public class RandomValidateCode {
  public static final String RANDOMCODEKEY = "randomcode_key";//放到session中的key
  private Random random = new Random();
  private String randString = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";//随机产生的字符串

  private int width = 80;//图片宽
  private int height = 26;//图片高
  private int lineSize = 40;//干扰线数量
  private int stringNum = 4;//随机产生字符数量

  /**
   * 生成随机图片
   */
  public void getRandcode(HttpServletRequest request,
              HttpServletResponse response) {
    HttpSession session = request.getSession();
    //BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类
    BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_BGR);
    //产生Image对象的Graphics对象,改对象可以在图像上进行各种绘制操作
    Graphics g = image.getGraphics();
    g.fillRect(0, 0, width, height);
    g.setFont(new Font("Times New Roman",Font.ROMAN_BASELINE,18));
    g.setColor(getRandColor(160, 200));
    //绘制干扰线
    for(int i=0;i<=lineSize;i++){
      drowLine(g);
    }
    //绘制随机字符
    String randomString = "";
    for(int i=1;i<=stringNum;i++){
      randomString=drowString(g,randomString,i);
    }
    session.removeAttribute(RANDOMCODEKEY);
    session.setAttribute(RANDOMCODEKEY, randomString);
    g.dispose();
    try {
      //将内存中的图片通过流动形式输出到客户端
      ImageIO.write(image, "JPEG", response.getOutputStream());
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  /*
   * 获得字体
   */
  private Font getFont(){
    return new Font("Fixedsys",Font.CENTER_BASELINE,18);
  }
  /*
   * 获得颜色
   */
  private Color getRandColor(int fc,int bc){
    if(fc > 255)
      fc = 255;
    if(bc > 255)
      bc = 255;
    int r = fc + random.nextInt(bc-fc-16);
    int g = fc + random.nextInt(bc-fc-14);
    int b = fc + random.nextInt(bc-fc-18);
    return new Color(r,g,b);
  }

  /*
   * 绘制字符串
   */
  private String drowString(Graphics g,String randomString,int i){
    g.setFont(getFont());
    g.setColor(new Color(random.nextInt(101),random.nextInt(111),random.nextInt(121)));
    String rand = String.valueOf(getRandomString(random.nextInt(randString.length())));
    randomString +=rand;
    g.translate(random.nextInt(3), random.nextInt(3));
    g.drawString(rand, 13*i, 16);
    return randomString;
  }
  /*
   * 绘制干扰线
   */
  private void drowLine(Graphics g){
    int x = random.nextInt(width);
    int y = random.nextInt(height);
    int xl = random.nextInt(13);
    int yl = random.nextInt(15);
    g.drawLine(x, y, x+xl, y+yl);
  }
  /*
   * 获取随机的字符
   */
  public String getRandomString(int num){
    return String.valueOf(randString.charAt(num));
  }
}

 @RequestMapping(value="/checkCode")
  public void checkCode(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    //设置相应类型,告诉浏览器输出的内容为图片
    response.setContentType("image/jpeg");

    //设置响应头信息，告诉浏览器不要缓存此内容
    response.setHeader("pragma", "no-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expire", 0);

    RandomValidateCode randomValidateCode = new RandomValidateCode();
    try {
      randomValidateCode.getRandcode(request, response);//输出图片方法
    } catch (Exception e) {
      e.printStackTrace();
    }
  }