html - JSP没有调用按钮？

Question

<form>
. . . 
    <div class="loginDiv">
        <%= new java.util.Date() %>
        <br/><br/>
        Username : <input type="text" class="resizedTextbox" name="username">&nbsp;&nbsp;
        Password : <input type="text" class="resizedTextbox" name="password">&nbsp;&nbsp;
        <input type="submit" name="btnLogin" value="LogIn">
            &nbsp;&nbsp;&nbsp;
            <a href="register.jsp">Register</a>
    </div>
</form>
               <%
                if(request.getAttribute("btnLogin") != null){
                    String username = request.getParameter("username");
                    String password = request.getParameter("password");
                    if(username != "" && password != ""){
                        out.print("Invalid Username/Password!");
                    }
                    else{
                        out.print("Invalid Username/Password!");
                    }
                }
               %>

我放置了一个断点，当我单击 btnLogin 时，request.getAttribute("btnLogin").. 中的代码永远不会被调用。为什么会这样？

Answer 1

尝试这样做：

if(request.getParameter("username") != null && request.getParameter("password") != null)

而不是这个：

if(request.getAttribute("btnLogin") != null){

Answer 2

<form action="Call this Login page here (eg: Login.jsp)" method="post">
            <div class="loginDiv">
                <%= new java.util.Date()%>
                <br/><br/>
                Username : <input type="text" class="resizedTextbox" name="username">&nbsp;&nbsp;
                Password : <input type="text" class="resizedTextbox" name="password">&nbsp;&nbsp;
                <input type="submit" name="btnLogin" value="LogIn">
                &nbsp;&nbsp;&nbsp;
                <a href="register.jsp">Register</a>
            </div>
        </form>
        <%            
            String username = request.getParameter("username");
            String password = request.getParameter("password");
            if (username != "" && password != "") {                
            } else {
                out.print("Invalid Username/Password!");
            }
        %>