.NET Core随笔把数据库数据查出来转JSON并输出

直接创建WEB项目即可；

  public class Startup
    {
        //startup.cs是站点启动时具体做了哪些事情，主要是开启了一个mvc服务。
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }
 
        public IConfiguration Configuration { get; }
 
        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options =>
            {
                // This lambda determines whether user consent for non-essential cookies is needed for a given request.
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });
 
            services.AddSession();
 
            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }
 
        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                app.UseHsts();
            }
 
            app.UseHttpsRedirection();
            app.UseStaticFiles();   //如果不添加将导致样式文件不能被客户端加载
            app.UseCookiePolicy();
            app.UseSession();
 
            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            }
                );
        }
    }

创建一个DB类用于查数据：

 public class DB : DbContext
    {
        public DB()
        {   //如果没有数据库，自动创建，有了什么都不干
            Database.EnsureCreated();
        }
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {    //对于这个上下文重写此方法以配置要使用的数据库（和其他选项）。对于上下文的每个实例调用此方法创建。
 
            //加载appsetting.json
            IConfiguration configuration = new ConfigurationBuilder()
                 .SetBasePath(Directory.GetCurrentDirectory())
              .AddJsonFile("appsettings.json").Build();
 
            string connectionString = configuration["DBSetting:ConnectString"];
            optionsBuilder.UseSqlServer(connectionString);
 
            base.OnConfiguring(optionsBuilder);
        }
 
        public DbSet<studen> studen { set; get; }
 
        public DbSet<xx> xx { set; get; }
 
    }
    //原文：https://blog.csdn.net/weixin_41609327/article/details/80821798 

appsettings.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "DBSetting": {
    "ConnectString": "server=.;database=test_core;uid=sa;pwd=123"
 
  },
  "AllowedHosts": "*"
}

有DB类肯定少不了help类

  /// 此类为抽象类，
    /// 不允许实例化，在应用时直接调用即可
    /// </summary>
    //  abstract   抽象类标识
    public abstract class SqlHelper
    {
        //加载appsetting.json
        static IConfiguration configuration = new ConfigurationBuilder()
              .SetBasePath(Directory.GetCurrentDirectory())
             .AddJsonFile("appsettings.json").Build();    
 
        /// <summary>
       /// 数据库连接字符串
       /// </summary>
        private static readonly string connectionString = configuration["DBSetting:ConnectString"];   //获取DBSetting下的ConnectString值
        private static Hashtable parmCache = Hashtable.Synchronized(new Hashtable()); 
 
        #region//ExecteNonQuery方法
 
        /// <summary>
        ///执行一个不需要返回值的SqlCommand命令，通过指定专用的连接字符串。
        /// 使用参数数组形式提供参数列表
        /// </summary>
        /// <param name="connectionString">一个有效的数据库连接字符串</param>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个数值表示此SqlCommand命令执行后影响的行数</returns>
        public static int ExecteNonQuery(string connectionString, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            //       =执行SQL语句
            SqlCommand cmd = new SqlCommand();
            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                //通过PrePareCommand方法将参数逐个加入到SqlCommand的参数集合中
                PrepareCommand(cmd, conn, null, cmdType, cmdText, commandParameters);
                int val = cmd.ExecuteNonQuery();
                //清空SqlCommand中的参数列表
                cmd.Parameters.Clear();
                return val;
            }
        }
 
        /// <summary>
        ///执行一个不需要返回值的SqlCommand命令，通过指定专用的连接字符串。
        /// 使用参数数组形式提供参数列表
        /// </summary>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个数值表示此SqlCommand命令执行后影响的行数</returns>
        public static int ExecteNonQuery(CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecteNonQuery(connectionString, cmdType, cmdText, commandParameters);
        }
 
        /// <summary>
        ///存储过程专用
        /// </summary>
        /// <param name="cmdText">存储过程的名字</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个数值表示此SqlCommand命令执行后影响的行数</returns>
        public static int ExecteNonQueryProducts(string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecteNonQuery(CommandType.StoredProcedure, cmdText, commandParameters);
        }
 
