MINOR: Collection/Option usage simplification via methods introduced in Java 9 & 11 (#18305)

Relevant methods:
1. `List.of`, `Set.of`, `Map.of` and similar (introduced in Java 9)
2. Optional: `isEmpty` (introduced in Java 11), `stream` (introduced in Java 9).

Reviewers: Mickael Maison <[email protected]>

Author: ijuma

clients/src/main/java/org/apache/kafka/clients/NetworkClient.java

@@ -1219,7 +1219,7 @@ public long maybeUpdate(long now) {
                 return metadataTimeout;
             }
 
-            if (!metadataAttemptStartMs.isPresent())
+            if (metadataAttemptStartMs.isEmpty())
                 metadataAttemptStartMs = Optional.of(now);
 
             // Beware that the behavior of this method and the computation of timeouts for poll() are
@@ -1412,7 +1412,7 @@ private long maybeUpdate(long now, Node node) {
             if (canSendRequest(nodeConnectionId, now)) {
                 Optional<AbstractRequest.Builder<?>> requestOpt = clientTelemetrySender.createRequest();
 
-                if (!requestOpt.isPresent())
+                if (requestOpt.isEmpty())
                     return Long.MAX_VALUE;
 
                 AbstractRequest.Builder<?> request = requestOpt.get();

clients/src/main/java/org/apache/kafka/common/Uuid.java

@@ -20,8 +20,6 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Base64;
-import java.util.Collections;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -51,11 +49,7 @@ public class Uuid implements Comparable<Uuid> {
     /**
      * The set of reserved UUIDs that will never be returned by the randomUuid method.
      */
-    public static final Set<Uuid> RESERVED = Collections.unmodifiableSet(new HashSet<>(Arrays.asList(
-            METADATA_TOPIC_ID,
-            ZERO_UUID,
-            ONE_UUID
-    )));
+    public static final Set<Uuid> RESERVED = Set.of(ZERO_UUID, ONE_UUID);
 
     private final long mostSignificantBits;
     private final long leastSignificantBits;

clients/src/main/java/org/apache/kafka/common/metrics/Sensor.java

@@ -367,7 +367,7 @@ public boolean hasExpired() {
     }
 
     synchronized List<KafkaMetric> metrics() {
-        return unmodifiableList(new ArrayList<>(this.metrics.values()));
+        return List.copyOf(this.metrics.values());
     }
 
     /**

clients/src/main/java/org/apache/kafka/common/security/oauthbearer/internals/secured/AccessTokenValidatorFactory.java

@@ -19,8 +19,6 @@
 
 import org.jose4j.keys.resolvers.VerificationKeyResolver;
 
-import java.util.Collections;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -57,7 +55,7 @@ public static AccessTokenValidator create(Map<String, ?> configs,
         List<String> l = cu.get(SASL_OAUTHBEARER_EXPECTED_AUDIENCE);
 
         if (l != null)
-            expectedAudiences = Collections.unmodifiableSet(new HashSet<>(l));
+            expectedAudiences = Set.copyOf(l);
 
         Integer clockSkew = cu.validateInteger(SASL_OAUTHBEARER_CLOCK_SKEW_SECONDS, false);
         String expectedIssuer = cu.validateString(SASL_OAUTHBEARER_EXPECTED_ISSUER, false);

clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinatorTest.java

@@ -223,7 +223,7 @@ private GroupRebalanceConfig buildRebalanceConfig(Optional<String> groupInstance
                                         groupInstanceId,
                                         retryBackoffMs,
                                         retryBackoffMaxMs,
-                                        !groupInstanceId.isPresent());
+                                        groupInstanceId.isEmpty());
     }
 
     @AfterEach
@@ -4135,7 +4135,7 @@ private static class RackAwareAssignor extends MockPartitionAssignor {
         @Override
         public Map<String, List<TopicPartition>> assign(Map<String, Integer> partitionsPerTopic, Map<String, Subscription> subscriptions) {
             subscriptions.forEach((consumer, subscription) -> {
-                if (!subscription.rackId().isPresent())
+                if (subscription.rackId().isEmpty())
                     throw new IllegalStateException("Rack id not provided in subscription for " + consumer);
                 rackIds.add(subscription.rackId().get());
             });

