diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/JmxEndpointsSupplier.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/JmxEndpointsSupplier.java
index 2885a80a6d..93d104ad25 100644
--- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/JmxEndpointsSupplier.java
+++ b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/jmx/JmxEndpointsSupplier.java
@@ -24,6 +24,7 @@ import org.springframework.boot.actuate.endpoint.EndpointsSupplier;
  * @author Phillip Webb
  * @since 2.0.0
  */
+@FunctionalInterface
 public interface JmxEndpointsSupplier extends EndpointsSupplier<ExposableJmxEndpoint> {
 
 }
diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/PathMappedEndpoint.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/PathMappedEndpoint.java
index 00fcface5b..799968338e 100644
--- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/PathMappedEndpoint.java
+++ b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/PathMappedEndpoint.java
@@ -26,6 +26,7 @@ import org.springframework.boot.actuate.endpoint.ExposableEndpoint;
  * @since 2.0.0
  * @see PathMapper
  */
+@FunctionalInterface
 public interface PathMappedEndpoint {
 
 	/**
diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/WebEndpointsSupplier.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/WebEndpointsSupplier.java
index 80ce5ab7ef..15bc503e6c 100644
--- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/WebEndpointsSupplier.java
+++ b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/WebEndpointsSupplier.java
@@ -24,6 +24,7 @@ import org.springframework.boot.actuate.endpoint.EndpointsSupplier;
  * @author Phillip Webb
  * @since 2.0.0
  */
+@FunctionalInterface
 public interface WebEndpointsSupplier extends EndpointsSupplier<ExposableWebEndpoint> {
 
 }
diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ControllerEndpointsSupplier.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ControllerEndpointsSupplier.java
index a625b43db0..4f7b7be77e 100644
--- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ControllerEndpointsSupplier.java
+++ b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/annotation/ControllerEndpointsSupplier.java
@@ -24,6 +24,7 @@ import org.springframework.boot.actuate.endpoint.EndpointsSupplier;
  * @author Phillip Webb
  * @since 2.0.0
  */
+@FunctionalInterface
 public interface ControllerEndpointsSupplier
 		extends EndpointsSupplier<ExposableControllerEndpoint> {
 
diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/reactive/AbstractWebFluxEndpointHandlerMapping.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/reactive/AbstractWebFluxEndpointHandlerMapping.java
index d494736428..9fd2d34172 100644
--- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/reactive/AbstractWebFluxEndpointHandlerMapping.java
+++ b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/reactive/AbstractWebFluxEndpointHandlerMapping.java
@@ -238,8 +238,9 @@ public abstract class AbstractWebFluxEndpointHandlerMapping
 	}
 
 	/**
-	 * An reactive web operation that can be handled by WebFlux.
+	 * A reactive web operation that can be handled by WebFlux.
 	 */
+	@FunctionalInterface
 	protected interface ReactiveWebOperation {
 
 		Mono<ResponseEntity<Object>> handle(ServerWebExchange exchange,
diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/servlet/AbstractWebMvcEndpointHandlerMapping.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/servlet/AbstractWebMvcEndpointHandlerMapping.java
index 23712e5717..9602432094 100644
--- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/servlet/AbstractWebMvcEndpointHandlerMapping.java
+++ b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/web/servlet/AbstractWebMvcEndpointHandlerMapping.java
@@ -214,8 +214,9 @@ public abstract class AbstractWebMvcEndpointHandlerMapping
 	}
 
 	/**
-	 * An reactive web operation that can be handled by WebFlux.
+	 * A servlet web operation that can be handled by Spring MVC.
 	 */
+	@FunctionalInterface
 	protected interface ServletWebOperation {
 
 		Object handle(HttpServletRequest request, Map<String, String> body);
diff --git a/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/reactive/ControllerEndpointHandlerMappingIntegrationTests.java b/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/reactive/ControllerEndpointHandlerMappingIntegrationTests.java
index e994b03da4..75be340a21 100644
--- a/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/reactive/ControllerEndpointHandlerMappingIntegrationTests.java
+++ b/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/reactive/ControllerEndpointHandlerMappingIntegrationTests.java
@@ -68,31 +68,27 @@ public class ControllerEndpointHandlerMappingIntegrationTests {
 
 	@Test
 	public void get() {
-		this.contextRunner.run(withWebTestClient(webTestClient -> {
-			webTestClient.get().uri("/actuator/example/one").accept(MediaType.TEXT_PLAIN)
-					.exchange().expectStatus().isOk().expectHeader()
-					.contentTypeCompatibleWith(MediaType.TEXT_PLAIN)
-					.expectBody(String.class).isEqualTo("One");
-		}));
+		this.contextRunner.run(withWebTestClient(
+				(webTestClient) -> webTestClient.get().uri("/actuator/example/one")
+						.accept(MediaType.TEXT_PLAIN).exchange().expectStatus().isOk()
+						.expectHeader().contentTypeCompatibleWith(MediaType.TEXT_PLAIN)
+						.expectBody(String.class).isEqualTo("One")));
 	}
 
