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- type Exception report
- message: java.lang.NullPointerException
- description The server encountered an internal error that prevented it from fulfilling this request.
- java.lang.NullPointerException
- DB.DataBaseConnection.close(DataBaseConnection.java:34)
- DB.UserDAOImpl.queryAll(UserDAOImpl.java:84)
- org.apache.jsp.QueryAll_jsp._jspService(QueryAll_jsp.java:100)
- org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
- javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
- org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:439)
- org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
- org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
- javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
- <%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
- <%@ page import="DB.*" %>
- <%@ page import="java.util.*" %>
- <title>QueryAll</title>
- <% request.setCharacterEncoding("utf-8"); %>
- <body>
- <%
- UserDAO userDAo=DAOFcatory.getUserDAOInstance();
- //set new user
- List<User> all=userDAo.queryAll();
- Iterator<User> iter=all.iterator();
- %>
- <table border="1" bgcolor="#c0c0c0" align="center">
- <tr>
- <td>Id</td>
- <td>Username</td>
- <td>Password</td>
- </tr>
- <%
- while(iter.hasNext()){
- User user1=iter.next();
- %>
- <tr>
- <td><%=user1.getUserid() %></td>
- <td><%=user1.getUsername()%></td>
- <td><%=user1.getPassword() %></td>
- </tr>
- <%
- }
- %>
- </table>
- package DB;
- import java.sql.Connection;
- import java.sql.DriverManager;
- import java.sql.SQLException;
- public class DataBaseConnection {
- private final String driver = "com.mysql.jdbc.Driver";
- private final String url = "jdbc:mysql:localhost:3306/javaweb";
- private final String user = "root";
- private final String pwd = "root";
- private Connection conn;
- public DataBaseConnection() {
- try {
- Class.forName(driver);
- this.conn = DriverManager.getConnection(url,user,pwd);
- }
- catch (ClassNotFoundException e){
- e.printStackTrace();
- }
- catch (SQLException e) {
- e.printStackTrace();
- }
- }
- public Connection getConnection() {
- return this.conn;
- }
- public void close(){
- try {
- this.conn.close();
- }
- catch (SQLException e) {
- e.printStackTrace();
- }
- }
- }
- package DB;
- public class User {
- private int userid;
- private String username;
- private String password;
- public int getUserid() {
- return userid;
- }
- public void setUserid(int userid) {
- this.userid = userid;
- }
- public String getUsername() {
- return username;
- }
- public void setUsername(String username) {
- this.username = username;
- }
- public String getPassword() {
- return password;
- }
- public void setPassword(String password) {
- this.password = password;
- }
- }
- package DB;
- import java.util.*;
- public interface UserDAO {
- //query by all
- public List<User> queryAll() throws Exception;
- package DB;
- import java.sql.PreparedStatement;
- import java.sql.ResultSet;
- import java.util.ArrayList;
- import java.util.List;
- import DB.User;
- import DB.DataBaseConnection;
- public class UserDAOImpl implements UserDAO{
- public List<User> queryAll() throws Exception {
- List<User> all = new ArrayList<User>();
- String sql = "select * from user";
- PreparedStatement pstmt = null;
- DataBaseConnection dbc = null;
- try {
- dbc = new DataBaseConnection();
- pstmt = dbc.getConnection().prepareStatement(sql);
- //query database
- ResultSet rs = pstmt.executeQuery();
- while(rs.next()) {
- User user = new User();
- user.setUserid(rs.getInt(1));
- user.setUsername(rs.getString(2));
- user.setPassword(rs.getString(3));
- //add data to List
- all.add(user);
- }
- rs.close();
- pstmt.close();
- }
- catch(Exception e) {
- e.printStackTrace();
- throw new Exception("Erro:operation abnormal");
- }
- finally {
- dbc.close();
- }
- return all;
- }
- package DB;
- import DB.*;
- public class DAOFcatory {
- public static UserDAO getUserDAOInstance() {
- return new UserDAOImpl();
- }
- }
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