PRIMEFACES - How to refresh a <p:graphicImage> from clicking a <p:commandButton>?

Question

I'm considering this showcase: http://www.primefaces.org/showcase/ui/dynamicImage.jsf in particular the sub-case "GraphicText on-the-fly".

My problem is implementing an extended version of this sub case with the addition of a . When the button is pressed i need that the image change dinamically.

In the DynamicImageController class I re-writed the getter associeted with the graphicImage:

public StreamedContent getGraphicText(){
     double random = Math.random();// a double value with a positive sign, greater than or equal to 0.0 and less than 1.0.
     if(random>0.5){
         BufferedImage bufferedImg = new BufferedImage(100, 25, BufferedImage.TYPE_INT_RGB);  
         Graphics2D g2 = bufferedImg.createGraphics();  
         g2.drawString("This is a text", 0, 10);  
         ByteArrayOutputStream os = new ByteArrayOutputStream();  
         try {
            ImageIO.write(bufferedImg, "png", os);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }  
         graphicText = new DefaultStreamedContent(new ByteArrayInputStream(os.toByteArray()), "image/png");
     } else {
         BufferedImage bufferedImg = new BufferedImage(100, 25, BufferedImage.TYPE_INT_RGB);  
         Graphics2D g2 = bufferedImg.createGraphics();  
         g2.drawString("This is another text", 0, 10);  
         ByteArrayOutputStream os = new ByteArrayOutputStream();  
         try {
            ImageIO.write(bufferedImg, "png", os);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }  
         graphicText = new DefaultStreamedContent(new ByteArrayInputStream(os.toByteArray()), "image/png");
     }
     return graphicText;
 }

I have this button:

<p:commandButton id="refreshImageButton" value="Refresh image random">
                <p:ajax update=":idForm" />
             </p:commandButton>

and the image:

<p:graphicImage value="#{dynamicImageController.graphicText}" />

idForm is the form id of the form containing my graphicImage and my commandButton

My question is:

Why if I press the F5 button on the keyboard the image change random consistent with the desired behavior in the getGraphicText method ? And why when I press the button the image doesn't change?

Thanks.

ps. my real problem is the integration of jcaptcha in primefaces, my integration is almost termineted, i miss only the refresh button for the captcha image

Answer 1

By default the graphicImage caches the image.
Set the cache attribute to false on your p:graphicImage
Something like this:
<p:graphicImage value="#{dynamicImageController.graphicText}" cache="false" />