GH-725: Added ExtensionReader

vector/src/main/codegen/templates/AbstractFieldReader.java

@@ -108,6 +108,23 @@ public void copyAsField(String name, ${name}Writer writer) {
   }
 
   </#list></#list>
+
+  public void read(ExtensionHolder holder) {
+    fail("Extension");
+  }
+
+  public void read(int arrayIndex, ExtensionHolder holder) {
+    fail("RepeatedExtension");
+  }
+
+  public void copyAsValue(AbstractExtensionTypeWriter writer) {
+    fail("CopyAsValueExtension");
+  }
+
+  public void copyAsField(String name, AbstractExtensionTypeWriter writer) {
+    fail("CopyAsFieldExtension");
+  }
+
   public FieldReader reader(String name) {
     fail("reader(String name)");
     return null;

vector/src/main/codegen/templates/BaseReader.java

@@ -73,7 +73,7 @@ public interface RepeatedMapReader extends MapReader{
 
   public interface ScalarReader extends
   <#list vv.types as type><#list type.minor as minor><#assign name = minor.class?cap_first /> ${name}Reader, </#list></#list>
-  BaseReader {}
+  ExtensionReader, BaseReader {}
 
   interface ComplexReader{
     StructReader rootAsStruct();

vector/src/main/codegen/templates/NullReader.java

@@ -86,6 +86,10 @@ public void read(int arrayIndex, Nullable${name}Holder holder){
   }
   </#list></#list>
 
+  public void read(ExtensionHolder holder) {
+    holder.isSet = 0;
+  }
+
   public int size(){
     return 0;
   }

vector/src/main/java/org/apache/arrow/vector/complex/reader/ExtensionReader.java

@@ -0,0 +1,44 @@
+/*
+ * 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.vector.complex.reader;
+
+import org.apache.arrow.vector.holders.ExtensionHolder;
+
+/** Interface for reading extension types. Extends the functionality of {@link BaseReader}. */
+public interface ExtensionReader extends BaseReader {
+
+  /**
+   * Reads to the given extension holder.
+   *
+   * @param holder the {@link ExtensionHolder} to read
+   */
+  void read(ExtensionHolder holder);
+
+  /**
+   * Reads and returns an object representation of the extension type.
+   *
+   * @return the object representation of the extension type
+   */
+  Object readObject();
+
+  /**
+   * Checks if the current value is set.
+   *
+   * @return true if the value is set, false otherwise
+   */
+  boolean isSet();
+}

vector/src/test/java/org/apache/arrow/vector/UuidVector.java

@@ -20,6 +20,9 @@
 import java.util.UUID;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.util.hash.ArrowBufHasher;
+import org.apache.arrow.vector.complex.impl.UuidReaderImpl;
+import org.apache.arrow.vector.complex.reader.FieldReader;
+import org.apache.arrow.vector.holder.UuidHolder;
 import org.apache.arrow.vector.types.pojo.Field;
 import org.apache.arrow.vector.types.pojo.FieldType;
 import org.apache.arrow.vector.types.pojo.UuidType;
@@ -79,11 +82,21 @@ public TransferPair makeTransferPair(ValueVector to) {
     return new TransferImpl((UuidVector) to);
   }
 
+  @Override
+  protected FieldReader getReaderImpl() {
+    return new UuidReaderImpl(this);
+  }
+
   public void setSafe(int index, byte[] value) {
     getUnderlyingVector().setIndexDefined(index);
     getUnderlyingVector().setSafe(index, value);
   }
 
+  public void get(int index, UuidHolder holder) {
+    holder.value = getUnderlyingVector().get(index);
+    holder.isSet = 1;
+  }
+
   public class TransferImpl implements TransferPair {
     UuidVector to;
     ValueVector targetUnderlyingVector;

