chore: minor readability improvements

google-cloud-spanner-cassandra/src/main/java/com/google/cloud/spanner/adapter/DriverConnectionHandler.java

@@ -223,7 +223,7 @@ private void recordMetrics(Instant startTime) {
     }
     final long latency = Duration.between(startTime, Instant.now()).toMillis();
     metricsRecorder.recordOperationCount(1);
-    metricsRecorder.recordOperationLatency(latency);
+    metricsRecorder.recordOperationLatency((double) latency);
   }
 
   private static int readNBytesJava8(InputStream in, byte[] b, int off, int len)
@@ -352,7 +352,7 @@ private PreparePayloadResult preparePayload(MessageContext ctx) {
       case ProtocolConstants.Opcode.BATCH:
         return prepareBatchMessage((Batch) decodeFrame(ctx.payload).message, ctx.streamId);
       case ProtocolConstants.Opcode.QUERY:
-        return prepareQueryMessage((Query) decodeFrame(ctx.payload).message, ctx.streamId);
+        return prepareQueryMessage((Query) decodeFrame(ctx.payload).message);
       default:
         return new PreparePayloadResult(DEFAULT_CONTEXT);
     }
@@ -394,7 +394,7 @@ private PreparePayloadResult prepareBatchMessage(Batch message, int streamId) {
     return new PreparePayloadResult(DEFAULT_CONTEXT_WITH_LAR, attachments, attachmentErrorResponse);
   }
 
-  private PreparePayloadResult prepareQueryMessage(Query message, int streamId) {
+  private PreparePayloadResult prepareQueryMessage(Query message) {
     ApiCallContext context;
     Map<String, String> attachments = Collections.emptyMap();
     if (startsWith(message.query, "SELECT")) {

google-cloud-spanner-cassandra/src/main/java/com/google/cloud/spanner/adapter/HealthCheckServer.java

@@ -15,14 +15,15 @@
 */
 package com.google.cloud.spanner.adapter;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+
 import com.sun.net.httpserver.HttpExchange;
 import com.sun.net.httpserver.HttpHandler;
 import com.sun.net.httpserver.HttpServer;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
-import java.nio.charset.StandardCharsets;
 import java.util.concurrent.atomic.AtomicBoolean;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -83,7 +84,7 @@ public void handle(HttpExchange exchange) throws IOException {
 
     private void sendResponse(HttpExchange exchange, int statusCode, String response)
         throws IOException {
-      byte[] responseBytes = response.getBytes(StandardCharsets.UTF_8);
+      byte[] responseBytes = response.getBytes(UTF_8);
       exchange.getResponseHeaders().set("Content-Type", "text/plain; charset=utf-8");
       exchange.sendResponseHeaders(statusCode, responseBytes.length);
       try (OutputStream os = exchange.getResponseBody()) {

google-cloud-spanner-cassandra/src/main/java/com/google/cloud/spanner/adapter/SpannerCqlRetryPolicy.java

@@ -124,11 +124,11 @@ public void close() {
     // nothing to do
   }
 
-  private RetryDecision retryOrRethrow(int retryCount, String error_msg) {
+  private RetryDecision retryOrRethrow(int retryCount, String errorMsg) {
     final RetryDecision decision =
         (retryCount < DEFAULT_MAX_RETRY_COUNT) ? RetryDecision.RETRY_SAME : RetryDecision.RETHROW;
     if (decision == RetryDecision.RETRY_SAME && LOG.isTraceEnabled()) {
-      LOG.trace(error_msg, logPrefix, retryCount);
+      LOG.trace(errorMsg, logPrefix, retryCount);
     }
     return decision;
   }

google-cloud-spanner-cassandra/src/main/java/com/google/cloud/spanner/adapter/configs/YamlConfigLoader.java

@@ -20,6 +20,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
+import javax.annotation.Nullable;
 import org.yaml.snakeyaml.Yaml;
 
 /**
@@ -35,6 +36,7 @@ public class YamlConfigLoader {
    * @param inputStream The input stream containing the YAML data.
    * @return A {@link UserConfigs} object representing the parsed configuration.
    */
+  @Nullable
   public static UserConfigs load(InputStream inputStream) {
     Yaml yaml = new Yaml();
     Map<String, Object> yamlMap = yaml.load(inputStream);

google-cloud-spanner-cassandra/src/main/java/com/google/cloud/spanner/adapter/util/MessageUtils.java

@@ -26,11 +26,11 @@
 import com.datastax.oss.protocol.internal.response.Supported;
 import com.datastax.oss.protocol.internal.response.error.Unprepared;
 import com.google.api.core.InternalApi;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.protobuf.ByteString;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufAllocator;
-import java.util.Collections;
 
 /**
  * Utility class for creating specific types of response frames used in the server protocol, encoded
@@ -53,8 +53,8 @@ public final class MessageUtils {
   private static final Supported SUPPORTED_MESSAGE =
       new Supported(
           ImmutableMap.of(
-              "CQL_VERSION", Collections.singletonList("3.0.0"),
-              "COMPRESSION", Collections.emptyList()));
+              "CQL_VERSION", ImmutableList.of("3.0.0"),
+              "COMPRESSION", ImmutableList.of()));
 
   private static final FrameCodec<ByteBuf> serverFrameCodec =
       FrameCodec.defaultServer(
@@ -112,7 +112,7 @@ public static ByteString supportedResponse(int streamId) {
   public static ByteString messageResponse(int streamId, Message message) {
     Frame responseFrame =
         Frame.forResponse(
-            PROTOCOL_VERSION, streamId, null, Frame.NO_PAYLOAD, Collections.emptyList(), message);
+            PROTOCOL_VERSION, streamId, null, Frame.NO_PAYLOAD, ImmutableList.of(), message);
     ByteBuf responseBuf = serverFrameCodec.encode(responseFrame);
     ByteString response = ByteString.copyFrom(responseBuf.nioBuffer());
     responseBuf.release();