@RequestMapping(value = "/captcha", method = RequestMethod.GET)
  @ResponseBody
  public void captcha(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException 
  {
    CaptchaUtil.outputCaptcha(request, response);
  }

package com.util;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

/**
* @ClassName: CaptchaUtil 
* @Description: 關于驗證碼的工具類
* @author 無名
* @date 2016-5-7 上午8:33:08 
* @version 1.0
 */
public final class CaptchaUtil
{
  private CaptchaUtil(){}
  
  /*
   * 隨機字符字典
   */
  private static final char[] CHARS = { '2', '3', '4', '5', '6', '7', '8',
    '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M',
    'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };
  
  /*
   * 隨機數(shù)
   */
  private static Random random = new Random();
  
  /*
   * 獲取6位隨機數(shù)
   */
  private static String getRandomString()
  {
    StringBuffer buffer = new StringBuffer();
    for(int i = 0; i < 6; i++)
    {
      buffer.append(CHARS[random.nextInt(CHARS.length)]);
    }
    return buffer.toString();
  }
  
  /*
   * 獲取隨機數(shù)顏色
   */
  private static Color getRandomColor()
  {
    return new Color(random.nextInt(255),random.nextInt(255),
        random.nextInt(255));
  }
  
  /*
   * 返回某顏色的反色
   */
  private static Color getReverseColor(Color c)
  {
    return new Color(255 - c.getRed(), 255 - c.getGreen(),
        255 - c.getBlue());
  }
  
  public static void outputCaptcha(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException 
  {

    response.setContentType("image/jpeg");

    String randomString = getRandomString();
    request.getSession(true).setAttribute("randomString", randomString);

    int width = 100;
    int height = 30;

    Color color = getRandomColor();
    Color reverse = getReverseColor(color);

    BufferedImage bi = new BufferedImage(width, height,
        BufferedImage.TYPE_INT_RGB);
    Graphics2D g = bi.createGraphics();
    g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 16));
    g.setColor(color);
    g.fillRect(0, 0, width, height);
    g.setColor(reverse);
    g.drawString(randomString, 18, 20);
    for (int i = 0, n = random.nextInt(100); i < n; i++) 
    {
      g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
    }

    // 轉成JPEG格式
    ServletOutputStream out = response.getOutputStream();
    JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
    encoder.encode(bi);
    out.flush();
  }
}

……

<tr>
  <th>captcha</th>
  <td>
       <input type="text" id="captcha" name="captcha" class="text" maxlength="10" />
       <img id="captchaImage" src="captcha.form"/>
   </td>
 </tr>

// 更換驗證碼
$('#captchaImage').click(function() 
{
  $('#captchaImage').attr("src", "captcha.form?timestamp=" + (new Date()).valueOf());
});