在进行登陆的时候，往往会需要输入验证码，那么验证码是怎么实现的呢?
首先我们的验证码图片是在JSP页面中展示的，所以先从JSP页面入手。
登录界面->后台生成图片和这个图片对应的数字（把数字存入session）->前台的jsp页面获得图片所对应的数字->当用户点击提交后判断用户输入的与存储的数字是否一样。
- 登录主页面（login.jsp）
1. <%@ page language="java""text/html; charset=UTF-8"
2. "UTF-8"%>
3. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
4. <html>
5. <head>
6. <meta http-equiv="Content-Type""text/html; charset=UTF-8">
7. <title>登录</title>
8. <script type="text/javascript">
9. function refresh() {
10. //IE存在缓存,需要new Date()实现更换路径的作用
11. "image").src="../login/image.jsp?"+new Date();
12. }
13. </script>
14. </head>
15. <body>
16. "../login/check.jsp""post""loginForm""loginForm">
17. 用户名：<input type="text""userName">
18. 密码：<input type="password""userPwd">
19. 验证码：<input type="text""code""4">
20. "image""0""refresh()""../login/image.jsp""点击更换图片">
21. "submit""登录">
22. </form>
23. </body>
24. </html> 2. 验证码生成jsp(image.jsp)
25. <%@pageimport="javax.imageio.ImageIO"%>
26. <%@pageimport="java.awt.Font"%>
27. <%@pageimport="java.awt.Graphics"%>
28. <%@pageimport="java.awt.image.BufferedImage"%>
29. <%@pageimport="java.util.Random"%>
30. <%@pageimport="java.awt.Color"%>
31. <%@ page language="java""image/JPEG; charset=UTF-8"
32. "UTF-8"%>
33. <%!
34. //获取随机颜色
35. intint bc){
36. new Random();
37. if(fc>255) fc=255;
38. if(bc>255) bc=255;
39. int r = fc + random.nextInt(bc - fc);
40. int g = fc + random.nextInt(bc - fc);
41. int b = fc + random.nextInt(bc - fc);
42. returnnew Color(r,g,b);
43. }
44. %>
45. <%
46. //设置页面不缓存
47. "Pragma", "No-cache");
48. "Cache-Control", "no-cache");
49. "Expires", 0);
50. //在内存中创建图像
51. int60;
52. int20;
53. new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
54. //获取图形上下文
55. Graphics g = image.getGraphics();
56. //随机类
57. new Random();
58. //设定背景
59. 200, 250));
60. 0, 0, width, height);
61. //设定字体
62. new"Times New Roman",Font.PLAIN,18));
63. //随机产生干扰线
64. 160, 200));
65. forint0; i < 100; i++) {
66. int x = random.nextInt(width);
67. int y = random.nextInt(height);
68. int12);
69. int12);
70. g.drawLine(x, y, x + xl, y + yl);
71. }
72. //随机产生4位验证码
73. "2","3","4","5","6","7","8","9","A","B","C","D","E","F","G","H","J","K","L","M","N","P","Q","R","S","T","U","V","W","X","Y","Z"};
74. "";
75. for(int0;i<4;i++){
76. String str = codes[random.nextInt(codes.length)];
77. code += str;
78. // 将认证码显示到图象中
79. new20110), 20110), 20110)));
80. //调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
81. 136, 16);
82. }
83. // 将认证码存入SESSION
84. "code", code);
85. // 图象生效
86. g.dispose();
87. // 输出图象到页面
88. "JPEG", response.getOutputStream());
89. //加上下面代码,运行时才不会出现java.lang.IllegalStateException: getOutputStream() has already been called ..........等异常
90. response.getOutputStream().flush();
91. response.getOutputStream().close();
92. response.flushBuffer();
93. out.clear();
94. out = pageContext.pushBody();
95. %> 3. 验证码检查页面（check.jsp：检查验证码是否输入正确）
96. <%@ page language="java""text/html; charset=UTF-8"
97. "UTF-8"%>
98. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
99. <html>
100. <head>
101. <meta http-equiv="Content-Type""text/html; charset=UTF-8">
102. <title>验证</title>
103. <script type="text/javascript">
104. function same(){
105. "login/login_login";
106. loginForm.submit();
107. }
108. function different(){
109. "请输入正确的验证码");
110. "login.jsp";
111. }
112. </script>
113. </head>
114. <body>
115. <%
