一个小问题，请看看

Question

把
String username=(String)(request.getParameter("username"));
String    password=(String)(request.getParameter("password"));
改成
String username=(request.getParameter("username")).toString();
String    password=(request.getParameter("password")).toString();
如果还不行的话，可能就是你的username或者password可能没传过来！

Answer 1

把
if((username.compareTo("admin")!=0)&&(password.compareTo("123")!=0))
改成
if((username.trim().compareTo("admin")!=0)&&(password.trim().compareTo("123")!=0))

Answer 2

修改这句:
<%
String username=(String)(request.getParameter("username"));
String    password=(String)(request.getParameter("password"));
if(username!=null&&username.trim().compareTo("admin")!=0&&password!=null&&password.trim().compareTo("123")!=0)//----->modify
out.println("Success!!");
else{%>
<jsp:forward page="logout.jsp"/>
<%}%>

Answer 3

修改这句:
<%
String username=(String)(request.getParameter("username"));
String    password=(String)(request.getParameter("password"));
if(username!=null&&username.trim().compareTo("admin")!=0&&password!=null&&password.trim().compareTo("123")!=0)//----->modify
out.println("Success!!");
else{%>
<jsp:forward page="logout.jsp"/>
<%}%>