org.apache.parquet.hadoop.metadata.GlobalMetaData Maven / Gradle / Ivy
/*
* 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.hadoop.metadata;
import static java.util.Collections.unmodifiableMap;
import static org.apache.parquet.Preconditions.checkNotNull;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import org.apache.parquet.schema.MessageType;
/**
* Merged metadata when reading from multiple files.
* THis is to allow schema evolution
*/
public class GlobalMetaData implements Serializable {
private static final long serialVersionUID = 1L;
private final MessageType schema;
private final Map> keyValueMetaData;
private final Set createdBy;
/**
* @param schema the union of the schemas for all the files
* @param keyValueMetaData the merged app specific metadata
* @param createdBy the description of the library that created the file
*/
public GlobalMetaData(MessageType schema, Map> keyValueMetaData, Set createdBy) {
super();
this.schema = checkNotNull(schema, "schema");
this.keyValueMetaData = unmodifiableMap(checkNotNull(keyValueMetaData, "keyValueMetaData"));
this.createdBy = createdBy;
}
/**
* @return the schema for the file
*/
public MessageType getSchema() {
return schema;
}
@Override
public String toString() {
return "GlobalMetaData{schema: "+schema+ ", metadata: " + keyValueMetaData + "}";
}
/**
* @return meta data for extensions
*/
public Map> getKeyValueMetaData() {
return keyValueMetaData;
}
/**
* @return the description of the library that created the file
*/
public Set getCreatedBy() {
return createdBy;
}
/**
* Will merge the metadata as if it was coming from a single file.
* (for all part files written together this will always work)
* If there are conflicting values an exception will be thrown
* @return the merged version of this
*/
public FileMetaData merge() {
String createdByString = createdBy.size() == 1 ?
createdBy.iterator().next() :
createdBy.toString();
Map mergedKeyValues = new HashMap();
for (Entry> entry : keyValueMetaData.entrySet()) {
if (entry.getValue().size() > 1) {
throw new RuntimeException("could not merge metadata: key " + entry.getKey() + " has conflicting values: " + entry.getValue());
}
mergedKeyValues.put(entry.getKey(), entry.getValue().iterator().next());
}
return new FileMetaData(schema, mergedKeyValues, createdByString);
}
}