addressing comments

athena-federation-sdk/src/main/java/com/amazonaws/athena/connector/lambda/data/ArrowTypeComparator.java

@@ -103,6 +103,7 @@ else if (lhs instanceof org.joda.time.LocalDateTime) {
                 else {
                     return ((java.time.LocalDateTime) lhs).compareTo((java.time.LocalDateTime) rhs);
                 }
+            case MAP:
             case LIST:
             case STRUCT: // struct maps to java.util.map
                 //This could lead to thrashing if used to sort a collection

athena-federation-sdk/src/main/java/com/amazonaws/athena/connector/lambda/data/BlockUtils.java

@@ -1144,10 +1144,10 @@ protected static void writeMap(BufferAllocator allocator,
      * @param allocator The BlockAllocator that can be used for allocating Arrow Buffers for fields which require conversion
      * to Arrow Buff before being written.
      * @param value The value to write.
-     * @note This method and its List complement violate the DRY mantra because ListWriter and StructWriter don't share
-     * a meaningful ancestor despite having identical methods. This requires us to either further wrap and abstract the writer
-     * or duplicate come code. In a future release we hope to have contributed a better option to Apache Arrow which allows
-     * us to simplify this method.
+     * @note This method and its List and struct complement violate the DRY mantra because
+     * ListWriter, StructWriter, and UnionMapWriter don't share a meaningful ancestor despite having identical methods.
+     * This requires us to either further wrap and abstract the writer or duplicate come code. In a future
+     * release we hope to have contributed a better option to Apache Arrow which allows us to simplify this method.
      */
     @VisibleForTesting
     protected static void writeMapValue(UnionMapWriter writer, Field field, BufferAllocator allocator, Object value)

athena-federation-sdk/src/main/java/com/amazonaws/athena/connector/lambda/examples/ExampleMetadataHandler.java

@@ -58,6 +58,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Comparator;
 import java.util.HashSet;
 import java.util.List;
@@ -482,6 +483,11 @@ protected static class ExampleTable
                             FieldBuilder.newBuilder("outerlist", new ArrowType.List())
                                     .addListField("innerList", Types.MinorType.VARCHAR.getType())
                                     .build())
+                    .addField(FieldBuilder.newBuilder("simplemap", new ArrowType.Map(false))
+                            .addField("entries", Types.MinorType.STRUCT.getType(), false, Arrays.asList(
+                                    FieldBuilder.newBuilder("key", Types.MinorType.VARCHAR.getType(), false).build(),
+                                    FieldBuilder.newBuilder("value", Types.MinorType.INT.getType()).build()))
+                            .build())
                     .addMetadata("partitionCols", "day,month,year")
                     .addMetadata("randomProp1", "randomPropVal1")
                     .addMetadata("randomProp2", "randomPropVal2").build();

athena-federation-sdk/src/main/java/com/amazonaws/athena/connector/lambda/examples/ExampleRecordHandler.java

@@ -60,7 +60,9 @@
 import org.apache.arrow.util.VisibleForTesting;
 import org.apache.arrow.vector.FieldVector;
 import org.apache.arrow.vector.complex.ListVector;
+import org.apache.arrow.vector.complex.MapVector;
 import org.apache.arrow.vector.complex.impl.UnionListWriter;
+import org.apache.arrow.vector.complex.impl.UnionMapWriter;
 import org.apache.arrow.vector.complex.writer.BaseWriter;
 import org.apache.arrow.vector.holders.NullableBigIntHolder;
 import org.apache.arrow.vector.holders.NullableBitHolder;
@@ -402,6 +404,25 @@ private FieldWriterFactory makeFactory(Field field, RowContext rowContext)
                     default:
                         throw new IllegalArgumentException("Unsupported type " + childType);
                 }
+            case MAP:
+                return (FieldVector vector, Extractor extractor, ConstraintProjector constraint) ->
+                        (FieldWriter) (Object context, int rowNum) -> {
+                            UnionMapWriter writer  = ((MapVector) vector).getWriter();
+                            writer.setPosition(rowNum);
+                            writer.startMap();
+                            writer.startEntry();
+                            byte[] bytes = "chars".getBytes(Charsets.UTF_8);
+                            try (ArrowBuf buf = vector.getAllocator().buffer(bytes.length)) {
+                                buf.writeBytes(bytes);
+                                writer.key().varChar("key").writeVarChar(0, (int) (buf.readableBytes()), buf);
+                            }
+
+                            writer.value().integer("value").writeInt(1001);
+                            writer.endEntry();
+                            writer.endMap();
+                            ((MapVector) vector).setNotNull(rowNum);
+                            return true;
+                        };
             default:
                 throw new IllegalArgumentException("Unsupported type " + fieldType);
         }

athena-federation-sdk/src/main/java/com/amazonaws/athena/connector/lambda/serde/v2/ArrowTypeSerDe.java

@@ -689,8 +689,8 @@ protected ArrowType doTypedDeserialize(JsonParser jparser, DeserializationContex
 
     private static final class MapSerDe
     {
-        private static final String KEY = "key";
-        private static final String VALUE = "value";
+        //Arrow map types are represented as Map(false)<entries: Struct<key:keyType,value:valueType>>
+        private static final Boolean keysSortedFalse = false;
 
         private static final class Serializer extends TypedSerializer<ArrowType>
         {
@@ -718,7 +718,7 @@ private Deserializer()
             protected ArrowType doTypedDeserialize(JsonParser jparser, DeserializationContext ctxt)
                     throws IOException
             {
-                return new ArrowType.Map(false);
+                return new ArrowType.Map(keysSortedFalse);
             }
         }
     }

athena-federation-sdk/src/test/java/com/amazonaws/athena/connector/lambda/examples/ExampleRecordHandlerTest.java

@@ -70,6 +70,7 @@
 import java.io.ByteArrayInputStream;
 import java.io.InputStream;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -132,6 +133,11 @@ public void setUp()
                         FieldBuilder.newBuilder("outerlist", new ArrowType.List())
                                 .addListField("innerList", Types.MinorType.VARCHAR.getType())
                                 .build())
+                .addField(FieldBuilder.newBuilder("simplemap", new ArrowType.Map(false))
+                        .addField("entries", Types.MinorType.STRUCT.getType(), false, Arrays.asList(
+                                FieldBuilder.newBuilder("key", Types.MinorType.VARCHAR.getType(), false).build(),
+                                FieldBuilder.newBuilder("value", Types.MinorType.INT.getType()).build()))
+                        .build())
                 .addMetadata("partitionCols", "year,month,day")
                 .build();