fixing warnings v3

java/flight/flight-core/src/main/java/org/apache/arrow/flight/CancelFlightInfoResult.java

@@ -105,7 +105,7 @@ public boolean equals(Object o) {
     if (this == o) {
       return true;
     }
-    if (o == null || getClass() != o.getClass()) {
+    if (!(o instanceof CancelFlightInfoResult)) {
       return false;
     }
     CancelFlightInfoResult that = (CancelFlightInfoResult) o;

java/flight/flight-core/src/main/java/org/apache/arrow/flight/ErrorFlightMetadata.java

@@ -61,7 +61,7 @@ public Iterable<byte[]> getAllByte(String key) {
 
   @Override
   public void insert(String key, String value) {
-    metadata.put(key, value.getBytes());
+    metadata.put(key, value.getBytes(StandardCharsets.UTF_8));
   }
 
   @Override

java/flight/flight-core/src/main/java/org/apache/arrow/flight/FlightCallHeaders.java

@@ -17,6 +17,8 @@
 
 package org.apache.arrow.flight;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+
 import java.util.Collection;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -46,7 +48,7 @@ public String get(String key) {
     }
 
     if (key.endsWith(Metadata.BINARY_HEADER_SUFFIX)) {
-      return new String((byte[]) Iterables.get(values, 0));
+      return new String((byte[]) Iterables.get(values, 0), UTF_8);
     }
 
     return (String) Iterables.get(values, 0);
@@ -63,13 +65,13 @@ public byte[] getByte(String key) {
       return (byte[]) Iterables.get(values, 0);
     }
 
-    return ((String) Iterables.get(values, 0)).getBytes();
+    return ((String) Iterables.get(values, 0)).getBytes(UTF_8);
   }
 
   @Override
   public Iterable<String> getAll(String key) {
     if (key.endsWith(Metadata.BINARY_HEADER_SUFFIX)) {
-      return this.keysAndValues.get(key).stream().map(o -> new String((byte[]) o)).collect(Collectors.toList());
+      return this.keysAndValues.get(key).stream().map(o -> new String((byte[]) o, UTF_8)).collect(Collectors.toList());
     }
     return (Collection<String>) (Collection<?>) this.keysAndValues.get(key);
   }
@@ -79,7 +81,7 @@ public Iterable<byte[]> getAllByte(String key) {
     if (key.endsWith(Metadata.BINARY_HEADER_SUFFIX)) {
       return (Collection<byte[]>) (Collection<?>) this.keysAndValues.get(key);
     }
-    return this.keysAndValues.get(key).stream().map(o -> ((String) o).getBytes()).collect(Collectors.toList());
+    return this.keysAndValues.get(key).stream().map(o -> ((String) o).getBytes(UTF_8)).collect(Collectors.toList());
   }
 
   @Override
@@ -105,6 +107,7 @@ public boolean containsKey(String key) {
     return this.keysAndValues.containsKey(key);
   }
 
+  @Override
   public String toString() {
     return this.keysAndValues.toString();
   }

java/flight/flight-core/src/main/java/org/apache/arrow/flight/FlightRuntimeException.java

@@ -39,7 +39,7 @@ public CallStatus status() {
   }
 
   @Override
-  public String toString() {
+  public String getMessage() {
     String s = getClass().getName();
     return String.format("%s: %s: %s", s, status.code(), status.description());
   }

java/flight/flight-core/src/main/java/org/apache/arrow/flight/FlightServer.java

@@ -21,6 +21,7 @@
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.lang.reflect.InvocationTargetException;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.ArrayList;
@@ -134,6 +135,7 @@ public boolean awaitTermination(final long timeout, final TimeUnit unit) throws
   }
 
   /** Shutdown the server, waits for up to 6 seconds for successful shutdown before returning. */
+  @Override
   public void close() throws InterruptedException {
     shutdown();
     final boolean terminated = awaitTermination(3000, TimeUnit.MILLISECONDS);
@@ -146,7 +148,7 @@ public void close() throws InterruptedException {
     server.shutdownNow();
 
