一、验证码

验证码本质上是一张图片，图片内容会随着程序的运行而随机生成

验证码的作用：防止应用恶意发送数据，一定程度上避免了恶意程序对网站的攻击。验证码本质上是一张图片，图片内容的准确解析不容易用程序来实现。验证码的绘制：绘制验证码图片不仅仅需要随机生成要绘制的内容，同时要配合Java中与绘图有关的一套API来完成。

二、效果演示

验证码Demo

三、给出完整代码

(1)服务器端代码ActionServlet.java

package session;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;/** * 服务器端合并Servlet *  * @author QianliangGuo */public class ActionServlet extends HttpServlet { @Override protected void service(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException { // 设置编码 request.setCharacterEncoding("utf-8"); // 获得session HttpSession session = request.getSession(); //设置session超时时间为10秒// session.setMaxInactiveInterval(10); // 获得请求路径 String uri = request.getRequestURI(); // 拆分路径,只保留login.do中的login String action = uri.substring(uri.lastIndexOf("/") + 1,uri.lastIndexOf(".")); // 判断请求路径是否为登录 if (action.equals("login")) { String uname = request.getParameter("uname"); String pwd = request.getParameter("pwd"); //获得用户提交的验证码字符 String vcode = request.getParameter("vcode"); //获得session中存储的最新验证码字符 String code = session.getAttribute("code").toString(); if (code.equals(vcode) &&uname.equals("123") && pwd.equals("123") ) { // 将登录的用户绑定到session session.setAttribute("uname", uname); // 重定向到index.jsp// response.sendRedirect("index.jsp"); //如果禁用了Cookie,使用URL重写 response.sendRedirect(response.encodeRedirectURL("index.jsp")); } else { // 登录失败,就转发到login.jsp request.setAttribute("msg", "输入有误,请重新登录!"); request.getRequestDispatcher("login.jsp").forward(request,response); } }else if(action.equals("logout")){ //使session失效 session.invalidate(); response.sendRedirect("login.jsp"); } }}

(2)绘制验证码CodeServlet.java

package session;import java.awt.Color;import java.awt.Font;import java.awt.Graphics;import java.awt.image.BufferedImage;import java.io.IOException;import java.io.OutputStream;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;import javax.servlet.http.HttpSession;/** * 绘制验证码 *  * @author QianliangGuo */public class CodeServlet extends HttpServlet { @Override protected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //验证码的servlet //0.创建空白图片 BufferedImage image = new BufferedImage(100,30,BufferedImage.TYPE_INT_RGB); //1.获取图片画笔 Graphics g = image.getGraphics(); Random r = new Random(); //2.设置画笔颜色 g.setColor(new Color(r.nextInt(255),r.nextInt(255),r.nextInt(255))); //3.绘制矩形的背景 g.fillRect(0, 0, 100, 30); //4.调用自定义的方法,获取长度为5的字母数字组合的字符串 String number = getNumber(5); //获得session HttpSession session = request.getSession(); //设置sesssion失效时间为30秒// session.setMaxInactiveInterval(30); //将这5个随机字符绑定到session中 session.setAttribute("code", number); g.setColor(new Color(0,0,0)); g.setFont(new Font(null,Font.BOLD,24)); //5.设置颜色字体后,绘制字符串 g.drawString(number, 5, 25); //6.绘制8条干扰线 for(int i=0;i<8;i++){ g.setColor(new Color(r.nextInt(255),r.nextInt(255),r.nextInt(255),r.nextInt(255))); g.drawLine(r.nextInt(100), r.nextInt(30), r.nextInt(100), r.nextInt(30)); } response.setContentType("img/jpeg"); OutputStream ops = response.getOutputStream(); ImageIO.write(image,"jpeg",ops); ops.close();  } private String getNumber(int size) { String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; String number = ""; Random r = new Random(); for(int i=0;i

(2)登录页面login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><% Object msg = request.getAttribute("msg"); if(msg!=null){ %> <%=msg.toString() %> <%} %>    

 用户名:
 密码:
 验证码:  
   

(3)展示验证码的页面validateCode.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>

(5)index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><% //小脚本:session验证 Object uname = session.getAttribute("uname"); if(uname == null){ //重定向到login.jsp response.sendRedirect("login.jsp"); return; } %>

欢迎登录:<%=uname.toString() %>