How to generate Image at server side in java [ blob-> string_image -> *.png or .jpg ]

Question

I want to generate an image on server side. My image is stored in a server database in blob format and I am able to convert it into string_image. Then how can I convert that string_image into actual .jpg or .png format?

Actually I am posting attachment as image on users facebook wall. How to generate the image at server side in Java? Is there any sample code to do it?

Answer 1

If you have the image in Blob format then you're best bet it to use ImageIO and read the blob input stream directly.

This will give you a java.awt.BufferedImage object which you can then render to any type of image using ImageIO. As an OutputStream, you can return that as a body/result from a HTTP GET controller.

BufferedImage image = ImageIO.read( blob.getInputStream() );
// Feel free to modify the image here using image.createGraphics()
// add a water mark if you're feeling adventurous
byte[] responseBody = toByteArray( image, "png" );

....    
protected byte[] toByteArray(BufferedImage image, String type) throws IOException {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ImageIO.write(image, type, baos);
    return baos.toByteArray();
}

I'm not intimately familiar with how facebook uses images. I think it differs depending on what you're doing. For facebook applications, I think you're still responsible for hosting the image, but facebook will act as a caching proxy and request the image just once, then serve it to all the client that need to see it. If it's a user posted image, then I think facebook stores the image completely (obviously a user uploading a picture does not have it on another server usually).

If you're looking to just display the image "as is" in response to aa web request, then you can pipe the output of the Blob directly the client, although this keeps database connections open for a while, you might be better copying to a disk cache then serving to the client.

I have to confess, I couldn't find anything useful about what a stirng_image actually is? Perhaps you could clarify if this answer doesn't meet your needs.