轉(zhuǎn)自：
http://www.matrix.org.cn/resource/article/0/910.html生成有4個隨機數(shù)字和雜亂背景的圖片，數(shù)字和背景顏色會改變，服務(wù)器端刷新（用history.go(-1)也會變）
原型參考ALIBABA??
http://china.alibaba.com/member/showimage------------產(chǎn)生驗證碼圖片的文件-----image.jsp-------------------------------------------
<%@?page?contentType="image/jpeg"?import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"?%>
<%!
Color?getRandColor(int?fc,int?bc){//給定范圍獲得隨機顏色
????????Random?random?=?new?Random();
????????if(fc>255)?fc=255;
????????if(bc>255)?bc=255;
????????int?r=fc+random.nextInt(bc-fc);
????????int?g=fc+random.nextInt(bc-fc);
????????int?b=fc+random.nextInt(bc-fc);
????????return?new?Color(r,g,b);
????????}
%>
<%
//設(shè)置頁面不緩存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires",?0);
//?在內(nèi)存中創(chuàng)建圖象
int?width=60,?height=20;
BufferedImage?image?=?new?BufferedImage(width,?height,?BufferedImage.TYPE_INT_RGB);
//?獲取圖形上下文
Graphics?g?=?image.getGraphics();
//生成隨機類
Random?random?=?new?Random();
//?設(shè)定背景色
g.setColor(getRandColor(200,250));
g.fillRect(0,?0,?width,?height);
//設(shè)定字體
g.setFont(new?Font("Times?New?Roman",Font.PLAIN,18));
//畫邊框
//g.setColor(new?Color());
//g.drawRect(0,0,width-1,height-1);
//?隨機產(chǎn)生155條干擾線，使圖象中的認證碼不易被其它程序探測到
g.setColor(getRandColor(160,200));
for?(int?i=0;i<155;i++)
{
????????int?x?=?random.nextInt(width);
????????int?y?=?random.nextInt(height);
????????int?xl?=?random.nextInt(12);
????????int?yl?=?random.nextInt(12);
????????g.drawLine(x,y,x+xl,y+yl);
}
//?取隨機產(chǎn)生的認證碼(4位數(shù)字)
String?sRand="";
for?(int?i=0;i<4;i++){
????String?rand=String.valueOf(random.nextInt(10));
????sRand+=rand;
????//?將認證碼顯示到圖象中
????g.setColor(new?Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//調(diào)用函數(shù)出來的顏色相同，可能是因為種子太接近，所以只能直接生成
????g.drawString(rand,13*i+6,16);
}
//?將認證碼存入SESSION
session.setAttribute("rand",sRand);
//?圖象生效
g.dispose();
//?輸出圖象到頁面
ImageIO.write(image,?"JPEG",?response.getOutputStream());
%>?
---------------使用驗證碼圖片的文件---------a.jsp------------------------------------
<%@?page?contentType="text/html;charset=gb2312"?%>
<!DOCTYPE?HTML?PUBLIC?"-//W3C//DTD?HTML?4.01?Transitional//EN">
<html>
<head>
<title>認證碼輸入頁面</title>
<meta?http-equiv="Content-Type"?content="text/html;?charset=gb2312">
<META?HTTP-EQUIV="Pragma"?CONTENT="no-cache">?
<META?HTTP-EQUIV="Cache-Control"?CONTENT="no-cache">?
<META?HTTP-EQUIV="Expires"?CONTENT="0">?
</head>
<body>
<form?method=post?action="check.jsp">
<table>
??? <tr>
??????? <td?align=left>系統(tǒng)產(chǎn)生的認證碼：</td>
??????? <td><img?border=0?src="image.jsp"></td>
??? </tr>
??? <tr>
??????? <td?align=left>輸入上面的認證碼：</td>
??????? <td><input?type=text?name=rand?maxlength=4?value=""></td>
??? </tr>
??? <tr>
??????? <td?colspan=2?align=center><input?type=submit?value="提交檢測"></td>
???? </tr>
</table>
</form>
</body>
</html>
-----------------驗證的頁面----------check.jsp
<%@?page?contentType="text/html;?charset=gb2312"?language="java"?import="java.sql.*"?errorPage=""?%>
<html>
<head>
<title>認證碼驗證頁面</title>
<meta?http-equiv="Content-Type"?content="text/html;?charset=gb2312">
<META?HTTP-EQUIV="Pragma"?CONTENT="no-cache">?
<META?HTTP-EQUIV="Cache-Control"?CONTENT="no-cache">?
<META?HTTP-EQUIV="Expires"?CONTENT="0">?
</head>
<body>
<%?
String?rand?=?(String)session.getAttribute("rand");
String?input?=?request.getParameter("rand");
%>
系統(tǒng)產(chǎn)生的認證碼為：?<%=?rand?%><br>
您輸入的認證碼為：?<%=?input?%><br>
<br>
<%
??if?(rand.equals(input))?{
%>
<font?color=green>輸入相同，認證成功！</font>
<%
??}?else?{
%>
<font?color=red>輸入不同，認證失敗！</font>
<%
??}
%>
</body>
</html>