convert object to blob (java.lang.ClassCastException: [B cannot be cast to java.sql.Blob)

Question

when I try to convert Oject into blob using (Blob), getting that java.lang.ClassCastException: [B cannot be cast to java.sql.Blob error.

but when I try to convert using the following code and write as an image file, gets the image corrupted.

Blob blob = null;

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutput out = null;
        try {
          out = new ObjectOutputStream(bos);   
          out.writeObject(myObj);

          byte[] yourBytes = bos.toByteArray();

          //blob.setBytes(1, yourBytes );
          blob = new SerialBlob(yourBytes);
        } finally {
          out.close();
          bos.close();
        }

How can I safely convert object (which is an image file saved as Blob) to Blob?

NOTE: due to requirement, I can only get as Object passing from other part.

Your question is very unclear. If the object you are trying to save is already a blob then why are you trying to convert it again? Are you sure your object isn't a buffered image? — Perception
– Perception, Commented Apr 4, 2013 at 3:42
first, the image is saved as blob in DB. when get from DB, the other method return me as an object , not as a blob. — kitokid
– kitokid, Commented Apr 4, 2013 at 3:45
To find out what class of the object being returned just do a System.out.println(obj.getClass()). Add the result of the printout to your question. — Perception
– Perception, Commented Apr 4, 2013 at 3:50
So your method is not returning a Blob, its returning an array of bytes. Which you can actually convert directly into a Blob, via its constructor. — Perception
– Perception, Commented Apr 4, 2013 at 3:59

VKPRO · Accepted Answer · 2013-04-04 04:39:05Z

1

You can use

If you are using hibernate

      Blob blob = Hibernate.createBlob(bytes, session);

If you are using JDBC

       Blob blob = connection.createBlob();
       blob.setBytes(1, bytes);

edited Apr 4, 2013 at 4:39

answered Apr 4, 2013 at 4:34

VKPRO

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Comments

Thihara · Accepted Answer · 2013-04-04 03:43:48Z

0

Because of the class cast exception you are receiving I'm going to go out on a limb here and say you are not actually getting a Blob from that end.

Do a debug and see what type is actually being sent.

And I may be wrong but as far as I know Clobs and Blobs are not serializable... So if the other side is a network, it will be kaboom...

answered Apr 4, 2013 at 3:43

Thihara

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Tirath · Accepted Answer · 2016-09-05 10:00:52Z

Not sure how relevant my answer is but have used the above answers as hint to arrive at this.

Using - below dependency

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>5.1.0.Final</version>
</dependency>

Property in model class was defined as -

java.sql.Blob message;

In mymodel.hbm.xml file inside a valid model mapping

<class name="packagepath.Pojo" table="pojotableindb">
<meta attribute="class-description">
     Pojo class is mapped to pojotableindb table
  </meta>
    <id name="id" column="ID" type="long">
    <!-- for auto increment -->
        <generator class="identity" />
    </id>
    <property name="message" column="MESSAGE" type="blob" />
</class>

Now, inside one of my DAO method I did something as below to insert a value in MESSAGE column -

Pojo pojo = new Pojo();
pojo.setMessageId(uuid);
//message is the string argument this DAO method receives         
activityTrack.setMessage(Hibernate.getLobCreator(session).createBlob(message.getBytes())); 

tx = session.beginTransaction();
session.save(pojo);
tx.commit();

Hoping this will help someone.

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