登陆验证码图片生成代码

//登陆验证码图片生成代码<转载>
//希望对需要的朋友有所帮助
//ShowExPwdServlet.java

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;
import javax.imageio.ImageIO;

public class ShowExPwdServlet extends HttpServlet
{
 private static int WIDTH = 60;
 private static int HEIGHT = 20;
 public void doGet(HttpServletRequest request,HttpServletResponse response)
   throws ServletException,IOException
 {  
  HttpSession session = request.getSession();
  response.setContentType("image/jpeg");
  ServletOutputStream sos = response.getOutputStream();

  //设置浏览器不要缓存此图片
  response.setHeader("Pragma","No-cache");
  response.setHeader("Cache-Control","no-cache");
  response.setDateHeader("Expires", 0);
  
  //创建内存图象并获得其图形上下文
  BufferedImage image =
   new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
  Graphics g = image.getGraphics();
  
  //产生随机的认证码
  char [] rands = generateCheckCode();
  
  //产生图像
  drawBackground(g);
  drawRands(g,rands);
  
  //结束图像的绘制过程，完成图像
  g.dispose();
  
  //将图像输出到客户端
  ByteArrayOutputStream bos = new ByteArrayOutputStream();
  ImageIO.write(image, "JPEG", bos);
  byte [] buf = bos.toByteArray();
  response.setContentLength(buf.length);
  //下面的语句也可写成：bos.writeTo(sos);
  sos.write(buf);
  bos.close();
  sos.close();

  //将当前验证码存入到Session中
  session.setAttribute("check_code",new String(rands));
  //直接使用下面的代码将有问题，Session对象必须在提交响应前获得
  //request.getSession().setAttribute("check_code",new String(rands));
 }
 
 private char [] generateCheckCode()
 {
  //定义验证码的字符表
  String chars = "0123456789abcdefghijklmnopqrstuvwxyz";
  char [] rands = new char[4];
  for(int i=0; i<4; i++)
  {
   int rand = (int)(Math.random() * 36);
   rands[i] = chars.charAt(rand);
  }
  return rands;
 }
 
 private void drawRands(Graphics g , char [] rands)
 {
  g.setColor(Color.BLACK);
  g.setFont(new Font(null,Font.ITALIC|Font.BOLD,18));
  //在不同的高度上输出验证码的每个字符  
  g.drawString("" + rands[0],1,17);
  g.drawString("" + rands[1],16,15);
  g.drawString("" + rands[2],31,18);
  g.drawString("" + rands[3],46,16);
 }
 
 private void drawBackground(Graphics g)
 {
   //画背景
  g.setColor(new Color(0xDCDCDC));
  g.fillRect(0, 0, WIDTH, HEIGHT);
  //随机产生120个干扰点
  for(int i=0; i<120; i++)
  {
   int x = (int)(Math.random() * WIDTH);
   int y = (int)(Math.random() * HEIGHT);
   int red = (int)(Math.random() * 255);
   int green = (int)(Math.random() * 255);
   int blue = (int)(Math.random() * 255);
   g.setColor(new Color(red,green,blue));  
   g.drawOval(x,y,1,0);
  }
 }
}

在web.xml中配置好之后,再在页面中调用,示例如下:

<tr>
 <td valign="top" align="right">校验码：</td>
 <td align="left">
  <input name="ctl00$CPH_Content$tb_ExPwd" type="text" maxlength="5" id="ctl00_CPH_Content_tb_ExPwd" class="unnamed1" style="width:56px;" />&nbsp;&nbsp;
  <span id="ctl00_CPH_Content_regval_ExPwd" style="color:Red;visibility:hidden;">校验码必须填写！</span>
 </td>
</tr>
<tr>
 <td align="right">&nbsp;</td>
 <td align="left">
  <script type="text/javascript">
   document.write('<img id="MzImgExpPwd" alt="" src="ShowExPwdServlet.do" />');
  </script>
  <br />
  <a href="#" onclick="document.getElementById('MzImgExpPwd').src='ShowExPwdServlet.do' )); return false">
   重新获得验证码
  </a>
  <br />
 </td>
</tr>