jsp+tomcat 怎么让网站加上验证用户功能

jsp+tomcat 如何让网站加上验证用户功能?
就好象我们输入tomcat   管理页面(   http://127.0.0.1:8080/manager/html)时，tomcat   要求我们先输入用户及密码,   请问如何实现呢?     听说设置一下XML文件就可以.

------解决方案--------------------
给你3种生成随即数的程序
<%! String sVerifyCode; //验证码字符串 %>

<%//设置页面不缓存
response.setHeader( "Pragma ", "No-cache ");
response.setHeader( "Cache-Control ", "no-cache ");
response.setDateHeader( "Expires ", 0);
response.reset();

try{
// 将认证码存入SESSION
//调用 runVerifyCode(int i) ,把i改成所要的验证码位数
VerifyCode VC = new VerifyCode();
session.setAttribute( "VerifyCode ",VC.runVerifyCode(4));
//session.setMaxInactiveInterval(60);

// 输出图象到页面
sVerifyCode = (String)session.getAttribute( "VerifyCode ");
OutputStream outs = response.getOutputStream();
ImageIO.write(VC.CreateImage(sVerifyCode), "JPEG ",outs);
}catch(Exception e){
return;
}
%>
代码如下
import java.awt.*;//导入类
import java.awt.image.*;
import java.util.*;
import javax.imageio.*;
public class VerifyCode {
static Random r = new Random();
static String ssource = "ABCDEFGHIJKLMNOPQRSTUVWXYZ " + "abcdefghijklmnopqrstuvwxyz " + "0123456789 ";
static char[] src = ssource.toCharArray();


//产生随机字符串

private static String randString (int length){
char[] buf = new char[length];
int rnd;
for(int i=0;i <length;i++){
rnd = Math.abs(r.nextInt()) % src.length;

buf[i] = src[rnd];
}
return new String(buf);
}

//调用该方法，产生随机字符串,
//参数i: 为字符串的长度
public String runVerifyCode(int i){
String VerifyCode = randString(i);
return VerifyCode;
}


//给定范围获得随机颜色
public 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);
}

//调用该方法将得到的验证码生成图象
//sCode:传递验证码 w:图象宽度 h:图象高度
public BufferedImage CreateImage(String sCode)
{
try{
//字符的字体
Font CodeFont = new Font( "Arial Black ",Font.PLAIN,16);
int iLength = sCode.length();//得到验证码长度
int width=22*iLength, height=20;//图象宽度与高度
int CharWidth = (int)(width-24)/iLength;//字符距左边宽度
int CharHeight = 16; //字符距上边高度

// 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 g = image.getGraphics();

//生成随机类
Random random = new Random();

// 设定背景色
g.setColor(getRandColor(200,240));
g.fillRect(0, 0, width, height);

//设定字体
g.setFont(CodeFont);

//画随机颜色的边框
g.setColor(getRandColor(10,50));
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
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);
}


for (int i=0;i <iLength;i++)
{
String rand = sCode.substring(i,i+1);
// 将认证码显示到图象中
g.setColor(new Color(20+random.nextInt(60),20+random.nextInt(120),20+random.nextInt(180)));
g.drawString(rand,CharWidth*i+14,CharHeight);
}
// 图象生效
g.dispose();
return image;
}catch(Exception e){
//e.printStackTrace();