小弟做图片验证,session.getAttribute取值,第一次值为NULL,第二次有值.
源代码如下:
login.jsp
<div id= "login ">
<form name= "login " method= "post " action= "loginin.jsp " onsubmit= "return check(this); ">
<div id= "user "> 用户 <input type= "text " name= "userid " /> </div>
<div id= "pass "> 密码 <input type= "password " name= "userpassword " /> </div>
<div id= "check "> 验证 <input type= "text " name= "checkcode " maxlength= "4 " /> <img id= "vimg " alt= "点击刷新 " onclick= "reloadVimg() " style= "cursor:hand " src= "/vimage "/> </div>
loginin.jsp
if(session.getAttribute( "post_validate_code ")==null||!equest.getParameter( "checkcode ").equals(session.getAttribute( "post_validate_code ").toString()))
{ loginuser=null;
out.println( " <script language= 'javascript '> alert( '验证码错误！！ ');history.back(1); </script> ");
return;
}
vimage.java(这是一个servlet)
String sRand= " ";
for (int i=0;i <4;i++)
{
String rand=String.valueOf(random.nextInt(10));
sRand+=rand;
// 将认证码显示到图象中
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
g.drawString(rand,13*i+2,15);
}
session.setAttribute( "post_validate_code ",sRand);
------解决方案--------------------
第一次因还没有赋值当然是null了,第而次用session.setAttribute( "post_validate_code ",sRand);这条语句赋了值当然就有值了.
------解决方案--------------------
程序是从上至下运行的
------解决方案--------------------
<div id= "login ">
<form name= "login " method= "post " action= "loginin.jsp " onsubmit= "return check(this); ">