Easiest way to convert a Blob into a byte array

Question

what is the easiest way to convert a Blob into a byte array?I am using MYSQL and i want to convert a Blob datatype into a byte array.

Iam using java programming language:)

Francophile

Answer 1

the mySql blob class has the following function :

blob.getBytes

use it like this:

//(assuming you have a ResultSet named RS)
Blob blob = rs.getBlob("SomeDatabaseField");

int blobLength = (int) blob.length();  
byte[] blobAsBytes = blob.getBytes(1, blobLength);

//release the blob and free up memory. (since JDBC 4.0)
blob.free();

Ogham

Thanks,actually blob is not having getbytes() method,only serialblob is having getbytes() method.How to do it for blob. – Francophile

are you using java.sql.Blob? – Ogham

this method gives a Lob is closed exception... what do I do ? – Scribbler

@AnuShibinJosephRaj i think you should post a full question on SO with an example of your code attached. – Ogham

is it a good way to just convert a blob in binary and send via httpclient post request? – Yakka

@Yakka that depends entirely on your situation. what i can tell you in advance is that it won't be very fast.. – Ogham

Answer 2

The easiest way is this.

byte[] bytes = resultSet.getBytes("my_field");

Cisterna

Excuse me, but I really I have not understood what rs is. – Beefburger

@MarcoSulla: A JDBC ResultSet – Cisterna

I believe this answer is valid only when the field is less than 1048576 bytes. – Illustrational

@AJ.P: This depends on the SQL dialect. In many dialects, there is no such restriction. – Cisterna

Answer 3

You can also get bytes array from Blob instance by this way:

Blob myBlob = null;
byte[] bytes = myBlob.getBinaryStream().readAllBytes();

Enrobe