Add prometheus tio actuator-webflux sample

See gh-86

actuator-webflux/build.gradle

@@ -11,6 +11,8 @@ dependencies {
 	implementation("org.springframework.boot:spring-boot-starter-webflux")
 	implementation(project(":aot-smoke-test-third-party-hints"))
 
+	runtimeOnly("io.micrometer:micrometer-registry-prometheus")
+
 	testImplementation("org.springframework.boot:spring-boot-starter-test")
 
 	aotTestImplementation(project(":aot-smoke-test-support"))

actuator-webflux/src/aotTest/java/com/example/actuator/webflux/ActuatorWebFluxApplicationAotTests.java

@@ -5,6 +5,8 @@
 import org.springframework.aot.smoketest.support.junit.AotSmokeTest;
 import org.springframework.test.web.reactive.server.WebTestClient;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 @AotSmokeTest
 class ActuatorWebFluxApplicationAotTests {
 
@@ -45,4 +47,15 @@ void shouldHaveOsInfoProperties(WebTestClient client) {
 				.isNotEmpty();
 	}
 
+	@Test
+	void prometheusWorks(WebTestClient client) {
+		client.get().uri("/actuator/prometheus").exchange().expectStatus().isOk().expectBody()
+				.consumeWith((result) -> assertThat(new String(result.getResponseBodyContent()))
+						// Check custom timer
+						.contains("custom_timer_seconds_max 5.0").contains("custom_timer_seconds_count 1.0")
+						.contains("custom_timer_seconds_sum 5.0")
+						// Check JVM metric
+						.contains("# TYPE jvm_threads_peak_threads gauge"));
+	}
+
 }

actuator-webflux/src/main/java/com/example/actuator/webflux/RegisterCustomTimer.java

@@ -0,0 +1,24 @@
+package com.example.actuator.webflux;
+
+import java.time.Duration;
+
+import io.micrometer.core.instrument.MeterRegistry;
+
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.stereotype.Component;
+
+@Component
+class RegisterCustomTimer implements CommandLineRunner {
+
+	private final MeterRegistry meterRegistry;
+
+	RegisterCustomTimer(MeterRegistry meterRegistry) {
+		this.meterRegistry = meterRegistry;
+	}
+
+	@Override
+	public void run(String... args) {
+		this.meterRegistry.timer("custom.timer").record(Duration.ofSeconds(5));
+	}
+
+}