content: /**
   * 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.apex.malhar.contrib.parquet;
  
  import java.io.IOException;
  import java.io.InputStream;
  
  import org.apache.apex.malhar.lib.io.fs.AbstractFileInputOperator;
  import org.apache.hadoop.classification.InterfaceStability;
  import org.apache.hadoop.fs.Path;
  import org.apache.parquet.example.data.Group;
  import org.apache.parquet.hadoop.ParquetReader;
  import org.apache.parquet.hadoop.example.GroupReadSupport;
  import org.apache.parquet.schema.MessageType;
  import org.apache.parquet.schema.MessageTypeParser;
  
  import com.datatorrent.api.Context.OperatorContext;
  
  /**
   * Base implementation of ParquetFileReader. Reads Parquet files from input
   * directory using GroupReadSupport. Derived classes need to implement
   * {@link #convertGroup(Group)} method to convert Group to other type. Example
   * of such implementation is {@link ParquetFilePOJOReader} that converts Group
   * to POJO.
   *
   * @since 3.4.0
   */
  @InterfaceStability.Evolving
  public abstract class AbstractParquetFileReader<T> extends AbstractFileInputOperator<T>
  {
    private transient ParquetReader<Group> reader;
    protected transient MessageType schema;
    /**
     * Parquet Schema as a string. E.g: message
     * org.apache.apex.malhar.contrib.parquet.eventsEventRecord {required INT32
     * event_id;required BINARY org_id (UTF8);required INT64 long_id;optional
     * BOOLEAN css_file_loaded;optional FLOAT float_val;optional DOUBLE
     * double_val;}
     */
    protected String parquetSchema;
  
    @Override
    public void setup(OperatorContext context)
    {
      super.setup(context);
      schema = MessageTypeParser.parseMessageType(parquetSchema);
    }
  
    /**
     * Opens the file to read using GroupReadSupport
     */
    @Override
    protected InputStream openFile(Path path) throws IOException
    {
      InputStream is = super.openFile(path);
      GroupReadSupport readSupport = new GroupReadSupport();
      readSupport.init(configuration, null, schema);
      reader = new ParquetReader<>(path, readSupport);
      return is;
    }
  
    /**
     * Reads next record in parquet file as a group. Returns null when end of file
     * is reached
     */
    @Override
    protected T readEntity() throws IOException
    {
      Group group = reader.read();
      if (group != null) {
        return convertGroup(group);
      }
      return null;
    }
  
    /**
     * Derived classes need to provide an implementation to convert a Parquet
     * Group to any other type. Each Parquet record is read as a <b>Group</b>
     * (parquet.example.data.Group) and is passed onto this method.
     *
     * @param group
     *          Parquet record represented as a Group
     * @return object of type T
     */
    protected abstract T convertGroup(Group group);
  
    /**
     * Get Parquet Schema as a String
     *
     * @return parquetSchema Parquet Schema as a string.
     */
    public String getParquetSchema()
    {
      return parquetSchema;
    }
  
    /**
     * Set Parquet Schema as a String
     *
     * @param parquetSchema
     *          Parquet Schema as a string
     */
    public void setParquetSchema(String parquetSchema)
    {
      this.parquetSchema = parquetSchema;
    }
  
  }
  