116. "userName");
117. "userPwd");
118. %>
119. "loginForm""loginForm""post">
120. "hidden""userName""user.userName">
121. "hidden""userPwd""user.userPwd">
122. </form>
123. <%
124. "code").toString();
125. "code");
126. if(rand.equals(input)){
127. "<script language='javascript'>same();</script>");
128. else{
129. "<script language='javascript'>different();</script>");
130. }
131. %>
132. </body>
</html>
最近学习了博主：孤傲苍狼的写法，在这里把它记录下来。
代码如下：
package com.qq.image;
/**
* @Description:
* @Author: ZHENGZHIQIANG
* @CreateTime: 2019-03-25 16:45
*/
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
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;
/**
* 生成随机图片，用来作为验证码
*/
@WebServlet("/imageServlet")
public class ImageServlet extends HttpServlet {
private static final long serialVersionUID = 3038623696184546092L;
public static final int WIDTH = 120;//生成的图片的宽度
public static final int HEIGHT = 30;//生成的图片的高度
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String createTypeFlag = request.getParameter("createTypeFlag");//接收客户端传递的createTypeFlag标识
//1.在内存中创建一张图片
BufferedImage bi = new BufferedImage(WIDTH, HEIGHT,BufferedImage.TYPE_INT_RGB);
//2.得到图片
Graphics g = bi.getGraphics();
//3.设置图片的背影色
setBackGround(g);
//4.设置图片的边框
setBorder(g);
//5.在图片上画干扰线
drawRandomLine(g);
//6.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
//7.将随机数存在session中
request.getSession().setAttribute("checkcode", random);
//8.设置响应头通知浏览器以图片的形式打开
response.setContentType("image/jpeg");//等同于response.setHeader("Content-Type", "image/jpeg");
//9.设置响应头控制浏览器不要缓存
response.setDateHeader("expries", -1);
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
//10.将图片写给浏览器
ImageIO.write(bi, "jpg", response.getOutputStream());
}
/**
* 设置图片的背景色
* @param g
*/
private void setBackGround(Graphics g) {
// 设置颜色
g.setColor(Color.WHITE);
// 填充区域
g.fillRect(0, 0, WIDTH, HEIGHT);
}
/**
* 设置图片的边框
* @param g
*/
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
* @param g
*/
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);
}
}
/**
* 画随机字符
* @param g
* @param createTypeFlag
* @return
* String... createTypeFlag是可变参数，
* Java1.5增加了新特性：可变参数：适用于参数个数不确定，类型确定的情况，java把可变参数当做数组处理。注意：可变参数必须位于最后一项
*/
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));
//常用的中国汉字
String baseChineseChar = "\u7684\u4e00\u4e86\u662f\u6211\u4e0d\u5728\u4eba\u4eec\u6709\u6765\u4ed6\u8fd9\u4e0a\u7740\u4e2a\u5730\u5230\u5927\u91cc\u8bf4\u5c31\u53bb\u5b50\u5f97\u4e5f\u548c\u90a3\u8981\u4e0b\u770b\u5929\u65f6\u8fc7\u51fa\u5c0f\u4e48\u8d77\u4f60\u90fd\u628a\u597d\u8fd8\u591a\u6ca1\u4e3a\u53c8\u53ef\u5bb6\u5b66\u53ea\u4ee5\u4e3b\u4f1a\u6837\u5e74\u60f3\u751f\u540c\u8001\u4e2d\u5341\u4ece\u81ea\u9762\u524d\u5934\u9053\u5b83\u540e\u7136\u8d70\u5f88\u50cf\u89c1\u4e24\u7528\u5979\u56fd\u52a8\u8fdb\u6210\u56de\u4ec0\u8fb9\u4f5c\u5bf9\u5f00\u800c\u5df1\u4e9b\u73b0\u5c71\u6c11\u5019\u7ecf\u53d1\u5de5\u5411\u4e8b\u547d\u7ed9\u957f\u6c34\u51e0\u4e49\u4e09\u58f0\u4e8e\u9ad8\u624b\u77e5\u7406\u773c\u5fd7\u70b9\u5fc3\u6218\u4e8c\u95ee\u4f46\u8eab\u65b9\u5b9e\u5403\u505a\u53eb\u5f53\u4f4f\u542c\u9769\u6253\u5462\u771f\u5168\u624d\u56db\u5df2\u6240\u654c\u4e4b\u6700\u5149\u4ea7\u60c5\u8def\u5206\u603b\u6761\u767d\u8bdd\u4e1c\u5e2d\u6b21\u4eb2\u5982\u88ab\u82b1\u53e3\u653e\u513f\u5e38\u6c14\u4e94\u7b2c\u4f7f\u5199\u519b\u5427\u6587\u8fd0\u518d\u679c\u600e\u5b9a\u8bb8\u5feb\u660e\u884c\u56e0\