Trivial code improvements

JAVA-4254

Author: stIncMale

driver-core/src/main/com/mongodb/internal/connection/BaseCluster.java

@@ -49,6 +49,8 @@
 import java.util.Deque;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Objects;
+import java.util.stream.Stream;
 import java.util.concurrent.ConcurrentLinkedDeque;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ThreadLocalRandom;
@@ -82,6 +84,7 @@
 import static java.util.Comparator.comparingInt;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
+import static java.util.stream.Collectors.toList;
 
 abstract class BaseCluster implements Cluster {
     private static final Logger LOGGER = Loggers.getLogger("cluster");
@@ -351,12 +354,12 @@ private static List<ServerTuple> atMostNRandom(final ArrayList<ServerDescription
     }
 
     private ServerSelector getCompleteServerSelector(final ServerSelector serverSelector, final ServerDeprioritization serverDeprioritization) {
-        ServerSelector latencyMinimizingServerSelector =
-                new LatencyMinimizingServerSelector(settings.getLocalThreshold(MILLISECONDS), MILLISECONDS);
-        CompositeServerSelector compositeSelector = settings.getServerSelector() == null
-                ? new CompositeServerSelector(asList(serverSelector, latencyMinimizingServerSelector))
-                : new CompositeServerSelector(asList(serverSelector, settings.getServerSelector(), latencyMinimizingServerSelector));
-        return serverDeprioritization.apply(compositeSelector);
+        List<ServerSelector> selectors = Stream.of(
+                serverSelector,
+                settings.getServerSelector(),
+                new LatencyMinimizingServerSelector(settings.getLocalThreshold(MILLISECONDS), MILLISECONDS)
+        ).filter(Objects::nonNull).collect(toList());
+        return serverDeprioritization.apply(new CompositeServerSelector(selectors));
     }
 
     protected ClusterableServer createServer(final ServerAddress serverAddress) {

driver-core/src/main/com/mongodb/internal/connection/OperationContext.java

@@ -97,16 +97,10 @@ private DeprioritizingSelector(final ServerSelector wrapped) {
             @Override
             public List<ServerDescription> select(final ClusterDescription clusterDescription) {
                 if (isEnabled(clusterDescription.getType())) {
-                    List<ServerDescription> filteredServerDescriptions = ClusterDescriptionHelper.getServersByPredicate(
+                    List<ServerDescription> nonDeprioritizedServerDescriptions = ClusterDescriptionHelper.getServersByPredicate(
                             clusterDescription, serverDescription -> !deprioritized.contains(serverDescription.getAddress()));
-                    ClusterDescription filteredClusterDescription = new ClusterDescription(
-                            clusterDescription.getConnectionMode(),
-                            clusterDescription.getType(),
-                            clusterDescription.getSrvResolutionException(),
-                            filteredServerDescriptions,
-                            clusterDescription.getClusterSettings(),
-                            clusterDescription.getServerSettings());
-                    List<ServerDescription> result = wrapped.select(filteredClusterDescription);
+                    List<ServerDescription> result = wrapped.select(
+                            copyWithServerDescriptions(clusterDescription, nonDeprioritizedServerDescriptions));
                     if (result.isEmpty()) {
                         // fall back to selecting from all servers ignoring the deprioritized ones
                         result = wrapped.select(clusterDescription);
@@ -116,6 +110,17 @@ public List<ServerDescription> select(final ClusterDescription clusterDescriptio
                     return wrapped.select(clusterDescription);
                 }
             }
+
+            private ClusterDescription copyWithServerDescriptions(
+                    final ClusterDescription clusterDescription, final List<ServerDescription> serverDescriptions) {
+                return new ClusterDescription(
+                        clusterDescription.getConnectionMode(),
+                        clusterDescription.getType(),
+                        clusterDescription.getSrvResolutionException(),
+                        serverDescriptions,
+                        clusterDescription.getClusterSettings(),
+                        clusterDescription.getServerSettings());
+            }
         }
     }
 }