using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Configuration;
using System.Collections;
using System.IO;

namespace FileGenerator
{
    
    class Program
    {
        
        static void Main(string[] args)
        {
            Program program = new Program();
            //IDictionary<string, string> dictionary = (IDictionary<string, string>)ConfigurationSettings.GetConfig("App.config");
            string path = ConfigurationManager.AppSettings["path"];
            int miniSize = int.Parse(ConfigurationManager.AppSettings["miniSize"]);
            int maxSize = int.Parse(ConfigurationManager.AppSettings["maxSize"]);
            long quantity = long.Parse(ConfigurationManager.AppSettings["quantity"]);
            string prefix = ConfigurationManager.AppSettings["prefix"];

            
            //Console.WriteLine(path);
            //Console.ReadLine();
            DirectoryInfo directory = new DirectoryInfo(path);
            if (!directory.Exists)
            {
                Directory.CreateDirectory(path);
            }
            int j = 0;
            while (j < quantity)
            {
                j++;
                string fileName = path + prefix + "_";
                Random random = new Random();
                for (int i = 1; i <= 10; i++)
                {
                    fileName = fileName + random.Next(10);
                }
                FileStream fs = new FileStream(fileName, FileMode.OpenOrCreate);
                StreamWriter sw = new StreamWriter(fs, System.Text.Encoding.GetEncoding("gb2312"));
                try
                {
                    string content = program.GetFileContent(miniSize, maxSize);
                    
                    sw.Flush();
                    sw.BaseStream.Seek(0, SeekOrigin.Begin);
                    sw.WriteLine(content);
                    sw.Flush();
                    sw.Close();
                    //char[] contentChar = content.ToCharArray();
                    //Encoder encoder = Encoding.UTF8.GetEncoder();
                    //byte[] bytes = new byte[4096];
                    //encoder.GetBytes(contentChar, 0, contentChar.Length, bytes, 0, true);
                    //fs.Seek(0, SeekOrigin.Begin);
                    //fs.Write(bytes, 0, bytes.Length);
                    //fs.Close();
                }
                catch (IOException)
                {
                    continue;
                    sw.Close();
                    
                    
                }
            }

        }

        public string GetFileContent(int miniSize, int maxSize)
        {
            List<string> strList = new List<string>();
            for (int i = 65; i < 90; i++)
            {
                char aa = (char)i;
                strList.Add(aa.ToString());
            }
            for (int i = 97; i < 122; i++)
            {
                char aa = (char)i;
                strList.Add(aa.ToString());
            }
            char[] number = new char[10];
            for (int i = 48; i <= 57; i++)
            {
                char aa = (char)i;
                strList.Add(aa.ToString());
                number[i - 48] = aa;
            }
            string content = "";
            double size = (miniSize + (maxSize - miniSize) * new Random().NextDouble())*1024;
            for (int i = 0; i < size; i++)
            {
                Random random = new Random();
                int index = random.Next(strList.Count-1);
                content = content + strList[index];
                //content = content + strList[strList.Count];
            }
            return content;
        }
    }
}

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="path" value="D:\SourceFolder\sftptest\"/>
    <add key="miniSize" value="20"/>
    <add key="maxSize" value="40"/>
    <add key="quantity" value="10"/>
    <add key ="prefix" value="test"/>
  </appSettings>
</configuration>