     int count = 0;
-    while (!server.isTerminated() & count < 30) {
+    while (!server.isTerminated() && count < 30) {
       count++;
       logger.debug("Waiting for termination");
       Thread.sleep(100);
@@ -216,22 +218,23 @@ public FlightServer build() {
           try {
             try {
               // Linux
-              builder.channelType(
-                  (Class<? extends ServerChannel>) Class
-                      .forName("io.netty.channel.epoll.EpollServerDomainSocketChannel"));
-              final EventLoopGroup elg = (EventLoopGroup) Class.forName("io.netty.channel.epoll.EpollEventLoopGroup")
-                  .newInstance();
+              builder.channelType(Class
+                      .forName("io.netty.channel.epoll.EpollServerDomainSocketChannel")
+                      .asSubclass(ServerChannel.class));
+              final EventLoopGroup elg = Class.forName("io.netty.channel.epoll.EpollEventLoopGroup")
+                      .asSubclass(EventLoopGroup.class).getConstructor().newInstance();
               builder.bossEventLoopGroup(elg).workerEventLoopGroup(elg);
             } catch (ClassNotFoundException e) {
               // BSD
               builder.channelType(
-                  (Class<? extends ServerChannel>) Class
-                      .forName("io.netty.channel.kqueue.KQueueServerDomainSocketChannel"));
-              final EventLoopGroup elg = (EventLoopGroup) Class.forName("io.netty.channel.kqueue.KQueueEventLoopGroup")
-                  .newInstance();
+                      Class.forName("io.netty.channel.kqueue.KQueueServerDomainSocketChannel")
+                              .asSubclass(ServerChannel.class));
+              final EventLoopGroup elg = Class.forName("io.netty.channel.kqueue.KQueueEventLoopGroup")
+                      .asSubclass(EventLoopGroup.class).getConstructor().newInstance();
               builder.bossEventLoopGroup(elg).workerEventLoopGroup(elg);
             }
-          } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
+          } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | NoSuchMethodException |
+                   InvocationTargetException e) {
             throw new UnsupportedOperationException(
                 "Could not find suitable Netty native transport implementation for domain socket address.");
           }
@@ -342,7 +345,8 @@ private void closeInputStreamIfNotNull(InputStream stream) {
       if (stream != null) {
         try {
           stream.close();
-        } catch (IOException ignored) {
+        } catch (IOException expected) {
+          // stream closes gracefully, doesn't expect an exception.
         }
       }
     }

java/flight/flight-core/src/main/java/org/apache/arrow/flight/FlightService.java

@@ -20,6 +20,7 @@
 import java.util.Collections;
 import java.util.Map;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
 import java.util.function.BooleanSupplier;
 import java.util.function.Consumer;
 
@@ -142,7 +143,7 @@ public void listActions(Flight.Empty request, StreamObserver<Flight.ActionType>
   }
 
   private static class GetListener extends OutboundStreamListenerImpl implements ServerStreamListener {
-    private ServerCallStreamObserver<ArrowMessage> responseObserver;
+    private final ServerCallStreamObserver<ArrowMessage> serverCallResponseObserver;
     private final Consumer<Throwable> errorHandler;
     private Runnable onCancelHandler = null;
     private Runnable onReadyHandler = null;
@@ -152,10 +153,10 @@ public GetListener(ServerCallStreamObserver<ArrowMessage> responseObserver, Cons
       super(null, responseObserver);
       this.errorHandler = errorHandler;
       this.completed = false;
-      this.responseObserver = responseObserver;
-      this.responseObserver.setOnCancelHandler(this::onCancel);
-      this.responseObserver.setOnReadyHandler(this::onReady);
-      this.responseObserver.disableAutoInboundFlowControl();
+      this.serverCallResponseObserver = responseObserver;
+      this.serverCallResponseObserver.setOnCancelHandler(this::onCancel);
+      this.serverCallResponseObserver.setOnReadyHandler(this::onReady);
+      this.serverCallResponseObserver.disableAutoInboundFlowControl();
     }
 
     private void onCancel() {
@@ -183,7 +184,7 @@ public void setOnReadyHandler(Runnable handler) {
 
     @Override
     public boolean isCancelled() {
-      return responseObserver.isCancelled();
+      return serverCallResponseObserver.isCancelled();
     }
 
