How to Generate Images as Response
You can use the Java 2D API to create images dynamically, encode them as PNG or JPEG and send them to the client. The following servlet draws a simple clock with the current time and sends it as response:
import java.awt.*;
import java.awt.image.*;
import javax.imageio.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
// Servlet that draws a clock
public class ClockServlet extends HttpServlet {
// create the image
private BufferedImage createClockImage() {
GregorianCalendar cal = new GregorianCalendar();
BufferedImage img = new BufferedImage(400, 400, BufferedImage.TYPE_3BYTE_BGR);
Graphics2D g = img.createGraphics();
// white background
g.setColor(Color.WHITE);
g.fillRect(0, 0, 400, 400);
// draw black circle around clock
g.setColor(Color.BLACK);
g.setStroke(new BasicStroke(5));
g.drawOval(20, 20, 360, 360);
// draw hour hand
double hourRad = cal.get(Calendar.HOUR) * 2 * Math.PI / 12 - 0.5 * Math.PI;
g.drawLine(200, 200, 200 + (int) (100 * Math.cos(hourRad)),
200 + (int) (100 * Math.sin(hourRad)));
// draw minute hand
double minuteRad = cal.get(Calendar.MINUTE) * 2 * Math.PI / 60 - 0.5 * Math.PI;
g.drawLine(200, 200, 200 + (int) (170 * Math.cos(minuteRad)),
200 + (int) (170 * Math.sin(minuteRad)));
return img;
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException {
response.setContentType("image/png");
OutputStream os = response.getOutputStream();
ImageIO.write(createClockImage(), "PNG", os); // write image as PNG (more)
}
}
