diff --git a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jms/activemq/ActiveMQConnectionFactoryCustomizer.java b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jms/activemq/ActiveMQConnectionFactoryCustomizer.java
index e42e4e03ff..f04e9ae9fb 100644
--- a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jms/activemq/ActiveMQConnectionFactoryCustomizer.java
+++ b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jms/activemq/ActiveMQConnectionFactoryCustomizer.java
@@ -25,6 +25,7 @@ import org.apache.activemq.ActiveMQConnectionFactory;
  * @author Stephane Nicoll
  * @since 1.5.5
  */
+@FunctionalInterface
 public interface ActiveMQConnectionFactoryCustomizer {
 
 	/**
diff --git a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/quartz/SchedulerFactoryBeanCustomizer.java b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/quartz/SchedulerFactoryBeanCustomizer.java
index d1d7492e7f..f5c909623a 100644
--- a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/quartz/SchedulerFactoryBeanCustomizer.java
+++ b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/quartz/SchedulerFactoryBeanCustomizer.java
@@ -26,6 +26,7 @@ import org.springframework.scheduling.quartz.SchedulerFactoryBean;
  * @author Vedran Pavic
  * @since 2.0.0
  */
+@FunctionalInterface
 public interface SchedulerFactoryBeanCustomizer {
 
 	/**
diff --git a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/SpringBootWebSecurityConfiguration.java b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/SpringBootWebSecurityConfiguration.java
index 0439bb0e59..fce4bd0804 100644
--- a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/SpringBootWebSecurityConfiguration.java
+++ b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/SpringBootWebSecurityConfiguration.java
@@ -228,7 +228,7 @@ public class SpringBootWebSecurityConfiguration {
 
 		@Override
 		protected void configure(HttpSecurity http) throws Exception {
-			http.requestMatcher(request -> false);
+			http.requestMatcher((request) -> false);
 		}
 
 	}
diff --git a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/DefaultServletWebServerFactoryCustomizer.java b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/DefaultServletWebServerFactoryCustomizer.java
index 5f2330273a..31e711a88a 100644
--- a/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/DefaultServletWebServerFactoryCustomizer.java
+++ b/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/DefaultServletWebServerFactoryCustomizer.java
@@ -446,8 +446,8 @@ public class DefaultServletWebServerFactoryCustomizer
 
 		private static void customizeMaxHttpPostSize(
 				UndertowServletWebServerFactory factory, final long maxHttpPostSize) {
-			factory.addBuilderCustomizers((builder -> builder
-					.setServerOption(UndertowOptions.MAX_ENTITY_SIZE, maxHttpPostSize)));
+			factory.addBuilderCustomizers((builder) -> builder
+					.setServerOption(UndertowOptions.MAX_ENTITY_SIZE, maxHttpPostSize));
 		}
 
 	}
diff --git a/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/amqp/RabbitAutoConfigurationTests.java b/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/amqp/RabbitAutoConfigurationTests.java
index 8dae849857..9132448dc8 100644
--- a/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/amqp/RabbitAutoConfigurationTests.java
+++ b/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/amqp/RabbitAutoConfigurationTests.java
@@ -170,7 +170,7 @@ public class RabbitAutoConfigurationTests {
 		this.contextRunner.withUserConfiguration(TestConfiguration.class)
 				.withPropertyValues("spring.rabbitmq.publisher-confirms=true",
 						"spring.rabbitmq.publisher-returns=true")
-				.run(context -> {
+				.run((context) -> {
 					CachingConnectionFactory connectionFactory = context
 							.getBean(CachingConnectionFactory.class);
 					RabbitTemplate rabbitTemplate = context.getBean(RabbitTemplate.class);
@@ -238,7 +238,7 @@ public class RabbitAutoConfigurationTests {
 		this.contextRunner.withUserConfiguration(TestConfiguration.class)
 				.withPropertyValues("spring.rabbitmq.template.mandatory:false",
 						"spring.rabbitmq.publisher-returns=true")
-				.run(context -> {
+				.run((context) -> {
 					RabbitTemplate rabbitTemplate = context.getBean(RabbitTemplate.class);
 					assertThat(getMandatory(rabbitTemplate)).isFalse();
 				});
diff --git a/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/ConditionalOnBeanTests.java b/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/ConditionalOnBeanTests.java
index 617c46b592..adc57e66a7 100644
--- a/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/ConditionalOnBeanTests.java
+++ b/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/ConditionalOnBeanTests.java
@@ -120,7 +120,7 @@ public class ConditionalOnBeanTests {
 						WithPropertyPlaceholderClassName.class,
 						OnBeanClassConfiguration.class)
 				.withPropertyValues("mybeanclass=java.lang.String")
-				.run(context -> assertThat(context).hasNotFailed());
+				.run((context) -> assertThat(context).hasNotFailed());
 	}
 
