jdbc数据库的连接步骤

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1.注册驱动Class.forName("com.jdbc.mysql.Driver")

2.获得链接Connection con = DriverManager.getConntection(url,user,password) url = " jdbc:mysql://localhost:3306/数据库名"

3.获得语句执行者：1.语句执行者statement 预处理对象：preparedStatement 向预对象中传入sql 语句：好处是防注入

4.执行语句：查询：executeQuery() 修改用：executeUpdate() 查询返回值是结果集，修改的返回值是整数

5.处理结果集 result.next() result.getXxx()

6.释放资源

代码：

public class sqlconnecte {
   public static void main(String[] args) throws ClassNotFoundException, SQLException {
       Class.forName("com.mysql.jdbc.Driver");
       Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/tomorrow","root","12345");
       System.out.println(conn);
       String sql = "SELECT * from contact WHERE hello IS ?" ;
       PreparedStatement psm = conn.prepareStatement(sql);
       psm.setString(1, null);
       ResultSet rs = psm.executeQuery();
       int num=0;
       while(rs.next()){
           String sq = "UPDATE contact SET hello=? WHERE hello IS null";
           PreparedStatement ps = conn.prepareStatement(sq);
           ps.setString(1,rs.getString("sname"));
           ps.executeUpdate();
           ps.close();
       }
       rs.close();
       psm.close();
   }
}

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