在用户登录的时候，为了防止机器人攻击都会设置输入验证码，本篇文章就是介绍java如何生成验证码并使用在springMVC项目中的。

　　第一步：引入生成图片验证码的工具类

import java.awt.Color;import java.awt.Font;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.RenderingHints;import java.awt.geom.AffineTransform;import java.awt.image.BufferedImage;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.OutputStream;import java.util.Arrays;import java.util.Random; import javax.imageio.ImageIO;/** * VerifyCodeUtils Description: (验证码生成) */public class VerifyCodeUtils{         //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    public static final String VERIFY_CODES = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ";    private static Random random = new Random();      /**     * 使用系统默认字符源生成验证码     * @param verifySize    验证码长度     * @return     */    public static String generateVerifyCode(int verifySize){        return generateVerifyCode(verifySize, VERIFY_CODES);    }    /**     * 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     */    public static String generateVerifyCode(int verifySize, String sources){        if(sources == null || sources.length() == 0){            sources = VERIFY_CODES;        }        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();    }         /**     * 生成随机验证码文件,并返回验证码值     * @param w     * @param h     * @param outputFile     * @param verifySize     * @return     * @throws IOException     */    public static String outputVerifyImage(int w, int h, File outputFile, int verifySize) throws IOException{        String verifyCode = generateVerifyCode(verifySize);        outputImage(w, h, outputFile, verifyCode);        return verifyCode;    }         /**     * 输出随机验证码图片流,并返回验证码值     * @param w     * @param h     * @param os     * @param verifySize     * @return     * @throws IOException     */    public static String outputVerifyImage(int w, int h, OutputStream os, int verifySize) throws IOException{        String verifyCode = generateVerifyCode(verifySize);        outputImage(w, h, os, verifyCode);        return verifyCode;    }         /**     * 生成指定验证码图像文件     * @param w     * @param h     * @param outputFile     * @param code     * @throws IOException     */    public static void outputImage(int w, int h, File outputFile, String code) throws IOException{        if(outputFile == null){            return;        }        File dir = outputFile.getParentFile();        if(!dir.exists()){            dir.mkdirs();        }        try{            outputFile.createNewFile();            FileOutputStream fos = new FileOutputStream(outputFile);            outputImage(w, h, fos, code);            fos.close();        } catch(IOException e){            throw e;        }    }         /**     * 输出指定验证码图片流     * @param w     * @param h     * @param os     * @param code     * @throws IOException     */    public static 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 static 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 static int getRandomIntColor() {        int[] rgb = getRandomRgb();        int color = 0;        for (int c : rgb) {            color = color << 8;            color = color | c;        }        return color;    }         private static int[] getRandomRgb() {        int[] rgb = new int[3];        for (int i = 0; i < 3; i++) {            rgb[i] = random.nextInt(255);        }        return rgb;    }     private static void shear(Graphics g, int w1, int h1, Color color) {        shearX(g, w1, h1, color);        shearY(g, w1, h1, color);    }         private static 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 static 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);            }         }     }}

第二步：调用验证码的接口

/**     * 生成验证码     * @param response     */    @RequestMapping(value="newVerify" ,method=RequestMethod.GET)    public void newVerify(HttpServletRequest request, HttpServletResponse response){            //生成随机字串         String verifyCode = VerifyCodeUtils.generateVerifyCode(4);        System.out.println(verifyCode);        System.out.println(request.getSession().getAttribute("verCode"));        //删除以前的        request.getSession().removeAttribute("verCode");        //进行更新        request.getSession().setAttribute("verCode", verifyCode.toLowerCase());        System.out.println(request.getSession().getAttribute("verCode"));        //生成图片         int w = 100, h = 30;         try {            VerifyCodeUtils.outputImage(w, h, response.getOutputStream(), verifyCode);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }     }

第三步：前台界面调用

没看错，就是这一句话即可，src里面填第二步设置的url即可，当然很多场景中都会遇到点击更换验证码的情况，则需要如下这段代码

看不清，换一张

$("#changeimg").click(function(){            $("#img").attr("src", "router/newVerify?date="+new Date());        });

这里之所以后面会跟一个date参数是防止浏览器看到相同的url直接从缓存读取链接，并无任何实际意义、

第四步：后台校验验证码

String verCode = (String)request.getSession().getAttribute("verCode");boolean flag = verCode.equals(yzm.toLowerCase());

flag为true则验证成功，false则验证码输入错误。

至此，结束。