Ошибка при выполнении примера сервлета сервлета Jsp

Question

Я выполняю простой пример crud, используя Jsp, Servlet и Mysql. Я вручную набрал код, заглянув в пример. Когда я пытаюсь выполнить его, я получаю эту ошибку. Ниже приводится описание сообщения об ошибке am getting. Пожалуйста, дайте мне знать, если вам нужны какие-либо файлы java/jsp для анализа.

HTTP Status 500 - javax.servlet.ServletException: Error instantiating servlet class com.daniel.controller.UserController 


type Exception report 

message javax.servlet.ServletException: Error instantiating servlet class com.daniel.controller.UserController 

description The server encountered an internal error that prevented it from fulfilling this request. 

exception 
org.apache.jasper.JasperException: javax.servlet.ServletException: Error instantiating servlet class com.daniel.controller.UserController 
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:555) 
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:461) 
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396) 
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340) 
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729) 
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) 


root cause 
**javax.servlet.ServletException**: Error instantiating servlet class com.daniel.controller.UserController 
    org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:742) 
    org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:712) 
    org.apache.jsp.index_jsp._jspService(index_jsp.java:99) 
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) 
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729) 
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438) 
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396) 
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340) 
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729) 
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) 


root cause 
**`java.lang.NullPointerException`** 
    java.util.Properties$LineReader.readLine(Unknown Source) 
    java.util.Properties.load0(Unknown Source) 
    java.util.Properties.load(Unknown Source) 
    com.daniel.util.DbUtil.getConnection(DbUtil.java:27) 
    com.daniel.dao.UserDao.<init>(UserDao.java:20) 
    com.daniel.controller.UserController.<init>(UserController.java:25) 
    sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) 
    sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) 
    sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) 
    java.lang.reflect.Constructor.newInstance(Unknown Source) 
    java.lang.Class.newInstance(Unknown Source) 
    org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:742) 
    org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:712) 
    org.apache.jsp.index_jsp._jspService(index_jsp.java:99) 
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) 
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729) 
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438) 
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396) 
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340) 
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729) 
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) 

Добавление com.daniel.controller.UserController файла

package com.daniel.controller; 

import java.io.IOException; 
import java.text.ParseException; 
import java.text.SimpleDateFormat; 

import javax.servlet.RequestDispatcher; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 

import com.daniel.dao.UserDao; 
import com.daniel.model.User; 


public class UserController extends HttpServlet { 
    private static final long serialVersionUID = 1L; 
    private static String INSERT_OR_EDIT = "/user.jsp"; 
    private static String LIST_USER = "/listUser.jsp"; 
    private UserDao dao; 

    public UserController() { 
     super(); 
     dao = new UserDao(); 

    } 

    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException,IOException 
    { 
     String forward= " "; 
     String action = req.getParameter("action"); 
     if(action.equalsIgnoreCase("delete")) 
     { 
      forward=LIST_USER; 
      int userid = Integer.parseInt(req.getParameter("userid")); 
      dao.deleteUser(userid); 
      req.setAttribute("users",dao.getAllUsers()); 
     } 
     else if(action.equalsIgnoreCase("edit")) 
     { 
      forward=INSERT_OR_EDIT; 
      int userid = Integer.parseInt(req.getParameter("userid")); 
      User user= dao.getUserById(userid); 
      req.setAttribute("users",user); 
     } 
     else if(action.equalsIgnoreCase("listUser")) 
     { 
      forward=LIST_USER; 
      req.setAttribute("users", dao.getAllUsers()); 
     } 
     else 
     { 
      forward=INSERT_OR_EDIT; 
     } 
     RequestDispatcher rd = req.getRequestDispatcher(forward); 
     rd.forward(req,resp); 
    } 

    public void doPost(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException 
    { 
     User user = new User(); 

     user.setFirstname(req.getParameter("firstname")); 
     user.setLastname(req.getParameter("lastname")); 
     try { 
      user.setDob(new SimpleDateFormat("MM/dd/yyyy").parse(req.getParameter("dob"))); 
     } catch (ParseException e) { 
      e.printStackTrace(); 
     } 
     user.setEmailid(req.getParameter("emailid")); 
     String userid = req.getParameter("userid"); 
     if(userid == null || userid.isEmpty()) 
     { 
      dao.addUser(user); 
     }else 
     { 
      user.setUserid(Integer.parseInt(userid)); 
      dao.updateUser(user); 
     } 
     RequestDispatcher rd = req.getRequestDispatcher(LIST_USER); 
     req.setAttribute("users",dao.getAllUsers()); 
     rd.forward(req,resp); 
    } 

