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\t分类名称\t");
            for(Sort s:list){
                System.out.println(s.getSid()+"\t"+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();
    }
}