        /// <summary>
        ///Sql语句专用
        /// </summary>
        /// <param name="cmdText">T_Sql语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个数值表示此SqlCommand命令执行后影响的行数</returns>
        public static int ExecteNonQueryText(string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecteNonQuery(CommandType.Text, cmdText, commandParameters);
        }
 
        #endregion
        #region//GetTable方法
 
        /// <summary>
        /// 执行一条返回结果集的SqlCommand，通过一个已经存在的数据库连接
        /// 使用参数数组提供参数
        /// </summary>
        /// <param name="connecttionString">一个现有的数据库连接</param>
        /// <param name="cmdTye">SqlCommand命令类型</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个表集合(DataTableCollection)表示查询得到的数据集</returns>
        public static DataTableCollection GetTable(string connecttionString, CommandType cmdTye, string cmdText, SqlParameter[] commandParameters)
        {
            SqlCommand cmd = new SqlCommand();
            DataSet ds = new DataSet();
            using (SqlConnection conn = new SqlConnection(connecttionString))
            {
                PrepareCommand(cmd, conn, null, cmdTye, cmdText, commandParameters);
                SqlDataAdapter adapter = new SqlDataAdapter();
                adapter.SelectCommand = cmd;
                adapter.Fill(ds);
            }
            DataTableCollection table = ds.Tables;
            return table;
        }
 
        /// <summary>
        /// 执行一条返回结果集的SqlCommand，通过一个已经存在的数据库连接
        /// 使用参数数组提供参数
        /// </summary>
        /// <param name="cmdTye">SqlCommand命令类型</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个表集合(DataTableCollection)表示查询得到的数据集</returns>
        public static DataTableCollection GetTable(CommandType cmdTye, string cmdText, SqlParameter[] commandParameters)
        {
            return GetTable(connectionString, cmdTye, cmdText, commandParameters);
        }
 
        /// <summary>
        /// 执行存储过程专用
        /// </summary>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个表集合(DataTableCollection)表示查询得到的数据集</returns>
        public static DataTableCollection GetTableProducts(string cmdText, SqlParameter[] commandParameters)
        {
            return GetTable(CommandType.StoredProcedure, cmdText, commandParameters);
        }
 
        /// <summary>
        /// 执行Sql语句专用
        /// </summary>
        /// <param name="cmdText"> T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个表集合(DataTableCollection)表示查询得到的数据集</returns>
        public static DataTableCollection GetTableText(string cmdText, SqlParameter[] commandParameters)
        {
            return GetTable(CommandType.Text, cmdText, commandParameters);
        }
        #endregion
 
        /// <summary>
        /// 为执行命令准备参数
        /// </summary>
        /// <param name="cmd">SqlCommand 命令</param>
        /// <param name="conn">已经存在的数据库连接</param>
        /// <param name="trans">数据库事物处理</param>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">Command text，T-SQL语句 例如 Select * from Products</param>
        /// <param name="cmdParms">返回带参数的命令</param>
        private static void PrepareCommand(SqlCommand cmd, SqlConnection conn, SqlTransaction trans, CommandType cmdType, string cmdText, SqlParameter[] cmdParms)
        {
            //判断数据库连接状态
            if (conn.State != ConnectionState.Open)
                conn.Open();
            cmd.Connection = conn;
            cmd.CommandText = cmdText;
            //判断是否需要事物处理
            if (trans != null)
                cmd.Transaction = trans;
            cmd.CommandType = cmdType;
            if (cmdParms != null)
            {
                foreach (SqlParameter parm in cmdParms)
                    cmd.Parameters.Add(parm);
            }
        }
 
