验证码的生成

例子：

生成验证码的servlet：

package yzy.servlet;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
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.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.Random;

/**
 * 验证码Servlet
 *
 * @version 1.0
 */
public class VerificationCodeImageServlet extends HttpServlet {

    //使用到Algerian字体，系统里没有的话需要安装字体，字体只显示大写，去掉了1,0,i,o几个容易混淆的字符
    private final String VERIFY_CODES = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ";

    private Random random = new Random();

    public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);
        response.setContentType("image/jpeg");

        //生成随机字串
        String verifyCode = generateVerifyCode(4, VERIFY_CODES);
        //存入会话session
        HttpSession session = request.getSession(true);
        //删除以前的
        session.removeAttribute("verCode");
        session.setAttribute("verCode", verifyCode.toLowerCase());
        //生成图片
        int w = 100, h = 30;
        Cookie cookie = new Cookie("v_c_v", verifyCode);
        cookie.setPath("/");
        response.addCookie(cookie);
        outputImage(w, h, response.getOutputStream(), verifyCode);
    }

    /**
     * 使用指定源生成验证码
     * @param verifySize    验证码长度
     * @param sources   验证码字符源
     * @return
     */
    private String generateVerifyCode(int verifySize, String sources){
        int codesLen = sources.length();
        Random rand = new Random(System.currentTimeMillis());
        StringBuilder verifyCode = new StringBuilder(verifySize);
        for(int i = 0; i < verifySize; i++){
            verifyCode.append(sources.charAt(rand.nextInt(codesLen-1)));
        }
        return verifyCode.toString();
    }

    /**
     * 输出指定验证码图片流
     * @param w
     * @param h
     * @param os
     * @param code
     * @throws IOException
     */
    private void outputImage(int w, int h, OutputStream os, String code) throws IOException{
        int verifySize = code.length();
        BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Random rand = new Random();
        Graphics2D g2 = image.createGraphics();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
        Color[] colors = new Color[5];
        Color[] colorSpaces = new Color[] { Color.WHITE, Color.CYAN,
                Color.GRAY, Color.LIGHT_GRAY, Color.MAGENTA, Color.ORANGE,
                Color.PINK, Color.YELLOW };
        float[] fractions = new float[colors.length];
        for(int i = 0; i < colors.length; i++){
            colors[i] = colorSpaces[rand.nextInt(colorSpaces.length)];
            fractions[i] = rand.nextFloat();
        }
        Arrays.sort(fractions);

        g2.setColor(Color.GRAY);// 设置边框色
        g2.fillRect(0, 0, w, h);

        Color c = getRandColor(200, 250);
        g2.setColor(c);// 设置背景色
        g2.fillRect(0, 2, w, h-4);

        //绘制干扰线
        Random random = new Random();
        g2.setColor(getRandColor(160, 200));// 设置线条的颜色
        for (int i = 0; i < 20; i++) {
            int x = random.nextInt(w - 1);
            int y = random.nextInt(h - 1);
            int xl = random.nextInt(6) + 1;
            int yl = random.nextInt(12) + 1;
            g2.drawLine(x, y, x + xl + 40, y + yl + 20);
        }

        // 添加噪点
        float yawpRate = 0.05f;// 噪声率
        int area = (int) (yawpRate * w * h);
        for (int i = 0; i < area; i++) {
            int x = random.nextInt(w);
            int y = random.nextInt(h);
            int rgb = getRandomIntColor();
            image.setRGB(x, y, rgb);
        }

        shear(g2, w, h, c);// 使图片扭曲

        g2.setColor(getRandColor(100, 160));
        int fontSize = h-4;
        Font font = new Font("Algerian", Font.ITALIC, fontSize);
        g2.setFont(font);
        char[] chars = code.toCharArray();
        for(int i = 0; i < verifySize; i++){
            AffineTransform affine = new AffineTransform();
            affine.setToRotation(Math.PI / 4 * rand.nextDouble() * (rand.nextBoolean() ? 1 : -1), (w / verifySize) * i + fontSize/2, h/2);
            g2.setTransform(affine);
            g2.drawChars(chars, i, 1, ((w-10) / verifySize) * i + 5, h/2 + fontSize/2 - 10);
        }

