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