        /// <summary>
        /// Execute a SqlCommand that returns a resultset against the database specified in the connection string
        /// using the provided parameters.
        /// </summary>
        /// <param name="connectionString">一个有效的数据库连接字符串</param>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>A SqlDataReader containing the results</returns>
        public static SqlDataReader ExecuteReader(string connectionString, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            SqlCommand cmd = new SqlCommand();
            SqlConnection conn = new SqlConnection(connectionString);
            // we use a try/catch here because if the method throws an exception we want to
            // close the connection throw code, because no datareader will exist, hence the
            // commandBehaviour.CloseConnection will not work
            try
            {
                PrepareCommand(cmd, conn, null, cmdType, cmdText, commandParameters);
                SqlDataReader rdr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                cmd.Parameters.Clear();
                return rdr;
            }
            catch
            {
                conn.Close();
                throw;
            }
        }
        #region//ExecuteDataSet方法
 
        /// <summary>
        /// return a dataset
        /// </summary>
        /// <param name="connectionString">一个有效的数据库连接字符串</param>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>return a dataset</returns>
        public static DataSet ExecuteDataSet(string connectionString, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            SqlConnection conn = new SqlConnection(connectionString);
            SqlCommand cmd = new SqlCommand();
            try
            {
                PrepareCommand(cmd, conn, null, cmdType, cmdText, commandParameters);
                SqlDataAdapter da = new SqlDataAdapter();
                DataSet ds = new DataSet();
                da.SelectCommand = cmd;
                da.Fill(ds);
                return ds;
            }
            catch
            {
                conn.Close();
                throw;
            }
        }
 
        /// <summary>
        /// 返回一个DataSet
        /// </summary>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>return a dataset</returns>
        public static DataSet ExecuteDataSet(CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecuteDataSet(connectionString, cmdType, cmdText, commandParameters);
        }
 
        /// <summary>
        /// 返回一个DataSet
        /// </summary>
        /// <param name="cmdText">存储过程的名字</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>return a dataset</returns>
        public static DataSet ExecuteDataSetProducts(string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecuteDataSet(connectionString, CommandType.StoredProcedure, cmdText, commandParameters);
        }
 
        /// <summary>
        /// 返回一个DataSet
        /// </summary>
 
        /// <param name="cmdText">T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>return a dataset</returns>
        public static DataSet ExecuteDataSetText(string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecuteDataSet(connectionString, CommandType.Text, cmdText, commandParameters);
        }
 
        public static DataView ExecuteDataSet(string connectionString, string sortExpression, string direction, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            SqlConnection conn = new SqlConnection(connectionString);
            SqlCommand cmd = new SqlCommand();
            try
            {
                PrepareCommand(cmd, conn, null, cmdType, cmdText, commandParameters);
                SqlDataAdapter da = new SqlDataAdapter();
                DataSet ds = new DataSet();
                da.SelectCommand = cmd;
                da.Fill(ds);
                DataView dv = ds.Tables[].DefaultView;
                dv.Sort = sortExpression + " " + direction;
                return dv;
            }
            catch
            {
                conn.Close();
                throw;
            }
        }
        #endregion
 
        #region // ExecuteScalar方法
 
        /// <summary>
        /// 返回第一行的第一列
        /// </summary>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个对象</returns>
        public static object ExecuteScalar(CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecuteScalar(SqlHelper.connectionString, cmdType, cmdText, commandParameters);
        }
 
        /// <summary>
        /// 返回第一行的第一列存储过程专用
        /// </summary>
        /// <param name="cmdText">存储过程的名字</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个对象</returns>
        public static object ExecuteScalarProducts(string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecuteScalar(SqlHelper.connectionString, CommandType.StoredProcedure, cmdText, commandParameters);
        }
 
        /// <summary>
        /// 返回第一行的第一列Sql语句专用
        /// </summary>
        /// <param name="cmdText">者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>返回一个对象</returns>
        public static object ExecuteScalarText(string cmdText, params SqlParameter[] commandParameters)
        {
            return ExecuteScalar(SqlHelper.connectionString, CommandType.Text, cmdText, commandParameters);
        }
 
