A sample servlet that dynamically creates images

This is a sample servlet that dynamically generates JPEG images. Currently all image properties are hard-coded, but it should be trivial to provide a jsp form to collect them (e.g., color, font, dimensions, messages). The generated image contains dynamic data such as the appserver name, and OS name.

package javahowto;

import com.sun.image.codec.jpeg.JPEGCodec;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.*;
import javax.servlet.http.*;
import javax.servlet.*;

public class ImageServlet extends HttpServlet {
private static final int WIDTH = 450;
private static final int HEIGHT = 200;
private static final Color BACKGROUND_COLOR = new Color(100,149,237);
private static final Color COLOR = new Color(0,0,139);
private static final Font FONT = new Font("Times New Roman", Font.BOLD, 46);
private static final Font FOOT_FONT = new Font("Courier", Font.ITALIC, 14);
private static final Color FOOT_COLOR = Color.BLACK;

@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
   response.setContentType("image/jpg");
   ServletOutputStream out = response.getOutputStream();
   BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_BYTE_INDEXED);
   Graphics graphics = image.getGraphics();
   graphics.setColor(BACKGROUND_COLOR);
   graphics.fillRect(0, 0, image.getWidth(), image.getHeight());
   graphics.setColor(COLOR);
   graphics.setFont(FONT);
   graphics.drawString("Hello World!", 10, HEIGHT/2);
   graphics.setFont(FOOT_FONT);
   graphics.setColor(FOOT_COLOR);
   graphics.drawString("Created by " + getServletContext().getServerInfo(), 10, HEIGHT - 30);
   graphics.drawString("for http://javahowto.blogspot.com/ on " + System.getProperty("os.name"), 10, HEIGHT - 10);
   JPEGCodec.createJPEGEncoder(out).encode(image);
}
}

The web.xml file is as simple as declaring and mapping a servlet:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<servlet>
   <servlet-name>image</servlet-name>
   <servlet-class>javahowto.ImageServlet</servlet-class>
</servlet>
<servlet-mapping>
   <servlet-name>image</servlet-name>
   <url-pattern>/</url-pattern>
</servlet-mapping>
</web-app>

Build the project and deploy the image.war to any web server or appserver. Enter the URL http://localhost:8080/image/ to view the generated image. Here we are using the .war file base name as the default context-root and a / servlet path. I tested it on Glassfish v2 update 1, Tomcat 6, and JBoss-5.0.0.Beta4 successfully, except some redeployment errors on JBoss, which was resolved by deleting the .war and restarting server.

If the appserver is running on a headless server, you may need to set the system property java.awt.headless to true. Also note that a Sun-specific encoder class (com.sun.image.codec.jpeg.JPEGCodec) is used. It is in rt.jar of Sun's JDK, but may not be available in other vendors' JDK like IBM's JDK or BEA's (now Oracle's) JRockit. If a non-Sun Java is used, you will need to use the appropriate encoder class. Unfortunately, there seems to be no portable JPEG encoder class as of JDK 6.