使用Servlet动态生成验证码

      最近在重新看了一遍servlert，看到篇优质博客推荐给大家：https://www.cnblogs.com/xdp-gacl/p/3798190.html

      顺便把学习过程中的知识记录下来。

      今天是如何用servlet生成几种简单的验证码，当然了网上也有各种各样的验证码插件，感兴趣的自己找一下用。

      我们是通过BufferedImage这个类来生成生成图片， BufferedImage是Image的一个子类，BufferedImage生成的图片在内存里有一个图像缓冲区，利用这个缓冲区我们可以很方便的操作这个图片，通常用来做图片修改操作如大小变换、图片变灰、设置图片透明或不透明等。

      总共需要三个文件：

      DrawImage  Servlet，用来生成验证码图片。

      drawimage.jsp，用来测试的页面。

      CheckServlet，用来处理验证码。  

      DrawImage.java

package com.java.controller;

import javax.imageio.ImageIO;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;


public class DrawImage extends HttpServlet {
    public static final int WIDTH = 120;//生成图片的宽度
    public static final int HEIGHT = 30;//生成图片的高度

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

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
        //获取创建验证码类型
        String createTypeFlag = request.getParameter("createTypeFlag");
        //在内存中创建一张图片
        BufferedImage bi = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
        //获取图片
        Graphics g = bi.getGraphics();
        //设置图片背景颜色
        setBackGround(g);
        //设置背景边框
        setBorder(g);
        //在图片上画随机线条
        drawRandomLine(g);
        //写在图片上随机数
        //String random = drawRandomNum((Graphics2D) g,"ch");//生成中文验证码图片
        //String random = drawRandomNum((Graphics2D) g,"nl");//生成数字和字母组合的验证码图片
        //String random = drawRandomNum((Graphics2D) g,"n");//生成纯数字的验证码图片
        //String random = drawRandomNum((Graphics2D) g,"l");//生成纯字母的验证码图片
        String random = drawRandomNum((Graphics2D) g, createTypeFlag);//根据客户端传递的createTypeFlag标识生成验证码图片
        //将随机数存到session中
        request.getSession().setAttribute("checkcode", random);
        //设置响应头，通知浏览器以图片的形式打开
        response.setContentType("image/jpeg");//等价于response.setHeader("Content-Type","UTF-8");
        //设置响应头，控制浏览器不要缓存
        response.setDateHeader("expires", -1);
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        ImageIO.write(bi, "jpg", response.getOutputStream());
    }

