Address review comments.

Author: szetszwo

ratis-common/src/main/java/org/apache/ratis/util/FileUtils.java

@@ -395,13 +395,13 @@ static void listDir(Path dir, Consumer<Object> out, BiConsumer<String, Throwable
     try {
       listDir(dir, out);
     } catch (IOException e) {
-      err.accept("Failed to lsDir: " + dir, e);
+      err.accept("Failed to listDir: " + dir, e);
     }
   }
 
   static void listDir(Path dir, Consumer<Object> out) throws IOException {
     if (!Files.isDirectory(dir, LinkOption.NOFOLLOW_LINKS)) {
-      throw new NotDirectoryException( "Failed to lsDir: " + dir + " is not a directory.");
+      throw new NotDirectoryException( "Failed to listDir: " + dir + " is not a directory.");
     }
 
     try(Stream<Path> s = Files.list(dir)) {

ratis-examples/src/test/java/org/apache/ratis/examples/counter/server/TestManualRestoreSnapshot.java

@@ -45,7 +45,11 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
- * Test StateMachine related functionality
+ * Test manually restoring a snapshot.
+ * Due to hardware failures or software bugs,
+ * the state of a state machine can become corrupted.
+ * In such case, we may manually copy a snapshot from the leader
+ * and then install it to the corrupted state machine.
  */
 public class TestManualRestoreSnapshot extends BaseTest implements MiniRaftClusterWithGrpc.FactoryGet {
   public static final int NUM_SERVERS = 3;

ratis-server/src/main/java/org/apache/ratis/statemachine/impl/BaseStateMachine.java

@@ -50,7 +50,7 @@
  */
 public class BaseStateMachine implements StateMachine, StateMachine.DataApi,
     StateMachine.EventApi, StateMachine.LeaderEventApi, StateMachine.FollowerEventApi {
-  static final AtomicInteger ID_GENERATOR = new AtomicInteger();
+  private static final AtomicInteger ID_GENERATOR = new AtomicInteger();
 
   private final int id = ID_GENERATOR.incrementAndGet();
   private final CompletableFuture<RaftServer> server = new CompletableFuture<>();