parquet-column/src/main/java/parquet/column/values/ValuesReader.java

/**
 * Copyright 2012 Twitter, Inc.
 *
 * Licensed 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 parquet.column.values;

import java.io.IOException;

import parquet.io.api.Binary;

/**
 * Base class to implement an encoding for a given column type.
 *
 * A ValuesReader is provided with a page (byte-array) and is responsible
 * for deserializing the primitive values stored in that page.
 *
 * Given that pages are homogeneous (store only a single type), typical subclasses
 * will only override one of the read*() methods.
 *
 * @author Julien Le Dem
 */
public abstract class ValuesReader {

  /**
   * Called to initialize the column reader from a part of a page.
   *
   * The underlying implementation knows how much data to read, so a length
   * is not provided.
   *
   * Each page may contain several sections:
   * <ul>
   *  <li> repetition levels column
   *  <li> definition levels column
   *  <li> data column
   * </ul>
   *
   * This function is called with 'offset' pointing to the beginning of one of these sections,
   * and should return the offset to the section following it.
   *
   * @param valueCount count of values in this page
   * @param page the array to read from containing the page data (repetition levels, definition levels, data)
   * @param offset where to start reading from in the page
   * @return the offset of the end of the data for this section of the page
   * @throws IOException
   */
  public abstract int initFromPage(long valueCount, byte[] page, int offset) throws IOException;

  /**
   * usable when the encoding is doctionary based
   * @return the id of the next value from the page
   */
  public int readValueDictionaryId() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next boolean from the page
   */
  public boolean readBoolean() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next Binary from the page
   */
  public Binary readBytes() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next float from the page
   */
  public float readFloat() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next double from the page
   */
  public double readDouble() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next integer from the page
   */
  public int readInteger() {
    throw new UnsupportedOperationException();
  }

  /**
   * @return the next long from the page
   */
  public long readLong() {
    throw new UnsupportedOperationException();
  }

}