验证码 servlet

验证码实际上就是随机选择一些字符以图片的形式展现在页面上，如果进行提交操作的同时需要将图片上的字符同时提交，如果提交的字符与服务器session 保存的不同，则认为提交信息无效。为了避免自动程序分析解析图片，通常会在图片上随机生成一些干扰线或者将字符进行扭曲，增加自动识别的难度。

------------产生验证码图片的文件-----image.servlet-------------------------------------------

package untitled1;

import java.io.*;
import java.net.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;
import java.util.*;
import javax.imageio.*;
/** *//**
 *
 * @author http://www.tot.name
 * @version
 */
public class Image extends HttpServlet ...{

    /** *//** Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
     * @param request servlet request
     * @param response servlet response
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException ...{
        response.setContentType("image/jpeg");
        response.setHeader("Pragma","No-cache");
        response.setHeader("Cache-Control","no-cache");
        response.setDateHeader("Expires", 0);       
        HttpSession session=request.getSession();
        // 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 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();
        ServletOutputStream responseOutputStream =response.getOutputStream();
        // 输出图象到页面
        ImageIO.write(image, "JPEG", responseOutputStream);

        //以下关闭输入流！
        responseOutputStream.flush();
        responseOutputStream.close();
    }
    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);
    }
    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** *//** Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException ...{
        processRequest(request, response);
    }

    /** *//** Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException ...{
        processRequest(request, response);
    }

    /** *//** Returns a short description of the servlet.

     */
    public String getServletInfo() ...{
        return "Short description";
    }
    // </editor-fold>
}

 ---------------使用验证码图片的文件---------index.jsp------------------------------------

<%...@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
<html>
<head>
<title>认证码验证页面</title>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<META HTTP-EQUIV="Pragma" CONTENT="no-cache"> 
<META HTTP-EQUIV="Cache-Control" CONTENT="no-cache"> 
<META HTTP-EQUIV="Expires" CONTENT="0"> 
</head>

<body>
<%... 
String rand = (String)session.getAttribute("rand");
String input = request.getParameter("rand");
%>
系统产生的认证码为： <%= rand %><br>
您输入的认证码为： <%= input %><br>
<br>
<%...
  if (rand.equals(input)) {
%>
<font color=green>输入相同，认证成功！</font>
<%...
  } else {
%>
<font color=red>输入不同，认证失败！</font>
<%