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  • Java的数据库连接

    1、数据库的连接
    (1)select 查询操作:
    执行语句:ResultSet executeQuery(sql);
    处理结果集:rs.next();rs.getXxx();
    释放资源:ResultSet.close();
    (2)预处理对象 PreparedStatement:解决SQL注入问题
    sql语句:? 占位符;
    获得执行对象:prepareStatement(sql);
    执行语句:setXxx(int, Obj);executeQuery();
    释放资源:PreparedStatement.close();

    举个例子:

    package com.oracle.difficult;
    
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;
    import java.util.Scanner;
    
    public class demo04 {
    
        public static void main(String[] args) throws ClassNotFoundException, SQLException {
            //1、注册驱动
                    Class.forName("com.mysql.jdbc.Driver");
                    //2、获得连接
                    String url = "jdbc:mysql://localhost:3306/ceshi?characterEncoding=gbk";
                    String root = "root";
                    String  password = "123";
                    Connection  con =  DriverManager.getConnection(url, root, password);
                    
                    //3、获得语句执行平台
                    Statement  sta  =  con.createStatement();
                    //4、执行sql语句
                    Scanner  sc = new Scanner(System.in);
                    System.out.println("请输入用户名:");
                    String  user = sc.next();
                    System.out.println("请输入密码:");
                    String   pass = sc.next();
                    String sql = "select count(*) from user where uname = '"+user+"' "+"and pwd = '"+pass+"'";
                    //需要导包   import java.sql.ResultSet;
                    ResultSet rs = sta.executeQuery(sql);
                    /*//3、获得语句执行平台(预处理对象,解决SQL注入问题)
                    String  sql = "select count(*) from ceshi1 where id = ? and sname = ?";
                    PreparedStatement past = con.prepareStatement(sql);
                    //4、执行SQL语句
                    Scanner  sc = new Scanner(System.in);
                    System.out.println("请输入用户名:");
                    int  user = sc.nextInt();
                    System.out.println("请输入密码:");
                    String   pass = sc.next();
                    past.setInt(1, user);
                    past.setString(2, pass);
                    ResultSet  rs = past.executeQuery();*/
                    //5、处理结果集
                    int count = 0;
                    while(rs.next()){
                        count = rs.getInt(1);
                    }
                    if(count > 0){
                        System.out.println("登录成功!!");
                    }else{
                        System.out.println("登录失败");
                    }
                    //6、释放资源
                    rs.close();
                    sta.close();
                    con.close();
    
        }
    
    }

    SQL语句注入问题:

    (3)JDBCUtils工具类:
    将注册驱动、获得连接和释放资源(方法重载)封装起来;

    package com.oracle.tools;
    
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    public class JDBCUtils {
    
        public static  Connection get() {
                    //1、注册驱动
                    try {
                        Class.forName("com.mysql.jdbc.Driver");
                    } catch (ClassNotFoundException e) {
                        e.printStackTrace();
                    }
                    //2、获得连接
                    String url = "jdbc:mysql://localhost:3306/ceshi?characterEncoding=gbk";
                    String root = "root";
                    String pwd = "123";
                    Connection conn = null;
                    try {
                         conn = DriverManager.getConnection(url,root,pwd);
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                    return conn;
           }
            public static void  close(Connection conn,PreparedStatement pst){
                if(pst != null){
                    try {
                        pst.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
                if(conn != null){
                    try {
                        conn.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
            }
            public static void  close(Connection conn,PreparedStatement pst,ResultSet rs){
                if(rs != null){
                    try {
                        rs.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
                if(pst != null){
                    try {
                        pst.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
                if(conn != null){
                    try {
                        conn.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
            }
    }

    (4)项目分层(分包)

    view层:视图层,项目中的界面;
    controller层:控制层,获取界面上的数据;将要实现的功能交给业务层处理;
    service层作用: 业务层, 功能的实现, 与controller控制层和数据访问层DAO交互, 将对数据库的操作交给DAO数据访问层来处理
    dao层作用: 数据访问层, 用来操作数据库表的数据
    db数据库: 这里指MySQL
    domain 实体包: 存放JavaBean
    tools工具包:存放项目中使用到的工具类
    test测试包: 存放项目功能测试的代码

