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

Accepted Answer

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.

Read/write blob data in chunks with Hibernate

Solution

Problem