 	@Test
diff --git a/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/JavaPluginAction.java b/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/JavaPluginAction.java
index 03316c79df..9156863f83 100644
--- a/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/JavaPluginAction.java
+++ b/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/JavaPluginAction.java
@@ -113,7 +113,7 @@ final class JavaPluginAction implements PluginApplicationAction {
 	}
 
 	private void configureUtf8Encoding(Project project) {
-		project.afterEvaluate(evaluated -> evaluated.getTasks()
+		project.afterEvaluate((evaluated) -> evaluated.getTasks()
 				.withType(JavaCompile.class, (compile) -> {
 					if (compile.getOptions().getEncoding() == null) {
 						compile.getOptions().setEncoding("UTF-8");
diff --git a/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/web/servlet/MockServletWebServer.java b/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/web/servlet/MockServletWebServer.java
index 75df408649..9037dccc6b 100644
--- a/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/web/servlet/MockServletWebServer.java
+++ b/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/web/servlet/MockServletWebServer.java
@@ -214,6 +214,7 @@ public abstract class MockServletWebServer {
 	/**
 	 * Initializer (usually implement by adapting {@code Initializer}).
 	 */
+	@FunctionalInterface
 	protected interface Initializer {
 
 		void onStartup(ServletContext context) throws ServletException;
diff --git a/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionReporter.java b/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionReporter.java
index 3f2528bbe9..3d57a85ce7 100644
--- a/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionReporter.java
+++ b/spring-boot/src/main/java/org/springframework/boot/SpringBootExceptionReporter.java
@@ -30,6 +30,7 @@ import org.springframework.core.io.support.SpringFactoriesLoader;
  * @since 2.0.0
  * @see ApplicationContextAware
  */
+@FunctionalInterface
 public interface SpringBootExceptionReporter {
 
 	/**
diff --git a/spring-boot/src/main/java/org/springframework/boot/context/annotation/DeterminableImports.java b/spring-boot/src/main/java/org/springframework/boot/context/annotation/DeterminableImports.java
index 647f06c6b4..0f993ef39d 100644
--- a/spring-boot/src/main/java/org/springframework/boot/context/annotation/DeterminableImports.java
+++ b/spring-boot/src/main/java/org/springframework/boot/context/annotation/DeterminableImports.java
@@ -40,6 +40,7 @@ import org.springframework.core.type.AnnotationMetadata;
  * @author Andy Wilkinson
  * @since 1.5.0
  */
+@FunctionalInterface
 public interface DeterminableImports {
 
 	/**
diff --git a/spring-boot/src/main/java/org/springframework/boot/origin/OriginLookup.java b/spring-boot/src/main/java/org/springframework/boot/origin/OriginLookup.java
index 2859178c0b..95fff46bd1 100644
--- a/spring-boot/src/main/java/org/springframework/boot/origin/OriginLookup.java
+++ b/spring-boot/src/main/java/org/springframework/boot/origin/OriginLookup.java
@@ -24,6 +24,7 @@ package org.springframework.boot.origin;
  * @author Phillip Webb
  * @since 2.0.0
  */
+@FunctionalInterface
 public interface OriginLookup<K> {
 
 	/**
diff --git a/spring-boot/src/main/java/org/springframework/boot/origin/OriginProvider.java b/spring-boot/src/main/java/org/springframework/boot/origin/OriginProvider.java
index 19306277de..ebf3d9fe33 100644
--- a/spring-boot/src/main/java/org/springframework/boot/origin/OriginProvider.java
+++ b/spring-boot/src/main/java/org/springframework/boot/origin/OriginProvider.java
@@ -23,6 +23,7 @@ package org.springframework.boot.origin;
  * @since 2.0.0
  * @see Origin
  */
+@FunctionalInterface
 public interface OriginProvider {
 
 	/**
diff --git a/spring-boot/src/main/java/org/springframework/boot/web/server/WebServerFactoryCustomizer.java b/spring-boot/src/main/java/org/springframework/boot/web/server/WebServerFactoryCustomizer.java
index 5c8f9b6a83..405e09697c 100644
--- a/spring-boot/src/main/java/org/springframework/boot/web/server/WebServerFactoryCustomizer.java
+++ b/spring-boot/src/main/java/org/springframework/boot/web/server/WebServerFactoryCustomizer.java
@@ -36,6 +36,7 @@ import org.springframework.beans.factory.config.BeanPostProcessor;
  * @since 2.0.0
  * @see WebServerFactoryCustomizerBeanPostProcessor
  */
+@FunctionalInterface
 public interface WebServerFactoryCustomizer<T extends WebServerFactory> {
 
 	/**