登录验证码

验证码的作用是区分人与机器，防止机器刷数据；

验证码的验证分了两步，一步是请求获取验证码，一步是前台传的验证码与后台的验证码进行对比判断后进行后续操作；

在MyEclipse中新建一个Web Project项目，然后填充下面代码

该代码生成的验证码效果图：

验证码的代码如下：

验证码生成核心代码：

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * 动态生成一张验证码的图片
 * @author Administrator
 *
 */
public class ImageServlet extends HttpServlet {
	//生成随机字符串用到的全部字符串
	private static final char[] BASE_STRING = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".toCharArray();
	private Random random = new Random();
	private static final int WIDTH = 120;
	private static final int HEIGHT = 30;
	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		//随机的生成一个字符串
		String randomString = getRandomString(4);
		//根据这个字符串生成一张图片
		BufferedImage bi = getBufferedImageByString(randomString);
		//把这个字符串保存到session中
		req.getSession().setAttribute("code", randomString);
		//把生成好的图片返回给浏览器
		resp.setContentType("image/jpg");
		ImageIO.write(bi, "jpg", resp.getOutputStream());
	}
	private BufferedImage getBufferedImageByString(String randomString) {
		BufferedImage bi = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
		Graphics g = bi.getGraphics();
		//画一个白色的面板
		g.setColor(Color.white);
		g.fillRect(0, 0, WIDTH, HEIGHT);
		//画一个黑色的边框
		g.setColor(Color.black);
		g.drawRect(1, 1, WIDTH-2, HEIGHT-2);
		//把生成好的字符串画上去
		g.setColor(Color.red);
		g.setFont(new Font("Courier New", Font.BOLD, 20));
		char[] charArr = randomString.toCharArray();
		for(int i=0;i<charArr.length;i++){
			g.drawString(String.valueOf(charArr[i]), i*20+10, 15);
		}
		//增加干扰因素
		for(int i=0;i<5;i++){
			g.setColor(Color.black);
			int x1,y1,x2,y2;
			x1 = random.nextInt(WIDTH);
			y1 = random.nextInt(HEIGHT);
			x2 = random.nextInt(WIDTH);
			y2 = random.nextInt(HEIGHT);
			g.drawLine(x1, y1, x2, y2);
		}
		return bi;
	}
	public String getRandomString(int length) {
		char[] charArr = new char[length];
		for(int i=0;i<charArr.length;i++){
			charArr[i] = BASE_STRING[random.nextInt(BASE_STRING.length)];
		}
		return new String(charArr);
	}
	public static void main(String[] args) throws IOException {
		ImageServlet is = new ImageServlet();
		String str = is.getRandomString(4);
		BufferedImage bi = is.getBufferedImageByString(str);
		ImageIO.write(bi, "jpg", new File("d:/aaa.jpg"));
		System.out.println(str);
	}
}

登录的简单判断代码：

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 * 登录功能servlet
 * @author Administrator
 *
 */
public class LoginServlet extends HttpServlet {
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		//获取客户端输入的验证码
		String clientCode = req.getParameter("clientCode");
		//获取session中的验证码字符串
		String serverCode = (String) req.getSession().getAttribute("code");
		if(clientCode != null && clientCode.equalsIgnoreCase(serverCode)){
			resp.getWriter().print("login suceess...");
		}else{
			req.setAttribute("error", "验证错误，请重试!");
			req.getRequestDispatcher("/index.jsp").forward(req, resp);
		}
	}
}

配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <display-name></display-name>	
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
 	<servlet-name>ImageServlet</servlet-name> 
 	<servlet-class>com.servlet.ImageServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>ImageServlet</servlet-name>
  	<url-pattern>/imageServlet</url-pattern>
  </servlet-mapping>
  <servlet>
 	<servlet-name>LoginServlet</servlet-name> 
 	<servlet-class>com.servlet.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>LoginServlet</servlet-name>
  	<url-pattern>/loginServlet</url-pattern>
  </servlet-mapping>
</web-app>

简单的前台页面：

<%@ 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>My JSP 'index.jsp' starting page</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">
	<script type="text/javascript">
		function reloadPic(){
			var oImg = document.getElementById("imgId");
			oImg.src = "imageServlet?a=" + Math.random(); 
		}	
	</script>
  </head>
  <body>
  	<form action="loginServlet" method="post">
  		用户名：<input type="text"><br>
  		密码：<input type="text"><br>
  		验证码：<input type="text" name="clientCode">${error }
  		<img id="imgId" src="imageServlet" 
  		alt="验证码" title="如果看不清楚，请点我" onclick="reloadPic();"><br>
  		<input type="submit" value="登录">
  	</form>
  </body>
</html>

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