JDBC——架构层、驱动

JDBC(java Datebase Connector)

jdbc驱动程序

四种类型：

　　jdbc-odbc桥接驱动程序

　　Native-API

　　JDBC-Net

　　Native-Protocol　　(常见)

 public class DBToolOld
 {
     public static void main(String[] args)
     {
         // 1、注册驱动
         // DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
         // new驱动类的时候会注册一份，DriverManager.registerDriver又会去注册一份驱动
         // 硬编码在类中，不方便修改
         // System.setProperty("driver", "oracle.jdbc.driver.OracleDriver");
         // 因为key和value都是字符串，可以改到配置文件中
         // 需要约定好key的值，注册起来不太方便
         try
         {
             Class.forName("oracle.jdbc.driver.OracleDriver");
             // 2、获得连接对象
             String oracleUrl = "jdbc:oracle:thin:@192.168.6.100:1521:NIIT";
             Connection conn = DriverManager.getConnection(oracleUrl, "scott",
                     "tiger");
             // 3、开始执行SQL语句，先创建Statement对象
             Statement stmt = conn.createStatement();
             // 4、执行SQL语句，返回一个结果集，只有是SELECT语句、executeQuery才会返回结果集
             ResultSet rs = stmt
                     .executeQuery("SELECT empNo, ename, hireDate, sal FROM Emp");
             // 5、处理结果集
             while (rs.next())
             {
                 int empNo = rs.getInt(1); //根据列下标获得值
                 System.out.println(empNo);
                 String ename = rs.getString("ename"); //根据列名获得值，推荐这种方式
                 System.out.println(ename);
                 Date joinDate = rs.getDate("hireDate");
                 System.out.println(joinDate);
                 Double sal = rs.getDouble("sal");
                 System.out.println(sal);
                 System.out.println("============");
             }
             //6、关闭资源
             rs.close();
             stmt.close();
             conn.close();
         }
         catch (ClassNotFoundException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         catch (SQLException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }

     }
 }

实际上常用的是：

 public class DBTool
 {
     private static DBTool instance;

     private DBTool()
     {

     }

     public static DBTool getInstance()
     {
         if (instance == null)
         {
             instance = new DBTool(); // 如果该实例为空，表示没实例化，在自己这里实例化，否则直接返回已经实例化好的对象
         }
         return instance;
     }

     public Connection getConnection()
     {
         Connection conn = null;
         try
         {
             Properties p = new Properties();
             p.load(new FileReader("db.properties"));
             String driverName = p.getProperty("driverName");
             String url = p.getProperty("url");
             String userName = p.getProperty("username");
             String pwd = p.getProperty("password");
             Class.forName(driverName);
             conn = DriverManager.getConnection(url, userName, pwd);
         }
         catch (IOException | SQLException | ClassNotFoundException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         return conn;
     }

     public static void closeAll(Connection conn, Statement stmt, ResultSet rs)
     {
         close(rs);
         close(stmt);
         close(conn);
     }

     private static void close(AutoCloseable ac)
     {
         try
         {
             if (ac != null)
             {
                 ac.close();
                 ac = null;
             }
         }
         catch (Exception e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }
 }

此时驱动配置文件使用映射：

 driverName = com.mysql.jdbc.Driver
 url = jdbc:mysql://192.168.6.66:3307/hn
 username = zxj
 password = wxniit