验证码
主要：绘制，验证
在一些网站的注册页面，通常在最后会让用户输入验证码，以此防止恶意注册，有些也会在登陆页面，防止暴力破解密码等．
页面的验证码，实际上是一个图片，这个图片事先人们是不知道的，它是由程序随机绘制成的，并且，在产生的时候，程序记录下来了它的值.(便于后面的验证)
servlet 服务器小程序，可以实现绘制验证码的功能，绘制的步骤如下：
１．建立图片缓存对象
BufferImage bi = new BufferImage(width,height,绘制类型参数)；
原型：BufferedImage(arg0, arg1, arg2)
２．得到绘制对象
Graphics g = bi.getGraphics();
３．设置底纹颜色
Color c = new Color(arg0,arg1,arg2);// ３个参数分别是三原色的值．
g.setColor(c);
g.fillRect(0, 0, 70, 30); //填充矩形，０，０ 表示的起始点．
４．产生随机数字，得到随机字符，对图像进行绘制 （并且记录下来）
字符区间：char[] ch = "asdfghjklzxcvbnmASDFGHJKLZXCVBNM123456789".toCharArray();
字符缓存：StringBuffer sb = new StringBuffer();
随机数 ：Random r = new Random();
//逐个绘制随机字符 并设置特定的颜色
for(int i=0;i<4;i++)
{
int index = r.nextInt(ch.length()); //产生一个随机数
//对字符分别设置绘制字体颜色
g.setFont(new Font("宋体"，Font.Bold,20)); //设置宋体，２０号字体
g.setColor(new Color(r.nexInt(255),r.nexInt(255),r.nexInt(255))); //设置随机颜色，
g.drawString(ch[index]+" ",i*20,25); //绘制字符，后面的参数为位置
sb.append(ch[index]); //添加字符到字符缓存区，（追加）
}
request.getSession().setAttribute("picCode",sb.toString()); //将验证码放到session中,方便后面的验证
５．通过图片ＩＯ写到前台
ImageIO.write(bi,"JPG",response.getOutputStream()); //通过输出流写到前台， JPG格式
到这里就能够在页面上面看到随机生成的验证码图片了．
验证：
验证就是在注册界面或者是登陆界面活取验证码 ，然后从ｓｅｓｓｉｏｎ中活取验证码，然后二者比较相等，验证是否输入正确．
从ｓｅｓｓｉｏｎ中活取验证码
String checkCode = request.getSession().getAttribute("picCode");
从前台活取输入的验证码
String code = request.getParameter("code");
验证
if(checkCode.equalsIgnoreCase(code)==false) response.sendRedirect("register.jsp"); //验证不成功跳转到制定页面
至此，验证码的相关基础的内容已经完毕，
代码：
myImage.java (servlet程序)
1 package cn.hpu.servlet;
2
3 import java.awt.Color;
4 import java.awt.Font;
5 import java.awt.Graphics;
6 import java.awt.image.BufferedImage;
7 import java.io.IOException;
8 import java.nio.Buffer;
9 import java.util.Random;
10
11 import javax.imageio.ImageIO;
12 import javax.servlet.ServletException;
13 import javax.servlet.annotation.WebServlet;
14 import javax.servlet.http.HttpServlet;
15 import javax.servlet.http.HttpServletRequest;
16 import javax.servlet.http.HttpServletResponse;
17
18 import sun.net.NetworkServer;
19
20 /**
21 * Servlet implementation class myImage
22 */
23 @WebServlet("/myImage")
24 public class myImage extends HttpServlet {
25 private static final long serialVersionUID = 1L;
26
27 /**
28 * @see HttpServlet#HttpServlet()
29 */
30 public myImage() {
31 super();
32 // TODO Auto-generated constructor stub
33 }
34
35 /**
36 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
37 */
38 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
39 // TODO Auto-generated method stub
40 // response.getWriter().append("Served at: ").append(request.getContextPath());
41 doPost(request, response);
42
43 }
44
45 /**
46 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
47 */
48 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
49 // TODO Auto-generated method stub
50 // doGet(request, response);
51 request.setCharacterEncoding("UTF-8");
52 response.setCharacterEncoding("UTF-8");
53
54 BufferedImage bi =new BufferedImage(70,30, BufferedImage.TYPE_INT_RGB);
55 Graphics g = bi.getGraphics();
56 Color c = new Color(100, 190,180);
57 g.setColor(c);
58 g.fillRect(0, 0, 70, 30);
59
60
61 char[] ch = "asdfghjklzxcvbnmASDFGHJKLZXCVBNM123456789".toCharArray();
62 StringBuffer sb= new StringBuffer();
63 Random r = new Random();
64
65 for (int i = 0; i < 4; i++) {
66 int index = r.nextInt(ch.length);
67 Font f = new Font("宋体",Font.BOLD, 20);
68 g.setFont(f);
69 g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));
70 g.drawString(ch[index]+" ", i*18+3, 20);
71 sb.append(ch[index]);
72 }
73 request.getSession().setAttribute("picCode", sb.toString());
74 ImageIO.write(bi, "JPG", response.getOutputStream());
75
76
77 }
78
79 }
register.java (servlet程序)
1 package cn.hpu.servlet;
2
3 import java.io.IOException;
4 import java.io.PrintWriter;
5 import java.sql.Date;
6
7 import javax.servlet.ServletException;
8 import javax.servlet.annotation.WebServlet;
9 import javax.servlet.http.HttpServlet;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12
13 import org.apache.catalina.connector.Response;
14
15 import cn.hpu.model.user;
16 import cn.hpu.service.StuManager;
17 import cn.hpu.service.StuManagerimplement;
18
19 /**
20 * Servlet implementation class register
21 */
22 @WebServlet("/register")
23 public class register extends HttpServlet {
24 private static final long serialVersionUID = 1L;
25
26 /**
27 * @see HttpServlet#HttpServlet()
28 */
29 public register() {
30 super();
31 // TODO Auto-generated constructor stub
32 }
33
34 /**
35 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
36 */
37 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
38 // TODO Auto-generated method stub
39 response.getWriter().append("Served at: ").append(request.getContextPath());
40 doPost(request, response);
41 }
42
43 /**
44 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
45 */
46 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
47 // TODO Auto-generated method stub
48 // doGet(request, response);
49 //设置中文
50 request.setCharacterEncoding("UTF-8");
51 response.setCharacterEncoding("UTF-8");
52
53 //获取数据
54 String name = request.getParameter("name");
55 String pwd = request.getParameter("password");
56 String code = request.getParameter("code");
57 String checkCode = (String) request.getSession().getAttribute("picCode");
58
59 user usr = new user();
60 usr.setName(name);
61 usr.setCode(code);
62 usr.setPassword(pwd);
63
64 if(checkCode.equalsIgnoreCase(code)==false){
65
66 // PrintWriter out = response.getWriter();
67 // out.println("验证码错误！\n３秒后自动跳转注册页面");
68
69 response.sendRedirect("register.jsp");
70 }
71
72 StuManager stuM = new StuManagerimplement();
73 boolean flag= false ;
74 try {
75 flag = stuM.add(usr);
76 if(flag) response.sendRedirect("index.jsp");
77
78 } catch (Exception e) {
79 // TODO: handle exception
80 }
81 }
82
83 }