     @Override
@@ -228,7 +229,7 @@ public StreamObserver<ArrowMessage> doPutCustom(final StreamObserver<Flight.PutR
     // When the ackStream is completed, the FlightStream will be closed with it
     ackStream.setAutoCloseable(fs);
     final StreamObserver<ArrowMessage> observer = fs.asObserver();
-    executors.submit(() -> {
+    Future<?> unused = executors.submit(() -> {
       try {
         producer.acceptPut(makeContext(responseObserver), fs, ackStream).run();
       } catch (Throwable ex) {
@@ -277,7 +278,8 @@ public void pollFlightInfo(Flight.FlightDescriptor request, StreamObserver<Fligh
    * Broadcast the given exception to all registered middleware.
    */
   private void handleExceptionWithMiddleware(Throwable t) {
-    final Map<Key<?>, FlightServerMiddleware> middleware = ServerInterceptorAdapter.SERVER_MIDDLEWARE_KEY.get();
+    final Map<FlightServerMiddleware.Key<?>, FlightServerMiddleware> middleware = ServerInterceptorAdapter
+            .SERVER_MIDDLEWARE_KEY.get();
     if (middleware == null || middleware.isEmpty()) {
       logger.error("Uncaught exception in Flight method body", t);
       return;
@@ -377,7 +379,7 @@ public StreamObserver<ArrowMessage> doExchangeCustom(StreamObserver<ArrowMessage
     responseObserver.request(1);
     final StreamObserver<ArrowMessage> observer = fs.asObserver();
     try {
-      executors.submit(() -> {
+      Future<?> unused = executors.submit(() -> {
         try {
           producer.doExchange(makeContext(responseObserver), fs, listener);
         } catch (Exception ex) {
@@ -416,7 +418,7 @@ public boolean isCancelled() {
     }
 
     @Override
-    public <T extends FlightServerMiddleware> T getMiddleware(Key<T> key) {
+    public <T extends FlightServerMiddleware> T getMiddleware(FlightServerMiddleware.Key<T> key) {
       final Map<Key<?>, FlightServerMiddleware> middleware = ServerInterceptorAdapter.SERVER_MIDDLEWARE_KEY.get();
       if (middleware == null) {
         return null;

java/flight/flight-core/src/main/java/org/apache/arrow/flight/auth/AuthConstants.java

@@ -20,8 +20,8 @@
 import org.apache.arrow.flight.FlightConstants;
 
 import io.grpc.Context;
+import io.grpc.Metadata;
 import io.grpc.Metadata.BinaryMarshaller;
-import io.grpc.Metadata.Key;
 import io.grpc.MethodDescriptor;
 
 /**
@@ -32,7 +32,7 @@ public final class AuthConstants {
   public static final String HANDSHAKE_DESCRIPTOR_NAME = MethodDescriptor
       .generateFullMethodName(FlightConstants.SERVICE, "Handshake");
   public static final String TOKEN_NAME = "Auth-Token-bin";
-  public static final Key<byte[]> TOKEN_KEY = Key.of(TOKEN_NAME, new BinaryMarshaller<byte[]>() {
+  public static final Metadata.Key<byte[]> TOKEN_KEY = Metadata.Key.of(TOKEN_NAME, new BinaryMarshaller<byte[]>() {
 
     @Override
     public byte[] toBytes(byte[] value) {

java/flight/flight-core/src/main/java/org/apache/arrow/flight/auth2/BearerTokenAuthenticator.java

@@ -55,7 +55,6 @@ public AuthResult authenticate(CallHeaders incomingHeaders) {
    * Validate the bearer token.
    * @param bearerToken The bearer token to validate.
    * @return A successful AuthResult if validation succeeded.
-   * @throws Exception If the token validation fails.
    */
   protected abstract AuthResult validateBearer(String bearerToken);
 

java/flight/flight-core/src/main/java/org/apache/arrow/flight/grpc/AddWritableBuffer.java

@@ -72,7 +72,7 @@ public class AddWritableBuffer {
       tmpBufChainOut = tmpBufChainOut2;
 
     } catch (Exception ex) {
-      new RuntimeException("Failed to initialize AddWritableBuffer, falling back to slow path", ex).printStackTrace();
+      throw new RuntimeException("Failed to initialize AddWritableBuffer, falling back to slow path", ex);
     }
 
     bufConstruct = tmpConstruct;

java/flight/flight-core/src/main/java/org/apache/arrow/flight/grpc/ClientInterceptorAdapter.java

@@ -46,9 +46,9 @@
  */
 public class ClientInterceptorAdapter implements ClientInterceptor {
 
-  private final List<Factory> factories;
+  private final List<FlightClientMiddleware.Factory> factories;
 
-  public ClientInterceptorAdapter(List<Factory> factories) {
+  public ClientInterceptorAdapter(List<FlightClientMiddleware.Factory> factories) {
     this.factories = factories;
   }
 

java/flight/flight-core/src/main/java/org/apache/arrow/flight/grpc/GetReadableBuffer.java

@@ -51,7 +51,7 @@ public class GetReadableBuffer {
       tmpField = f;
       tmpClazz = clazz;
     } catch (Exception e) {
-      new RuntimeException("Failed to initialize GetReadableBuffer, falling back to slow path", e).printStackTrace();
+      throw new RuntimeException("Failed to initialize GetReadableBuffer, falling back to slow path", e);
     }
     READABLE_BUFFER = tmpField;
     BUFFER_INPUT_STREAM = tmpClazz;

java/flight/flight-core/src/main/java/org/apache/arrow/flight/grpc/MetadataAdapter.java

