Hibernate version:
3.0.5

Name and version of the database you are using:
MySQL

hey guys!
i would like to store images to a database using Hibernate.

can you give me any clues on how to do that?
is java.awt.Image suitable or should i use anything else?

thanks a lot in advance!

Use a BLOB would be the most common method. Or store the file on the file system and use a string as a reference to the file. When wondering a question like that, think this "how would the data be stored in the db?", if you can't think of a variable type then you probably can't do it.

thanks for your answer!

i tried the "blob" approach, but my main problem lies in how the
image should be serialized at all.
java.awt.image is does not implement "serializable", so what's the way to tell hibernate how to serialize the object to the database?

i get the following exception when i try to store the object:

----

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: sun.awt.image.ToolkitImage
at org.hibernate.type.SerializableType.toBytes(SerializableType.java:74)
at org.hibernate.type.SerializableType.deepCopyNotNull(SerializableType.java:70)
at org.hibernate.type.MutableType.deepCopy(MutableType.java:25)
at org.hibernate.type.TypeFactory.deepCopy(TypeFactory.java:290)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:227)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:160)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:108)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:184)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:173)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:96)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:69)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:468)
at org.hibernate.engine.Cascades$5.cascade(Cascades.java:154)
at org.hibernate.engine.Cascades.cascadeAssociation(Cascades.java:771)
at org.hibernate.engine.Cascades.cascade(Cascades.java:720)
at org.hibernate.engine.Cascades.cascadeCollection(Cascades.java:895)
at org.hibernate.engine.Cascades.cascadeAssociation(Cascades.java:792)
at org.hibernate.engine.Cascades.cascade(Cascades.java:720)
at org.hibernate.engine.Cascades.cascade(Cascades.java:847)
at org.hibernate.event.def.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:363)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:265)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:160)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:108)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:184)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:173)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:96)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:69)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:468)
at org.hibernate.engine.Cascades$5.cascade(Cascades.java:154)
at org.hibernate.engine.Cascades.cascadeAssociation(Cascades.java:771)
at org.hibernate.engine.Cascades.cascade(Cascades.java:720)
at org.hibernate.engine.Cascades.cascadeCollection(Cascades.java:895)
at org.hibernate.engine.Cascades.cascadeAssociation(Cascades.java:792)
at org.hibernate.engine.Cascades.cascade(Cascades.java:720)
at org.hibernate.engine.Cascades.cascade(Cascades.java:847)
at org.hibernate.event.def.AbstractFlushingEventListener.cascadeOnFlush(AbstractFlushingEventListener.java:121)
at org.hibernate.event.def.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:112)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:59)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:26)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:730)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:324)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:86)
at net.bitalchemy.omnitheca.persistence.StorageTools.save(StorageTools.java:19)
at .....

Then you're main problem is to work out how to convert java.awt.image to a blob. Logic would dictate that at some point the image was in a format that could be read i.e. JPEG, so you need to find your orignal image and convert it to a byte stream.

These sample methods may give some idea about conversion to byte[] and vice-versa.

private byte[] getImage(String imagePath)
{
try
{
//obtain a writer
Iterator writers = ImageIO.getImageWritersByFormatName("png");
ImageWriter writer = (ImageWriter)writers.next();

//set destination for writer
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageOutputStream ios = ImageIO.createImageOutputStream(baos);
writer.setOutput(ios);

//get the image e.g. "C:\\Work\\eclipseworkspace\\TestProject\\icons\\RedRectangle.png"
File file = new File(imagePath);
BufferedImage bi = ImageIO.read(file);

//write the image
writer.write(bi);

//convert to byte array
return baos.toByteArray();
}
catch(Exception e)
{
e.printStackTrace();
}
return null;
}

private Image getImage(byte[] bytes)
{
try
{
//set a byte stream reader
ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
ImageInputStream iis = ImageIO.createImageInputStream(bais);

//convert to image
BufferedImage bi = ImageIO.read(iis);

return bi;
}
catch(Exception e)
{
e.printStackTrace();
}
return null;
}

thanks ndzpac!
that's very helpful.

i wonder if i should write a custom serializer for java.awt.Image
or just have my persistable class return a byte array in
"getImage".

first approach would be:
class MyClass {
private Image img;
public Image getImage() {
//return the Image object
}
//....
}
like this, the class is very clean and easy to use, but i have to write
some custom serializer and tell hibernate it should use that custom
serializer for the "img" property in my class.
(how to do that???)


second approach:
class MyClass {
private Image img;
public byte[] getImage() {
//return the byte array of the Image
}
//....
}


do you have experience with custom serializers in hibernate?

I don’t think that you have to do some custom serialization to store image in database.

If you want to store an image, just you have to do is

POJO:

class MyClass
{
private Object image;
.....


MAPPING file:
In hibernate mapping file set type to binary or blob for this field

<property
name="image"
column="IMAGE"
type="binary"



So when you want to store:

MyClass obj = new MyClass ();
byte[] imageBytes = getImage("somepathforimage");
obj.setImage(imageBytes);
.....
session.save(obj);

And after retrieving the object from database you can convert into image object:

Image image = getImage((byte[]) obj.getImage());


HTH

i got it working!
can now serialize a byte[] to mysql!

next problem:
in my mapping file i have
<property name="media" column="media_blob" type="binary"/>

which hibernate translates into a "blob" column for mysql.
sadly, a mysql "blob" can only hold 255 bytes.
i need a "medium_blob" which would be 16MB.

how do i tell hibernate to use a bigger blob variant?

thanks in advance

ok, i found it out by myself.
for anyone who gets to that thread in the future:
set the "length" attribute of the property to sth.
that requires a bigger type of blob.

for mysql 4.1 eg, when you say 'type="java.sql.Blob"'
in the mapping file, you will get a "blob" in the database, which
is 65 k.
if you want sth. bigger do
<property name="media" column="media_blob" type="java.sql.Blob" length="65538"/>

and you will get a "mediumblob" in the DB which can hold 16 MB.