servlet实现简单验证码

1.创建演示登录界面

https://www.cnblogs.com/YorkZhangYang/p/12538576.html

2.创建生成验证码的servlet类VerifyCodeImg.java

package 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.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class VerifyCodeImg
 */
@WebServlet("/VerifyCodeImg")
public class VerifyCodeImg extends HttpServlet {
    private static final long serialVersionUID = 1L;

    private static final int WIDTH = 100;//设置验证码图片宽度
    private static final int HEIGHT = 30;//设置验证码图片高度
    private static final int LENGTH = 4;//设置验证码长度
    public static final int LINECOUNT=20;//干扰线的数目

    //验证码的字符库
    private static final String str="0123456789"+
                                    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"+
                                    "abcdefghijklmnopqrstuvwxyz";

    //通过随机数取字符库中的字符组合成4位验证码
    private static Random random=new Random();

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置数据类型为图片
        resp.setContentType("image/jpeg");

        //设置不进行缓存
        resp.setHeader("pragma", "no-cache");
        resp.setHeader("cache-control", "no-cache");
        resp.setHeader("expires", "0");



        //获取画笔
        BufferedImage image=new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_3BYTE_BGR);
        Graphics g=image.getGraphics();

        //设置背景颜色并绘制矩形背景
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, WIDTH, HEIGHT);

        //验证码的绘制
        String code=drawChar(g);
        System.out.println("验证码:"+code);
        
        

        //随机线的绘制
        for (int i=0;i<LINECOUNT;i++){
            drawLine(g);
        }

        //在session中存入当前的code码，便于验证
        req.getSession().setAttribute("code",code);

        //绘制图片
        g.dispose();

        //将图片输出到response中
        ImageIO.write(image, "JPEG", resp.getOutputStream());
    }


    //获取不同颜色
    public  Color getColor(){
        return new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255));
    }

    //获取字体样式
    public Font getFont() {
        return new Font("Fixedsys", Font.CENTER_BASELINE, 20);
    }

    //绘制字符
    public String drawChar(Graphics g){
        String code="";
        g.setFont(getFont());
        for (int i=0;i<LENGTH;i++){
            char c=str.charAt(random.nextInt(str.length()));
            g.setColor(getColor());
            g.drawString(c+"", 20* i + 10, 20);
            code=code+c;
        }
        return code;
    }

    //绘制随机线
    public  void drawLine(Graphics g) {
        int x = random.nextInt(WIDTH);
        int y = random.nextInt(HEIGHT);
        int xl = random.nextInt(13);
        int yl = random.nextInt(15);
        g.setColor(getColor());
        g.drawLine(x, y, x + xl, y + yl);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

3.修改前台页面Login.jsp

 <div class="form-group">
                    <label for="validateCode" class="col-sm-4 control-label">验证码</label>
                    <div class="col-sm-4">
                      <input type="text" class="form-control" id="validateCode" name="validateCode" placeholder="验证码">
                    </div>
                    <div class="col-sm-4">
                        <img id="verifyCode" src="${pageContext.request.contextPath}/VerifyCodeImg" alt="Loading" width="75px" height="35px" onclick="changeCode()">
                      </div>
                  </div>

4.实现点击修改的js代码changeCode方法

//验证码更换
      function changeCode() {
          var codeImg=document.getElementById("verifyCode");
          //这里URL后追加随机数，使程序每次访问的都是不同的资源，防止浏览器缓存，即产生不同的验证码
          codeImg.src="/LoginTest/VerifyCodeImg?d="+Math.random();
      }

5.显示界面

参考文章：

https://www.cnblogs.com/Alice-Thinker/p/8400318.html