        g2.dispose();
        ImageIO.write(image, "jpg", os);
    }

    private Color getRandColor(int fc, int bc) {
        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);
    }

    private int getRandomIntColor() {
        int[] rgb = getRandomRgb();
        int color = 0;
        for (int c : rgb) {
            color = color << 8;
            color = color | c;
        }
        return color;
    }

    private int[] getRandomRgb() {
        int[] rgb = new int[3];
        for (int i = 0; i < 3; i++) {
            rgb[i] = random.nextInt(255);
        }
        return rgb;
    }

    private void shear(Graphics g, int w1, int h1, Color color) {
        shearX(g, w1, h1, color);
        shearY(g, w1, h1, color);
    }

    private void shearX(Graphics g, int w1, int h1, Color color) {

        int period = random.nextInt(2);

        boolean borderGap = true;
        int frames = 1;
        int phase = random.nextInt(2);

        for (int i = 0; i < h1; i++) {
            double d = (double) (period >> 1)
                    * Math.sin((double) i / (double) period
                    + (6.2831853071795862D * (double) phase)
                    / (double) frames);
            g.copyArea(0, i, w1, 1, (int) d, 0);
            if (borderGap) {
                g.setColor(color);
                g.drawLine((int) d, i, 0, i);
                g.drawLine((int) d + w1, i, w1, i);
            }
        }

    }

    private void shearY(Graphics g, int w1, int h1, Color color) {

        int period = random.nextInt(40) + 10; // 50;

        boolean borderGap = true;
        int frames = 20;
        int phase = 7;
        for (int i = 0; i < w1; i++) {
            double d = (double) (period >> 1)
                    * Math.sin((double) i / (double) period
                    + (6.2831853071795862D * (double) phase)
                    / (double) frames);
            g.copyArea(i, 0, 1, h1, 0, (int) d);
            if (borderGap) {
                g.setColor(color);
                g.drawLine(i, (int) d, i, 0);
                g.drawLine(i, (int) d + h1, i, h1);
            }

        }

    }

}

有验证码的jsp页面（前端验证）：

<form action="${pageContext.request.contextPath}/main.do" method="post">
                <div class="name">
                    <input type="text" id="name" name="username" placeholder="请输入登录用户名">
                    <p></p>
                </div>
                <div class="pwd">
                    <input type="password" id="pwd" name="password" placeholder="6-16位密码，区分大小写，不能用空格">
                    <p></p>
                </div>
                <div class="idcode">
                    <input type="text" id="verificationCode" placeholder="请输入验证码">
                    <a href='#' onclick="javascript:changeImg()">&nbsp;&nbsp;&nbsp;&nbsp;换一张</a>
                    <span><img id="img" src="${pageContext.request.contextPath}/verificationCode.do"/></span>
                    <div class="clear"></div>
                </div>
                <div class="autoLogin">
                    <label for="">
                        <input type="checkbox" checked="checked">
                        下次自动登录
                    </label>
                    <a href="">忘记密码</a>
                </div>
                <div class="btn-red">
                    <input onclick="return checkVerificationCode();" type="submit" value="登录" id="login-btn">
                </div>
            </form>

对应的js代码：

<script type="text/javascript">
            function changeImg() {
                var img = document.getElementById("img");
                img.src = "${pageContext.request.contextPath}/verificationCode.do?date=" + new Date();
            }

            function checkVerificationCode() {
                var verificationCode = document.getElementById('verificationCode').value;
                var flag = (getCookie('v_c_v').toLowerCase() == verificationCode.toLowerCase());
                if (!flag) {
                    alert('验证码输入错误');
                }
                return flag;
            }

            function getCookie(cookie_name) {
                var allCookies = document.cookie;
                var cookie_pos = allCookies.indexOf(cookie_name);   //如果找到了索引，就代表cookie存在
                if (cookie_pos != -1) {
                    cookie_pos += cookie_name.length + 1;
                    var cookie_end = allCookies.indexOf(";", cookie_pos);
                    if (cookie_end == -1) {
                        cookie_end = allCookies.length;
                    }
                    return unescape(allCookies.substring(cookie_pos, cookie_end));
                }
                return null;
            }
        </script>