java - 从 servlet 向 html 页面发送警报

Question

我正在尝试使用 java servlet 创建一个注册页面。我如何通知 html 页面上表单中的空字段？这是我的代码的一部分

       String uName = request.getParameter("username");
       String pass = request.getParameter("passwd");
       String rpass = request.getParameter("rpasswd");
       String email = request.getParameter("email");
       if(uName == "" || pass == "" || rpass == "" || email == "") {
         //what must i put here to send notification to html page
       }

Answer 1

您可以使用 request.getAttribute() 来做到这一点 & request.setAttribute() ，例如:

 String uName = request.getParameter("username");
       String pass = request.getParameter("passwd");
       String rpass = request.getParameter("rpasswd");
       String email = request.getParameter("email");
       if(uName == null|| pass == null || rpass == null || email == null) {
       //here you can set attribute like any error message
       request.setAttribute("error", "Please fill all fields in form");
        request.getRequestDispatcher("yourjsppage").forward(request,response); 
       }

要显示上面的消息，请在jsp页面中执行如下操作:

//this line will print whatever is in error :  Please fill all fields in form
<p class="text-center" style="color: green">${error}</p>

在表单中进行验证的另一种方法，您可以使用required属性，如下所示:

<form  method="post" action=""> 

 <label for="userid">Name:</label>  
   <input type="text" name="username" required  /><br/>
<label for="passid">Email:</label> 
<input type="text" name="email"  required /> 
<br/>
<input type="submit"  value="Signup"/>

</form>

希望这有帮助!