Replace lambdas with method references

Closes gh-9049

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayAutoConfiguration.java

@@ -108,7 +108,7 @@ public class FlywayAutoConfiguration {
 			this.flywayDataSource = flywayDataSource.getIfAvailable();
 			this.migrationStrategy = migrationStrategy.getIfAvailable();
 			this.flywayCallbacks = flywayCallbacks
-					.getIfAvailable(() -> Collections.emptyList());
+					.getIfAvailable(Collections::emptyList);
 		}
 
 		@PostConstruct

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/core/ReactorCoreAutoConfiguration.java

@@ -30,6 +30,7 @@ import org.springframework.context.annotation.Configuration;
  * {@link EnableAutoConfiguration Auto-configuration} for Reactor Core.
  *
  * @author Brian Clozel
+ * @author Eddú Meléndez
  */
 @Configuration
 @ConditionalOnClass({ Mono.class, Flux.class })
@@ -39,7 +40,7 @@ public class ReactorCoreAutoConfiguration {
 	@Autowired
 	protected void initialize(ReactorCoreProperties properties) {
 		if (properties.getStacktraceMode().isEnabled()) {
-			Hooks.onOperator(h -> h.operatorStacktrace());
+			Hooks.onOperator(Hooks.OperatorHook::operatorStacktrace);
 		}
 	}
 

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/thymeleaf/ThymeleafAutoConfiguration.java

@@ -138,7 +138,7 @@ public class ThymeleafAutoConfiguration {
 				ObjectProvider<Collection<IDialect>> dialectsProvider) {
 			this.templateResolvers = templateResolvers;
 			this.dialects = dialectsProvider
-					.getIfAvailable(() -> Collections.emptyList());
+					.getIfAvailable(Collections::emptyList);
 		}
 
 		@Bean
@@ -222,7 +222,7 @@ public class ThymeleafAutoConfiguration {
 				ObjectProvider<Collection<IDialect>> dialectsProvider) {
 			this.templateResolvers = templateResolvers;
 			this.dialects = dialectsProvider
-					.getIfAvailable(() -> Collections.emptyList());
+					.getIfAvailable(Collections::emptyList);
 		}
 
 		@Bean

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/WebFluxAutoConfiguration.java

@@ -73,6 +73,7 @@ import org.springframework.web.reactive.result.view.ViewResolver;
  * @author Stephane Nicoll
  * @author Andy Wilkinson
  * @author Phillip Webb
+ * @author Eddú Meléndez
  * @since 2.0.0
  */
 @Configuration
@@ -157,7 +158,7 @@ public class WebFluxAutoConfiguration {
 		public void configureViewResolvers(ViewResolverRegistry registry) {
 			if (this.viewResolvers != null) {
 				AnnotationAwareOrderComparator.sort(this.viewResolvers);
-				this.viewResolvers.forEach(resolver -> registry.viewResolver(resolver));
+				this.viewResolvers.forEach(registry::viewResolver);
 			}
 		}
 

spring-boot/src/test/java/org/springframework/boot/context/properties/source/AbstractPropertyMapperTests.java

@@ -27,6 +27,7 @@ import org.springframework.core.env.PropertySource;
  *
  * @author Phillip Webb
  * @author Madhura Bhave
+ * @author Eddú Meléndez
  */
 public abstract class AbstractPropertyMapperTests {
 
@@ -52,7 +53,7 @@ public abstract class AbstractPropertyMapperTests {
 		PropertySource<?> propertySource = new MapPropertySource("test",
 				Collections.singletonMap(name, value));
 		return getMapper().map(propertySource, ConfigurationPropertyName.of(name))
-				.stream().map((mapping) -> mapping.getPropertySourceName()).iterator();
+				.stream().map(PropertyMapping::getPropertySourceName).iterator();
 	}
 
 }

spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertyNameTests.java

@@ -37,6 +37,7 @@ import static org.assertj.core.api.Assertions.fail;
  *
  * @author Phillip Webb
  * @author Madhura Bhave
+ * @author Eddú Meléndez
  */
 public class ConfigurationPropertyNameTests {
 
@@ -235,7 +236,7 @@ public class ConfigurationPropertyNameTests {
 	}
 
 	private Iterator<String> streamElements(String name) {
-		return ConfigurationPropertyName.of(name).stream().map((e) -> e.toString())
+		return ConfigurationPropertyName.of(name).stream().map(Element::toString)
 				.iterator();
 	}