MyBatis原理分析手写持久层框架1

public static void main(String[] args) { 
      Connection connection = null;
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;
  try {
  // 加载数据库驱动
  Class.forName("com.mysql.jdbc.Driver");
  // 通过驱动管理类获取数据库链接
  connection =
DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis? characterEncoding=utf-8", "root", "root");
  // 定义sql语句？表示占位符
  String sql = "select * from user where username = ?";
  // 获取预处理statement
  preparedStatement = connection.prepareStatement(sql);
  // 设置参数，第一个参数为sql语句中参数的序号(从1开始)，第二个参数为设置的参数值 preparedStatement.setString(1, "tom");
  // 向数据库发出sql执行查询，查询出结果集
  resultSet = preparedStatement.executeQuery();
  // 遍历查询结果集
  while (resultSet.next()) {
    int id = resultSet.getInt("id");
    String username = resultSet.getString("username");
  // 封装User
    user.setId(id);
    user.setUsername(username);
  }
    System.out.println(user);
  }
  } catch (Exception e) {
    e.printStackTrace();
  } finally {
      // 释放资源
        if (resultSet != null) {
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (preparedStatement != null) {
            try {
                preparedStatement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (connection != null) {
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
  }
}