How do I extract a BLOB from a database?
Created Nov 29, 1999
Lennart Jorelid
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
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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); } } |
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