EJB-Blob Clobs

When working with a database, it is often necessary to store large files such as images, videos, and documents. Blobs (Binary Large Objects) and Clobs (Character Large Objects) are types of data that can be used to store such files.

Enterprise JavaBeans (EJB) is a specification for developing large-scale, distributed applications in Java. It includes support for working with Blobs and Clobs, making it a useful tool for creating applications that involve large files.

To work with Blobs and Clobs in EJB, there are a few things you need to know.

Creating a Blob/Clob

To create a Blob or Clob, you can use the createBlob() or createClob() methods provided by the JDBC Connection object. For example, to create a Blob:

Connection conn = dataSource.getConnection();
Blob myBlob = conn.createBlob();

Reading and Writing Blob/Clob Data

Once you have a Blob or Clob object, you can read data from it or write data to it. To read data, you can use the getBinaryStream() or getCharacterStream() methods, respectively. For example, to read the contents of a Blob into a byte array:

byte[] data = myBlob.getBytes(1, (int) myBlob.length());

To write data to a Blob or Clob, you can use the setBinaryStream() or setCharacterStream() methods, respectively. For example, to write a byte array to a Blob:

OutputStream out = myBlob.setBinaryStream(1);
out.write(data);
out.close();

Using Blobs and Clobs with EJB

To use Blobs and Clobs in a EJB application, you can create entity beans to represent the data in the database. For example, to create an entity bean to represent an image:

@Entity
public class ImageEntity {
    @Id
    private int id;
    @Lob
    private Blob data;
 
    // getters and setters
}

In this example, the @Lob annotation is used to indicate that the data field should be stored as a Blob in the database.

Conclusion

Blobs and Clobs are a powerful tool for working with large files in a database. With support for Blobs and Clobs in EJB, it is easy to create applications that can handle even the largest files. With this guide, you should be well on your way to using Blobs and Clobs in your own EJB applications.