parquet.column.values.ValuesReader Maven / Gradle / Ivy
/**
* 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.ParquetDecodingException;
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:
*
* - repetition levels column
*
- definition levels column
*
- data column
*
*
* 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
*
* @throws IOException
*/
public abstract void initFromPage(int valueCount, byte[] page, int offset) throws IOException;
/**
* Called to return offset of the next section
* @return offset of the next section
*/
public int getNextOffset() {
throw new ParquetDecodingException("Unsupported: cannot get offset of the next section.");
}
/**
* usable when the encoding is dictionary 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();
}
/**
* Skips the next value in the page
*/
abstract public void skip();
}