refactor: minor improvements

Signed-off-by: Chris Laprun <metacosm@gmail.com>

Author: metacosm

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/LeaderElectionManager.java

@@ -15,8 +15,8 @@
  */
 package io.javaoperatorsdk.operator;
 
-import java.util.Arrays;
 import java.util.Collection;
+import java.util.List;
 import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
 import java.util.function.Predicate;
@@ -39,6 +39,7 @@
 public class LeaderElectionManager {
 
   private static final Logger log = LoggerFactory.getLogger(LeaderElectionManager.class);
+  private static final List<String> REQUIRED_VERBS = List.of("create", "update", "get");
 
   public static final String NO_PERMISSION_TO_LEASE_RESOURCE_MESSAGE =
       "No permission to lease resource.";
@@ -153,7 +154,6 @@ public void stop() {
   }
 
   private void checkLeaseAccess() {
-    var verbsRequired = Arrays.asList("create", "update", "get");
     SelfSubjectRulesReview review = new SelfSubjectRulesReview();
     review.setSpec(new SelfSubjectRulesReviewSpecBuilder().withNamespace(leaseNamespace).build());
     var reviewResult = configurationService.getKubernetesClient().resource(review).create();
@@ -168,16 +168,15 @@ private void checkLeaseAccess() {
                         || rule.getResourceNames().contains(leaseName))
             .map(ResourceRule::getVerbs)
             .flatMap(Collection::stream)
-            .distinct()
-            .collect(Collectors.toList());
-    if (verbsAllowed.contains(UNIVERSAL_VALUE) || verbsAllowed.containsAll(verbsRequired)) {
+            .collect(Collectors.toUnmodifiableSet());
+    if (verbsAllowed.contains(UNIVERSAL_VALUE) || verbsAllowed.containsAll(REQUIRED_VERBS)) {
       return;
     }
 
     var missingVerbs =
-        verbsRequired.stream()
+        REQUIRED_VERBS.stream()
             .filter(Predicate.not(verbsAllowed::contains))
-            .collect(Collectors.toList());
+            .collect(Collectors.joining(","));
 
     throw new OperatorException(
         NO_PERMISSION_TO_LEASE_RESOURCE_MESSAGE