    /**
     * 写在图片上的随机数
     * @param g
     * @param createTypeFlag
     * @return
     */
    private String drawRandomNum(Graphics2D g, String... createTypeFlag) {
        //设置颜色
        g.setColor(Color.red);
        //设置字体
        g.setFont(new Font("宋体",Font.BOLD,20));
        //一些中国汉字
        String baseChineseChar = "u7684u4e00u4e86u662fu6211u4e0du5728u4ebau4eecu6709u6765u4ed6u8fd9u4e0au7740u4e2a" +
                "u5730u5230u5927u91ccu8bf4u5c31u53bbu5b50u5f97u4e5fu548cu90a3u8981u4e0bu770bu5929u65f6u8fc7u51fau5c0fu4e48" +
                "u8d77u4f60u90fdu628au597du8fd8u591au6ca1u4e3au53c8u53efu5bb6u5b66u53eau4ee5u4e3bu4f1au6837u5e74u60f3u751fu540c" +
                "u8001u4e2du5341u4eceu81eau9762u524du5934u9053u5b83u540eu7136u8d70u5f88u50cfu89c1u4e24u7528u5979u56fdu52a8u8fdbu6210" +
                "u56deu4ec0u8fb9u4f5cu5bf9u5f00u800cu5df1u4e9bu73b0u5c71u6c11u5019u7ecfu53d1u5de5u5411u4e8bu547du7ed9u957fu6c34" +
                "u51e0u4e49u4e09u58f0u4e8eu9ad8u624bu77e5u7406u773cu5fd7u70b9u5fc3u6218u4e8cu95eeu4f46u8eabu65b9u5b9eu5403u505a" +
                "u53ebu5f53u4f4fu542cu9769u6253u5462u771fu5168u624du56dbu5df2u6240u654cu4e4bu6700u5149u4ea7u60c5u8defu5206" +
                "u603bu6761u767du8bddu4e1cu5e2du6b21u4eb2u5982u88abu82b1u53e3u653eu513fu5e38u6c14u4e94u7b2cu4f7fu5199u519b" +
                "u5427u6587u8fd0u518du679cu600eu5b9au8bb8u5febu660eu884cu56e0u522bu98deu5916u6811u7269u6d3bu90e8u95e8u65e0" +
                "u5f80u8239u671bu65b0u5e26u961fu5148u529bu5b8cu5374u7ad9u4ee3u5458u673au66f4u4e5du60a8u6bcfu98ceu7ea7u8ddf" +
                "u7b11u554au5b69u4e07u5c11u76f4u610fu591cu6bd4u9636u8fdeu8f66u91cdu4fbfu6597u9a6cu54eau5316u592au6307u53d8" +
                "u793eu4f3cu58ebu8005u5e72u77f3u6ee1u65e5u51b3u767eu539fu62ffu7fa4u7a76u5404u516du672cu601du89e3u7acbu6cb3" +
                "u6751u516bu96beu65e9u8bbau5417u6839u5171u8ba9u76f8u7814u4ecau5176u4e66u5750u63a5u5e94u5173u4fe1u89c9u6b65" +
                "u53cdu5904u8bb0u5c06u5343u627eu4e89u9886u6216u5e08u7ed3u5757u8dd1u8c01u8349u8d8au5b57u52a0u811au7d27u7231" +
                "u7b49u4e60u9635u6015u6708u9752u534au706bu6cd5u9898u5efau8d76u4f4du5531u6d77u4e03u5973u4efbu4ef6u611fu51c6" +
                "u5f20u56e2u5c4bu79bbu8272u8138u7247u79d1u5012u775bu5229u4e16u521au4e14u7531u9001u5207u661fu5bfcu665au8868" +
                "u591fu6574u8ba4u54cdu96eau6d41u672au573au8be5u5e76u5e95u6df1u523bu5e73u4f1fu5fd9u63d0u786eu8fd1u4eaeu8f7b" +
                "u8bb2u519cu53e4u9ed1u544au754cu62c9u540du5440u571fu6e05u9633u7167u529eu53f2u6539u5386u8f6cu753bu9020u5634" +
                "u6b64u6cbbu5317u5fc5u670du96e8u7a7fu5185u8bc6u9a8cu4f20u4e1au83dcu722cu7761u5174u5f62u91cfu54b1u89c2u82e6" +
                "u4f53u4f17u901au51b2u5408u7834u53cbu5ea6u672fu996du516cu65c1u623fu6781u5357u67aau8bfbu6c99u5c81u7ebfu91ce" +
                "u575au7a7au6536u7b97u81f3u653fu57ceu52b3u843du94b1u7279u56f4u5f1fu80dcu6559u70edu5c55u5305u6b4cu7c7bu6e10" +
                "u5f3au6570u4e61u547cu6027u97f3u7b54u54e5u9645u65e7u795eu5ea7u7ae0u5e2eu5566u53d7u7cfbu4ee4u8df3u975eu4f55u725bu53d6u5165u5cb8" +
                "u6562u6389u5ffdu79cdu88c5u9876u6025u6797u505cu606fu53e5u533au8863u822cu62a5u53f6u538bu6162u53d4u80ccu7ec6";
        //数字和字母结合
        String baseNumLetter = "0123456789ABCDEFGHJKLMNOPQRSTUVWXYZ";
        //纯数字
        String baseNum = "0123456789";
        //纯英文
        String baseLetter = "ABCDEFGHJKLMNOPQRSTUVWXYZ";
        //判断验证码类型
        if(createTypeFlag.length>0&&null!=createTypeFlag[0]){
            if (createTypeFlag[0].equals("ch")) {
                                // 截取汉字
                               return createRandomChar(g, baseChineseChar);
                         }else if (createTypeFlag[0].equals("nl")) {
                              // 截取数字和字母的组合
                               return createRandomChar(g, baseNumLetter);
                          }else if (createTypeFlag[0].equals("n")) {
                               // 截取数字
                             return createRandomChar(g, baseNum);
                         }else if (createTypeFlag[0].equals("l")) {
                                // 截取字母
                                return createRandomChar(g, baseLetter);
                            }
        }else {
            // 默认截取数字和字母的组合
            return createRandomChar(g, baseNumLetter);
        }
        return "";
    }

