此实现工分三个文件，即：CreatImage.java 生成图像流的类，提供用于生成图片流的方法；images.jsp 图片包装，用于将图片加入到response输出流中；login.jsp 调用前面的jsp，显示验证码。
下面是源代码：
1 package com;
2
3 import java.awt.Color;
4 import java.awt.Font;
5 import java.awt.Graphics;
6 import java.awt.Image;
7 import java.awt.image.BufferedImage;
8 import java.util.Random;
9
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12 import javax.servlet.http.HttpSession;
13
14 public class CreatImage{
15
16 private static final long serialVersionUID = 1L;
17 Image image = null;
18 HttpServletRequest request = null;
19 HttpServletResponse response = null;
20
21 public CreatImage(HttpServletRequest request, HttpServletResponse response){
22 this.request = request;
23 this.response = response;
24 }
25
26 public Color getRandColor(int fc,int bc){//给定范围获得随机颜色
27 Random random = new Random();
28 if(fc>255) fc=255;
29 if(bc>255) bc=255;
30 int r=fc+random.nextInt(bc-fc);
31 int g=fc+random.nextInt(bc-fc);
32 int b=fc+random.nextInt(bc-fc);
33 return new Color(r,g,b);
34 }
35
36 public BufferedImage creatImage(){
37 int width=100, height=26;
38 //生成随机类
39 Random random = new Random();
40 BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
41 //获取图形上下文
42 Graphics g = image.getGraphics();
43 // 设定背景色
44 g.setColor(getRandColor(200,250));
45 g.fillRect(0, 0, width, height);
46 //设定字体
47 g.setFont(new Font("Times New Roman",Font.PLAIN,22));
48
49 //画边框
50 //g.setColor(getRandColor(200,250));
51 //g.drawRect(0,0,width,height);
52
53 // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
54 g.setColor(getRandColor(160,200));
55 for (int i=0;i<155;i++){
56 int x = random.nextInt(width);
57 int y = random.nextInt(height);
58 int xl = random.nextInt(12);
59 int yl = random.nextInt(12);
60 g.drawLine(x,y,x+xl,y+yl);
61 }
62 // 取随机产生的认证码(4位数字)
63 //String rand = request.getParameter("rand");
64 //rand = rand.substring(0,rand.indexOf("."));
65 String str1=randomStr(4);// 得到随机字符
66 HttpSession session = request.getSession();
67 session.setAttribute("validatenumber",str1);
68 //System.out.println(str1);
69 for (int i=0;i<4;i++){
70 String rand=str1.substring(i,i+1);
71 // 将认证码显示到图象中
72 g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
73 //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
74 g.drawString(rand,20*i+12,20);
75 }
76 // 图象生效
77 g.dispose();
78 return image;
79 }
80
81 // 得到随机字符
82 public String randomStr(int n) {
83 String str1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
84 String str2 = "";
85 int len = str1.length() - 1;
86 double r;
87 for (int i = 0; i < n; i++) {
88 r = (Math.random()) * len;
89 str2 = str2 + str1.charAt((int) r);
90 }
91 return str2;
92 }
93 }
2
3 import java.awt.Color;
4 import java.awt.Font;
5 import java.awt.Graphics;
6 import java.awt.Image;
7 import java.awt.image.BufferedImage;
8 import java.util.Random;
9
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12 import javax.servlet.http.HttpSession;
13
14 public class CreatImage{
15
16 private static final long serialVersionUID = 1L;
17 Image image = null;
18 HttpServletRequest request = null;
19 HttpServletResponse response = null;
20
21 public CreatImage(HttpServletRequest request, HttpServletResponse response){
22 this.request = request;
23 this.response = response;
24 }
25
26 public Color getRandColor(int fc,int bc){//给定范围获得随机颜色
27 Random random = new Random();
28 if(fc>255) fc=255;
29 if(bc>255) bc=255;
30 int r=fc+random.nextInt(bc-fc);
31 int g=fc+random.nextInt(bc-fc);
32 int b=fc+random.nextInt(bc-fc);
33 return new Color(r,g,b);
34 }
35
36 public BufferedImage creatImage(){
37 int width=100, height=26;
38 //生成随机类
39 Random random = new Random();
40 BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
41 //获取图形上下文
42 Graphics g = image.getGraphics();
43 // 设定背景色
44 g.setColor(getRandColor(200,250));
45 g.fillRect(0, 0, width, height);
46 //设定字体
47 g.setFont(new Font("Times New Roman",Font.PLAIN,22));
48
49 //画边框
50 //g.setColor(getRandColor(200,250));
51 //g.drawRect(0,0,width,height);
52
53 // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
54 g.setColor(getRandColor(160,200));
55 for (int i=0;i<155;i++){
56 int x = random.nextInt(width);
57 int y = random.nextInt(height);
58 int xl = random.nextInt(12);
59 int yl = random.nextInt(12);
60 g.drawLine(x,y,x+xl,y+yl);
61 }
62 // 取随机产生的认证码(4位数字)
63 //String rand = request.getParameter("rand");
64 //rand = rand.substring(0,rand.indexOf("."));
65 String str1=randomStr(4);// 得到随机字符
66 HttpSession session = request.getSession();
67 session.setAttribute("validatenumber",str1);
68 //System.out.println(str1);
69 for (int i=0;i<4;i++){
