package com.hoo.util;   import java.awt.Color;  import java.awt.Font;  import java.awt.Graphics;  import java.awt.image.BufferedImage;  import java.util.Random; import javax.imageio.ImageIO;  import javax.servlet.http.HttpServletRequest;  import javax.servlet.http.HttpServletResponse;  /**  * <b>function:</b> 验证码生成工具类  * @project NetWorkService  * @package com.hoo.util  * @fileName ValidCodeUtils.java  * @createDate 2010-8-3 下午03:05:50  * @author hoojo  */  @SuppressWarnings("unused")  public class ValidCodeUtils {  /*********************************************************************   * 验证码宽度   */  public static int WIDTH = 60;  /***   * 验证码高度   */  public static int HEIGHT = 20;  /**********************************************************************   * 验证码背景颜色COLOR_FC_BG 应当小于COLOR_BC_BG   */  public static int COLOR_FC_BG = 200;  /***   * 验证码背景颜色COLOR_FC_BG 应当小于COLOR_BC_BG   */  public static int COLOR_BC_BG = 250;  /**********************************************************************   * 验证码背景干扰线颜色COLOR_FC_LINE 应当小于COLOR_BC_LINE   */  public static int COLOR_FC_LINE = 160;  /***   * 验证码背景干扰线颜色COLOR_FC_LINE 应当小于COLOR_BC_LINE   */  public static int COLOR_BC_LINE = 200;  /***************************************************************************   * 验证码颜色COLOR_FC_CODE 应当小于COLOR_BC_CODE   */  public static int COLOR_FC_CODE = 20;  /***   * 验证码颜色COLOR_FC_CODE 应当小于COLOR_BC_CODE   */  public static int COLOR_BC_CODE = 170;  /***************************************************************************   * 生成在指定范围内的颜色   * @param fc 范围fc color值 小于255   * @param bc 范围bc color值 小于255   * @return Color   */  private static Color getRandColor(int fc, int bc) {      Random random = new Random();      if (fc < 0)   fc = 0;      if (bc < 0)   bc = 1;      if (fc > 255)   fc = 255;      if (bc > 255)   bc = 255;      if (bc == fc)    bc += 10;      int temp = 0;      if (bc < fc) {   temp = bc;   bc = fc;   fc = temp;      }      int r = fc + random.nextInt(bc - fc);      int g = fc + random.nextInt(bc - fc);      int b = fc + random.nextInt(bc - fc);      return new Color(r, g, b);  } /**   * <b>function:</b> 生成图片方法   * @createDate 2010-8-3 下午03:06:22   * @author hoojo   * @param request HttpServletRequest   * @param response HttpServletResponse   * @return boolean   * @throws Exception   */  public static boolean getImage(HttpServletRequest request, HttpServletResponse response) throws Exception{      response.reset();      response.setContentType("image/jpeg");      // 设置页面不缓存      response.setHeader("Pragma", "No-cache");      response.setHeader("Cache-Control", "no-cache");      response.setDateHeader("Expires", 0);      // 在内存中创建图象           BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);     // 获取图形上下文      Graphics img = image.getGraphics();      // 生成随机类      Random random = new Random();     // 设定背景色      img.setColor(getRandColor(COLOR_FC_BG, COLOR_BC_BG));      img.fillRect(0, 0, WIDTH, HEIGHT);     // 设定字体      img.setFont(new Font("Times New Roman", Font.PLAIN, 18));     // 画边框      // g.setColor(new Color());      // g.drawRect(0,0,width-1,height-1);     // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到      img.setColor(getRandColor(COLOR_FC_LINE, COLOR_BC_LINE));      for (int i = 0; i < 155; i++) {   int x = random.nextInt(WIDTH);   int y = random.nextInt(HEIGHT);   int xl = random.nextInt(12);   int yl = random.nextInt(12);   img.drawLine(x, y, x + xl, y + yl);      }     // 取随机产生的认证码(4位数字)      String codeValue = "";      for (int i = 0; i < 4; i++) {   //String rand = String.valueOf(random.nextInt(10));   String rand = getRandomChar();   codeValue = codeValue.concat(rand);   img.setFont(getRandomFont());//随机字体   // 将认证码显示到图象中   img.setColor(getRandColor(COLOR_FC_CODE, COLOR_BC_CODE));   img.drawString(rand, 13 * i + 6, 16);      }      request.getSession().setAttribute("codeValue", codeValue);      // 图象生效      img.dispose();      // 输出图象到页面      return ImageIO.write(image, "JPEG", response.getOutputStream());  }  /**   * 随机生成字符，含大写、小写、数字   * <b>function:</b> 功能   * @createDate 2010-8-23 上午10:33:55   * @author hoojo   * @return   */  public static String getRandomChar() {      int index = (int) Math.round(Math.random() * 2);      String randChar = "";      switch (index) {      case 0://大写字符   randChar = String.valueOf((char)Math.round(Math.random() * 25 + 65));   break;      case 1://小写字符   randChar = String.valueOf((char)Math.round(Math.random() * 25 + 97));   break;      default://数字   randChar = String.valueOf(Math.round(Math.random() * 9));   break;      }      return randChar;  }  /**   * <b>function:</b> 随机生成字体、文字大小   * @createDate 2010-8-23 上午10:44:22   * @author hoojo   * @return   */  public static Font getRandomFont() {      String[] fonts = {"Georgia", "Verdana", "Arial", "Tahoma", "Time News Roman", "Courier New", "Arial Black", "Quantzite"};      int fontIndex = (int)Math.round(Math.random() * (fonts.length - 1));      int fontSize = (int) Math.round(Math.random() * 4 + 16);      return new Font(fonts[fontIndex], Font.PLAIN, fontSize);  }  } 其中验证码的值是保存在session中：request.getSession().setAttribute("codeValue", codeValue);  比较用户输入的值和session中的codeValue是否相等即可； 下面是jsp页面调用servlet：ValidCodeServlet.java ValidCodeServlet中调用了上面的ValidCodeUtils 验证码生成工具类 package com.hoo.servlet; import java.io.IOException;  import javax.servlet.ServletException;  import javax.servlet.http.HttpServlet;  import javax.servlet.http.HttpServletRequest;  import javax.servlet.http.HttpServletResponse; import com.hoo.util.ValidCodeUtils; @SuppressWarnings("serial")  public class ValidCodeServlet extends HttpServlet {  public void doGet(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {      try {   ValidCodeUtils.getImage(request, response);      } catch (Exception e) {   e.printStackTrace();      }  } public void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {      doGet(request, response);  }  }   jsp页面调用servlet方法即可   js：reloadValidCode方法 function reloadValidCode(o) {  o.src = "${pageContext.request.contextPath }/validCodeServlet?timed=" + new Date().getMilliseconds();  }  这里的"timed=" + new Date().getMilliseconds();是需要防止IE缓存用的 html标签：  <img src="${pageContext.request.contextPath }/validCodeServlet" title="看不清，点击刷新" onclick="reloadValidCode(this)"/>  直接跟Servlet名称配置的url即可，和web.xml配置对应。主要调用路径${pageContext.request.contextPath }/validCodeServlet这样会带上根目录，比较保险。 web.xml中validCodeServlet配置  <servlet>  <servlet-name>validCodeServlet</servlet-name>  <servlet-class>com.hoo.servlet.ValidCodeServlet</servlet-class>  </servlet> <servlet-mapping>  <servlet-name>validCodeServlet</servlet-name>  <url-pattern>/validCodeServlet</url-pattern>  </servlet-mapping>