@@ -17,6 +17,7 @@
 
 package org.apache.arrow.flight.grpc;
 
+import java.nio.charset.StandardCharsets;
 import java.util.HashSet;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -42,39 +43,39 @@ public MetadataAdapter(Metadata metadata) {
 
   @Override
   public String get(String key) {
-    return this.metadata.get(Key.of(key, Metadata.ASCII_STRING_MARSHALLER));
+    return this.metadata.get(Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER));
   }
 
   @Override
   public byte[] getByte(String key) {
     if (key.endsWith(Metadata.BINARY_HEADER_SUFFIX)) {
-      return this.metadata.get(Key.of(key, Metadata.BINARY_BYTE_MARSHALLER));
+      return this.metadata.get(Metadata.Key.of(key, Metadata.BINARY_BYTE_MARSHALLER));
     }
-    return get(key).getBytes();
+    return get(key).getBytes(StandardCharsets.UTF_8);
   }
 
   @Override
   public Iterable<String> getAll(String key) {
-    return this.metadata.getAll(Key.of(key, Metadata.ASCII_STRING_MARSHALLER));
+    return this.metadata.getAll(Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER));
   }
 
   @Override
   public Iterable<byte[]> getAllByte(String key) {
     if (key.endsWith(Metadata.BINARY_HEADER_SUFFIX)) {
-      return this.metadata.getAll(Key.of(key, Metadata.BINARY_BYTE_MARSHALLER));
+      return this.metadata.getAll(Metadata.Key.of(key, Metadata.BINARY_BYTE_MARSHALLER));
     }
     return StreamSupport.stream(getAll(key).spliterator(), false)
         .map(String::getBytes).collect(Collectors.toList());
   }
 
   @Override
   public void insert(String key, String value) {
-    this.metadata.put(Key.of(key, Metadata.ASCII_STRING_MARSHALLER), value);
+    this.metadata.put(Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER), value);
   }
 
   @Override
   public void insert(String key, byte[] value) {
-    this.metadata.put(Key.of(key, Metadata.BINARY_BYTE_MARSHALLER), value);
+    this.metadata.put(Metadata.Key.of(key, Metadata.BINARY_BYTE_MARSHALLER), value);
   }
 
   @Override
@@ -85,13 +86,14 @@ public Set<String> keys() {
   @Override
   public boolean containsKey(String key) {
     if (key.endsWith("-bin")) {
-      final Key<?> grpcKey = Key.of(key, Metadata.BINARY_BYTE_MARSHALLER);
+      final Metadata.Key<?> grpcKey = Metadata.Key.of(key, Metadata.BINARY_BYTE_MARSHALLER);
       return this.metadata.containsKey(grpcKey);
     }
-    final Key<?> grpcKey = Key.of(key, Metadata.ASCII_STRING_MARSHALLER);
+    final Metadata.Key<?> grpcKey = Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER);
     return this.metadata.containsKey(grpcKey);
   }
 
+  @Override
   public String toString() {
     return this.metadata.toString();
   }

java/flight/flight-core/src/main/java/org/apache/arrow/flight/grpc/ServerInterceptorAdapter.java

@@ -61,7 +61,7 @@ public static class KeyFactory<T extends FlightServerMiddleware> {
     private final FlightServerMiddleware.Key<T> key;
     private final FlightServerMiddleware.Factory<T> factory;
 
-    public KeyFactory(Key<T> key, Factory<T> factory) {
+    public KeyFactory(FlightServerMiddleware.Key<T> key, FlightServerMiddleware.Factory<T> factory) {
       this.key = key;
       this.factory = factory;
     }

java/flight/flight-core/src/main/java/org/apache/arrow/flight/grpc/StatusUtils.java

@@ -17,6 +17,7 @@
 
 package org.apache.arrow.flight.grpc;
 
+import java.nio.charset.StandardCharsets;
 import java.util.Iterator;
 import java.util.Objects;
 import java.util.function.Function;
@@ -171,7 +172,7 @@ private static ErrorFlightMetadata parseTrailers(Metadata trailers) {
       if (key.endsWith(Metadata.BINARY_HEADER_SUFFIX)) {
         metadata.insert(key, trailers.get(keyOfBinary(key)));
       } else {
-        metadata.insert(key, Objects.requireNonNull(trailers.get(keyOfAscii(key))).getBytes());
+        metadata.insert(key, Objects.requireNonNull(trailers.get(keyOfAscii(key))).getBytes(StandardCharsets.UTF_8));
       }
     }
     return metadata;