        /// <summary>
        /// Execute a SqlCommand that returns the first column of the first record against the database specified in the connection string
        /// using the provided parameters.
        /// </summary>
        /// <remarks>
        /// e.g.:
        ///  Object obj = ExecuteScalar(connString, CommandType.StoredProcedure, "PublishOrders", new SqlParameter("@prodid", 24));
        /// </remarks>
        /// <param name="connectionString">一个有效的数据库连接字符串</param>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>An object that should be converted to the expected type using Convert.To{Type}</returns>
        public static object ExecuteScalar(string connectionString, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            SqlCommand cmd = new SqlCommand();
 
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                PrepareCommand(cmd, connection, null, cmdType, cmdText, commandParameters);
                object val = cmd.ExecuteScalar();
                cmd.Parameters.Clear();
                return val;
            }
        }
 
        /// <summary>
        /// Execute a SqlCommand that returns the first column of the first record against an existing database connection
        /// using the provided parameters.
        /// </summary>
        /// <remarks>
        /// e.g.:
        ///  Object obj = ExecuteScalar(connString, CommandType.StoredProcedure, "PublishOrders", new SqlParameter("@prodid", 24));
        /// </remarks>
        /// <param name="connectionString">一个有效的数据库连接字符串</param>
        /// <param name="cmdType">SqlCommand命令类型 (存储过程， T-SQL语句， 等等。)</param>
        /// <param name="cmdText">存储过程的名字或者 T-SQL 语句</param>
        /// <param name="commandParameters">以数组形式提供SqlCommand命令中用到的参数列表</param>
        /// <returns>An object that should be converted to the expected type using Convert.To{Type}</returns>
        public static object ExecuteScalar(SqlConnection connection, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            SqlCommand cmd = new SqlCommand();
            PrepareCommand(cmd, connection, null, cmdType, cmdText, commandParameters);
            object val = cmd.ExecuteScalar();
            cmd.Parameters.Clear();
            return val;
        }
 
        #endregion
 
        /// <summary>
        /// add parameter array to the cache
        /// </summary>
        /// <param name="cacheKey">Key to the parameter cache</param>
        /// <param name="cmdParms">an array of SqlParamters to be cached</param>
        public static void CacheParameters(string cacheKey, params SqlParameter[] commandParameters)
        {
            parmCache[cacheKey] = commandParameters;
        }
 
        /// <summary>
        /// Retrieve cached parameters
        /// </summary>
        /// <param name="cacheKey">key used to lookup parameters</param>
        /// <returns>Cached SqlParamters array</returns>
        public static SqlParameter[] GetCachedParameters(string cacheKey)
        {
            SqlParameter[] cachedParms = (SqlParameter[])parmCache[cacheKey];
            if (cachedParms == null)
                return null;
            SqlParameter[] clonedParms = new SqlParameter[cachedParms.Length];
            for (int i = , j = cachedParms.Length; i < j; i++)
                clonedParms[i] = (SqlParameter)((ICloneable)cachedParms[i]).Clone();
            return clonedParms;
        }
        /// <summary>
        /// 检查是否存在
        /// </summary>
        /// <param name="strSql">Sql语句</param>
        /// <returns>bool结果</returns>
        public static bool Exists(string strSql)
        {
            int cmdresult = Convert.ToInt32(ExecuteScalar(connectionString, CommandType.Text, strSql, null));
            if (cmdresult == )
            {
                return false;
            }
            else
            {
                return true;
            }
        }
 
        /// <summary>
        /// 检查是否存在
        /// </summary>
        /// <param name="strSql">Sql语句</param>
        /// <param name="cmdParms">参数</param>
        /// <returns>bool结果</returns>
        public static bool Exists(string strSql, params SqlParameter[] cmdParms)
        {
            int cmdresult = Convert.ToInt32(ExecuteScalar(connectionString, CommandType.Text, strSql, cmdParms));
            if (cmdresult == )
            {
                return false;
            }
            else
            {
                return true;
            }
        }
 
