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A module that is everything required to understands Druid Segments

There is a newer version: 30.0.1

/*
 * 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.druid.frame.write.columnar;

import org.apache.datasketches.memory.WritableMemory;
import org.apache.druid.frame.allocation.MemoryAllocator;
import org.apache.druid.frame.read.columnar.ComplexFrameColumnReader;
import org.apache.druid.java.util.common.StringUtils;
import org.apache.druid.segment.BaseObjectColumnValueSelector;
import org.apache.druid.segment.serde.ComplexMetricSerde;

/**
 * Column writer for complex columns.
 *
 * Dual to {@link ComplexFrameColumnReader}.
 */
public class ComplexFrameColumnWriter implements FrameColumnWriter
{
  private final ComplexMetricSerde serde;
  private final BaseObjectColumnValueSelector selector;
  private final ComplexFrameMaker maker;

  ComplexFrameColumnWriter(
      final BaseObjectColumnValueSelector selector,
      final MemoryAllocator allocator,
      final ComplexMetricSerde serde
  )
  {
    this.selector = selector;
    this.serde = serde;
    this.maker = new ComplexFrameMaker(allocator, StringUtils.toUtf8(serde.getTypeName()));
  }

  @Override
  public boolean addSelection()
  {
    final Object complexObject = selector.getObject();
    return maker.add(complexObject == null ? null : serde.toBytes(complexObject));
  }

  @Override
  public void undo()
  {
    maker.undo();
  }

  @Override
  public long size()
  {
    return maker.size();
  }

  @Override
  public long writeTo(final WritableMemory memory, final long startPosition)
  {
    return maker.writeTo(memory, startPosition);
  }

  @Override
  public void close()
  {
    maker.close();
  }
}