protectedvoiddoGet(HttpServletRequest request, HttpServletResponse   response) throwsServletException, IOException {

// 告知浏览当作图片处理

response.setContentType("image/jpeg");

// 告诉浏览器不缓存

response.setHeader("pragma", "no-cache");

response.setHeader("cache-control", "no-cache");

response.setHeader("expires", "0");

// 产生由4位数字构成的验证码

int length = 4;

String valcode   = "";

Random rd =   new Random();

for(int i=0;   i<length; i++)

valcode+=rd.nextInt(10);

// 把产生的验证码存入到Session中

HttpSession   session = request.getSession();

session.setAttribute("valcode", valcode);

// 产生图片

int width = 80;

int height = 25;

BufferedImageimg   = newBufferedImage(width, height,BufferedImage.TYPE_INT_RGB);

// 获取一个Graphics

Graphics g   = img.getGraphics();

// 填充背景色

g.setColor(Color.WHITE);

g.fillRect(0,   0, width, height);

// 填充干扰线50

for(int i=0;   i<50; i++){

g.setColor(new   Color(rd.nextInt(100)+155,rd.nextInt(100)+155,rd.nextInt(100)+155));

g.drawLine(rd.nextInt(width),   rd.nextInt(height),rd.nextInt(width), rd.nextInt(height));

}

// 绘制边框

g.setColor(Color.GRAY);

g.drawRect(0,   0, width-1, height-1);

// 绘制验证码

Font[]   fonts = {new Font("隶书",Font.BOLD,18),new Font("楷体",Font.BOLD,18),new Font("宋体",Font.BOLD,18),new Font("幼圆",Font.BOLD,18)};

for(int i=0;   i<length; i++){

g.setColor(new   Color(rd.nextInt(150),rd.nextInt(150),rd.nextInt(150)));

g.setFont(fonts[rd.nextInt(fonts.length)]);

g.drawString(valcode.charAt(i)+"", width/valcode.length()*i+2, 18);

}

// 输出图像

g.dispose();

ImageIO.write(img,   "jpeg", response.getOutputStream());

}

<servlet>

<description></description>

<display-name>ValcodeServlet</display-name>

<servlet-name>ValcodeServlet</servlet-name><servlet-class>org.icer.jee.valcode.servlet.ValcodeServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>ValcodeServlet</servlet-name>

<url-pattern>/ValcodeServlet</url-pattern>

</servlet-mapping>

<formname="form1"method="post"action="LoginServlet">

验证码：

<inputname="vcode"type="text"class="input02"id="vcode">

<imgsrc="ValcodeServlet"align="absmiddle"title="看不清，点击换一张"onClick="this.src=this.src+'?'"/>

<inputtype="submit"name="button"id="button"value="   提交 ">

</form>

protectedvoiddoPost(HttpServletRequest request, HttpServletResponse   response) throwsServletException, IOException {

// 获取验证码

String   valcode = request.getSession().getAttribute("valcode").toString();

// 获取用户填写的验证码

String   vcode = request.getParameter("vcode");

// 进行验证

if(!valcode.equals(vcode))

System.out.println(">>>验证码错误！");

else

System.out.println(">>>验证码正确！");

}