JDBC

JDBC: Java Database Connectivity SUN 公司提供的一套操作数据库的标准规范。

一、 JDBC与数据库驱动

接口与实现的关系

二、JDBC规范(掌握四个核心对象)

1. DriverManager : 注册驱动
2. Connection：与数据库进行连接
3. Statement： 操作数据库SQL语句的对象
4. ResultSet： 结果集或者一张虚拟表

 public static void main(String[] args) throws SQLException {
        System.out.println("test jjjjDemo");
        Connection con = null;
        DriverManager.registerDriver(new com.mysql.jdbc.Driver());
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb2", "root", "password");
        Statement stmt = conn.createStatement(); // 得到执行SQL的对象
        ResultSet rs = stmt.executeQuery("select * from employee");
        while (rs.next()) {
            System.out.println(rs.getObject(1)); // 访问数据库的第一列
            System.out.println(rs.getObject(2)); // // 访问数据库的第二列
            System.out.println(rs.getObject(3));
            System.out.println(rs.getObject(4));
            System.out.println(rs.getObject(5));
            System.out.println(rs.getObject(6));
            System.out.println(rs.getObject(7));
            System.out.println(rs.getObject(8));
            System.out.println("================================");
        }
        // 结果集关闭 释放支援
        rs.close();
        stmt.close();
        conn.close();
    }

DriverManager 优缺点

导致注册两次
强烈依赖数据库的驱动 jar

DriverManager.registerDriver(new com.mysql.jdbc.Driver()); 

 public Driver() throws SQLException {

    }
    // 静态代码块随着类的加载而加载，导致注册两侧
    static {
        try {
            DriverManager.registerDriver(new Driver());
        } catch (SQLException var1) {
            throw new RuntimeException("Can't register driver!");
        }
    }

改为直接加载驱动

  public static void main(String[] args) throws SQLException, ClassNotFoundException {
        System.out.println("test jjjjDemo");
        Connection con = null;
        //DriverManager.registerDriver(new com.mysql.jdbc.Driver());
        Class.forName("com.mysql.jdbc.Driver"); // 加载驱动(反射)
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb2", "root", "password");
        Statement stmt = conn.createStatement(); // 得到执行SQL的对象
        ResultSet rs = stmt.executeQuery("select * from employee");
        while (rs.next()) {
            System.out.println(rs.getObject(1));
            System.out.println(rs.getObject(2));
            System.out.println(rs.getObject(3));
            System.out.println(rs.getObject(4));
            System.out.println(rs.getObject(5));
            System.out.println(rs.getObject(6));
            System.out.println(rs.getObject(7));
            System.out.println(rs.getObject(8));
            System.out.println("================================");
        }
        // 结果集关闭 释放支援
        rs.close();
        stmt.close();
        conn.close();
    }

URL：SUN 公司与数据库厂商之间的协议

协议 子协议       IP           端口号   数据库
jdbc: mysql: // localhost:  3306     /mydb2