public static int WIDTH = 120; 
public static int HEIGHT = 25; 
 
public void doGet(HttpServletRequest request, HttpServletResponse response) 
    throws ServletException, IOException { 
 
  response.setContentType("text/html"); 
  //创建内存图像 
  BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB); 
  //勾勒图像 
  Graphics graphics = image.getGraphics(); 
  //设置背景 
  graphics.setColor(Color.WHITE); 
  graphics.fillRect(0, 0, WIDTH, HEIGHT); 
  //设置边框 
  graphics.setColor(Color.BLUE); 
  graphics.drawRect(1, 1, WIDTH-2, HEIGHT-2); 
  //画干扰线 
  graphics.setColor(Color.YELLOW); 
  for(int i=0;i<8;i++){ 
    int xStart = new Random().nextInt(WIDTH); 
    int yStart = new Random().nextInt(HEIGHT); 
    int xEnd = new Random().nextInt(WIDTH); 
    int yEnd = new Random().nextInt(HEIGHT); 
    graphics.drawLine(xStart, yStart, xEnd, yEnd); 
  } 
  //写随机数 
  graphics.setColor(Color.RED); 
  int x = 5; 
  for(int i=0;i<4;i++){ 
    graphics.drawString(new Random().nextInt(9)+"", x, 20); 
    x+=30; 
  } 
  response.setContentType("image/jpeg");//设置响应格式 
  ImageIO.write(image, "jpeg", response.getOutputStream()); 
   
}