老师，我这段用户登陆的代码哪里出错了为什么页面500报错了

package com.imooc.system;

import java.util.List;

public class UserServiceImpl {

    /**

     * 用户登陆

     */

public int login(List<User>  listUser,User user) {

List<User>  listUser1=listUser;

User user1=user;

for(User u1:listUser1) {

if(u1.equals(user1)) {

return 1;//用户信息匹配成功，允许登陆

}

}

return -1;//用户信息匹配失败

}

}

package com.imooc.Servlet;

import java.io.IOException;

import java.util.List;

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 com.imooc.system.User;

import com.imooc.system.UserServiceImpl;

/**

 * Servlet implementation class loginServlet

 */

@WebServlet("/loginServlet")

public class loginServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

    /**

     * @see HttpServlet#HttpServlet()

     */

    public loginServlet() {

        super();

        // TODO Auto-generated constructor stub

    }

/**

* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

*/

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

}

/**

* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

*/

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

    String code1=(String)request.getSession().getAttribute("KAPTCHA_SESSION_KEY");

    String code2=request.getParameter("verifyCode");

    if(code1!=null&&code1.equals(code2)) {

    String name=request.getParameter("username");

    String password=request.getParameter("password");

    User u=new User(name,password);

    List<User> us=(List<User>)request.getServletContext().getAttribute("collection");

    UserServiceImpl use=new UserServiceImpl();

    int i=use.login(us, u);

    //如果等于1是登陆成功

    if(i==1) {

    request.getSession().setAttribute("name", name);//用于监听器进行判断是否登陆

    request.getSession().setAttribute("password", password);

    request.getRequestDispatcher("/pase/admin/categoryList.jsp").forward(request, response);

    }else {

    request.setAttribute("msg", "密码输入不正确");

    request.getRequestDispatcher("/login.jsp").forward(request, response);

    }

    }else {

    request.setAttribute("msg", "验证码输入不正确");

    request.getRequestDispatcher("/login.jsp").forward(request, response);

    return;

    }

}

}

package com.imooc.system;

import java.util.ArrayList;

import java.util.List;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

public class InitListener implements ServletContextListener {

@Override

public void contextDestroyed(ServletContextEvent arg0) {

// TODO Auto-generated method stub

}

@Override

public void contextInitialized(ServletContextEvent arg0) {

// TODO Auto-generated method stub

           List<User> li=new ArrayList<>();

           User e=new User("aaa","123456");

           li.add(e);

           arg0.getServletContext().setAttribute("collection", li);

}

}