session的典型案例三:实现一次性验证码

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生成验证码的工具类：

package com.sa.util;import java.awt.Color;import java.awt.Font;import java.awt.Graphics2D;import java.awt.image.BufferedImage;import java.io.IOException;import java.util.Random;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import com.sun.image.codec.jpeg.JPEGCodec;import com.sun.image.codec.jpeg.JPEGImageEncoder;/** * 验证码图片生成Servlet类，直接调用该Servlet即可使用 * 取值的时候调用session.getAttribute("code")得到生成的值 * @author <a href="mailto:weijunqiang2010@gmail.com">Ajunboys</a> * */@WebServlet("/verifycode")public class VerifyCodeUtil extends HttpServlet {    private static final long serialVersionUID = 1L;    static final char[] dictionary = {            '2','3','4','5','6','7','8','9'            ,'a','b','c','d','e','f','g','h','i','j'            ,'k','m','n','p','q','r','s','t'            ,'u','v','w','x','y','z'            ,'A','B','C','D','E','F','G','H','J'            ,'K','L','M','N','P','Q','R','S','T'            ,'U','V','W','X','Y','Z'            /*'1','l','0','O','o','#','@','$','%','&','(',')','|','/','*'//暂时不用特殊字符(包括：数字1,0；字母：l,o,O)            ,'^','!','~','\\'*/    };    static Random random = new Random();    /**     * 产生n[4,4+]个随机数     * @param n     * @return     */    static String getRandomString(int n){        StringBuffer buffer = new StringBuffer();        if (n < 4) {            n = 4;        }        for (int i = 0; i < n; i++) {            buffer.append(dictionary[random.nextInt(dictionary.length)]);        }        return buffer.toString();    }    /**     * 随机颜色     * @return     */    static Color getRandomColor(){        return new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255));    }    /**     * 颜色反色     * @param c     * @return     */    static Color getReverseColor(Color c){        return new Color(255 - c.getRed(), 255 - c.getGreen(), 255 - c.getBlue());    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doPost(request, response);    }    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        response.setContentType("image/jpeg");        String randomString = getRandomString(6);        request.getSession(true).setAttribute("code", randomString);        int width = 100; //验证码图片宽度        int height = 30; //验证码图片高度        Color color = getRandomColor();        Color reverse = getReverseColor(color);        //创建一个彩图        BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);        //绘图对象        Graphics2D g = bi.createGraphics();        g.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 16));        g.setColor(color);        g.fillRect(0, 0, width, height);        g.setColor(reverse);        g.drawString(randomString, 18, 20);        //绘制最多100个噪音点        for (int i = 0, n = random.nextInt(100); i < n; i++) {            g.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);        }        ServletOutputStream out = response.getOutputStream();        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);        encoder.encode(bi);        out.flush();        out.close();    }}

登录页面：

<%--  Created by IntelliJ IDEA.  User: 123  Date: 2017/10/9  Time: 8:57  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %><html><head>    <title>验证码</title>    <script>        function reload() {            console.log(1);            var img = document.getElementById("img");            img.src = "<%=request.getContextPath()%>/verifycode?num="+Math.random();            //img.src=img.src        }    </script></head><body>    <form action="<%=request.getContextPath()%>/loginServlet" method="post">        name:<input type="text" name="name"/>        password:<input type="password" name="password"/>        verify:<input type="text" name="verify"/>        <img src="<%=request.getContextPath()%>/verifycode" id="img"/>        <a href="javascript:reload();">看不清,换一张?</a>        <input type="submit" value="提交">    </form></body></html>

逻辑判断：

package com.sa.servlet;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;//@WebServlet(name = "loginServlet")public class LoginServlet extends HttpServlet {    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        System.out.println(1);        String verifyCode=(String) request.getParameter("verify");          String code=(String) request.getSession().getAttribute("code");          if(code.equalsIgnoreCase(verifyCode)){              response.sendRedirect(request.getContextPath()+"/pages/success.jsp");          }else{              response.sendRedirect(request.getContextPath()+"/pages/failed.jsp");          }    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {    }}

测试：

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