add warning message when using lock hint with unsupported transaction

Author: rahul2393

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AbstractReadContext.java

@@ -58,6 +58,7 @@
 import java.util.Map;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.logging.Logger;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.GuardedBy;
 
@@ -67,6 +68,7 @@
  */
 abstract class AbstractReadContext
     implements ReadContext, AbstractResultSet.Listener, SessionTransaction {
+  private static final Logger logger = Logger.getLogger(AbstractReadContext.class.getName());
 
   abstract static class Builder<B extends Builder<?, T>, T extends AbstractReadContext> {
     private SessionImpl session;
@@ -951,8 +953,14 @@ ResultSet readInternalWithOptions(
     } else if (defaultDirectedReadOptions != null) {
       builder.setDirectedReadOptions(defaultDirectedReadOptions);
     }
-    if (readOptions.hasLockHint() && !isReadOnly()) {
-      builder.setLockHint(readOptions.lockHint());
+    if (readOptions.hasLockHint()) {
+      if (isReadOnly()) {
+        logger.warning(
+            "Lock hint is only supported for ReadWrite transactions. "
+                + "Overriding lock hint to default unspecified.");
+      } else {
+        builder.setLockHint(readOptions.lockHint());
+      }
     }
     final int prefetchChunks =
         readOptions.hasPrefetchChunks() ? readOptions.prefetchChunks() : defaultPrefetchChunks;