servlet response输出验证码

下面是两个工具代码：一个是生成验证码字符串，一个是生成验证码图片（它是基于生成验证码字符串类的）

public class CreateVerificationCode {
    /**
     * 验证码难度级别
     */
    public enum SecurityCodeLevel {
        Simple,
        Medium,
        Hard
    }

    public static String getSecurityCode() {
        return (String) getSecurityCode(4, SecurityCodeLevel.Medium, false);
    }

    public static String getSecurityCode(int length, SecurityCodeLevel level, boolean isCanRepeat) {
        int len = length;
        //除去容易混淆的0和o，1和l
        char[] codes = {
                '1', '2', '3', '4', '5', '6', '7', '8', '9',
                'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
                'j', 'm', 'n', 'p', 'q', 'r', 's', 't','u',
                'v', 'w', 'x', 'y', 'z','A','B','C','D','E',
                'F','G','H','J','K','L','M','N','P','Q','R','S',
                'T','U','V','W','X','Y','Z'};
        if(level==SecurityCodeLevel.Simple){
            codes= Arrays.copyOfRange(codes,0,9);
        }else if (level==SecurityCodeLevel.Medium){
            codes= Arrays.copyOfRange(codes,0,33);
        }
        int n=codes.length;
        //抛出运行时异常
        if (len>n&&isCanRepeat==false){
            throw new RuntimeException(
                    String.format("调用securitycode.getSecurityCode(%1$s,len,level,isCanRepeat,n)"));}
        char[] result=new char[len];
        //判断能否出现重复的字符
        if (isCanRepeat){
            for(int i=0;i<result.length;i++){
                //索引0 and n-1
                int r=(int)(Math.random()*n);
                //将result中的第i个元素设为codes[r]存放的数值
                result[i]=codes[r];
            }
        }else {
            for (int i=0;i<result.length;i++){
                int r=(int)(Math.random()*n);
                //将result中的第i个元素设为codes[r]存放的数值
                result[i]=codes[r];
                codes[r]=codes[n-1];
                n--;
            }
        }
        return String.valueOf(result);
    }
}

**
 * 可生成数字，大写，小写字母及三者混合类型的验证码，支持自定义干扰线，图文颜色
 */
public class CreateVerificationCodeImage {
    private String securityCode;
    public CreateVerificationCodeImage(String securityCode){
        this.securityCode=securityCode;
    }
    //高度
    private static final int CAPTCHA_HEIGHT = 35;
    //宽度
    private static final int CAPTCHA_WIDTH  = 100;
    //数字的长度
    //private static final int NUMBER_CNT     = 6;
    private Random r = new Random();
    //  字体
    private String[] fontNames = { "宋体", "华文楷体", "黑体", "华文新魏", "华文隶书", "微软雅黑", "楷体_GB2312" };
    //private String[] fontNames = { "宋体",  "黑体", "微软雅黑"};

    /**
     * 机能概要:生成随机的颜色
     * @return
     */
    private Color randomColor() {
        int red = r.nextInt(150);
        int green = r.nextInt(150);
        int blue = r.nextInt(150);
        return new Color(red, green, blue);
    }

    /**
     * 机能概要:生成随机的字体
     * @return
     */
    private  Font randomFont() {
        int index = r.nextInt(fontNames.length);
        String fontName = fontNames[index];// 生成随机的字体名称
        int style = r.nextInt(4);// 生成随机的样式, 0(无样式), 1(粗体), 2(斜体), 3(粗体+斜体)
        int size = r.nextInt(5) + 24; // 生成随机字号, 24 ~ 28
        // int size = r.nextInt(5) + 15; // 生成随机字号, 20 ~ 24
        return new Font(fontName, style, size);
    }

    // 画干扰线
    private  void drawLine(BufferedImage image) {
        int num = 5;// 一共画5条
        Graphics2D g2 = (Graphics2D) image.getGraphics();
        for (int i = 0; i < num; i++) {// 生成两个点的坐标，即4个值
            int x1 = r.nextInt(CAPTCHA_WIDTH);
            int y1 = r.nextInt(CAPTCHA_HEIGHT);
            int x2 = r.nextInt(CAPTCHA_WIDTH);
            int y2 = r.nextInt(CAPTCHA_HEIGHT);
            g2.setStroke(new BasicStroke(1.5F));
            g2.setColor(randomColor()); // 随机生成干扰线颜色
            g2.drawLine(x1, y1, x2, y2);// 画线
        }
    }
    // 创建BufferedImage，生成图片
    public BufferedImage createImage() {
        BufferedImage image = new BufferedImage(CAPTCHA_WIDTH, CAPTCHA_HEIGHT, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = (Graphics2D) image.getGraphics();
        // 背景色,白色
        g2.setColor(new Color(255, 255, 255));
        g2.fillRect(0, 0, CAPTCHA_WIDTH, CAPTCHA_HEIGHT);

        // 向图片中画4个字符  String securityCode
        for (int i = 0; i < securityCode.length(); i++) {// 循环四次，每次生成一个字符
            String s = securityCode.charAt(i) + "";// 随机生成一个字母
            // float x = i * 1.0F * CAPTCHA_WIDTH / NUMBER_CNT; // 设置当前字符的x轴坐标
            float x = i * 1.0F * CAPTCHA_WIDTH / 4+7F; // 设置当前字符的x轴坐标
            g2.setFont(randomFont()); // 设置随机字体
            g2.setColor(randomColor()); // 设置随机颜色
            g2.drawString(s, x, CAPTCHA_HEIGHT-7); // 画图,依次将字符写入到图片的相应位置-------------------
        }
        drawLine(image); // 添加干扰线
        return image;
    }
}

通过response输出验证码

 protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取验证码的内容
        String vericode= CreateVerificationCode.getSecurityCode();
        System.out.println(vericode);
        HttpSession session=req.getSession();
        session.setAttribute("verityCode",vericode);
        //设置返回的内容
        resp.setContentType("img/jpeg");
        //浏览器不缓存响应内容--验证码图片，点一次就要刷新一次，所以不能有缓存出现
     /*   resp.setHeader("Pragma","No-cache");
        resp.setHeader("Cache-Control","no-cache");*/
        //设置验证码失效时间
        resp.setDateHeader("Expires",0);
        //以字节流发过去，交给img的src属性去解析即可
        ImageIO.write(new CreateVerificationCodeImage(vericode).createImage(),"JPEG",resp.getOutputStream());
    }

前端去获取验证码图片

 <td>验证码</td>
      <td><input type="text"  required/><img id="tu" src="${pageContext.request.contextPath}/res03">&nbsp;&nbsp; <a onclick="changeImg()" href="#">看不清换一张</a></td>

<script type="text/javascript">
  function changeImg() {
      //处理前端缓存
  document.getElementById('tu').src="${pageContext.request.contextPath}/res03?"+Math.random();
  }
</script>

转载：https://blog.csdn.net/qq_41063141/article/details/93661226