     各举一个例子:

    view层:

    package com.oracle.view;
    
    import java.util.List;
    import java.util.Scanner;
    
    import com.oracle.controller.Sortcontroller;
    import com.oracle.controller.UserController;
    import com.oracle.domain.Sort;
    
    public class Mainview {
            private UserController userController = new UserController();
            private Sortcontroller  sortcontroller = new Sortcontroller();
            public void  mainShow(){
                System.out.println("--------欢迎进入商城--------");
                System.out.println("1、登陆");
                System.out.println("2、注册");
                System.out.println("3、退出");
                System.out.println("请输入你的选择");        
            }
            public void IndexShow(){
                System.out.println("-------------首页-------------");
                System.out.println("1、新增分类");
                System.out.println("2、修改分类");
                System.out.println("3、删除分类");
                System.out.println("4、查询所有分类");
                System.out.println("5、返回上级菜单");
                System.out.println("请输入你的选择");    
            }
            //登录页面
            public void login(){
                System.out.println("-----------登陆页面-------------");
                System.out.println("请输入用户名:");
                Scanner  sc = new Scanner(System.in);
                String username = sc.next();
                System.out.println("请输入密码:");
                String password = sc.next();
                //调用Controller 层的登陆方法
                int count =  userController.login(username, password);
                if(count > 0){
                    System.out.println("登陆成功!!");
                    run2();
                }else{
                    System.out.println("登陆失败");
                }
            }
            //注册页面
            public void register(){
                System.out.println("-----------注册页面-------------");
                System.out.println("请输入用户名:");
                Scanner  sc = new Scanner(System.in);
                String username = sc.next();
                System.out.println("请输入密码:");
                String password = sc.next();
                //调用Controller 层的注册方法
                System.out.println(userController.registerUser(username, password));
            }
            //一级菜单
            public void run(){
                Scanner sc = new Scanner(System.in);
                while(true){
                    mainShow();
                    int  choose = sc.nextInt();
                    switch(choose){
                    case 1:
                        //登陆
                        login();
                        break;
                    case 2:
                        register();
                        break;
                    case 3:
                        return;
                    }
                }
            }
            //二级菜单
            public void run2(){
                Scanner sc = new Scanner(System.in);
                while(true){
                    IndexShow();
                    int choose = sc.nextInt();
                    switch(choose){
                    case 1:
                        add();
                        break;
                    case 2:
                        update();
                        break;
                    case 3:
                        break;
                    case 4:
                        getAll();
                        break;
                    case 5:
                        return;
                    }
                }
            }
            //新增分类页面
            public  void  add(){
                Scanner sc = new Scanner(System.in);
                System.out.println("--------------新增页面------------");
                System.out.println("请输入你要新增的分类名称");
                String  sname = sc.next();
                //调用controller新增的方法
                System.out.println(sortcontroller.addSort(sname));
            }
            //查询所有分类页面
            public void getAll(){
                System.out.println("-------------查询所有分类-------------");
                //调用controller的查询方法
                List<Sort> list = sortcontroller.getAll();
                System.out.println("分类编号	分类名称	");
                for(Sort s:list){
                    System.out.println(s.getSid()+"	"+s.getSname());
                }
            }
            //修改分类页面
            public void update(){
                getAll();
                System.out.println("请输入要您要修改的分类编号");
                Scanner sc = new  Scanner(System.in);
                int  id = sc.nextInt();
                System.out.println("请输入你要修改的分类名称");
                String  sname = sc.next();
                //调用Controller的修改方法
                String mes = sortcontroller.updateSort(id, sname);
                System.out.println(mes);
            }
    }

    controller层:

    package com.oracle.controller;
    
    import com.oracle.domain.User;
    import com.oracle.service.UserService;
    
    public class UserController {
        //封装前台数据传给后台
        //接收后台数据传给后台
                private  UserService  userService = new UserService();
                public int login(String username,String password){
                    return  userService.login(username, password);
                }
                public String registerUser(String username,String password){
                    return  userService.registerUser(username, password);
                }
                /*public String register(String uname,String pwd){
                      User  user = new User();
                }*/
    }

    service层:

    package com.oracle.service;
    
    import java.sql.SQLException;
    
    import com.oracle.dao.Userdao;
    import com.oracle.domain.User;
    
