所以，我试图从下拉列表中获取值并将它们添加到ArrayList中，以便以后可以显示它，但是我不知道该怎么做？
HTML（form.html）
<html>
<head>
<title>Form</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<form action="fruits" method="get">
<table>
<tr>
<td>select fruit(s)</td>
<td>
<select name="Values">
<option value="a">APPLE</option>
<option value="b">BANNANA</option>
<option value="o">ORANGE</option>
</select>
</td>
</tr>
</table>
<input type="submit" value="next" name="send">
<input type="submit" value="done" name="list">
</form>
</body>
</html>
基本上是当用户按下next（发送）按钮时，该servlet应该采用values参数，并将其存储到arraylist中供以后使用，并且应将它们定向回表单页面，以便他们可以进行更多选择或通过按一下done（list）按钮查看他们选择了哪些选项
Servlet（水果Servlet）
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
PrintWriter out = response.getWriter();
response.setContentType("text/html;charset=UTF-8");
String wasSent = request.getParameter("send");
String Submitted = request.getParameter("list");
ArrayList<Double> fruitsList = new ArrayList<Double>();
if (wasSent != null) {
String fruits = request.getParameter("Values");
fruitsList.add(fruits);
request.setAttribute("List", fruitsList);
RequestDispatcher rs = request.getRequestDispatcher("form.html");
rs.forward(request, response);
} else if (Submitted != null) {
//get the list and display all the values
}
}
在您的servlet中，您可以使用session设置数组中的值，这样，该值将被保存，直到您从会话中将其删除为止。您的代码如下所示：
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
PrintWriter out = response.getWriter();
response.setContentType("text/html;charset=UTF-8");
String fruits = request.getParameter("Values");
ArrayList<String> fruitsList1 = new ArrayList<String>();
//get values which are in session
ArrayList<String> fruitsList = (ArrayList<String>)request.getSession().getAttribute("List");
//if attribute value is not null
if (fruitsList != null) {
//add new values
fruitsList.add(fruits);
request.getSession().setAttribute("List", fruitsList);
RequestDispatcher rs = request.getRequestDispatcher("form.html");
rs.forward(request, response);
} else if (fruitsList== null) {
//adding value selected in array list
fruitsList1.add(fruits);
//setting values
request.getSession().setAttribute("List", fruitsList1);
RequestDispatcher rs = request.getRequestDispatcher("form.html");
rs.forward(request, response);
} else{
//remove values
}
}