Java验证码生成函数

public void imageSecurityCode(){
		char[]  chars = {'0','1','2','3','4','5','6','7','8','9','a',
						 'b','c','d','e','f','g','h','i','j','k','l',
						 'm','n','o','p','q','r','s','t','u','v','w',
						 'x','y','z','A','B','C','D','E','F','G','H',
						 'I','J','K','L','M','N','O','P','Q','R','S',
						 'T','U','V','W','X','Y','Z'};
		
		//定义图片的宽度以及高度
		int width = 161;
		int height = 50;
		//创建一个图片对象
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
		//得到图片对象的环境对象
		Graphics g = image.createGraphics();
		
		Random random = new Random();
		//用随机颜色填充图像背景
		g.setColor(new Color(239,239,239));
		g.fillRect(0, 0, width, height);
		
		//设置字体，下面准备画随机数
		g.setFont(new Font("", Font.PLAIN, 40));
		//随机字符串
		StringBuilder rand = new StringBuilder();
		for(int i = 0; i < 5; i++){
			//生成六个随机字符
			String str = String.valueOf(chars[random.nextInt(61)]);
			rand.append(str);
			g.setColor(new Color(20 + random.nextInt(80), 20 + random.nextInt(100), 20 + random.nextInt(90)));
			//将随机字符画在图像上
			g.drawString(str, (27 + random.nextInt(3)) * i + 8, 40);
			
			//生成干扰线
			for(int j = 0; j < 12; j++){
				int x = random.nextInt(width);
				int y = random.nextInt(height);
				int x1 = random.nextInt(9);
				int y1 = random.nextInt(9);
				g.drawLine(x, y, x + x1, y + y1);
			}
		}
		
		//使图片生效
		g.dispose();

                //将生成的随机数字符串写入memcached
		CommonSessionFactory.getCommonSession(request, response).setAttribute(CacheConstant.DM_SECURITY_CODE, rand.toString());

                //首先设置页面不缓存
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);

               //输出图片到页面
		try {
			ImageIO.write(image, "jpg", response.getOutputStream());
		} catch (IOException e) {
			e.printStackTrace();
		}