java实现图片验证码

package cn.seeker.utils;

import javax.imageio.ImageIO;

import java.awt.*;

import java.awt.image.BufferedImage;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.OutputStream;

import java.util.*;

import java.util.List;

public class CaptchaUtil {

    public static String [] fuhao = { "+" , "-" , "*" , "/" };

    public static int num = 0 ;

    //生成随机算式

    public static String random(){

        List list = new ArrayList();

        Random ran = new Random();

        int n1 = ran.nextInt( 10 );

        int n2 = ran.nextInt( 10 );

        String f = fuhao[ran.nextInt(fuhao.length)];

        StringBuilder sb = new StringBuilder( 4 );

        switch (f){

            case "+" :

                num = n1+n2;

                break ;

            case "-" :

                num =n1-n2;

                break ;

            case "*" :

                num = n1*n2;

                break ;

            case "/" :

                if (n2 == 0 ){

                    n2 = ran.nextInt( 10 )+ 1 ;

                    num = n1/n2;

                } else {

                    num = n1/n2;

                }

                break ;

        }

        sb.append(n1);

        sb.append(f);

        sb.append(n2);

        sb.append( "=" );

        return sb.toString();

    }

    public static void outputImage(String str, OutputStream os){

        Random ran = new Random();

        //创建图片对象

        BufferedImage img = new BufferedImage( 100 , 40 , BufferedImage.TYPE_INT_RGB);

        //获取画布

        Graphics g = img.getGraphics();

        //设置背景

        g.setColor(Color.white);

        g.fillRect( 0 , 0 , 100 , 40 );

        //写字

        g.setColor(Color.black);

        g.setFont( new Font( "微软雅黑" ,Font.PLAIN, 30 ));

        g.drawString(str, 10 , 40 );

        //随机三条线

        g.drawLine(ran.nextInt( 100 ),ran.nextInt( 40 ),

                ran.nextInt( 100 ),ran.nextInt( 40 ));

        g.drawLine(ran.nextInt( 100 ),ran.nextInt( 40 ),

                ran.nextInt( 100 ),ran.nextInt( 40 ));

        g.drawLine(ran.nextInt( 100 ),ran.nextInt( 40 ),

                ran.nextInt( 100 ),ran.nextInt( 40 ));

        // 4. 输出结果

        // 常见的压缩格式：jpeg(有损压缩), png(无损压缩) ...

        try {

            ImageIO.write(img, "png" , os);

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

}

<%--

   Created by IntelliJ IDEA.

   User: Administrator

   Date: 2018/10/14

   Time: 15:43

   To change this template use File | Settings | File Templates.

--%>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

< html >

< head >

    < title >注册</ title >

    < style >

        img { cursor: pointer}

    </ style >

</ head >

< body >

< form action = "/regist" method = "post" >

    < img src = "/captcha.png" onclick = "changeImg(this)" >

    输入验证码：< input type = "text" name = "cap" >

    < input type = "submit" value = "提交" >

</ form >

< script >

    function changeImg(img) {

        // 浏览器有一个缓存特性,

        // 第一次从服务器获取图片，浏览器第二次发送请求时发现地址没有改变，就会使用第一次的图片，而不会真正发送请求

        // 为了让浏览器每次都把请求发送给服务器，给一个时间参数

        img.src = "/captcha.png?t="+new Date().getTime(); // 给src赋一个新值，就会向新值的地址发送一次请求

    }

</ script >

</ body >

</ html >

package cn.seeker.controller;

import cn.seeker.utils.CaptchaUtil;

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 (urlPatterns = "/captcha.png" )

public class CaptchaServlet extends HttpServlet {

    @Override

    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType( "image/png" );

        //获取随机字符串

        String random = CaptchaUtil.random();

        //输出图片

        CaptchaUtil.outputImage(random,response.getOutputStream());

        //存入结果

        request.getSession().setAttribute( "res" ,CaptchaUtil.num);

    }

}

package cn.seeker.controller;

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 (urlPatterns = "/regist" )

public class registServlet extends HttpServlet {

    @Override

    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String cap = req.getParameter( "cap" );

        Integer res = (Integer)req.getSession().getAttribute( "res" );

        if (Integer.parseInt(cap) == res) {

            // 填写正确，注册成功

            req.getSession().removeAttribute( "res" );

            System.out.println( "注册成功" );

            resp.sendRedirect( "/index.jsp" );

        } else {

            req.setAttribute( "error" , "验证码不正确" );

            req.getRequestDispatcher( "/jsp/regist.jsp" ).forward(req,resp);

        }

    }

}