public static void main(String[] args) {
            Connection connection = null;
            PreparedStatement preparedStatement = null;
            ResultSet resultSet = null;
            
            try {
                //1、加载数据库驱动
                Class.forName("com.mysql.jdbc.Driver");
                //2、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");
                //3、定义sql语句 ?表示占位符
            String sql = "select * from user where username = ?";
                //4、获取预处理statement
                preparedStatement = connection.prepareStatement(sql);
                //5、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, "王五");
                //6、向数据库发出sql执行查询，查询出结果集
                resultSet =  preparedStatement.executeQuery();
                //7、遍历查询结果集
                while(resultSet.next()){
                    User user 
                    System.out.println(resultSet.getString("id")+"  "+resultSet.getString("username"));
                }
            } catch (Exception e) {
                e.printStackTrace();
            }finally{
                //8、释放资源
                if(resultSet!=null){
                    try {
                        resultSet.close();
                    } catch (SQLException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                if(preparedStatement!=null){
                    try {
                        preparedStatement.close();
                    } catch (SQLException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                if(connection!=null){
                    try {
                        connection.close();
                    } catch (SQLException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }

            }

        }