Servlet：response生成图片验证码
src 目录下com.xieyuan包MyServlet.java文件（Servlet文件）
package com.xieyuan;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLEncoder;
import java.util.Random;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.sun.corba.se.impl.javax.rmi.CORBA.Util;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
public class MyServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public MyServlet() {
super();
}
/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
execute(request, response);
}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
execute(request, response);
}
private static final char CHARS[]={'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'
};
public static Random random=new Random();
//生成随机数字，len为需要随机数字的个数
public static String getRandomString(int len)
{
StringBuilder builder=new StringBuilder();
for(int i=0;i<len;i++)
{
builder.append(CHARS[random.nextInt(CHARS.length)]) ;
}
return builder.toString();
}
//随机生成颜色，座位背景色
public static Color getColor()
{
return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255));
}
//取颜色的反色
public static Color getReverseColor(Color color)
{
return new Color(255-color.getRed(),255-color.getGreen(),255-color.getBlue());
}
private void execute(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException
{
response.setCharacterEncoding("utf-8");
//设置返回的文件编码
response.setContentType("image/jpeg");
//获取随机码
String getRandomCode=getRandomString(5);
//将随机码放到Session中
request.getSession().setAttribute("randomcode", getRandomCode);
int width=100;
int height=30;
Color color=getColor();
Color reverseColor=getReverseColor(color);
//创建一个彩色图片
BufferedImage bi=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
Graphics2D g=bi.createGraphics();
g.setFont(new Font(null,Font.BOLD,16));
g.setColor(color);
g.fillRect(0,0,width,height);
g.setColor(reverseColor);
g.drawString(getRandomCode, 18,20);
//绘制噪点,最多100个
for(int i=0,n=random.nextInt(100);i<n;i++)
{
g.drawRect(random.nextInt(width), random.nextInt(height), 1,1);
}
ServletOutputStream out=response.getOutputStream();
JPEGImageEncoder encoder=JPEGCodec.createJPEGEncoder(out);
encoder.encode(bi);
out.flush();
}
/**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
}
}
配置好web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<servlet>
<description>This is the description of my J2EE component</description>
<display-name>This is the display name of my J2EE component</display-name>
<servlet-name>MyServlet</servlet-name>
<servlet-class>com.xieyuan.MyServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>MyServlet</servlet-name>
<url-pattern>/servlet/MyServlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
接着部署您的WEB 应用，此时访问：
http://127.0.0.1:8080/Test/servlet/MyServlet
可以看到一张图片验证码。但是，这种效果好吗？这,并不是我们想要的，图片验证码应该混搭在HTML页面里，做登录等功能才对。
那么，接下来我们来做个JSP页面，直接使用项目WebRoot目录下的，index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
<script language="JavaScript" >
function reloadImage()
{
<!--将按钮状态设置为不可用，当图片加载完成触发onload后，按钮状态就为可用了。这样可用避免重复获取-->
document.getElementById("btn").disabled=true;
<!--第一次连接的时候不会有问题，第二次连接时，假如你后面没有new Date().getTime(),加参数就会连接的时候拿缓存，没有连到服务器。加上时间函数就能保证你每次得到的不是浏览器的缓存。-->
document.getElementById("img").src="servlet/MyServlet?timestamp="+new Date().getTime();
}
</script>
</head>
<body>
<img src="servlet/MyServlet" id="img" onload="btn.disabled=false;" /><br/><br/>
<input type="button" value="换一张图片" onClick="reloadImage()" id="btn" /><br/>
<script>document.write("页面最后更新："+document.lastModified)</script>
</body>
</html>
此时，我直接访问：http://127.0.0.1:8080/Test/
结果就是我们想要的了
可以看到，无论我们点击多少次 “换一张图片”按钮，网页始终没有刷新，页面最后更新时间也没变，变的就是图片验证码！
