jsp servlet 实现登陆验证码

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1.生成验证码的servlet

 - 1.生成验证码的servletpackage com.nanjing.zzu.ssp.common;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;import java.awt.*;import java.awt.image.BufferedImage;import java.io.IOException;import java.io.OutputStream;import java.util.Random;public class RandomCodeServlet extends HttpServlet {    public void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        this.doPost(request, response);    }    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        Random random = new Random();        int width = 70, height = 25;        // 创建BufferedImage对象，设置图片的长度宽度和色彩。        BufferedImage image = new BufferedImage(width, height,                BufferedImage.TYPE_INT_RGB);        OutputStream os = response.getOutputStream();        // 取得Graphics对象，用来绘制图片        Graphics g = image.getGraphics();        // 绘制图片背景和文字,释放Graphics对象所占用的资源。        g.setColor(getRandColor(200, 250));        // 设置内容生成的位置        g.fillRect(0, 0, width, height);        // 设置内容的字体和大小        g.setFont(new Font("Times New Roman", Font.PLAIN, 25));        // 设置内容的颜色：主要为生成图片背景的线条        g.setColor(getRandColor(160, 200));        // 画边框。        g.setColor(Color.BLACK);        g.drawRect(0, 0, width - 1, height - 1);        // 随机产生160条干扰线，使图象中的认证码不易被其它程序探测到。        g.setColor(Color.BLACK);        // 图片背景上随机生成155条线条，避免通过图片识别破解验证码        for (int i = 0; i < 30; i++) {            int x = random.nextInt(width);            int y = random.nextInt(height);            int xl = random.nextInt(12);            int yl = random.nextInt(12);            g.drawLine(x, y, x + xl, y + yl);        }        // 生成四位的随机数,生成一个数，写一个        String[] s = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K",                "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W",                "X", "Y", "Z","1","2","3","4","5","6","7","8","9","0"};        String content = "";        for (int i = 0; i < 4; i++) {            String rand = "";            if (random.nextBoolean()) {                rand = String.valueOf(random.nextInt(10));            } else {                int index = random.nextInt(35);                rand = s[index];            }            content += rand;            g.setColor(new Color(20 + random.nextInt(10), 20 + random                    .nextInt(110), 20 + random.nextInt(110)));            g.drawString(rand, 13 * i + 6, 20);        }        // 释放此图形的上下文以及它使用的所有系统资源，类似于关闭流        g.dispose();        // 将生成的验证码值(即运算结果的值)放到session中，以便于后台做验证。        HttpSession session = request.getSession();        session.setAttribute("result", content);        // 通过ImageIO对象的write静态方法将图片输出。        ImageIO.write(image, "JPEG", os);        os.close();    }    /**     * 生成随机颜色     *     * @param fc     * @param bc     * @return     */    public Color getRandColor(int fc, int bc) {        Random random = new Random();        if (fc > 255)            fc = 255;        if (bc > 255)            bc = 255;        int r = fc + random.nextInt(bc - fc);        int g = fc + random.nextInt(bc - fc);        int b = fc + random.nextInt(bc - fc);        return new Color(r, g, b);    }}

2.配置xml

 <servlet>        <servlet-name>RandomCode</servlet-name>        <servlet-class>com.nanjing.zzu.ssp.common.RandomCodeServlet</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>RandomCode</servlet-name>        <url-pattern>*.RandomCode</url-pattern>    </servlet-mapping>

3.登陆页面

<script type="text/javascript">   function changeImg()   {    document.getElementById("validatecodeimg").src=Math.round(Math.random()*10000)+".RandomCode ";   }</script>