JBoss.orgCommunity Documentation

Chapter 4. Resources

4.1. <a4j:mediaOutput>
4.1.1. Basic usage
4.1.2. Handling content
4.1.3. Reference data

This chapter covers those components used to handle and manage resources and beans.

The <a4j:mediaOutput> component is used for generating images, video, sounds, and other resources defined on the fly.

The mimeType attribute describes the type of output content, and corresponds to the type in the header of the HTTP request. The element attribute defines XHTML element used to display the content:

Example 4.1. <a4j:mediaOutput> example

This example uses the <a4j:mediaOutput> component to generate a JPEG image of verification digits. The code on the application page is a single element:

<a4j:mediaOutput element="img" cacheable="false" session="false"
                 createContent="#{mediaBean.paint}" value="#{mediaData}" 
                 mimeType="image/jpeg" />

The <a4j:mediaOutput> component uses the MediaBean.paint method to create the image. The method generates a random number, which is then converted into an output stream and rendered to a JPEG image. The MediaBean class is as follows:

package demo;

import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;
import javax.imageio.ImageIO;
public class MediaBean {
    public void paint(OutputStream out, Object data) throws IOException {
        Integer high = 9999;
        Integer low = 1000;
        Random generator = new Random();
        Integer digits = generator.nextInt(high - low + 1) + low;
        if (data instanceof MediaData) {            
            MediaData paintData = (MediaData) data;
            BufferedImage img = new BufferedImage(paintData.getWidth(),paintData.getHeight(),BufferedImage.TYPE_INT_RGB);
            Graphics2D graphics2D = img.createGraphics();
            graphics2D.drawString(digits.toString(), 20, 35);

Another class, MediaData is required by the value attribute for keeping data to be used as input for the content creation method. The MediaData class is as follows:

package demo;

import java.awt.Color;
import java.awt.Font;
import java.io.Serializable;
public class MediaData implements Serializable {
    private static final long serialVersionUID = 1L;
    Integer Width=110;
    Integer Height=50;
    Color Background=new Color(190, 214, 248);
    Color DrawColor=new Color(0,0,0);
    Font font = new Font("Serif", Font.TRUETYPE_FONT, 30);
    /* Corresponding getters and setters */

The <a4j:mediaOutput> component uses the MediaBean and MediaData classes to generate a new image on each page refresh.

Serializable interface

A bean class passed using the value attribute of <a4j:mediaOutput> should implement the Serializable interface so that it will be encoded to the URL of the resource.