输出随机图片

输出随机图片(CAPTCHA图像):Completely Automated Public Turing Test to Tell Computers and Humans Apart (全自动区分计算机和人类的测试) 
相关主要类(JDK 查看API)
BufferedImage:内存图像
Graphics：画笔
ImageIO：输出图像
放在html页面上<img src/>

注意：浏览器默认会缓存图片

        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());
		
	}