JSP一个正确的验证码

image.jsp页面

<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" pageEncoding="utf-8"%>
<%!
Color getRandColor(int fc,int bc){//给定范围获得随机颜色
        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);
        }
%>
<%
//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));

//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
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 rand = request.getParameter("rand");
//rand = rand.substring(0,rand.indexOf("."));
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
session.setAttribute("rand",sRand);


// 图象生效
g.dispose();

// 输出图象到页面
ImageIO.write(image, "JPEG", response.getOutputStream());
out.clear();
out = pageContext.pushBody();
%> 

login.jsp页面

  <form action="doLogin.jsp" method="post">
   用户名：<input type="text" name="username"/><br>
   密码：<input type="password" name="password"/><br>
  验证码:<input type="text" name="pass"/><img src= "image.jsp "> <br/>
   <input type="submit" value="提交" />
   </form>

doLogin.jsp页面

<%@ page language="java" import="java.util.*,com.wang.entity.*,com.wang.biz.*" pageEncoding="utf-8"%>
<%
	request.setCharacterEncoding("utf-8");
	String username = request.getParameter("username");
	String password = request.getParameter("password");
	Users users = new Users(username,password);
	UsersBiz usersBiz = new UsersBizImpl();
	Users t_user = usersBiz.CheckUser(users);
	String pass = request.getParameter("pass");
	String rand = session.getAttribute("rand").toString();
	if(!pass.equals(rand)){
		request.setAttribute("err","验证码错误");
		request.getRequestDispatcher("login.jsp").forward(request,response);
	}
	else if(t_user == null){
		request.setAttribute("err","用户名错误");
		request.getRequestDispatcher("login.jsp").forward(request,response);
	}
	else if(!t_user.getPassword().equals(password)){
		request.setAttribute("err","密码错误");
		request.getRequestDispatcher("login.jsp").forward(request,response);
	}
	else{
		session.setAttribute("user",t_user);
		response.sendRedirect("/message/listMsg.jsp");
	}
%>