java连接数据库——JDBC连接数据库

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" )); // 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

 

java连接数据库——JDBC连接数据库

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