de.akquinet.jbosscc.guttenbase.export.AbstractExportDumpObject Maven / Gradle / Ivy

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package de.akquinet.jbosscc.guttenbase.export;

import org.apache.commons.io.IOUtils;

import java.io.Externalizable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.sql.SQLException;

/**
 * Since CLOBs/BLOBs may be quite big. we do not load them into memory
 * completely, but read them in chunks and write the data to the output stream
 * in a loop.
*
 * 
 * © 2012-2020 akquinet tech@spree
 * 
 *
 * @author M. Dahm
 */
public abstract class AbstractExportDumpObject implements Externalizable
{
  private static final long serialVersionUID = 1L;

  public static final int DEFAULT_BUFFER_SIZE = 1024 * 1024 * 10;
  private transient final InputStream _inputStream;

  private transient File _tempFile;
  private transient FileInputStream _fileInputStream;

  public AbstractExportDumpObject()
  {
    this(null);
  }

  public AbstractExportDumpObject(final InputStream inputStream)
  {
    _inputStream = inputStream;
  }

  /**
   * Read data in chunks and write it to the outputstream to avoid out of memory
   * errors.
   */
  @Override
  public void writeExternal(final ObjectOutput output) throws IOException
  {
    final byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];

    for (int n = _inputStream.read(buffer); n > 0; n = _inputStream.read(buffer))
    {
      byte[] buf = buffer;

      if (n < DEFAULT_BUFFER_SIZE)
      {
        buf = new byte[n];
        System.arraycopy(buffer, 0, buf, 0, n);
      }

      output.writeObject(buf);
      output.flush();
    }

    output.writeObject(null);
  }

  /**
   * Store read data in temporary file to avoid out of memory errors.
   */
  @Override
  public void readExternal(final ObjectInput input) throws IOException, ClassNotFoundException
  {
    if (_tempFile == null)
    {
      _tempFile = File.createTempFile("GB-DUMP-", null);
      _tempFile.deleteOnExit();
    }

    final FileOutputStream fileOutputStream = new FileOutputStream(_tempFile);

    for (byte[] buffer = (byte[]) input.readObject(); buffer != null; buffer = (byte[]) input.readObject())
    {
      fileOutputStream.write(buffer, 0, buffer.length);
    }

    fileOutputStream.close();
  }

  public long length()
  {
    return _tempFile.length();
  }

  public byte[] getBytes(final long pos, final int length) throws SQLException
  {
    try
    {
      final InputStream inputStream = getBinaryStream(pos, length);
      final byte[] bytes = new byte[length];
      inputStream.read(bytes);
      inputStream.close();

      return bytes;
    }
    catch (final IOException e)
    {
      throw new SQLException("getBytes", e);
    }
  }

  public InputStream getBinaryStream() throws SQLException
  {
    return getBinaryStream(0, length());
  }

  public InputStream getBinaryStream(final long pos, @SuppressWarnings("unused") final long length) throws SQLException
  {
    try
    {
      _fileInputStream = new FileInputStream(_tempFile);
      _fileInputStream.skip(pos);
      return _fileInputStream;
    }
    catch (final IOException e)
    {
      throw new SQLException("getBinaryStream", e);
    }
  }

  public final void free()
  {
    if (_tempFile != null && _tempFile.exists())
    {
      _tempFile.delete();
      _tempFile = null;
    }

    if (_fileInputStream != null)
    {
      IOUtils.closeQuietly(_fileInputStream);
      _fileInputStream = null;
    }
  }
}