Simplify some Stream API usages

See gh-19291

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/NamedContributorsMapAdapter.java

@@ -43,7 +43,7 @@ abstract class NamedContributorsMapAdapter<V, C> implements NamedContributors<C>
 	NamedContributorsMapAdapter(Map<String, V> map, Function<V, ? extends C> valueAdapter) {
 		Assert.notNull(map, "Map must not be null");
 		Assert.notNull(valueAdapter, "ValueAdapter must not be null");
-		map.keySet().stream().forEach((key) -> Assert.notNull(key, "Map must not contain null keys"));
+		map.keySet().forEach((key) -> Assert.notNull(key, "Map must not contain null keys"));
 		map.values().stream().map(valueAdapter)
 				.forEach((value) -> Assert.notNull(value, "Map must not contain null values"));
 		this.map = Collections.unmodifiableMap(new LinkedHashMap<>(map));

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/SimpleStatusAggregator.java

@@ -69,7 +69,7 @@ public class SimpleStatusAggregator implements StatusAggregator {
 
 	@Override
 	public Status getAggregateStatus(Set<Status> statuses) {
-		return statuses.stream().filter(this::contains).sorted(this.comparator).findFirst().orElse(Status.UNKNOWN);
+		return statuses.stream().filter(this::contains).min(this.comparator).orElse(Status.UNKNOWN);
 	}
 
 	private boolean contains(Status status) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/mongo/embedded/EmbeddedMongoAutoConfigurationTests.java

@@ -96,7 +96,7 @@ class EmbeddedMongoAutoConfigurationTests {
 			features.add(Feature.ONLY_WINDOWS_2008_SERVER);
 		}
 		load("spring.mongodb.embedded.features="
-				+ String.join(", ", features.stream().map(Feature::name).collect(Collectors.toList())));
+				+ features.stream().map(Feature::name).collect(Collectors.joining(", ")));
 		assertThat(this.context.getBean(EmbeddedMongoProperties.class).getFeatures())
 				.containsExactlyElementsOf(features);
 	}