
+							assertThat(context).hasSingleBean(TomcatMetrics.class);
+							SimpleMeterRegistry registry = new SimpleMeterRegistry();
+							context.getBean(TomcatMetrics.class).bindTo(registry);
+							assertThat(
+									registry.find("tomcat.sessions.active.max").meter())
+											.isNotNull();
+							assertThat(registry.find("tomcat.threads.current").meter())
+									.isNotNull();
+						});
+	}
+
 	@Test
 	public void autoConfiguresTomcatMetricsWithEmbeddedReactiveTomcat() {
 		new ReactiveWebApplicationContextRunner(
 				AnnotationConfigReactiveWebServerApplicationContext::new)
-						.withConfiguration(AutoConfigurations
-								.of(TomcatMetricsAutoConfiguration.class))
+						.withConfiguration(AutoConfigurations.of(
+								TomcatMetricsAutoConfiguration.class,
+								ReactiveWebServerAutoConfiguration.class))
 						.withUserConfiguration(ReactiveWebServerConfiguration.class)
 						.run((context) -> {
 							assertThat(context).hasSingleBean(TomcatMetrics.class);
@@ -134,4 +162,14 @@ public class TomcatMetricsAutoConfigurationTests {
 
 	}
 
+	@Configuration
+	static class EarlyMeterBinderInitializationConfiguration {
+
+		@Bean
+		public ServletContextInitializer earlyInitializer(ApplicationContext context) {
+			return (servletContext) -> context.getBeansOfType(MeterBinder.class);
+		}
+
+	}
+
 }