Java服务器端验证？

Question

我不明白为什么我的服务器端不工作。我们刚刚开始学习 jsp，我们并没有深入研究 servlet，所以只是 java 代码（当然还有 html 和 javascript）。我必须验证是否所有营地都已满员。

HTML：

<form method="post" action="server.jsp">

Name: <input type="text" value="" name="name" size="30">
Surname: <input type="text" value="" name="surname">
Age: <select name="age" size="1">
                        <option value="selectcard">---</option>
                        <% int i; for (i = 16; i <=80; i++){
                        out.print("<option>" + i + "</option>");
                        }
                        %>
                        </select>
How did you know about us?
                        <br><input type="radio" value="a friend"     name="know_us">a friend
                        <br><input type="radio" value="a teacher" name="know_us">a teacher
                        <br><input type="radio" value="the board" name="know_us">the board
                        <br><input type="radio" value="on internet" name="know_us">on internet
                        <br><input type="radio" value="other" name="know_us">other (specify) <input type="text" value="" name="know_us">

<input type="submit" name="submit" id="submit" value="submit">
<input type="reset" name="reset" id="reset" value="clear">
</form>

服务器端：

<%
    String name = request.getParameter("name");
    String surname = request.getParameter("surname");
    String age = request.getParameter("age");
    String know_us = request.getParameter("know_us");

if (name == null){
    out.print("<span style='color: red;'>There was an error</span>");
}else if(surname == null){
    out.print("<span style='color: red;'>There was an error</span>");
}else if(age.equals("selectcard")){
    out.print("<span style='color: red;'>There was an error</span>");
}else if(know_us == null){
    out.print("<span style='color: red;'>There was an error</span>");
}else{
    out.print("<h1 style='color: #666; text-align: center;'>Success!</h1>");
}
%>

我的 javascript 正在运行，所以我没有在此处包含它。每当我不填写字段时，它不会给我任何错误？它只显示“成功”。请帮忙，我很沮丧！ D：

Answer 1

也尝试寻找一个空字符串。

if (name == null || name.isEmpty())