Question - How Do I Extract A Blob From A Database?
Answer -
A BLOB (Binary Large OBject) is essentially an array of bytes (byte[]), stored in the database. You extract the data in two steps:
Call the getBlob method of the Statement class to retrieve a java.sql.Blob object.
Call either getBinaryStream or getBytes in the extracted Blob object to retrieve the java byte[] which is the Blob object.
Note that a Blob is essentially a pointer to a byte array (called LOCATOR in database-talk), so the java.sql.Blob object essentially wraps a byte pointer. Thus, you must extract all data from the database blob before calling commit or
private void runGetBLOB()
{
try
{ // Prepare a Statement:
PreparedStatement stmnt = conn.prepareStatement("select aBlob from BlobTable");
// Execute
ResultSet rs = stmnt.executeQuery();
while(rs.next())
{
try
{
// Get as a BLOB
Blob aBlob = rs.getBlob(1);
byte[] allBytesInBlob = aBlob.getBytes(1, (int) aBlob.length());
}
catch(Exception ex)
{
// The driver could not handle this as a BLOB...
// Fallback to default (and slower) byte[] handling
byte[] bytes = rs.getBytes(1);
}
}
// Close resources
rs.close();
stmnt.close();
}
catch(Exception ex)
{
this.log("Error when trying to read BLOB: " + ex);
}
}