 	@Test
 	public void getWithUnacceptableContentType() {
-		this.contextRunner.run(withWebTestClient(webTestClient -> {
-			webTestClient.get().uri("/actuator/example/one")
-					.accept(MediaType.APPLICATION_JSON).exchange().expectStatus()
-					.isEqualTo(HttpStatus.NOT_ACCEPTABLE);
-		}));
+		this.contextRunner.run(withWebTestClient((webTestClient) -> webTestClient.get()
+				.uri("/actuator/example/one").accept(MediaType.APPLICATION_JSON)
+				.exchange().expectStatus().isEqualTo(HttpStatus.NOT_ACCEPTABLE)));
 	}
 
 	@Test
 	public void post() {
-		this.contextRunner.run(withWebTestClient(webTestClient -> {
-			webTestClient.post().uri("/actuator/example/two")
-					.syncBody(Collections.singletonMap("id", "test")).exchange()
-					.expectStatus().isCreated().expectHeader()
-					.valueEquals(HttpHeaders.LOCATION, "/example/test");
-		}));
+		this.contextRunner.run(withWebTestClient(
+				(webTestClient) -> webTestClient.post().uri("/actuator/example/two")
+						.syncBody(Collections.singletonMap("id", "test")).exchange()
+						.expectStatus().isCreated().expectHeader()
+						.valueEquals(HttpHeaders.LOCATION, "/example/test")));
 	}
 
 	private ContextConsumer<AssertableReactiveWebApplicationContext> withWebTestClient(
diff --git a/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/servlet/ControllerEndpointHandlerMappingIntegrationTests.java b/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/servlet/ControllerEndpointHandlerMappingIntegrationTests.java
index 6800099e43..242a9e5591 100644
--- a/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/servlet/ControllerEndpointHandlerMappingIntegrationTests.java
+++ b/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/web/servlet/ControllerEndpointHandlerMappingIntegrationTests.java
@@ -67,31 +67,27 @@ public class ControllerEndpointHandlerMappingIntegrationTests {
 
 	@Test
 	public void get() {
-		this.contextRunner.run(withWebTestClient(webTestClient -> {
-			webTestClient.get().uri("/actuator/example/one").accept(MediaType.TEXT_PLAIN)
-					.exchange().expectStatus().isOk().expectHeader()
-					.contentTypeCompatibleWith(MediaType.TEXT_PLAIN)
-					.expectBody(String.class).isEqualTo("One");
-		}));
+		this.contextRunner.run(withWebTestClient(
+				(webTestClient) -> webTestClient.get().uri("/actuator/example/one")
+						.accept(MediaType.TEXT_PLAIN).exchange().expectStatus().isOk()
+						.expectHeader().contentTypeCompatibleWith(MediaType.TEXT_PLAIN)
+						.expectBody(String.class).isEqualTo("One")));
 	}
 
 	@Test
 	public void getWithUnacceptableContentType() {
-		this.contextRunner.run(withWebTestClient(webTestClient -> {
-			webTestClient.get().uri("/actuator/example/one")
-					.accept(MediaType.APPLICATION_JSON).exchange().expectStatus()
-					.isEqualTo(HttpStatus.NOT_ACCEPTABLE);
-		}));
+		this.contextRunner.run(withWebTestClient((webTestClient) -> webTestClient.get()
+				.uri("/actuator/example/one").accept(MediaType.APPLICATION_JSON)
+				.exchange().expectStatus().isEqualTo(HttpStatus.NOT_ACCEPTABLE)));
 	}
 
 	@Test
 	public void post() {
-		this.contextRunner.run(withWebTestClient(webTestClient -> {
-			webTestClient.post().uri("/actuator/example/two")
-					.syncBody(Collections.singletonMap("id", "test")).exchange()
-					.expectStatus().isCreated().expectHeader()
-					.valueEquals(HttpHeaders.LOCATION, "/example/test");
-		}));
+		this.contextRunner.run(withWebTestClient(
+				(webTestClient) -> webTestClient.post().uri("/actuator/example/two")
+						.syncBody(Collections.singletonMap("id", "test")).exchange()
+						.expectStatus().isCreated().expectHeader()
+						.valueEquals(HttpHeaders.LOCATION, "/example/test")));
 	}
 
 	private ContextConsumer<AssertableWebApplicationContext> withWebTestClient(