70 String rand=str1.substring(i,i+1);
71 // 将认证码显示到图象中
72 g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
73 //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
74 g.drawString(rand,20*i+12,20);
75 }
76 // 图象生效
77 g.dispose();
78 return image;
79 }
80
81 // 得到随机字符
82 public String randomStr(int n) {
83 String str1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
84 String str2 = "";
85 int len = str1.length() - 1;
86 double r;
87 for (int i = 0; i < n; i++) {
88 r = (Math.random()) * len;
89 str2 = str2 + str1.charAt((int) r);
90 }
91 return str2;
92 }
93 }
1 <%@ page language="java" contentType="image/jpeg ; charset=UTF-8"
2 pageEncoding="UTF-8" import="java.awt.*,java.awt.image.*,javax.imageio.*,java.io.*"%>
3 <%@ page import ="com.CreatImage"%>
4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
5 <html>
6 <head>
7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
8 <title>Insert title here</title>
9 </head>
10 <body>
11 <%
12 response.setHeader("Pragma","No-cache");
13 response.setHeader("Cache-Control","no-cache");
14 response.setDateHeader("Expires", 0);
15
16 CreatImage c = new CreatImage(request,response);
17 BufferedImage image = c.creatImage();
18 OutputStream b = response.getOutputStream();
19 %>
20 <%
21 ImageIO.write(image, "JPEG", response.getOutputStream());
22 //必须添加以下两行否则tomcat下jsp出现getOutputStream() has already been called for this response异常
23 out.clear();
24 out = pageContext.pushBody();
25 %>
26 </body>
27 </html>
2 pageEncoding="UTF-8" import="java.awt.*,java.awt.image.*,javax.imageio.*,java.io.*"%>
3 <%@ page import ="com.CreatImage"%>
4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
5 <html>
6 <head>
7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
8 <title>Insert title here</title>
9 </head>
10 <body>
11 <%
12 response.setHeader("Pragma","No-cache");
13 response.setHeader("Cache-Control","no-cache");
14 response.setDateHeader("Expires", 0);
15
16 CreatImage c = new CreatImage(request,response);
17 BufferedImage image = c.creatImage();
18 OutputStream b = response.getOutputStream();
19 %>
20 <%
21 ImageIO.write(image, "JPEG", response.getOutputStream());
22 //必须添加以下两行否则tomcat下jsp出现getOutputStream() has already been called for this response异常
23 out.clear();
24 out = pageContext.pushBody();
25 %>
26 </body>
27 </html>
注意 contentType="image/jpeg ; charset=UTF-8"
1 <%@ page language="java" contentType="text/html; charset=UTF-8"
2 pageEncoding="UTF-8"%>
3 <%
4 String path = request.getContextPath();
5 %>
6 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
7 <html>
8 <head>
9 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
10 <title>Insert title here</title>
11 <script>
12 function changeCode()
13 {
14 document.getElementById("cc").src="<%=path%>/images.jsp?a="+Math.random();
15 }
16 </script>
17 </head>
18 <body>
19 <form action="" method="post">
20 <table cellspacing="2px" cellpadding="2px" align="center">
21 <tr>
22 <td>用户名：</td>
23 <td><input type="text" id="name" value=""/></td>
24 </tr>
25 <tr>
26 <td>密 码：</td>
27 <td><input type="password" id="password" value=""/></td>
28 </tr>
29 <tr height="26px">
30 <td>验证码：</td><td valign="middle"><input type="text" id="validate"></td>
31 <td><a href="#" onclick="changeCode();"><img alt="" border="0" id="cc" src="<%=path %>/images.jsp"/></a></td>
32 </tr>
33 <tr>
34 <td colspan="2" align="center"><input type="button" name="button" value="submit"/></td>
35 </tr>
36 </table>
37 </form>
38 </body>
39 </html>
40
41
2 pageEncoding="UTF-8"%>
3 <%
4 String path = request.getContextPath();
5 %>
6 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
7 <html>
8 <head>
9 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
10 <title>Insert title here</title>
11 <script>
12 function changeCode()
13 {
14 document.getElementById("cc").src="<%=path%>/images.jsp?a="+Math.random();
15 }
16 </script>
17 </head>
18 <body>
19 <form action="" method="post">
20 <table cellspacing="2px" cellpadding="2px" align="center">
21 <tr>
22 <td>用户名：</td>
23 <td><input type="text" id="name" value=""/></td>
24 </tr>
25 <tr>
26 <td>密 码：</td>
27 <td><input type="password" id="password" value=""/></td>
28 </tr>
29 <tr height="26px">
30 <td>验证码：</td><td valign="middle"><input type="text" id="validate"></td>
31 <td><a href="#" onclick="changeCode();"><img alt="" border="0" id="cc" src="<%=path %>/images.jsp"/></a></td>
32 </tr>
33 <tr>
34 <td colspan="2" align="center"><input type="button" name="button" value="submit"/></td>
35 </tr>
36 </table>
37 </form>
38 </body>
39 </html>
40
41
应各位的请求，我把效果图和源文件都放了上来，这样的实现方式我也是参考了别人的博客，不妥之处，还请各位指摘。
