Read/write blob data in chunks with Hibernate

Question

Is there a way to read and write from a blob in chunks using Hibernate. Right now I am getting OutOfmemoryException because the whole blob data is loaded in memory into a byte[].

To be more specific, let's say I want to save a large file into a database table called File.

public class File {
   private byte[] data;
}

I open the file in a FileInputStream and then what? How do I tell Hibernate that I need to stream the content and will not give the whole byte[] array at once? Should I use Blob instead of byte[]? Anyway how can I stream the content?

Regarding reading, is there a way I can tell hibernate that (besides the lazy loading it does) I need the blob to be loaded in chunks, so when I retrieve my File it should not give me OutOfMemoryException.

I am using:

• Oracle 11.2.0.3.0
• Hibernate 4.2.3 Final
• Oracle Driver 11.2

Answer 1

If going the Blob route, have you tried using Hibernate's LobHelper createBlob method, which takes an InputStream? To create a Blob and persist to the database, you would supply the FileInputStream object and the number of bytes.

Your File bean/entity class could map the Blob like this (using JPA annotations):

@Lob
@Column(name = "DATA")
private Blob data;

// Getter and setter

And the business logic/data access class could create the Blob for your bean/entity object like this, taking care not to close the input stream before persisting to the database:

FileInputStream fis = new FileInputStream(file);
Blob data = getSession().getLobHelper().createBlob(fis, file.length());
fileEntity.setData(data);
// Persist file entity object to database

To go the other way and read the Blob from the database as a stream in chunks, you could call the Blob's getBinaryStream method, giving you the InputStream and allowing you to set the buffer size later if needed:

InputStream is = fileEntity.getData().getBinaryStream();

Struts 2 has a convenient configuration available that can set the InputStream result's buffer size.