JSP开发之生成图片验证码技术的详解

package cn.hncu.servlets;


import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CodeImgServlet extends HttpServlet {
  @Override
  protected void service(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    //☆1☆--相比纯java方式有变化的地方
    resp.setContentType("image/jpeg");//设置http响应头---告诉浏览器我现在发的是这个图片格式的数据，你用相应的方式来解析

    //定义图片的宽和高
    int w=60;
    int h=30;

    //声明一个RGB格式的内存中的图片
    BufferedImage img = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
    Graphics g = img.getGraphics();

    //把背景变白色
    g.setColor(Color.white);
    g.fillRect(0, 0, w, h);
    //设置字体
    g.setFont(new Font("aa",Font.BOLD,18));

    //产生并draw出4个随机数字
    Random r = new Random();
    for(int i=0;i4;i++){
      int a = r.nextInt(10);//生成0~9之间的随机整数
      int y = 15+r.nextInt(20);//产生随机的垂直位置
      //产生随机颜色
      Color c = new Color(r.nextInt(256),r.nextInt(256),r.nextInt(256));
      g.setColor(c);

      g.drawString(""+a, i*15, y);
    }

    //画几条干扰线
    for(int i=0;i10;i++){
      //产生随机颜色
      Color c = new Color(r.nextInt(256),r.nextInt(256),r.nextInt(256));
      g.setColor(c);
      g.drawLine(r.nextInt(60), r.nextInt(30), r.nextInt(60), r.nextInt(30));
    }

    g.dispose();//类似于IO中的flush(),把图形数据刷到img中
    //把内存图片img对象保存到一个jpg文件
    ImageIO.write(img, "JPEG", resp.getOutputStream() );//☆2☆

  }
}

?xml version="1.0" encoding="UTF-8"?>
web-app version="3.0" 
  xmlns="http://java.sun.com/xml/ns/javaee" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
  http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
 display-name>/display-name> 

 !-- 安全目录中的jsp文件如果要允许外面访问，得在web.xml进行配置，配置成一个jsp-servlet -->
 servlet>
  servlet-name>ajsp/servlet-name>
  !-- 配置servlet用servlet-class, 配置jsp页面用jsp-file标签 -->
  jsp-file>/WEB-INF/jsps/a.jsp/jsp-file>
 /servlet>
 !-- 
  servlet>
  servlet-name>CodeImgServlet/servlet-name>
  servlet-class>cn.hncu.servlets.CodeImgServlet/servlet-class>
  /servlet>
  servlet>
  servlet-name>LoginServlet/servlet-name>
  servlet-class>cn.hncu.servlets.LoginServlet/servlet-class>
  /servlet>
  -->
   servlet>
    servlet-name>CodeImgServlet/servlet-name>
    servlet-class>cn.hncu.servlets.CodeImgServlet/servlet-class>
   /servlet>
   servlet>
    servlet-name>LoginServlet/servlet-name>
    servlet-class>cn.hncu.servlets.LoginServlet/servlet-class>
   /servlet>


 !-- 给servlet配置访问路径 -->

 servlet-mapping>
  servlet-name>ajsp/servlet-name>
  url-pattern>/x/a.asp/url-pattern>
 /servlet-mapping>
 servlet-mapping>
  servlet-name>CodeImgServlet/servlet-name>
  url-pattern>/code/url-pattern>
 /servlet-mapping>
 servlet-mapping>
  servlet-name>LoginServlet/servlet-name>
  url-pattern>/LoginServlet/url-pattern>
 /servlet-mapping>


 welcome-file-list>
  welcome-file>index.jsp/welcome-file>
 /welcome-file-list>
/web-app>

%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
html>
 head>
 script type="text/javascript">
   function changeImg(){
     var img = document.getElementById("codeImg");
     // 当src每次的路径方式变化时，就会去重新请求一次后台。
     img.src="code?"+new Date().getTime();
   }

 /script>

 /head>

 body>
  h2>用户注册/h2>
   form action="LoginServlet" method="post">
      姓名:input type="text" name="name">br/>
      密码:input type="password" name="pwd">br/>
    !-- 
     验证码:input type="text" name="code"/>img src="imgs/a.jpg"/>br/>
     --> 
     验证码:input type="text" name="code"/>img id="codeImg" src="code"/>a href="javascript:changeImg();" rel="external nofollow" >看不清/a>br/>
     input type="submit" value="注册">
   /form>
   br/>br/>
   hr/>
   a href="WEB-INF/jsps/a.jsp" rel="external nofollow" >WA---a.jsp/a> br/>
   a href="/helloWebProj/x/a.asp" rel="external nofollow" >AC---a.jsp/a> br/>
 /body>
/html>

 servlet>
     servlet-name>ajsp/servlet-name>
    !-- 配置servlet用servlet-class, 配置jsp页面用jsp-file标签 -->
     jsp-file>/WEB-INF/jsps/a.jsp/jsp-file>
   /servlet>  
   servlet>
    servlet-name>CodeImgServlet/servlet-name>
    servlet-class>cn.hncu.servlets.CodeImgServlet/servlet-class>
   /servlet>
   servlet>
    servlet-name>LoginServlet/servlet-name>
    servlet-class>cn.hncu.servlets.LoginServlet/servlet-class>
   /servlet>


 !-- 给servlet配置访问路径 -->

 servlet-mapping>
  servlet-name>ajsp/servlet-name>
  url-pattern>/x/a.asp/url-pattern>
 /servlet-mapping>
 servlet-mapping>
  servlet-name>CodeImgServlet/servlet-name>
  url-pattern>/code/url-pattern>
 /servlet-mapping>
 servlet-mapping>
  servlet-name>LoginServlet/servlet-name>
  url-pattern>/LoginServlet/url-pattern>
 /servlet-mapping>