import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class RadomCodeServlet extends HttpServlet
{

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  doPost(request,response);
 }

 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  //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
  int width=60, height=20;
  BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

  //获取图形上下文
  Graphics g = image.getGraphics();

  //生成随机类
  Random random = new Random();

  //设定背景色
  g.setColor(getRandColor(200,250));
  g.fillRect(0, 0, width, height);

  //设定字体
  g.setFont(new Font("Times New Roman",Font.PLAIN,18));
  
  //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
  g.setColor(getRandColor(160,200));
  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);
          g.drawLine(x,y,x+xl,y+yl);
  }
  
  //取随机产生的认证码(4位数字)
  String sRand="";
  for (int i=0;i<4;i++)
  {
      String rand=String.valueOf(random.nextInt(10));
      sRand+=rand;
      // 将认证码显示到图象中
      g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
      g.drawString(rand,13*i+6,16);
  }

  //将认证码存入SESSION
  request.getSession().setAttribute("rand",sRand);

  //图象生效
  g.dispose();

  //输出图象到页面
  ImageIO.write(image, "JPEG", response.getOutputStream());  
 }
 
 //给定范围获得随机颜色
 private Color getRandColor(int fc,int bc)
 {
        Random random = new Random();
        if(fc>255) fc=255;
        if(bc>255) bc=255;
        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);
    }
 调用:
 <td height="25">
            <div align="right">
             <font color="#000000">验证码：</font>
            </div>
           </td>
           <td align="left">
            <input type="text" name="randCode" size=10></input>
            <img style="cursor:hand" name="validatecode"
             src=" servlet/RadomCodeServlet" height="17" align="middle"
             onclick="document.validatecode.src=' servlet/RadomCodeServlet'">
           </td>

public class MD5
{
  private static MD5 md5 = null;
  private MD5(){}
  public static MD5 getInstance()
  {
    if (md5 == null)
    {
      md5 = new MD5();
    }
    return md5;
  }

  /**
   * Description:encrypt the String by "MD5"
   * @param str String
   * @return String
   */
  public String calcMD5(String str)
  {
    try
    {
      MessageDigest alga = MessageDigest.getInstance("MD5");
      alga.update(str.getBytes());
      byte[] digesta = alga.digest();
      return byte2hex(digesta);
    }
    catch (Exception e)
    {
      //System.out.println(e.getMessage());
      return null;
    }
  }

  private String byte2hex(byte[] b)
  {
    String hs = "";
    String stmp = "";
    for (int n = 0; n < b.length; n++)
    {
      stmp = (Integer.toHexString(b[n] & 0XFF));
      if (stmp.length() == 1)
      {
        hs = hs + "0" + stmp;
      }
      else
      {
        hs = hs + stmp;
      }
      if (n < b.length - 1)
      {
        hs = hs + "";
      }
    }
    return hs;
  }
}

import org.jasig.cas.authentication.principal.Credentials;

public class LoginInfoCredentials
    implements Credentials
{

    private String account;
    private String password;
    private String randCode;

    public LoginInfoCredentials()
    {
    }

    public String getAccount()
    {
        return account;
    }

    public void setAccount(String account)
    {
        this.account = account;
    }

    public String getPassword()
    {
        return password;
    }

    public void setPassword(String password)
    {
        this.password = password;
    }

    public String getRandCode()
    {
        return randCode;
    }

    public void setRandCode(String randCode)
    {
        this.randCode = randCode;
    }
}


package com.jama.credentials;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.jasig.cas.authentication.principal.*;

// Referenced classes of package com.jama.credentials:
//            LoginInfoCredentials

public class LoginInfoToPrincipalResolver
    implements CredentialsToPrincipalResolver
{

    private final Log log = LogFactory.getLog(getClass());

    public LoginInfoToPrincipalResolver()
    {
    }

    public Principal resolvePrincipal(Credentials credentials)
    {
        LoginInfoCredentials loginInfo = (LoginInfoCredentials)credentials;
        if(log.isDebugEnabled())
        {
            log.debug((new StringBuilder("Creating SimplePrincipal for [")).append(loginInfo.getAccount()).append("]").toString());
        }
        return new SimplePrincipal(loginInfo.getAccount());
    }

    public boolean supports(Credentials credentials)
    {
        return credentials != null && com/jama/credentials/LoginInfoCredentials.isAssignableFrom(credentials.getClass());
    }
}

function rtrim(str) {
        var pattern = new RegExp("[\\s]+$","gi");
        return str.replace(pattern,"");
}
function trim(str) {
        return rtrim(ltrim(str));
}

<body onload = "detect()">
test :
     <a id="list" >  </a>

</BODY>
</HTML>


xmlhttp.jsp
<%@ page language="java" contentType="text/html;charset=GB2312"%>
<%@ page import ="java.util.*"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
</HEAD>

<BODY>
<%
  Random randor=new Random();
  out.println(randor.nextInt());
%>
</BODY>
</HTML>

  } catch (JRException e) {
   throw new DemoException("Report Export Failed.");
  }
 }

jsp调用方法：
 <%
    
   
 String filePath=getServletContext().getRealPath("/")+"report.jasper"; 

 CustomerServiceImpl  custs=new CustomerServiceImpl();
    byte[] bytes=null;
  String begNo=request.getParameter("beginCustNo");
  String endNo=request.getParameter("endCustNo");
  String type=request.getParameter("type");

  if(type.equals("Pdf")){ 
      bytes= custs.generatePDF(begNo,endNo,"客户资料明细表",filePath);
  }else if(type.equals("Excel")){
   bytes=custs.generateExcel(begNo,endNo,"客户资料明细表",filePath);
  }else
     bytes=custs.generateHtml(begNo,endNo,"客户资料明细表",filePath);

 if(bytes!=null){
  if(type.equals("Pdf")){
         response.setContentType("application/pdf");
  }else if(type.equals("Excel")){
     response.setContentType("application/vnd.ms-excel");
  }else
   response.setContentType("text/html");
    response.setContentLength(bytes.length);
    ServletOutputStream ouputStream = response.getOutputStream();
    ouputStream.write(bytes,0,bytes.length);
    ouputStream.flush();
    ouputStream.close();
 }else
 {
  out.println("error");
 }
 

  %>