java - 对警告 "Cannot resolve variable"感到困惑

Question

在login.java中我使用req.setAttribute("username", req.getParameter("username"));和welcome.jsp 我正在使用 Hello ${username} 但 Intellij 给了我警告:

Cannot resolve variable 'username'

该变量有效。为什么我会收到此警告？

login.java

package ch.yourclick.zt;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/login")
public class Login extends HttpServlet {
    @Override
    public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setAttribute("username", req.getParameter("username"));
        req.setAttribute("password", req.getParameter("password"));
        req.getRequestDispatcher("/welcome.jsp").forward(req, resp);
    }
}

Answer 1

您有 2 个选择:

选项 1

<% String username = (String) request.getAttribute("username"); %>
<%= username %>

选项 2

${requestScope.username}