u522b\u98de\u5916\u6811\u7269\u6d3b\u90e8\u95e8\u65e0\u5f80\u8239\u671b\u65b0\u5e26\u961f\u5148\u529b\u5b8c\u5374\u7ad9\u4ee3\u5458\u673a\u66f4\u4e5d\u60a8\u6bcf\u98ce\u7ea7\u8ddf\u7b11\u554a\u5b69\u4e07\u5c11\u76f4\u610f\u591c\u6bd4\u9636\u8fde\u8f66\u91cd\u4fbf\u6597\u9a6c\u54ea\u5316\u592a\u6307\u53d8\u793e\u4f3c\u58eb\u8005\u5e72\u77f3\u6ee1\u65e5\u51b3\u767e\u539f\u62ff\u7fa4\u7a76\u5404\u516d\u672c\u601d\u89e3\u7acb\u6cb3\u6751\u516b\u96be\u65e9\u8bba\u5417\u6839\u5171\u8ba9\u76f8\u7814\u4eca\u5176\u4e66\u5750\u63a5\u5e94\u5173\u4fe1\u89c9\u6b65\u53cd\u5904\u8bb0\u5c06\u5343\u627e\u4e89\u9886\u6216\u5e08\u7ed3\u5757\u8dd1\u8c01\u8349\u8d8a\u5b57\u52a0\u811a\u7d27\u7231\u7b49\u4e60\u9635\u6015\u6708\u9752\u534a\u706b\u6cd5\u9898\u5efa\u8d76\u4f4d\u5531\u6d77\u4e03\u5973\u4efb\u4ef6\u611f\u51c6\u5f20\u56e2\u5c4b\u79bb\u8272\u8138\u7247\u79d1\u5012\u775b\u5229\u4e16\u521a\u4e14\u7531\u9001\u5207\u661f\u5bfc\u665a\u8868\u591f\u6574\u8ba4\u54cd\u96ea\u6d41\u672a\u573a\u8be5\u5e76\u5e95\u6df1\u523b\u5e73\u4f1f\u5fd9\u63d0\u786e\u8fd1\u4eae\u8f7b\u8bb2\u519c\u53e4\u9ed1\u544a\u754c\u62c9\u540d\u5440\u571f\u6e05\u9633\u7167\u529e\u53f2\u6539\u5386\u8f6c\u753b\u9020\u5634\u6b64\u6cbb\u5317\u5fc5\u670d\u96e8\u7a7f\u5185\u8bc6\u9a8c\u4f20\u4e1a\u83dc\u722c\u7761\u5174\u5f62\u91cf\u54b1\u89c2\u82e6\u4f53\u4f17\u901a\u51b2\u5408\u7834\u53cb\u5ea6\u672f\u996d\u516c\u65c1\u623f\u6781\u5357\u67aa\u8bfb\u6c99\u5c81\u7ebf\u91ce\u575a\u7a7a\u6536\u7b97\u81f3\u653f\u57ce\u52b3\u843d\u94b1\u7279\u56f4\u5f1f\u80dc\u6559\u70ed\u5c55\u5305\u6b4c\u7c7b\u6e10\u5f3a\u6570\u4e61\u547c\u6027\u97f3\u7b54\u54e5\u9645\u65e7\u795e\u5ea7\u7ae0\u5e2e\u5566\u53d7\u7cfb\u4ee4\u8df3\u975e\u4f55\u725b\u53d6\u5165\u5cb8\u6562\u6389\u5ffd\u79cd\u88c5\u9876\u6025\u6797\u505c\u606f\u53e5\u533a\u8863\u822c\u62a5\u53f6\u538b\u6162\u53d4\u80cc\u7ec6";
//数字和字母的组合
String baseNumLetter = "0123456789ABCDEFGHJKLMNOPQRSTUVWXYZ";
//纯数字
String baseNum = "0123456789";
//纯字母
String baseLetter = "ABCDEFGHJKLMNOPQRSTUVWXYZ";
//createTypeFlag[0]==null表示没有传递参数
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 随机字符
*/
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();
}
}package com.qq.image;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* @Description:
* @Author: ZHENGZHIQIANG
* @CreateTime: 2019-03-25 16:46
*/
@WebServlet("/CheckServlet")
public class CheckServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String clientCheckcode = request.getParameter("validateCode");//接收客户端浏览器提交上来的验证码
String serverCheckcode = (String) request.getSession().getAttribute("checkcode");//从服务器端的session中取出验证码
if (clientCheckcode.equals(serverCheckcode)) {//将客户端验证码和服务器端验证比较，如果相等，则表示验证通过
System.out.println("验证码验证通过！");
}else {
System.out.println("验证码验证失败！");
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>在Form表单中使用验证码</title>
<script type="text/javascript">
//刷新验证码
function changeImg(){
document.getElementById("validateCodeImg").src="/imageServlet?"+Math.random();
}
</script>
</head>
<body>
<form action="/CheckServlet" method="post">
验证码：<input type="text" name="validateCode"/>
<img alt="验证码看不清，换一张" src="/imageServlet" id="validateCodeImg" onclick="changeImg()">
<a href="javascript:void(0)" onclick="changeImg()">看不清，换一张</a>
<br/>
<input type="submit" value="提交">
</form>
</body>
</html>
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