转自：http://www.cnblogs.com/xdp-gacl/p/3798190.html
一、BufferedImage类介绍
生成验证码图片主要用到了一个BufferedImage类，如下：
创建一个DrawImage Servlet，用来生成验证码图片
1 package gacl.response.study;
2 import java.awt.Color;
3 import java.awt.Font;
4 import java.awt.Graphics;
5 import java.awt.Graphics2D;
6 import java.awt.image.BufferedImage;
7 import java.io.IOException;
8 import java.util.Random;
9 import javax.imageio.ImageIO;
10 import javax.servlet.ServletException;
11 import javax.servlet.http.HttpServlet;
12 import javax.servlet.http.HttpServletRequest;
13 import javax.servlet.http.HttpServletResponse;
14 /**
15 * 生成随机图片，用来作为验证码
16 */
17 public class DrawImage extends HttpServlet {
18 private static final long serialVersionUID = 3038623696184546092L;
19
20 public static final int WIDTH = 120;//生成的图片的宽度
21 public static final int HEIGHT = 30;//生成的图片的高度
22
23 public void doGet(HttpServletRequest request, HttpServletResponse response)
24 throws ServletException, IOException {
25 this.doPost(request, response);
26 }
27
28 public void doPost(HttpServletRequest request, HttpServletResponse response)
29 throws ServletException, IOException {
30 String createTypeFlag = request.getParameter("createTypeFlag");//接收客户端传递的createTypeFlag标识
31 //1.在内存中创建一张图片
32 BufferedImage bi = new BufferedImage(WIDTH, HEIGHT,BufferedImage.TYPE_INT_RGB);
33 //2.得到图片
34 Graphics g = bi.getGraphics();
35 //3.设置图片的背影色
36 setBackGround(g);
37 //4.设置图片的边框
38 setBorder(g);
39 //5.在图片上画干扰线
40 drawRandomLine(g);
41 //6.写在图片上随机数
42 //String random = drawRandomNum((Graphics2D) g,"ch");//生成中文验证码图片
43 //String random = drawRandomNum((Graphics2D) g,"nl");//生成数字和字母组合的验证码图片
44 //String random = drawRandomNum((Graphics2D) g,"n");//生成纯数字的验证码图片
45 //String random = drawRandomNum((Graphics2D) g,"l");//生成纯字母的验证码图片
46 String random = drawRandomNum((Graphics2D) g,createTypeFlag);//根据客户端传递的createTypeFlag标识生成验证码图片
47 //7.将随机数存在session中
48 request.getSession().setAttribute("checkcode", random);
49 //8.设置响应头通知浏览器以图片的形式打开
50 response.setContentType("image/jpeg");//等同于response.setHeader("Content-Type", "image/jpeg");
51 //9.设置响应头控制浏览器不要缓存
52 response.setDateHeader("expries", -1);
53 response.setHeader("Cache-Control", "no-cache");
54 response.setHeader("Pragma", "no-cache");
55 //10.将图片写给浏览器
56 ImageIO.write(bi, "jpg", response.getOutputStream());
57 }
58
59 /**
60 * 设置图片的背景色
61 * @param g
62 */
63 private void setBackGround(Graphics g) {
64 // 设置颜色
65 g.setColor(Color.WHITE);
66 // 填充区域
67 g.fillRect(0, 0, WIDTH, HEIGHT);
68 }
69
70 /**
71 * 设置图片的边框
72 * @param g
73 */
74 private void setBorder(Graphics g) {
75 // 设置边框颜色
76 g.setColor(Color.BLUE);
77 // 边框区域
78 g.drawRect(1, 1, WIDTH - 2, HEIGHT - 2);
79 }
80
81 /**
82 * 在图片上画随机线条
83 * @param g
84 */
85 private void drawRandomLine(Graphics g) {
86 // 设置颜色
87 g.setColor(Color.GREEN);
88 // 设置线条个数并画线
89 for (int i = 0; i < 5; i++) {
90 int x1 = new Random().nextInt(WIDTH);
91 int y1 = new Random().nextInt(HEIGHT);
92 int x2 = new Random().nextInt(WIDTH);
93 int y2 = new Random().nextInt(HEIGHT);
94 g.drawLine(x1, y1, x2, y2);
95 }
96 }
97
98 /**
99 * 画随机字符
100 * @param g
101 * @param createTypeFlag
102 * @return
103 * String... createTypeFlag是可变参数，
104 * 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
105 */
106 private String drawRandomNum(Graphics2D g,String... createTypeFlag) {
107 // 设置颜色
108 g.setColor(Color.RED);
109 // 设置字体
110 g.setFont(new Font("宋体", Font.BOLD, 20));
111 //常用的中国汉字
112 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";
113 //数字和字母的组合
114 String baseNumLetter = "0123456789ABCDEFGHJKLMNOPQRSTUVWXYZ";
115 //纯数字
116 String baseNum = "0123456789";
117 //纯字母
118 String baseLetter = "ABCDEFGHJKLMNOPQRSTUVWXYZ";
119 //createTypeFlag[0]==null表示没有传递参数
120 if (createTypeFlag.length > 0 && null != createTypeFlag[0]) {
121 if (createTypeFlag[0].equals("ch")) {
122 // 截取汉字
123 return createRandomChar(g, baseChineseChar);
124 }else if (createTypeFlag[0].equals("nl")) {
125 // 截取数字和字母的组合
126 return createRandomChar(g, baseNumLetter);
127 }else if (createTypeFlag[0].equals("n")) {
128 // 截取数字
129 return createRandomChar(g, baseNum);
