java实现图片验证码

这段时间一直在忙着搞课设，没顾得上写，今天终于找到了一点时间，赶快开写啦~

ImageServlet.java（image.do）：用于生成验证码图片

package com.ymw.web.servlet;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class ImageServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        int width = 80;// 验证码图片宽度
        int height = 26;// 验证码图片高度
        BufferedImage image = new BufferedImage(width, height,
                BufferedImage.TYPE_3BYTE_BGR);
        Graphics g = image.getGraphics();
        Random random = new Random();// 创建一个随机类
        g.setColor(getRandColor(200, 250));// 背景颜色要偏淡
        g.fillRect(0, 0, width, height);// 画背景
        g.setColor(getRandColor(0, 255));// 边框颜色
        g.drawRect(0, 0, width - 1, height - 1);// 画边框
        g.setColor(getRandColor(160, 200));// 随机产生5条干扰线，使图象中的认证码不易被其它程序探测到
        for (int i = 0; i < 8; i++) {
            int x = random.nextInt(width);
            int y = random.nextInt(height);
            int x1 = random.nextInt(width);
            int y1 = random.nextInt(height);
            g.drawLine(x, y, x1, y1);
        }
        g.setColor(getRandColor(160, 200));// 随机产生100点，使图象中的认证码不易被其它程序探测到
        for (int i = 0; i < 100; i++) {
            int x = random.nextInt(width);
            int y = random.nextInt(height);
            g.drawLine(x, y, x, y);
        }
        Font font = new Font("Times New Roman", Font.ITALIC, 20); // 创建字体，字体的大小应该根据图片的高度来定。
        g.setFont(font);// 设置字体
        int length = 4; // 设置默认生成4个验证码
        String s = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; // 设置备选验证码:包括"a-z"和数字"0-9"
        String sRand = "";

        // 用随机产生的颜色将验证码绘制到图像中。
        // 生成随机颜色(因为是做前景，所以偏深)
        // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
        g.setColor(new Color(20 + random.nextInt(110),
                20 + random.nextInt(110), 20 + random.nextInt(110)));
        for (int i = 0; i < length; i++) {
            String ch = String.valueOf(s.charAt(random.nextInt(s.length())));
            sRand += ch;
            g.drawString(ch, 11 * i + 12, (random.nextInt(5) - 2) * i + 20);
        }
        // 将生成的字符串存储在session中（这点很重要！之后验证时要用到！）
        HttpSession session = request.getSession();
        session.setAttribute("checkCode", sRand);
        g.dispose();// 图像生效
        // 禁止图像缓存
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);
        response.setContentType("image/jpeg");
        // 创建二进制的输出流
        ServletOutputStream sos = response.getOutputStream();
        // 将图像输出到Servlet输出流中。
        ImageIO.write(image, "jpeg", sos);
        sos.flush();
        sos.close();
    }

    public Color getRandColor(int lower, int upper) {
        Random random = new Random();
        if (upper > 255)
            upper = 255;
        if (upper < 1)
            upper = 1;
        if (lower < 1)
            lower = 1;
        if (lower > 255)
            lower = 255;
        int r = lower + random.nextInt(upper - lower);
        int g = lower + random.nextInt(upper - lower);
        int b = lower + random.nextInt(upper - lower);
        return new Color(r, g, b);
    }
}

login.jsp：使用到验证码的页面（该页面要提交给Login.do—LoginServlet.java）

<script> function changeImage(){ var obj = document.getElementById("image"); obj.src = "image.do?r="+Math.random(); } </script>

    。。。

<tr>
    <td class="field">验证码：</td>
    <td><input type="text" name="veryCode" /><img id="image" src="image.do" /><a onclick="changeImage()" style="cursor:pointer">看不清楚？点击这里更换</a><br />${imageCodeResult }</td>
</tr>

style=”cursor:pointer”鼠标移上是手型；

LoginServlet.java：用于处理login.jsp提交上来的请求

public class LoginServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        request.setCharacterEncoding("utf-8");//解决乱码问题
        String veryCode = request.getParameter("veryCode");//得到用户输入的验证码

            //先将从session中获取的验证码与用户输入的验证码进行比较，如果相同再验证用户名和密码，否则将错误信息带回登陆界面
            if(veryCode.equals(session.getAttribute("checkCode"))){

            //进行其他信息的验证

             }else {

                String imageCodeResult="验证码输入错误，请重新输入！";
                //千万不要忘记把表示验证情况的信息放到request中去，否则前台是不能看到的
                request.setAttribute("imageCodeResult", imageCodeResult);
                request.getRequestDispatcher("login.jsp")
                .forward(request, response);

            }
        } 
}