使用Servlet生成验证码图片

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使用Servlet生成验证码效果

这里写图片描述

实现原理

使用java.awt.image.BufferedImage创建图片
在图片上绘制验证信息（我这里写一个数学表达式）
在图片上添加干扰线
用Servlet控制响应头使浏览器以图片的方式打开
并设置浏览器不缓存当前文档
用ImageIO.write()方法输出

import javax.imageio.ImageIO;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.awt.*;import java.awt.image.BufferedImage;import java.io.IOException;import java.util.Random;/** * Created by kay on 2016/10/21. */@WebServlet(name = "ResponseImage3",urlPatterns = {"/responseimage3"})public class ResponseImage3 extends HttpServlet {    public static final int WIDTH=120;    public static final int HEIGHT=30;    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        BufferedImage image=new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_BGR);        Graphics g=image.getGraphics();        //背景        g.setColor(Color.white);        g.fillRect(0,0,WIDTH,HEIGHT);        //边框        g.setColor(Color.BLACK);        g.drawRect(1,1,WIDTH-2,HEIGHT-2);        drawRandomLine(g);        //生成随机数        Random random=new Random();        int a=random.nextInt(100);        int b=random.nextInt(100);        int sum=a+b;        Graphics2D g1=(Graphics2D)g;        g1.setColor(Color.BLACK);        g1.setFont(new Font(null,Font.ITALIC,20));        g1.drawString(a+"+"+b+"= ?",20,HEIGHT-5);         //将验证结果保存到Session中        request.getSession().setAttribute("checkcode1",sum+"");        //设置浏览器以图片格式输出        response.setContentType("image/jpeg");        //设置响应头控制浏览器不要缓存        response.setDateHeader("expries", -1);        response.setHeader("Cache-Control", "no-cache");        response.setHeader("Pragma", "no-cache");        //将图片写给浏览器        ImageIO.write(image, "jpg", response.getOutputStream());    }    //画几条随机的干扰线    private void drawRandomLine(Graphics g) {        // 设置颜色        g.setColor(Color.GREEN);        // 设置线条个数并画线        for (int i = 0; i < 5; i++) {            int x1 = new Random().nextInt(WIDTH);            int y1 = new Random().nextInt(HEIGHT);            int x2 = new Random().nextInt(WIDTH);            int y2 = new Random().nextInt(HEIGHT);            g.drawLine(x1, y1, x2, y2);        }    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doPost(request,response);    }}

前台写一个Form表单用来验证

<%--  Created by IntelliJ IDEA.  User: Administrator  Date: 2016/10/21  Time: 17:41  To change this template use File | Settings | File Templates.--%><%@ page import="java.util.*" contentType="text/html;charset=UTF-8" language="java" %><html><head>    <title>Title</title>    <script type="text/javascript">        //刷新验证码        function changeImg(){            document.getElementById("validateCodeImg").src="${pageContext.request.contextPath}/responseimage3?"+Math.random();        }    </script></head><body><form action="${pageContext.request.contextPath}/checkimage" method="post">    验证码：<input type="text" name="validateCode"/>    <img alt="验证码看不清，换一张" src="${pageContext.request.contextPath}/responseimage3" id="validateCodeImg" onclick="changeImg()">    <a href="javascript:void(0)" onclick="changeImg()">看不清，换一张</a>    <br/>    <input type="submit" value="提交"></form></body></html>

注意：function changeImg(){            document.getElementById("validateCodeImg").src="${pageContext.request.contextPath}/responseimage3?"+Math.random();}
调用生成验证码图片的Servlet的时候传入一个随机的参数（Math.random），是为了与上一次的请求相区别，服务器对2次相同的请求会返回同一个结果，为了刷新图片那需要使用不同的请求。

提交验证码之后传到CheckImage这个servlet来检查是否输入正确

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;/** * Created by kay on 2016/10/21. */@WebServlet(name = "CheckImage",urlPatterns = {"/checkimage"})public class CheckImage extends HttpServlet {    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        String clientCheckcode = request.getParameter("validateCode");//接收客户端浏览器提交上来的验证码        String serverCheckcode = (String) request.getSession().getAttribute("checkcode");//从服务器端的session中取出验证码        String checkcode1=(String) request.getSession().getAttribute("checkcode1");        if (clientCheckcode.equals(checkcode1)) {//将客户端验证码和服务器端验证比较，如果相等，则表示验证通过            System.out.println("验证码验证通过！");            response.sendRedirect(request.getContextPath()+"/success.jsp");        }else {            System.out.println("验证码验证失败！");            response.sendRedirect(request.getContextPath()+"/failure.jsp");        }    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doPost(request,response);    }}

到此这个小功能就完成了。点击图片更换验证码，输入结果进行验证。

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