    /**
     * 创建随机字符
     * @param g
     * @param baseChar
     * @return
     */
        private String createRandomChar(Graphics2D g,String baseChar) {
              StringBuffer sb = new StringBuffer();
              int x = 5;
              String ch ="";
                 // 控制字数
               for (int i = 0; i < 4; i++) {
                        // 设置字体旋转角度
                       int degree = new Random().nextInt() % 30;
                        ch = baseChar.charAt(new Random().nextInt(baseChar.length())) + "";
                       sb.append(ch);
                        // 正向角度
                       g.rotate(degree * Math.PI / 180, x, 20);
                      g.drawString(ch, x, 20);
                       // 反向角度
                       g.rotate(-degree * Math.PI / 180, x, 20);
                       x += 30;
                    }
                return sb.toString();
              }



    /**
     * 设置背景颜色
     */
    private void setBackGround(Graphics g) {
        // 设置颜色
        g.setColor(Color.WHITE);
        // 填充区域
        g.fillRect(0, 0, WIDTH, HEIGHT);
    }

    /**
     * 设置背景边框
     */
    private void setBorder(Graphics g) {
        //设置边框颜色
        g.setColor(Color.BLUE);
        // 边框区域
        g.drawRect(1, 1, WIDTH - 2, HEIGHT - 2);
    }

    /**
     * 在图片上画随机线条
     */
    private void drawRandomLine(Graphics g) {
        // 设置颜色
        g.setColor(Color.GREEN);
        // 设置线条个数并画线
        for (int i = 0; i < 5; i++) {
            int x1 = new Random().nextInt(WIDTH);
            int y1 = new Random().nextInt(HEIGHT);
            int x2 = new Random().nextInt(WIDTH);
            int y2 = new Random().nextInt(HEIGHT);
            g.drawLine(x1, y1, x2, y2);
        }

    }
}

   在Form表单中测试验证码：

<%@ page contentType="text/html;charset=UTF-8" language="java" import="java.util.*" %>
<html>
<head>
    <title>验证码</title>
    <script>
    //刷新验证码
    function changeImg(object,createTpeFlag){
    document.getElementById(object.id).src="${pageContext.request.contextPath}/drawimage?createTypeFlag="+createTpeFlag+"&"+Math.random();
    }
    </script>
</head>
<body>
<form action="${pageContext.request.contextPath}/CheckServlet" method="post">
    数字字母混合验证码:<input   type="text" name="validateCode" >
    <img src="${pageContext.request.contextPath}/drawimage" id="validateCodeImg1" onclick="changeImg(this,'nl')" alt="看不清，换一张">
    <br/>
    中文验证码:<input   type="text" name="validateCode" >
    <img src="${pageContext.request.contextPath}/drawimage?createTypeFlag=ch" id="validateCodeImg2" onclick="changeImg(this,'ch')" alt="看不清，换一张">
    <br/>
    英文验证码:<input   type="text" name="validateCode" >
    <img src="${pageContext.request.contextPath}/drawimage?createTypeFlag=l" id="validateCodeImg3" onclick="changeImg(this,'l')" alt="看不清，换一张">
    <br/>
    数字验证码:<input   type="text" name="validateCode" >
    <img src="${pageContext.request.contextPath}/drawimage?createTypeFlag=n" id="validateCodeImg4" onclick="changeImg(this,'n')" alt="看不清，换一张">
    <br/>
    <input type="submit" value="提交验证码">
</form>
</body>
</html>

  CheckServlet.java处理表单提交：

  

package com.java.controller;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class CheckServlet extends HttpServlet {
   public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
      String checkcode= request.getSession().getAttribute("checkcode").toString();
      String code=(String) request.getParameter("validateCode");
       String message="";
      if(checkcode.equals(code)){
           message="验证码正确";
      }
      else{
          message="验证码错误";
      }
       response.setContentType("text/html;charset=utf-8");
       response.getWriter().print(message);
   }
} 

  好了，现在我们可以测试一下啦。

   

   我们输入正确的验证码之后浏览器就会返回提示