java连接数据库——JDBC连接数据库

DBUtil.java   // 数据库操作文件

package com.bjpowernode.jdbc.util;



import java.io.File;

import java.io.FileInputStream;

import java.io.InputStream;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.sql.Statement;

import java.util.Properties;



public class DBUtil {

    

    private static String driver ;

    private static String url    ;

    private static String uname  ;

    private static String pwd    ;

    

    static{

        

        try {

            //创建集合类对象

            Properties properties = new Properties();

            //把文件封装成字节输入流

            InputStream inStream = new FileInputStream(new File("./src/DBConfig.properties"));


/* 
 等同于     ResourceBundle isStream = ResourceBundle.getBundle("com.bjpowernode.jdbc.util.DBConfig"); //注意：DBConfig 不要添加后缀



*/ //把字节流加载到集合类中，在内存中以key和value的格式形成

            properties.load(inStream);

            //通过key获得value

            driver = properties.getProperty("driver");

            url = properties.getProperty("url");

            uname = properties.getProperty("uname");

            pwd = properties.getProperty("pwd");

        } catch (Exception e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

            throw new RuntimeException("读取配置文件失败！",e);

        }

        

    }

    

    //获得连接

    public static Connection getConnection (){

        Connection  conn  = null;

        try {

            //1:注册驱动

            Class.forName(driver);

            

            conn = DriverManager.getConnection(url,uname,pwd);

        } catch (Exception e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

            throw new RuntimeException("连接数据库失败！",e);

        }

        return conn;

    }

    

    //释放资源

    public static void close(ResultSet rs ,Statement pstm ,Connection conn){

        try{

            if (rs != null){

                rs.close();

            }

            

        }catch(SQLException e){

            e.printStackTrace();

            throw new RuntimeException("rs关闭失败！",e);

        }

        try{

            if (pstm != null){

                pstm.close();

            }

            

        }catch(SQLException e){

            e.printStackTrace();

            throw new RuntimeException("pstm关闭失败！",e);

        }

        try{

            if (conn != null){

                conn.close();

            }

            

        }catch(SQLException e){

            e.printStackTrace();

            throw new RuntimeException("conn关闭失败！",e);

        }

        

        

    }

    //开启事务

    public static void beginTransaction(Connection conn){

        try {

            if(conn != null){

                conn.setAutoCommit(false);

            }

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

            throw new RuntimeException("开启事务失败！",e);

        }

    }

    //提交事务

    public static void commit(Connection conn){

        try {

            if(conn != null){

                conn.commit();

            }

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

            throw new RuntimeException("提交事务失败！",e);

        }

    }

    

    //回滚事务

    public static void rollback(Connection conn){

        try {

            if(conn != null){

                conn.rollback();

            }

        } catch (SQLException e) {

            e.printStackTrace();

            throw new RuntimeException("回滚事务失败！",e);

        }

    }

}

Transfer_transaction.java  // 调用数据库文件

 

package com.bjpowernode.jdbc.transfer;



import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;



import com.bjpowernode.jdbc.util.DBUtil;



public class Transfer_transaction {

    public static void main(String[] args) {

        transfer("zs","ls",100);

    }

    /**

     * 

     * @param from_act  : 转出账户

     * @param to_act    ：转入账户

     * @param money     ： 转账金额

     */

    private static void transfer(String from_act, String to_act, double money) {

        

        /*if(转出账户的金额 >= 转账金额)｛

            转出账户 - 转账金额

            转入账户 + 转账金额

        ｝else{

            提示余额不足

        }*/

        Connection conn  = null;

        //转出账户的金额

        try {

            //事务是针对连接开启的

            conn = DBUtil.getConnection();

            //开启事务

            DBUtil.beginTransaction(conn);

            

            double from_money = getMoneyByAct(conn,from_act);

            

            if(from_money >= money){//转出账户的金额 >= 转账金额

                //转账

                //转出账户 - 转账金额

                updateMoneyByAct(conn,from_money-money,from_act);

                //转入账户的金额

                double to_money = getMoneyByAct(conn,to_act);

                //模拟异常

//                Integer.parseInt("abc");

                //转入账户+ 转账金额

                updateMoneyByAct(conn,to_money+money,to_act);

                //提交事务

                DBUtil.commit(conn);

                System.out.println("转账成功！");

            }else{//提示余额不足

                System.out.println("余额不足！");

            }

        } catch (Exception e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

            System.out.println("转账失败！");

            //回滚事务

            DBUtil.rollback(conn);

        }finally{

            DBUtil.close(null, null, conn);

        }

        

    }

    /**

     * 通过账户修改账户金额

     * 

     * @param money : 需要修改的金额

     * @param act   ： 账户名称

     */

    private static void updateMoneyByAct(Connection conn ,double money, String act) {

        // TODO Auto-generated method stub

//        Connection conn = null;

        PreparedStatement pstm = null;

        

        try {

//            conn = DBUtil.getConnection();

            

            String sql = "update t_account set money = ? where act_no = ?";

            pstm = conn.prepareStatement(sql);

            

            pstm.setDouble(1, money);

            pstm.setString(2, act);

            

            pstm.executeUpdate();

            

            

            

        } catch (Exception e) {

            // TODO: handle exception

            

            throw new RuntimeException("修改金额失败",e);

        }finally{

            DBUtil.close(null, pstm, null);

        }

    }

    /**

     * 通过账户查询账户金额

     * @param act

     * @return

     */

    private static double getMoneyByAct(Connection conn ,String act) {

//        Connection conn = null;

        PreparedStatement pstm = null;

        ResultSet rs = null;

        double from_money = 0;

        try {

            //获得连接

//            conn = DBUtil.getConnection();

            String sql = "select money from t_account where act_no = ?";

            //创建数据库操作对象

            pstm = conn.prepareStatement(sql);

            //为占位符号赋值

            pstm.setString(1, act);

            //执行sql

            rs = pstm.executeQuery();

            /*while(rs.next()){

                from_money = rs.getDouble("money");

            }

            if(rs.next()){

                from_money = rs.getDouble("money");

            }

            */

            from_money = rs.next()?rs.getDouble("money"):0;

            

            

        } catch (Exception e) {

            throw new RuntimeException("查询账户余额失败！",e);

        }finally{

            DBUtil.close(rs, pstm, null);

        }

        return from_money;

    }

}

DBConfig.properties   //数据库配置文件

driver=com.mysql.jdbc.Driver

url=jdbc\:mysql\://127.0.0.1\:3366/bjpowernode

uname=root

pwd=root