验证码的生成和使用

验证码<input name="checkcode" type="text">
<img src="imageServlet" id="imageCode" alt="验证码" title="验证码">
<a href="javaScript:reLoadCode()">看不清</a><br/>

<script type="text/javascript">
alert("欢迎登录");
function reLoadCode(){
var time = new Date().getTime();
document.getElementById("imageCode").src="imageServlet?id="+time;
}
</script>

public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {

/*1、BufferedImage图像数据缓冲区

2、Graphics绘制图片

3、Color获取颜色

4、Random生成随机数

5、ImageIo输出图片*/
BufferedImage bi = new BufferedImage(70, 40, BufferedImage.TYPE_INT_RGB);
Graphics g = bi.getGraphics();
Color c = g.getColor();
g.setColor(Color.yellow);
g.fillRect(0, 0, 70, 40);
char[] ch= "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".toCharArray();
Random r = new Random();
StringBuffer sb = new StringBuffer();
for(int i=0; i<4; i++) {
int index = r.nextInt(ch.length);
Font f = new Font("宋体", Font.BOLD, 40);
g.setFont(f);
g.setColor(new Color(r.nextInt(255),r.nextInt(255), r.nextInt(255)));
g.drawString(ch[index]+"", i*15+3, 28);
sb.append(ch[index]);
}
request.getSession().setAttribute("pop", sb.toString());
ImageIO.write(bi, "JPG", response.getOutputStream());

}

String s1 = (String) request.getSession().getAttribute("pop");
String s2 = request.getParameter("checkcode");

if(true == flag && s1.equalsIgnoreCase(s2)) {
//if(c.equalsIgnoreCase(parm))
out.write("success");
}
else {
out.write("error");
}