vector/src/test/java/org/apache/arrow/vector/complex/impl/UuidReaderImpl.java

@@ -0,0 +1,51 @@
+/*
+ * 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.vector.complex.impl;
+
+import org.apache.arrow.vector.UuidVector;
+import org.apache.arrow.vector.holder.UuidHolder;
+import org.apache.arrow.vector.holders.ExtensionHolder;
+import org.apache.arrow.vector.types.Types.MinorType;
+import org.apache.arrow.vector.types.pojo.Field;
+
+public class UuidReaderImpl extends AbstractFieldReader {
+
+  private final UuidVector vector;
+
+  public UuidReaderImpl(UuidVector vector) {
+    super();
+    this.vector = vector;
+  }
+
+  @Override
+  public MinorType getMinorType() {
+    return vector.getMinorType();
+  }
+
+  public Field getField() {
+    return vector.getField();
+  }
+
+  public boolean isSet() {
+    return !vector.isNull(idx());
+  }
+
+  public void read(ExtensionHolder holder) {
+    UuidHolder uuidHolder = (UuidHolder) holder;
+    vector.get(idx(), uuidHolder);
+  }
+}

vector/src/test/java/org/apache/arrow/vector/complex/writer/TestComplexWriter.java

@@ -31,6 +31,7 @@
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.UUID;
 import org.apache.arrow.memory.ArrowBuf;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;
@@ -64,16 +65,19 @@
 import org.apache.arrow.vector.complex.impl.UnionMapReader;
 import org.apache.arrow.vector.complex.impl.UnionReader;
 import org.apache.arrow.vector.complex.impl.UnionWriter;
+import org.apache.arrow.vector.complex.impl.UuidWriterFactory;
 import org.apache.arrow.vector.complex.reader.BaseReader.StructReader;
 import org.apache.arrow.vector.complex.reader.BigIntReader;
 import org.apache.arrow.vector.complex.reader.FieldReader;
 import org.apache.arrow.vector.complex.reader.Float4Reader;
 import org.apache.arrow.vector.complex.reader.Float8Reader;
 import org.apache.arrow.vector.complex.reader.IntReader;
 import org.apache.arrow.vector.complex.writer.BaseWriter.ComplexWriter;
+import org.apache.arrow.vector.complex.writer.BaseWriter.ExtensionWriter;
 import org.apache.arrow.vector.complex.writer.BaseWriter.ListWriter;
 import org.apache.arrow.vector.complex.writer.BaseWriter.MapWriter;
 import org.apache.arrow.vector.complex.writer.BaseWriter.StructWriter;
+import org.apache.arrow.vector.holder.UuidHolder;
 import org.apache.arrow.vector.holders.DecimalHolder;
 import org.apache.arrow.vector.holders.DurationHolder;
 import org.apache.arrow.vector.holders.FixedSizeBinaryHolder;
@@ -93,6 +97,7 @@
 import org.apache.arrow.vector.types.pojo.ArrowType.Utf8;
 import org.apache.arrow.vector.types.pojo.Field;
 import org.apache.arrow.vector.types.pojo.FieldType;
+import org.apache.arrow.vector.types.pojo.UuidType;
 import org.apache.arrow.vector.util.CallBack;
 import org.apache.arrow.vector.util.DecimalUtility;
 import org.apache.arrow.vector.util.JsonStringArrayList;
@@ -2489,4 +2494,35 @@ public void unionWithVarCharAndBinaryHelpers() throws Exception {
           "row12", new String(vector.getLargeVarBinaryVector().get(11), StandardCharsets.UTF_8));
     }
   }
+
+  @Test
+  public void extensionWriterReader() throws Exception {
+    // test values
+    UUID u1 = UUID.randomUUID();
+
+    try (NonNullableStructVector parent = NonNullableStructVector.empty("parent", allocator)) {
+      // write
+
+      ComplexWriter writer = new ComplexWriterImpl("root", parent);
+      StructWriter rootWriter = writer.rootAsStruct();
+
+      {
+        ExtensionWriter extensionWriter = rootWriter.extension("uuid1", new UuidType());
+        extensionWriter.setPosition(0);
+        extensionWriter.addExtensionTypeWriterFactory(new UuidWriterFactory());
+        extensionWriter.writeExtension(u1);
+      }
+      // read
+      StructReader rootReader = new SingleStructReaderImpl(parent).reader("root");
+      {
+        FieldReader uuidReader = rootReader.reader("uuid1");
+        uuidReader.setPosition(0);
+        UuidHolder uuidHolder = new UuidHolder();
+        uuidReader.read(uuidHolder);
+        final ByteBuffer bb = ByteBuffer.wrap(uuidHolder.value);
+        UUID actualUuid = new UUID(bb.getLong(), bb.getLong());
+        assertEquals(u1, actualUuid);
+      }
+    }
+  }
 }