    public class UserService {
            //UserService层只能调用Dao层方法(相对)
            //view层调用controller层调用service层调用dao层
           private Userdao   userDao = new Userdao();
           public  int login(String username,String password){
               int count = 0;
               try {
                 count = userDao.login(username, password);
            } catch (SQLException e) {
                e.printStackTrace();
            }
              return count;
           }
           //注册方法
           public String register(User user){
               int row = 0;
               String mes = "";
               try {
                row = userDao.register(user);
            } catch (SQLException e) {
                e.printStackTrace();
            }
               if(row > 0){
                   mes = "注册成功";
               }else{
                   mes = "注册失败";
               }
               return mes;
           }
           //-----------
           public String registerUser(String username,String password){
                 int count = 0;
                 String mes ="";
                 try {
                    count = userDao.registerUser(username, password);
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                 if(count == 0){
                     int row = 0;
                     try {
                         row =userDao.updateUser(username, password);
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                     if(row > 0){
                         mes = "注册成功!";
                     }else{
                         mes = "注册失败!";
                     }
                 }else{
                     mes = "用户名已存在!";
                 }
                 return mes;
           }
    }

    dao层:

    package com.oracle.dao;
    
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    import com.oracle.domain.User;
    import com.oracle.tools.JDBCUtils;
    
    public class Userdao {
            //登陆验证用户名或密码是否正确
           public int login(String username,String password) throws SQLException{
               Connection conn = JDBCUtils.get();
               String sql = "select count(*) from user where uname = ? and pwd = ?";
               PreparedStatement pst = conn.prepareStatement(sql);
               pst.setString(1, username);
               pst.setString(2, password);
               ResultSet rs = pst.executeQuery();
               int count = 0;
               while(rs.next()){
                   count=rs.getInt(1);
               }
               return count;
           }
           //注册方法
           //1注册用户
           public int registerUser(String username,String password) throws SQLException{
               Connection conn = JDBCUtils.get();
               String sql = "select count(*) from user where uname = ? ";
               PreparedStatement pst = conn.prepareStatement(sql);
               pst.setString(1, username);
               ResultSet rs = pst.executeQuery();
               int count = 0;
               while(rs.next()){
                   count=rs.getInt(1);
               }
               JDBCUtils.close(conn, pst, rs);
               return count;
           }
           //2添加用户
           public int updateUser(String username,String password) throws SQLException{
               Connection conn = JDBCUtils.get();
               String sql = "insert into user (uname,pwd) values (?,?)";
               PreparedStatement pst = conn.prepareStatement(sql);
               pst.setString(1, username);
               pst.setString(2, password);
               int row = pst.executeUpdate();
               JDBCUtils.close(conn, pst);
               return row;
           } 
           public  int  register(User user) throws SQLException{
               Connection conn = JDBCUtils.get();
               String sql = "insert into user(uname,pwd) values(?,?)";
               PreparedStatement pst = conn.prepareStatement(sql);
               pst.setString(1, user.getUsername());
               pst.setString(2, user.getPassword());
               int row = pst.executeUpdate();
               JDBCUtils.close(conn, pst);
               return  row;
           }
    }

    domain层:

    package com.oracle.domain;
    
    public class User {
            private  int  uid;
            private  String  username;
            private  String  password;
            public int getUid() {
                return uid;
            }
            public void setUid(int uid) {
                this.uid = uid;
            }
            public String toString() {
                return "User [uid=" + uid + ", username=" + username + ", password=" + password + "]";
            }
            public User() {
                super();
            }
            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;
            }
            
    }

    tools层:

    package com.oracle.tools;
    
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    public class JDBCUtils {
    
        public static  Connection get() {
                    //1、注册驱动
                    try {
                        Class.forName("com.mysql.jdbc.Driver");
                    } catch (ClassNotFoundException e) {
                        e.printStackTrace();
                    }
                    //2、获得连接
                    String url = "jdbc:mysql://localhost:3306/ceshi?characterEncoding=gbk";
                    String root = "root";
                    String pwd = "123";
                    Connection conn = null;
                    try {
                         conn = DriverManager.getConnection(url,root,pwd);
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                    return conn;
           }
            public static void  close(Connection conn,PreparedStatement pst){
                if(pst != null){
                    try {
                        pst.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
                if(conn != null){
                    try {
                        conn.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
            }
            public static void  close(Connection conn,PreparedStatement pst,ResultSet rs){
                if(rs != null){
                    try {
                        rs.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
                if(pst != null){
                    try {
                        pst.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
                if(conn != null){
                    try {
                        conn.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
            }
    }

    test层:

    package com.oracle.test;
    
    import com.oracle.view.Mainview;
    
    public class test {
    
        public static void main(String[] args) {
            new Mainview().run();
        }
    }
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  • 原文地址:https://www.cnblogs.com/scw123/p/9801843.html
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