tools/src/main/java/org/apache/arrow/tools/StreamToFile.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.arrow.tools;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.channels.Channels;
import org.apache.arrow.compression.CommonsCompressionFactory;
import org.apache.arrow.memory.BufferAllocator;
import org.apache.arrow.memory.RootAllocator;
import org.apache.arrow.vector.VectorSchemaRoot;
import org.apache.arrow.vector.ipc.ArrowFileWriter;
import org.apache.arrow.vector.ipc.ArrowStreamReader;

/** Converts an Arrow stream to an Arrow file. */
public class StreamToFile {
  /** Reads an Arrow stream from <code>in</code> and writes it to <code>out</code>. */
  public static void convert(InputStream in, OutputStream out) throws IOException {
    BufferAllocator allocator = new RootAllocator(Integer.MAX_VALUE);
    try (ArrowStreamReader reader =
        new ArrowStreamReader(in, allocator, CommonsCompressionFactory.INSTANCE)) {
      VectorSchemaRoot root = reader.getVectorSchemaRoot();
      // load the first batch before instantiating the writer so that we have any dictionaries.
      // Only writeBatches if we load the first one.
      boolean writeBatches = reader.loadNextBatch();
      try (ArrowFileWriter writer = new ArrowFileWriter(root, reader, Channels.newChannel(out))) {
        writer.start();
        while (writeBatches) {
          writer.writeBatch();
          if (!reader.loadNextBatch()) {
            break;
          }
        }
        writer.end();
      }
    }
  }

  /**
   * Main method. Defaults to reading from standard in and standard out. If there are two arguments
   * the first is interpreted as the input file path, the second is the output file path.
   */
  public static void main(String[] args) throws IOException {
    InputStream in = System.in;
    OutputStream out = System.out;
    if (args.length == 2) {
      in = new FileInputStream(new File(args[0]));
      out = new FileOutputStream(new File(args[1]));
    }
    convert(in, out);
  }
}