数据库连接时总是空指针异常？测试表单信息无误，就是查询数据库时出错

Question

java.lang.NullPointerException
at com.Users.LoginServlet.doPost(LoginServlet.java:58)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:154)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:92)
at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:106)
at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:173)
at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:229)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:274)
at com.caucho.server.port.TcpConnection.run(TcpConnection.java:514)
at com.caucho.util.ThreadPool.runTasks(ThreadPool.java:527)
at com.caucho.util.ThreadPool.run(ThreadPool.java:449)
at java.lang.Thread.run(Unknown Source)

源代码：
package com.Users;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.Service.LoginService;

/**

• 登录控制层 ： LoginServlet
• 将用户个人信息保存到 Session范围内
• 根据status对页面进行分别显示

• @author daichen
  *
  /
  public class LoginServlet extends HttpServlet
  {
  private static final long serialVersionUID = 1L;
  /

  • 注入 LoginService 服务 */ private LoginService loginService;

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse res)
  throws ServletException, IOException
  {
  doGet(req,res);
  }
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException
  {
  request.setCharacterEncoding("GBK");
  response.setCharacterEncoding("GBK");
  User user = null;
  // 获取表单提交的登录信息
  String userId = null;
  String password = null;
  userId = request.getParameter("userId");
  password = request.getParameter("password");
  // 先判断用户信息是否否为空
  if(userId == null || "".equals(userId) || password == null || "".equals(password))
  {
  // 用户信息有误 , 回到 login.jsp 页面
  response.getWriter().println("

  对不起，你输入的信息有误 .请重新确认！

  ");
  return;
  }
  else
  {
  // 到数据表 user 中查找该用户 , 返回一个 User 对象
  System.out.println(userId+" "+password);

      user = loginService.userLogin(userId,password);
  
      // 并对查询到的结果进行处理
  
      if(user != null)
      {
          // 获取请求域的session对象
          HttpSession session = request.getSession();
          // 对三种权限分开添加到  Session 域中 
          if(user.getStatus() == 0){
              session.setAttribute("geneUser", user);
          }
          if(user.getStatus() == 1){
              session.setAttribute("admin", user);
          }
          if(user.getStatus() == 2){
              session.setAttribute("superAdmin", user);
          }
          // 成功获取到用户信息 , 转到   index.jsp
          RequestDispatcher rd = request.getRequestDispatcher("/WEB-INF/jsp/index.jsp");
          rd.forward(request, response);
          return;
      } 
      else
      {
          // 查询没有该用户 , 转到  login.jsp
          response.getWriter().print("<h3><font color='#f00'>对不起，你还未注册用户 </h3></font>"
                  + userId + "<h3><font color='#f00'>请先前去注册！</h3></font>");
          RequestDispatcher rd = request.getRequestDispatcher("/WEB-INF/jsp/register.jsp");
          rd.forward(request, response);
          return;
      }
  }
  

  }
  }

Answer 1

http://www.pc6.com/java/j_55284.html