Connection conn;
        Statement stmt;
        ResultSet rs = null;
        try {
            Class.forName("");
            conn = DriverManager.getConnection("","","");
            stmt = conn.createStatement();
            String sql = "select * from user";
            rs = stmt.executeQuery(sql);
            while(rs.next()){
                System.out.println(rs.getString("columnName"));
            }
            rs.close();
            stmt.close();
            conn.close();
        }catch (ClassNotFoundException e){
            System.out.println("未找到相应的数据库驱动");
        } catch (SQLException e) {
            e.printStackTrace();
        }