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";//隨機產生的字符串

  private int width = 80;//圖片寬
  private int height = 26;//圖片高
  private int lineSize = 40;//干擾線數(shù)量
  private int stringNum = 4;//隨機產生字符數(shù)量

  /**
   * 生成隨機圖片
   */
  public void getRandcode(HttpServletRequest request,
              HttpServletResponse response) {
    HttpSession session = request.getSession();
    //BufferedImage類是具有緩沖區(qū)的Image類,Image類是用于描述圖像信息的類
    BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_BGR);
    //產生Image對象的Graphics對象,改對象可以在圖像上進行各種繪制操作
    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));
    //繪制干擾線
    for(int i=0;i<=lineSize;i++){
      drowLine(g);
    }
    //繪制隨機字符
    String randomString = "";
    for(int i=1;i<=stringNum;i++){
      randomString=drowString(g,randomString,i);
    }
    session.removeAttribute(RANDOMCODEKEY);
    session.setAttribute(RANDOMCODEKEY, randomString);
    g.dispose();
    try {
      //將內存中的圖片通過流動形式輸出到客戶端
      ImageIO.write(image, "JPEG", response.getOutputStream());
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  /*
   * 獲得字體
   */
  private Font getFont(){
    return new Font("Fixedsys",Font.CENTER_BASELINE,18);
  }
  /*
   * 獲得顏色
   */
  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);
  }

  /*
   * 繪制字符串
   */
  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;
  }
  /*
   * 繪制干擾線
   */
  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);
  }
  /*
   * 獲取隨機的字符
   */
  public String getRandomString(int num){
    return String.valueOf(randString.charAt(num));
  }
}

 @RequestMapping(value="/checkCode")
  public void checkCode(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    //設置相應類型,告訴瀏覽器輸出的內容為圖片
    response.setContentType("image/jpeg");

    //設置響應頭信息，告訴瀏覽器不要緩存此內容
    response.setHeader("pragma", "no-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expire", 0);

    RandomValidateCode randomValidateCode = new RandomValidateCode();
    try {
      randomValidateCode.getRandcode(request, response);//輸出圖片方法
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  <div class="layui-form-item">
          <div class="layui-row">
            <div class="layui-col-xs7">
              <label class="layadmin-user-login-icon layui-icon layui-icon-vercode" for="LAY-user-login-vercode"></label>
              <input type="text" name="code" id="LAY-user-login-vercode" lay-verify="required" placeholder="圖形驗證碼" class="layui-input">
            </div>
            <div class="layui-col-xs5">
              <div style="margin-left: 10px;">
                <img src="${pageContext.request.contextPath}checkCode" class="layadmin-user-login-codeimg" id="LAY-user-get-vercode" onclick="this.src=this.src+'?'" alt="">
              </div>
            </div>
          </div>
        </div>