int width = 100;
    int height = 50;
    //創(chuàng)建圖片對象
    BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

    //美化圖片
    Graphics g = image.getGraphics();
    //1：填充背景
    g.setColor(Color.pink);
    g.fillRect(0, 0, width, height);

    //畫邊框
    g.setColor(Color.blue);
    g.drawRect(0, 0, width - 1, height - 1);

    //生成一個驗證碼字符串
    String strCheckCode = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    Random random = new Random();
    StrCheckCode = "";
    for (int i = 1; i <= 4; i++) {
      int index = random.nextInt(strCheckCode.length());
      char ch = strCheckCode.charAt(index);
      StrCheckCode += ch;//拼接驗證碼
      g.drawString(ch + "", width / 5 * i, height / 2);
    }

    //畫干擾線
    for (int i = 0; i < 5; i++) {
      int x1 = random.nextInt(width);
      int x2 = random.nextInt(width);

      int y1 = random.nextInt(height);
      int y2 = random.nextInt(height);
      g.drawLine(x1, x2, y1, y2);
    }

    //輸出，顯示出來
    ImageIO.write(image, "jpg", resp.getOutputStream());
  }

//點擊驗證碼圖片，重新生成新驗證
    $(function () {
      $("#imgCheckCode").click(function () {
        var img = document.getElementById("imgCheckCode");
        var date = new Date();
        img.src = "http://localhost:8080/blogs_war_exploded/checkCode?op=setCheckCode&a=" + date;
      })
    })

<div class="inputCheckCode">
      <div class="inputCheckCodeLeftIco">&#10148</div>
      <div class="inputCheckCodeRightInput">
        <input type="text" name="checkCode" id="checkCode" placeholder="驗證碼" autocomplete="off"/>
      </div>
      <img src="http://localhost:8080/blogs_war_exploded/checkCode?op=setCheckCode" id="imgCheckCode">
    </div>