Java tutorial
/* * 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.parquet.format; import static org.apache.parquet.format.FileMetaData._Fields.CREATED_BY; import static org.apache.parquet.format.FileMetaData._Fields.KEY_VALUE_METADATA; import static org.apache.parquet.format.FileMetaData._Fields.NUM_ROWS; import static org.apache.parquet.format.FileMetaData._Fields.ROW_GROUPS; import static org.apache.parquet.format.FileMetaData._Fields.SCHEMA; import static org.apache.parquet.format.FileMetaData._Fields.VERSION; import static org.apache.parquet.format.event.Consumers.fieldConsumer; import static org.apache.parquet.format.event.Consumers.listElementsOf; import static org.apache.parquet.format.event.Consumers.listOf; import static org.apache.parquet.format.event.Consumers.struct; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.util.List; import org.apache.thrift.TBase; import org.apache.thrift.TException; import org.apache.thrift.protocol.TCompactProtocol; import org.apache.thrift.protocol.TProtocol; import org.apache.thrift.transport.TIOStreamTransport; import org.apache.parquet.format.event.Consumers.Consumer; import org.apache.parquet.format.event.Consumers.DelegatingFieldConsumer; import org.apache.parquet.format.event.EventBasedThriftReader; import org.apache.parquet.format.event.TypedConsumer.I32Consumer; import org.apache.parquet.format.event.TypedConsumer.I64Consumer; import org.apache.parquet.format.event.TypedConsumer.StringConsumer; /** * Utility to read/write metadata * We use the TCompactProtocol to serialize metadata * * @author Julien Le Dem * */ public class Util { public static void writePageHeader(PageHeader pageHeader, OutputStream to) throws IOException { write(pageHeader, to); } public static PageHeader readPageHeader(InputStream from) throws IOException { return read(from, new PageHeader()); } public static void writeFileMetaData(org.apache.parquet.format.FileMetaData fileMetadata, OutputStream to) throws IOException { write(fileMetadata, to); } public static FileMetaData readFileMetaData(InputStream from) throws IOException { return read(from, new FileMetaData()); } /** * reads the meta data from the stream * @param from the stream to read the metadata from * @param skipRowGroups whether row groups should be skipped * @return the resulting metadata * @throws IOException */ public static FileMetaData readFileMetaData(InputStream from, boolean skipRowGroups) throws IOException { FileMetaData md = new FileMetaData(); if (skipRowGroups) { readFileMetaData(from, new DefaultFileMetaDataConsumer(md), skipRowGroups); } else { read(from, md); } return md; } /** * To read metadata in a streaming fashion. * * @author Julien Le Dem * */ public static abstract class FileMetaDataConsumer { abstract public void setVersion(int version); abstract public void setSchema(List<SchemaElement> schema); abstract public void setNumRows(long numRows); abstract public void addRowGroup(RowGroup rowGroup); abstract public void addKeyValueMetaData(KeyValue kv); abstract public void setCreatedBy(String createdBy); } /** * Simple default consumer that sets the fields * * @author Julien Le Dem * */ public static final class DefaultFileMetaDataConsumer extends FileMetaDataConsumer { private final FileMetaData md; public DefaultFileMetaDataConsumer(FileMetaData md) { this.md = md; } @Override public void setVersion(int version) { md.setVersion(version); } @Override public void setSchema(List<SchemaElement> schema) { md.setSchema(schema); } @Override public void setNumRows(long numRows) { md.setNum_rows(numRows); } @Override public void setCreatedBy(String createdBy) { md.setCreated_by(createdBy); } @Override public void addRowGroup(RowGroup rowGroup) { md.addToRow_groups(rowGroup); } @Override public void addKeyValueMetaData(KeyValue kv) { md.addToKey_value_metadata(kv); } } public static void readFileMetaData(InputStream from, FileMetaDataConsumer consumer) throws IOException { readFileMetaData(from, consumer, false); } public static void readFileMetaData(InputStream from, final FileMetaDataConsumer consumer, boolean skipRowGroups) throws IOException { try { DelegatingFieldConsumer eventConsumer = fieldConsumer().onField(VERSION, new I32Consumer() { @Override public void consume(int value) { consumer.setVersion(value); } }).onField(SCHEMA, listOf(SchemaElement.class, new Consumer<List<SchemaElement>>() { @Override public void consume(List<SchemaElement> schema) { consumer.setSchema(schema); } })).onField(NUM_ROWS, new I64Consumer() { @Override public void consume(long value) { consumer.setNumRows(value); } }).onField(KEY_VALUE_METADATA, listElementsOf(struct(KeyValue.class, new Consumer<KeyValue>() { @Override public void consume(KeyValue kv) { consumer.addKeyValueMetaData(kv); } }))).onField(CREATED_BY, new StringConsumer() { @Override public void consume(String value) { consumer.setCreatedBy(value); } }); if (!skipRowGroups) { eventConsumer = eventConsumer.onField(ROW_GROUPS, listElementsOf(struct(RowGroup.class, new Consumer<RowGroup>() { @Override public void consume(RowGroup rowGroup) { consumer.addRowGroup(rowGroup); } }))); } new EventBasedThriftReader(protocol(from)).readStruct(eventConsumer); } catch (TException e) { throw new IOException("can not read FileMetaData: " + e.getMessage(), e); } } private static TProtocol protocol(OutputStream to) { return protocol(new TIOStreamTransport(to)); } private static TProtocol protocol(InputStream from) { return protocol(new TIOStreamTransport(from)); } private static InterningProtocol protocol(TIOStreamTransport t) { return new InterningProtocol(new TCompactProtocol(t)); } private static <T extends TBase<?, ?>> T read(InputStream from, T tbase) throws IOException { try { tbase.read(protocol(from)); return tbase; } catch (TException e) { throw new IOException("can not read " + tbase.getClass() + ": " + e.getMessage(), e); } } private static void write(TBase<?, ?> tbase, OutputStream to) throws IOException { try { tbase.write(protocol(to)); } catch (TException e) { throw new IOException("can not write " + tbase, e); } } }