clients/src/test/java/org/apache/kafka/common/network/SelectorTest.java

@@ -891,7 +891,7 @@ private KafkaMetric getMetric(String name, Map<String, String> tags) throws Exce
             .filter(entry ->
                 entry.getKey().name().equals(name) && entry.getKey().tags().equals(tags))
             .findFirst();
-        if (!metric.isPresent())
+        if (metric.isEmpty())
             throw new Exception(String.format("Could not find metric called %s with tags %s", name, tags.toString()));
 
         return metric.get().getValue();
@@ -1112,7 +1112,7 @@ private KafkaMetric getMetric(String name) throws Exception {
         Optional<Map.Entry<MetricName, KafkaMetric>> metric = metrics.metrics().entrySet().stream()
                 .filter(entry -> entry.getKey().name().equals(name))
                 .findFirst();
-        if (!metric.isPresent())
+        if (metric.isEmpty())
             throw new Exception(String.format("Could not find metric called %s", name));
 
         return metric.get().getValue();

connect/api/src/main/java/org/apache/kafka/connect/data/SchemaBuilder.java

@@ -420,7 +420,7 @@ public Schema valueSchema() {
     public Schema build() {
         return new ConnectSchema(type, isOptional(), defaultValue, name, version, doc,
                 parameters == null ? null : Collections.unmodifiableMap(parameters),
-                fields == null ? null : Collections.unmodifiableList(new ArrayList<>(fields.values())), keySchema, valueSchema);
+                fields == null ? null : List.copyOf(fields.values()), keySchema, valueSchema);
     }
 
     /**
@@ -441,4 +441,4 @@ private static void checkNotNull(String fieldName, Object val, String fieldToSet
         if (val == null)
             throw new SchemaBuilderException("Invalid SchemaBuilder call: " + fieldName + " must be specified to set " + fieldToSet);
     }
-}
+}

connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorCheckpointTask.java

@@ -46,7 +46,6 @@
 import java.util.concurrent.ExecutionException;
 import java.util.function.Function;
 import java.util.stream.Collectors;
-import java.util.stream.Stream;
 
 import static org.apache.kafka.connect.mirror.MirrorUtils.adminCall;
 
@@ -196,7 +195,7 @@ Map<TopicPartition, Checkpoint> checkpointsForGroup(Map<TopicPartition, OffsetAn
         return upstreamGroupOffsets.entrySet().stream()
             .filter(x -> shouldCheckpointTopic(x.getKey().topic())) // Only perform relevant checkpoints filtered by "topic filter"
             .map(x -> checkpoint(group, x.getKey(), x.getValue()))
-            .flatMap(o -> o.map(Stream::of).orElseGet(Stream::empty)) // do not emit checkpoints for partitions that don't have offset-syncs
+            .flatMap(o -> o.stream()) // do not emit checkpoints for partitions that don't have offset-syncs
             .filter(x -> x.downstreamOffset() >= 0)  // ignore offsets we cannot translate accurately
             .filter(this::checkpointIsMoreRecent) // do not emit checkpoints for partitions that have a later checkpoint
             .collect(Collectors.toMap(Checkpoint::topicPartition, Function.identity()));

connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorMaker.java

@@ -102,11 +102,7 @@ public class MirrorMaker {
 
     private static final long SHUTDOWN_TIMEOUT_SECONDS = 60L;
 
-    public static final List<Class<?>> CONNECTOR_CLASSES = Collections.unmodifiableList(
-        Arrays.asList(
-            MirrorSourceConnector.class,
-            MirrorHeartbeatConnector.class,
-            MirrorCheckpointConnector.class));
+    public static final List<Class<?>> CONNECTOR_CLASSES = List.of(MirrorSourceConnector.class, MirrorHeartbeatConnector.class, MirrorCheckpointConnector.class);
 
     private final Map<SourceAndTarget, Herder> herders = new HashMap<>();
     private CountDownLatch startLatch;

connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorSourceConnector.java

@@ -420,7 +420,7 @@ private Set<String> toTopics(Collection<TopicPartition> tps) {
     void syncTopicAcls()
             throws InterruptedException, ExecutionException {
         Optional<Collection<AclBinding>> rawBindings = listTopicAclBindings();
-        if (!rawBindings.isPresent())
+        if (rawBindings.isEmpty())
             return;
         List<AclBinding> filteredBindings = rawBindings.get().stream()
             .filter(x -> x.pattern().resourceType() == ResourceType.TOPIC)