130 }else if (createTypeFlag[0].equals("l")) {
131 // 截取字母
132 return createRandomChar(g, baseLetter);
133 }
134 }else {
135 // 默认截取数字和字母的组合
136 return createRandomChar(g, baseNumLetter);
137 }
138
139 return "";
140 }
141
142 /**
143 * 创建随机字符
144 * @param g
145 * @param baseChar
146 * @return 随机字符
147 */
148 private String createRandomChar(Graphics2D g,String baseChar) {
149 StringBuffer sb = new StringBuffer();
150 int x = 5;
151 String ch ="";
152 // 控制字数
153 for (int i = 0; i < 4; i++) {
154 // 设置字体旋转角度
155 int degree = new Random().nextInt() % 30;
156 ch = baseChar.charAt(new Random().nextInt(baseChar.length())) + "";
157 sb.append(ch);
158 // 正向角度
159 g.rotate(degree * Math.PI / 180, x, 20);
160 g.drawString(ch, x, 20);
161 // 反向角度
162 g.rotate(-degree * Math.PI / 180, x, 20);
163 x += 30;
164 }
165 return sb.toString();
166 }
167 }
运行结果如下：
二、在Form表单中使用验证码图片
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
3 <html>
4 <head>
5 <title>在Form表单中使用验证码</title>
6 <script type="text/javascript">
7 //刷新验证码
8 function changeImg(){
9 document.getElementById("validateCodeImg").src="${pageContext.request.contextPath}/servlet/DrawImage?"+Math.random();
10 }
11 </script>
12 </head>
13
14 <body>
15 <form action="${pageContext.request.contextPath}/servlet/CheckServlet" method="post">
16 验证码：<input type="text" name="validateCode"/>
17 <img alt="验证码看不清，换一张" src="${pageContext.request.contextPath}/servlet/DrawImage" id="validateCodeImg" onclick="changeImg()">
18 <a href="javascript:void(0)" onclick="changeImg()">看不清，换一张</a>
19 <br/>
20 <input type="submit" value="提交">
21 </form>
22 </body>
23 </html>
运行结果：
DrawImage Servlet除了可以生成的字母和数字的组合的验证码图片之外，还可以生成汉字，纯数字，纯字母的验证码图片，只需要向DrawImage Servlet传递约定好的生成标识符参数即可，如下所示：
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
3 <html>
4 <head>
5 <title>在Form表单中使用验证码</title>
6 <script type="text/javascript">
7 //刷新验证码
8 function changeImg(obj,createTypeFlag){
9 document.getElementById(obj.id).src="${pageContext.request.contextPath}/servlet/DrawImage?createTypeFlag="+createTypeFlag+"&"+Math.random();
10 }
11 </script>
12 </head>
13
14 <body>
15 <form action="${pageContext.request.contextPath}/servlet/CheckServlet" method="post">
16 数字字母混合验证码：<input type="text" name="validateCode"/>
17 <img alt="验证码看不清，换一张" src="${pageContext.request.contextPath}/servlet/DrawImage" id="validateCodeImg1" onclick="changeImg(this,'nl')">
18 <br/>
19 中文验证码：<input type="text" name="validateCode"/>
20 <img alt="验证码看不清，换一张" src="${pageContext.request.contextPath}/servlet/DrawImage?createTypeFlag=ch" id="validateCodeImg2" onclick="changeImg(this,'ch')">
21 <br/>
22 英文验证码：<input type="text" name="validateCode"/>
23 <img alt="验证码看不清，换一张" src="${pageContext.request.contextPath}/servlet/DrawImage?createTypeFlag=l" id="validateCodeImg3" onclick="changeImg(this,'l')">
24 <br/>
25 数字验证码：<input type="text" name="validateCode"/>
26 <img alt="验证码看不清，换一张" src="${pageContext.request.contextPath}/servlet/DrawImage?createTypeFlag=n" id="validateCodeImg4" onclick="changeImg(this,'n')">
27 <br/>
28 <input type="submit" value="提交">
29 </form>
30 </body>
31 </html>
运行结果如下：
三、服务器端对form表单提交上来的验证码处理
1 package gacl.response.study;
2 import java.io.IOException;
3 import javax.servlet.ServletException;
4 import javax.servlet.http.HttpServlet;
5 import javax.servlet.http.HttpServletRequest;
6 import javax.servlet.http.HttpServletResponse;
7 /**
8 * @author gacl
9 * 服务器端接收到验证码后的处理
10 */
11 public class CheckServlet extends HttpServlet {
12 public void doGet(HttpServletRequest request, HttpServletResponse response)
13 throws ServletException, IOException {
14 String clientCheckcode = request.getParameter("validateCode");//接收客户端浏览器提交上来的验证码
15 String serverCheckcode = (String) request.getSession().getAttribute("checkcode");//从服务器端的session中取出验证码
16 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
17 System.out.println("验证码验证通过！");
18 }else {
19 System.out.println("验证码验证失败！");
20 }
21 }
22
23 public void doPost(HttpServletRequest request, HttpServletResponse response)
24 throws ServletException, IOException {
25 doGet(request, response);
26 }
27
28 }