  //原文：https://blog.csdn.net/weixin_41609327/article/details/80786764
    }

SqlHelp

public DataTable GetStuden()
        {
            string sql = "select * from studen;";
            var data = SqlHelper.GetTable(CommandType.Text,sql,new SqlParameter[] { });
            return data[];
        }

DAL

一个保存类：

public static class save
    {
 
        public static void JsonWrite(string configpath,string str,out string name,out string filename)
        {
            //string configpath = System.AppDomain.CurrentDomain.BaseDirectory + "/json/";
 
            configpath = configpath + "/json/";
 
            if (!Directory.Exists(configpath))//如果目录不存在就创建
            {
                Directory.CreateDirectory(configpath);
            }
            filename = configpath + "/";
 
            name = "Json_" + DateTime.Now.ToString("yyyy_MM_dd_HH_mm_ss_ffff") + ".json";//用日期对文件命名;     
 
            filename = filename + name;     //   一个  文件的 绝对路径   out   出去  给使用
            //创建或打开文件，  AppendText 向文件末尾追加记录
            StreamWriter mySw = File.AppendText(filename);     //      查找是否有该路径的文件     并打开
            string a = str;
            mySw.WriteLine(a);     //    写入某数据
 
            //关闭文件
            mySw.Close();      //    关闭写入流
        }
    }

保存文件类

到控制器下载了。

 public IActionResult Json()
        {
            using (var db = new DB())
            {
                List<studen> list =  db.studen.GroupBy(b=>new { b.Id,b.Name }).Select(b => new studen
                {
                    Id = b.Key.Id,
                    Name = b.Key.Name
                }).ToList();
                db.studen.ToList();
 
                var xx = db.xx.GroupBy(x => new { x.id }).Select(v => new xx
                {
                    id=v.Key.id,
                    name= v.Sum(x => x.name)
                }).ToList();
                string json = "[";
                foreach (var item in list)
                {
                    json += "{\"id\":\""+item.Id+"\",\"name\":\""+item.Name+"\" },";
                }
                json = json.Substring(, json.Length - );       //删除最后一个逗号，
                json += "]";
                //string root = Directory.GetParent(AppContext.BaseDirectory).Parent.Parent.Parent.FullName;   //Parent退到上个目录
                string contentRootPath = _hostingEnvironment.ContentRootPath;      //    .net core获取基目录的用法
                string name;                                                                                    //    out   出来的是路径加上json文件名
                string file;                                                          //    绝对路径
                save.JsonWrite(contentRootPath, json.ToString(),out name, out file);     //写入文件 并保存
 
                HttpContext.Session.SetString("file",file);      //   core    的   Session    就得这么用  还得using   Microsoft.AspNetCore.Http;
 
                //     读取某json文件
                string str = "";
 
                using (FileStream fs = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))   //  获取文件流
                {
                    using (StreamReader sr = new StreamReader(fs, Encoding.GetEncoding("utf-8")))   //    读取文件流
                    {
                        str = sr.ReadToEnd().ToString();      //     获取  文件的  全部  转 字符串
                        sr.Close();
                    }
                    fs.Close();
                }
 
             }
            //           new filestram   须文件的绝对路径    获取文件流        输入出的文件格式         输出的文件名称
            return File(new FileStream(HttpContext.Session.GetString("file"), FileMode.Open), "application/octet-stream", $"导出测试{DateTime.Now.ToString("yyyy年MM月dd日HH点mm分ss秒")}.json");
 
            if (System.IO.File.Exists("文件的绝对路径"))
            { //删除文件
                System.IO.File.Delete("文件的绝对路径");
            }
        }
 
        //public IActionResult download()
        //{
        //    return File(new FileStream(HttpContext.Session.GetString("file"), FileMode.Open), "application/octet-stream", $"导出测试{DateTime.Now.ToString("yyyyMMddHHmmss")}.json");
        //}