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?
Use a byte array:
@Lob
@Column(length=100000)
private byte[] data;
If you want to use streams, create the blob using Hibernate.createBlob(..)
length attribute. I also use java nio to read from a file : myEntity.data = Files.readAllBytes(myPath).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);
}
