我需要在我的JSP页面中使用request.getParameter("action")，以定义应执行的命令（<input type="hidden" name="action" value="open_list"/>）。结果为null。问题是什么？或如何以其他方式传递命令？
CommandFactory.java
public class CommandFactory {
public Command defineCommand(HttpServletRequest request) {
Command current = new ErrorCommand();
String action = request.getParameter("action");
if (action == null || action.isEmpty()) {
return current;
}
try {
CommandEnum currentEnum = CommandEnum.valueOf(action.toUpperCase());
current = currentEnum.getCommand();
} catch (IllegalArgumentException e){
request.setAttribute("wrongAction", action);
}
return current;
}
}
MainServlet.java
public class MainServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public MainServlet() {
super();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
processRequest(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
processRequest(request, response);
}
private void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
CommandFactory client = new CommandFactory();
Command command = client.defineCommand(request);
String page = command.execute(request, response);
if (page != null) {
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(page);
dispatcher.forward(request, response);
}else {
response.sendRedirect(PageURL.ERROR_PAGE);
}
}
}
JSP页面
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<form name="hotelList" method="GET" action="/MainServlet">
<input type="hidden" name="action" value="open_list"/>
<table>
<tr>
<th>ID</th>
<th>NAME</th>
<th>ADDRESS</th>
<th>RATING</th>
<th>OWNERNAME</th>
</tr>
<c:forEach items="${list}" var="hotel">
<tr>
<td>${hotel.id}</td>
<td>${hotel.name}</td>
<td>${hotel.address}</td>
<td>${hotel.rating}</td>
<td>${hotel.ownerName}</td>
</tr>
</c:forEach>
</table>
</form>
</body>
</html>
我试图重现您的问题，您无法通过页面上的type="submit"进行任何控制。
当您单击提交按钮时，它将正确显示servlet中的request.getParameter("action")。
<form name="hotelList" method="GET" action="MainServlet">
<input type="hidden" name="action" value="open_list"/>
<input type="submit" value="Send">
</form>