如何将java.sql.Blob写入JPA实体？

Question

I have a JPA entity with java.sql.Blob:

@Entity
public class LargeData {

  @Lob
  private java.sql.Blob data;

  //getters/setters
}

How to create instance of this entity? I want to set Blob with setData() method, but how to get Blob from JPA? java.sql.Blob is only interface, there are different implementations for different databases, so I assume JPA should give me right implementation. How to get it?

Answer 1

Use a byte array:

@Lob
@Column(length=100000)
private byte[] data;

If you want to use streams, create the blob using Hibernate.createBlob(..)

Answer 2

use a file stream. However, this appears to have various complications, depending on your database, driver, and JPA implementation. I built a generic solution, that was slow, and failed with large files, then found a Hibernate-specific solution that worked with Oracle 11.2.0.4

I'm using Spring Data / JPA, but the issue seems to be around Hibernate, not Spring.

Hibernate:

private void testLoadFile() throws SQLException, IOException {


  File f = new File("//C:/tmp/6mb_file.wmv");
  BufferedInputStream fstream = new BufferedInputStream(new FileInputStream(f));

  Session session = entityManager.unwrap(Session.class);
  Blob blob = Hibernate.getLobCreator(session).createBlob(fstream, f.length());

  FileBLOBEntity file = new FileBLOBEntity();

  file.setName("//C:/tmp/6mb_file.wmv");
  file.setTheData(blob);
  blobRepository.saveAndFlush(file);
}

Generic Spring/JPA:

private void testLoadFile() throws SQLException, IOException {

  File f = new File("//C:/tmp/6mb_file.wmv");
  BufferedInputStream fstream = new BufferedInputStream(new FileInputStream(f));

  Blob blob = connection.getConnection().createBlob();
  BufferedOutputStream bstream = new  BufferedOutputStream(blob.setBinaryStream(1));
  // stream copy runs a high-speed upload across the network
  StreamUtils.copy(fstream, bstream);

  FileBLOBEntity file = new FileBLOBEntity();

  file.setName("//C:/tmp/6mb_file.wmv");
  file.setTheData(blob);
  // save runs a low-speed download across the network.  this is where
  // Spring does the SQL insert.  For a large file, I get an OutOfMemory exception here.
  blobRepository.saveAndFlush(file);
}

and for retrieval:

public void unloadFile() throws SQLException, IOException {

  File f = new File("//C:/tmp/6mb_file.wmv" + "_fromDb");

  FileOutputStream fstream = new FileOutputStream(f);

  FileBLOBEntity file = blobRepository.findByName("//C:/tmp/6mb_file.wmv");
  Blob data = file.getTheData();

  InputStream bstream = data.getBinaryStream();
  StreamUtils.copy(bstream, fstream);

}