Use the Apache Parquet Column framework in the Java Library to implement the data column operation
Use the Apache Parquet Column framework in the Java Library to implement the data column operation
Brief introduction
Apache Parquet is a column -type storage file format widely used in the field of big data.As an efficient data storage format, Parquet provides a rich class library to process and operate storage data.Among them, the Apache Parquet Column framework provides developers with a convenient and fast way to handle the column -level operation in the Parquet file.This article will introduce how to use the Apache Parquet Column framework in the Java library to implement the data column operation.
Set environment
Before starting to use the Apache Parquet Column framework, you need to set the Java development environment and import related Parquet libraries.You can import the required class library by adding the following dependencies to the pom.xml file of the project:
<dependencies>
<dependency>
<groupId>org.apache.parquet</groupId>
<artifactId>parquet-column</artifactId>
<version>1.12.0</version>
</dependency>
</dependencies>
Read the Parquet file
First, we need to read the existing ParQuet files.By using the `ParQuetFileRereader` class and` ParquetFileRereader.open` method, we can open a ParQuet file and get the entrance point for reading the column data.
String parquetFilePath = "path/to/your/parquet/file.parquet";
ParquetFileReader reader = ParquetFileReader.open(new Configuration(), new Path(parquetFilePath));
Similarly, you can use the method of `Reader.getRowgroups () to obtain all the lines in the file.
Get the quota data
Next, we can use the `metadatautils` class and` ReadColumnmetadata to read to read the meta -data in the file.To read the quota data, the path of the column needs to be provided.The format of the path is similar to `/path/to/you/color/color.The following is an example of reading a column called "Colmn1":
String columnPath = "/column1";
ColumnDescriptor columnDescriptor = reader.getFileMetaData().getSchema().getColumnDescription(new String[]{columnPath});
ColumnReader columnReader = reader.getColumnReader(columnDescriptor);
Read data
After the above steps, we are ready to read the data.You can use the `ColumnReader` object to call the` ReadcurrentValue` method to read the data of the current position and use the method of the relevant data type to decoding.For example, if column is a column of a string type, you can use the `Getbinary` method of the` ColumnReader` object to read the string data.
Binary binaryValue = columnReader.getBinary();
String value = binaryValue.toStringUsingUTF8();
System.out.println(value);
Process the next data item
After reading the current position, we can move to the next data item.Using the `Consume` method of the` ColumnReader` object to move the current position to the next data item.
columnReader.consume();
Repeat the above two steps until you traverse the entire column data.
Turn off the reader
When a reader is no longer needed, it should be closed to release resources.Using the `Close` method of the` ParqueTFileRereader` object to turn off the reader.
reader.close();
For example code
Below is a complete sample code that demonstrates how to use Apache Parquet Column framework to read the column data in the Parquet file:
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.parquet.column.ColumnDescriptor;
import org.apache.parquet.column.ColumnReader;
import org.apache.parquet.column.ColumnReaderImpl;
import org.apache.parquet.column.page.PageReadStore;
import org.apache.parquet.example.data.Group;
import org.apache.parquet.example.data.simple.SimpleGroup;
import org.apache.parquet.hadoop.ParquetFileReader;
import org.apache.parquet.hadoop.metadata.ParquetMetadata;
import org.apache.parquet.io.api.Binary;
import org.apache.parquet.schema.OriginalType;
import org.apache.parquet.schema.PrimitiveType;
import org.apache.parquet.schema.Type;
import org.apache.parquet.schema.Types;
import org.apache.parquet.tools.metadata.IndexedColumn;
import org.apache.parquet.tools.read.SimpleReadSupport;
import java.io.IOException;
public class ParquetColumnReaderExample {
public static void main(String[] args) {
String parquetFilePath = "path/to/your/parquet/file.parquet";
Configuration configuration = new Configuration();
try (ParquetFileReader reader = ParquetFileReader.open(configuration, new Path(parquetFilePath))) {
IndexedColumn indexedColumn = new IndexedColumn("column1");
int columnIndex = reader.getFileMetaData().getSchema().getPaths().indexOf(indexedColumn);
if (columnIndex >= 0) {
PageReadStore pageReadStore;
while ((pageReadStore = reader.readNextRowGroup()) != null) {
ColumnDescriptor columnDescriptor = reader.getFileMetaData()
.getSchema().getColumns().get(columnIndex);
ColumnReaderImpl columnReader = new ColumnReaderImpl(columnDescriptor,
pageReadStore.getPageReader(columnDescriptor),
new SimpleReadSupport(),
reader.getFilterCompat());
while (columnReader.getCurrentDefinitionLevel() >= columnDescriptor.getMaxDefinitionLevel()) {
if (columnDescriptor.getType() == PrimitiveType.PrimitiveTypeName.BINARY) {
Binary binaryValue = columnReader.getBinary();
String value = binaryValue.toStringUsingUTF8();
System.out.println(value);
}
columnReader.consume();
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
This article introduces how to use the Apache Parquet Column framework in the Java library to implement the data column operation.Through the steps of initialized readers, reading quota data, reading data, and closing the reader, we can easily operate the column data in the ParQuet file.I hope this article will help you understand and use the Apache Parquet Column framework.
