Add producer for map type

Author: martin-traverse

adapter/avro/src/main/java/org/apache/arrow/adapter/avro/ArrowToAvroUtils.java

@@ -25,6 +25,7 @@
 import org.apache.arrow.adapter.avro.producers.AvroFloatProducer;
 import org.apache.arrow.adapter.avro.producers.AvroIntProducer;
 import org.apache.arrow.adapter.avro.producers.AvroLongProducer;
+import org.apache.arrow.adapter.avro.producers.AvroMapProducer;
 import org.apache.arrow.adapter.avro.producers.AvroNullProducer;
 import org.apache.arrow.adapter.avro.producers.AvroNullableProducer;
 import org.apache.arrow.adapter.avro.producers.AvroStringProducer;
@@ -56,6 +57,7 @@
 import org.apache.arrow.vector.VarBinaryVector;
 import org.apache.arrow.vector.VarCharVector;
 import org.apache.arrow.vector.complex.ListVector;
+import org.apache.arrow.vector.complex.MapVector;
 import org.apache.arrow.vector.complex.StructVector;
 import org.apache.arrow.vector.types.Types;
 
@@ -156,6 +158,17 @@ private static BaseAvroProducer<?> createProducer(FieldVector vector, boolean nu
         Producer<?> itemProducer = createProducer(itemVector, itemVector.getField().isNullable());
         return new AvroArraysProducer(listVector, itemProducer);
 
+      case MAP:
+
+        MapVector mapVector = (MapVector) vector;
+        StructVector entryVector = (StructVector) mapVector.getDataVector();
+        VarCharVector keyVector = (VarCharVector) entryVector.getChildrenFromFields().get(0);
+        FieldVector valueVector = entryVector.getChildrenFromFields().get(1);
+        Producer<?> keyProducer = new AvroStringProducer(keyVector);
+        Producer<?> valueProducer = createProducer(valueVector, valueVector.getField().isNullable());
+        Producer<?> entryProducer = new AvroStructProducer(entryVector, new Producer<?>[] {keyProducer, valueProducer});
+        return new AvroMapProducer(mapVector, entryProducer);
+
       // Not all Arrow types are supported for encoding (yet)!
 
       default:

adapter/avro/src/main/java/org/apache/arrow/adapter/avro/producers/AvroMapProducer.java

@@ -0,0 +1,64 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.arrow.adapter.avro.producers;
+
+import org.apache.arrow.vector.FieldVector;
+import org.apache.arrow.vector.complex.MapVector;
+import org.apache.avro.io.Encoder;
+
+import java.io.IOException;
+
+/**
+ * Producer which produces map type values to avro encoder. Write the data to {@link MapVector}.
+ */
+public class AvroMapProducer extends BaseAvroProducer<MapVector> {
+
+  private final Producer<? extends FieldVector> delegate;
+
+  /** Instantiate a AvroMapProducer. */
+  public AvroMapProducer(MapVector vector, Producer<? extends FieldVector> delegate) {
+    super(vector);
+    this.delegate = delegate;
+  }
+
+  @Override
+  public void produce(Encoder encoder) throws IOException {
+
+    int startOffset = vector.getOffsetBuffer().getInt(currentIndex * (long) Integer.BYTES);
+    int endOffset = vector.getOffsetBuffer().getInt((currentIndex + 1) * (long) Integer.BYTES);
+    int nEntries = endOffset - startOffset;
+
+    encoder.writeMapStart();
+    encoder.setItemCount(nEntries);
+
+    for (int i = 0; i < nEntries; i++) {
+      encoder.startItem();
+      delegate.produce(encoder);
+    }
+
+    encoder.writeMapEnd();
+    currentIndex++;
+  }
+
+  @Override
+  @SuppressWarnings("unchecked")
+  public boolean resetValueVector(MapVector vector) {
+    ((Producer<FieldVector>) delegate).resetValueVector(vector.getDataVector());
+    return super.resetValueVector(vector);
+  }
+}