idea登录界面输入账户会突然清空

Question

用idea设计的一个学生管理系统，为什么在登录界面时候能注册成功，但是用这个账户登录就是突然账户密码清空，反正就是进不去里面

以下是loginservlet代码

package com.lili.servlet;

import com.alibaba.fastjson.JSON;
import com.lili.dao.impl.UserDaoImpl;
import com.lili.entity.User;
import com.lili.service.impl.UserServiceImpl;

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 javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("application/json");
        PrintWriter out = response.getWriter();
        String user = request.getParameter("username");
        String passwd = request.getParameter("password");
        List<User> userList = new ArrayList<>();
        List<User> List = new UserServiceImpl(new UserDaoImpl()).findUser(user, passwd);
        if (userList.size() > 0) {
            // 添加进session
            HttpSession session = request.getSession(true);
            session.setAttribute("user", userList.get(0));
            // 设置过期时间5分钟
            session.setMaxInactiveInterval(60 * 5);
        }
        String str = JSON.toJSONString(userList);
        out.write(str);
        out.flush();
        out.close();
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

Answer 1

代码写错了。
List修改为userList

package com.lili.servlet;
 
import com.alibaba.fastjson.JSON;
import com.lili.dao.impl.UserDaoImpl;
import com.lili.entity.User;
import com.lili.service.impl.UserServiceImpl;
 
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 javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
 
@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("application/json");
        PrintWriter out = response.getWriter();
        String user = request.getParameter("username");
        String passwd = request.getParameter("password");
        List<User> userList = new UserServiceImpl(new UserDaoImpl()).findUser(user, passwd);
        if (userList.size() > 0) {
            // 添加进session
            HttpSession session = request.getSession(true);
            session.setAttribute("user", userList.get(0));
            // 设置过期时间5分钟
            session.setMaxInactiveInterval(60 * 5);
        }
        String str = JSON.toJSONString(userList);
        out.write(str);
        out.flush();
        out.close();
    }
 
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}