compiler/frontend/spark/src/main/java/org/apache/nemo/compiler/frontend/spark/transform/HDFSTextFileTransform.java

/*
 * 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.nemo.compiler.frontend.spark.transform;

import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.mapred.JobConf;
import org.apache.nemo.common.ir.OutputCollector;
import org.apache.nemo.common.ir.vertex.transform.NoWatermarkEmitTransform;
import org.apache.nemo.common.ir.vertex.transform.Transform;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

/**
 * Transform which saves elements to a HDFS text file for Spark.
 *
 * @param <I> input type.
 */
public final class HDFSTextFileTransform<I> extends NoWatermarkEmitTransform<I, String> {
  private final String path;
  private Path fileName;
  private List<I> elements;

  /**
   * Constructor.
   *
   * @param path the path to write elements.
   */
  public HDFSTextFileTransform(final String path) {
    this.path = path;
  }

  @Override
  public void prepare(final Transform.Context context, final OutputCollector<String> outputCollector) {
    fileName = new Path(path + UUID.randomUUID().toString());
    this.elements = new ArrayList<>();
  }

  @Override
  public void onData(final I element) {
    elements.add(element);
  }

  @Override
  public void close() {
    try (
      final FileSystem fileSystem = fileName.getFileSystem(new JobConf());
      final FSDataOutputStream outputStream = fileSystem.create(fileName, false);
    ) {
      for (final I element : elements) {
        outputStream.writeBytes(element + "\n");
      }
      outputStream.close();
    } catch (final IOException e) {
      throw new RuntimeException(e);
    }
  }
}