JSP頁面：
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>login.jsp</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<form name="form1" action="./servlet/LogonFormServlet" method="post">
<table align="center" width="299" height="153">
<tr>
<td><div><strong>用戶名：</strong><input type="text" name="username"></div></td>
</tr>
<tr>
<td><strong>密 碼：</strong><input type="password" name="pwd"></td>
</tr>
<tr>
<td>驗證碼：<input type="text" name="check_code">
<img src="./servlet/CheckCodeServlet"></img></td>
</tr>
<tr>
<td align="center"><input type="submit" value="登 錄">
<input type="reset" value="重 設">
</td>
</tr>
</table><br>
</form>
</body>
</html>
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
package cn;
import java.awt.*;
import java.awt.image.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.imageio.*;
public class CheckCodeServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public CheckCodeServlet() {
super();
}
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
private static int WIDTH = 60;
private static int HEIGHT = 20;
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
//PrintWriter out = response.getWriter();
HttpSession session = request.getSession();
response.setContentType("image/jpeg");
ServletOutputStream sos = response.getOutputStream();
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
//創建內存圖像
BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_BGR);
Graphics g = image.getGraphics();
//產生隨機的驗證碼
char[] rands = generateChekCode();
//產生背景
drawground(g);
drawRands(g,rands);
//方法結束
g.dispose();
//輸出到客戶端
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ImageIO.write(image, "jpeg", bos);
byte[] buf = bos.toByteArray();
response.setContentLength(buf.length);
sos.write(buf);
bos.close();
sos.close();
//將當前的驗證碼存入session中
session.setAttribute("check_code", new String(rands));
}
//產生隨機數
private char[] generateChekCode(){
//定義驗證的字符串
String chars = "1234567890abcdefghijklmnopqrstuvwxyz";
char [] rands = new char[4];
for(int i=0;i<rands.length;i++)
{
int rand = (int)(Math.random() * 36);
rands[i] = chars.charAt(rand);
}
return rands;
}
//產生圖像
private void drawRands(Graphics g,char[] rands)
{
g.setColor(Color.BLACK);
g.setFont(new Font(null,Font.ITALIC|Font.BOLD,18));
//在不同的高度上輸出驗證碼文字
g.drawString(""+rands[0],3,15);
g.drawString(""+rands[1],17,15);
g.drawString(""+rands[2],32,15);
g.drawString(""+rands[3],46,16);
System.out.println(rands);
}
//畫背景
private void drawground(Graphics g)
{
g.setColor(Color.green);
g.fillRect(0, 0, WIDTH, HEIGHT);
//隨機產生120個干擾點
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);
}
}
}
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
package cn;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class LogonFormServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public LogonFormServlet() {
super();
}
public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=GB2312");
PrintWriter out = response.getWriter();
HttpSession session = request.getSession(false);
System.out.println(session+"AAAAAAAAAA");
if(session==null){
out.println("驗證碼問題");
return;
}
String savedCode = (String)session.getAttribute("check_code");
if(savedCode == null){
out.println("驗證碼不對");
return;
}
String checkCode = (String) request.getParameter("check_code");
if(!savedCode.equals(checkCode))
{
out.println("驗證碼無效");
return;
}
session.removeAttribute("check_code");
out.println("驗證碼通過");
}
}