} 

Добавление com.daniel.dao.UserDao

package com.daniel.dao; 

import java.sql.Connection; 
import java.sql.PreparedStatement; 
import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.sql.Statement; 
import java.util.ArrayList; 
import java.util.List; 

import com.daniel.model.User; 
import com.daniel.util.DbUtil; 

public class UserDao 
{ 
    private Connection con; 

    public UserDao() 
    { 
     con= DbUtil.getconnection(); 
    } 

    public void addUser(User user) 
    { 
     try 
     { 
     PreparedStatement ps = con.prepareStatement("insert into users(firstname,lastname,dob,emailid) values(?,?,?,?)"); 
     ps.setString(1,user.getFirstname()); 
     ps.setString(2,user.getLastname()); 
     ps.setDate(3,new java.sql.Date(user.getDob().getTime())); 
     ps.setString(4,user.getEmailid()); 

     ps.executeUpdate(); 
     }catch (SQLException e) 
     { 
      e.printStackTrace(); 
     } 
    } 

    public void deleteUser(int userid) 
    { 
     try 
     { 
      PreparedStatement ps = con.prepareStatement("delete from users where userid=?"); 
      ps.setInt(1,userid); 
      ps.executeUpdate(); 
     }catch (SQLException e) 
     { 
      e.printStackTrace(); 
     } 
    } 

    public void updateUser(User user) 
    { 
     try 
     { 
      PreparedStatement ps = con.prepareStatement("update user set firstname=?,lastname=?,dob=?,emailid=?"+ "where userid=?"); 
      ps.setString(1,user.getFirstname()); 
      ps.setString(2,user.getLastname()); 
      ps.setDate(3,new java.sql.Date(user.getDob().getTime())); 
      ps.setString(4,user.getEmailid()); 
      ps.setInt(5,user.getUserid()); 

      ps.executeUpdate(); 
     }catch (SQLException e) 
     { 
      e.printStackTrace(); 
     } 
    } 

    public List<User> getAllUsers() 
    { 
     List<User> users = new ArrayList<User>(); 
     try 
     { 
      Statement st = con.createStatement(); 
      ResultSet rs = st.executeQuery("select * from users"); 
      while(rs.next()) 
      { 
       User user = new User(); 
       user.setUserid(rs.getInt("userid")); 
       user.setFirstname(rs.getString("firstname")); 
       user.setLastname(rs.getString("lastname")); 
       user.setDob(rs.getDate("dob")); 
       user.setEmailid(rs.getString("emailid")); 
       users.add(user); 
      } 
     }catch (SQLException e) 
     { 
      e.printStackTrace(); 
     } 
     return users; 
    } 

     public User getUserById(int userid) 
     { 
      User user = new User(); 
      try 
      { 
       PreparedStatement ps = con.prepareStatement("select * from users where userid=?"); 
       ResultSet rs = ps.executeQuery(); 
       if(rs.next()) 
       { 

        user.setUserid(rs.getInt("userid")); 
        user.setFirstname(rs.getString("firstname")); 
        user.setLastname(rs.getString("lastname")); 
        user.setDob(rs.getDate("dob")); 
        user.setEmailid(rs.getString("emailid")); 

       } 
      }catch (SQLException e) 
      { 
       e.printStackTrace(); 
      } 
      return user; 
    } 
} 

Добавление com.daniel.util.DbUtil

package com.daniel.util; 

import java.io.FileNotFoundException; 
import java.io.IOException; 
import java.io.InputStream; 
import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.SQLException; 
import java.util.Properties; 

public class DbUtil 
{ 
    private static Connection con=null; 

    public static Connection getconnection() 
    { 
    if(con!=null) 
    { 
     return con; 
    } 
    else 
    { 
     try 
     { 
      Properties prop = new Properties(); 
      InputStream ip = DbUtil.class.getClassLoader().getResourceAsStream("/db.properties"); 
      prop.load(ip); 
      String driver = prop.getProperty("driver"); 
      String url = prop.getProperty("url"); 
      String user = prop.getProperty("user"); 
      String pwd = prop.getProperty("password"); 

      Class.forName(driver); 

      con = DriverManager.getConnection(url, user, pwd); 
     } 
     catch (ClassNotFoundException e) { 
      e.printStackTrace(); 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } catch (FileNotFoundException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
    } 
    return con; 
    } 
} 

Answer 1

В классе DbUtil попробуйте удалить это/на g etResourceAsStream, как показано ниже, и убедитесь, что ваш файл db.properties находится в вашем каталоге src.

InputStream ip = DbUtil.class.getClassLoader().getResourceAsStream("db.properties");