.NET FileStream文件流，StreamReader文本流，MemoryStream内存流几种流的实例

一、FileStream文件流

1.读取数据

　　 public class ReadFile
    {
        /// <summary>
        /// 读取文件
        /// FileMode.Create  创建一个新文件,如果文件已经存在则改写旧文件
        /// FileMode.CreateNew 创建一个文件,如果文件存在会发生异常,提示文件已经存在
        /// FileMode.Open  打开文件，如果文件不存在则异常
        /// FileMode.OpenOrCreate  打开文件，如果文件不存在，则创建一个新的文件并且打开文件
        /// FileMode.Append   打开现有文件，并且在现有文件内容后面追加，如果文件不存在则异常
        /// FileMode.Truncate 根据现有操作系统，截取文件里面的内容，如果文件不存在则异常
        /// </summary>
        public static void Read(string FilePath)
        {
            FileStream fileStream = null;
            try
            {
            　　fileStream = new FileStream(FilePath, FileMode.Truncate);
                byte[] bytes = new byte[fileStream.Length];
                int read = fileStream.Read(bytes, 0, bytes.Length);
                var result = Encoding.UTF8.GetString(bytes);
            }
            catch (Exception e)
            {
                if (fileStream != null)
                {
                    fileStream.Dispose();
                }
                Console.WriteLine(e.Message);
            }
            finally
            {
                if (fileStream != null)
                {
                    fileStream.Close();
                    fileStream.Dispose();
                }
            }
        }
    }

2.写入数据

　　 public class WriteFile
    {
        public static void WriteText(string FilePath,string writeString)
        {
            FileStream fileStream = null;
            try
            {
                //根据路径打开文件
                fileStream = new FileStream(@"C:\Users\Administrator\source\repos\OperatFile\OperatFile\1.txt", FileMode.Append);
                //把字符串转化成字节
                byte[] bytes = Encoding.UTF8.GetBytes(writeString);
                //写入到文件
                fileStream.Write(bytes, 0, bytes.Length);
            }
            catch (Exception e)
            {
　　　　　　　　　　if (fileStream != null)
                {
                    fileStream.Dispose();
                }
                Console.WriteLine(e.Message);
            }
            finally
            {
                //关闭和释放
                if (fileStream != null)
                {
                    fileStream.Close();
                    fileStream.Dispose();
                }
            }
        }
    }

二、StreamReader文本流

1.读取数据

　　 public class SteamReadFile
    {
        /// <summary>
        /// 读取文件
        /// </summary>
        /// <param name="filePath">文件路径</param>
        public static void ReadFile(string FilePath)
        {
            try
            {
                using (StreamReader sr = new StreamReader(FilePath))
                {
                    var result = sr.ReadToEnd();
                    Console.WriteLine(result);
                }
            }
            catch (Exception e)
            {

                throw new Exception(e.Message);
            }
        }
    }

2.写入数据

　　 public class StreamWriteFile
    {
        /// <summary>
        /// 写入文件
        /// </summary>
        /// <param name="FilePath">文件路径</param>
        /// <param name="WriteString">待写入字符串</param>
        public static void WriteFile(string FilePath,string WriteString)
        {
            try
            {
                using (StreamWriter sr = new StreamWriter(FilePath))
                {
                    sr.WriteLine(WriteString);
                }
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }
        }
    }

3.写入日志实例

　　 public class LogHelper
    {
        /// <summary>
        /// 文件路径
        /// </summary>
        public static string FilePath = @"C:\Users\Administrator\source\repos\OperatFile\OperatFile\Files";
        static LogHelper()
        {
            //判断文件夹是否存在，如果不存在，则重新创建
            if (!Directory.Exists(FilePath))
            {
                Directory.CreateDirectory(FilePath);
            }
        }
　　　　　/// <summary>
        /// 日志写入
        /// Path.Combine(str1,str2,str3)  把传入的参数拼接起来，然后返回新的字符串
        /// File.AppendText(fullPath) 根据文件路径，把新写入的内容，拼接到文本后面
        /// </summary>
        public static void WriteLog()
        {
            try
            {
                var sb = BindData();
                string fullPath = Path.Combine(FilePath, $"{DateTime.Now.ToString("yyyy-MM-dd")}.txt");
                //判断文件是否存在，如果不存在，则新建文件
                if (!File.Exists(fullPath))
                {
                    File.Create(fullPath);
                }
                using (StreamWriter sw = File.AppendText(fullPath))
                {
                    sw.WriteLine(sb.ToString());
                }
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }

        }
　　　　　/// <summary>
        /// 绑定日志信息
        /// </summary>
        /// <returns></returns>
        private static StringBuilder BindData()
        {
            StringBuilder sb = new StringBuilder();
            DateTime operatDateTime = DateTime.Now;
            string content = "读写文件功能";
            string operators = "小明";
            sb.AppendLine($"操作时间：{operatDateTime}");
            sb.AppendLine($"操作内容：{content}");
            sb.AppendLine($"操作人：{operators}");
            sb.AppendLine("------------------------------------------------------------------------------------------");
            return sb;
        }
    }

三、MemoryStream内存流

　　　　　/// <summary>
        /// 根据URL读取内容到内存流
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        public static string DownLoadByUrl(string url)
        {
            string result = string.Empty;
            MemoryStream ms = null;
            HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
            HttpWebResponse response = request.GetResponse() as HttpWebResponse;
            using (var stream = response.GetResponseStream())
            {
　　　　　　　　　 byte[] buffer = new byte[response.ContentLength];
                int actuallyRead = 0, offset = 0;
                do
                {
                    actuallyRead = stream.Read(buffer, offset, buffer.Length - offset);
                    offset += actuallyRead;

                } while (actuallyRead > 0);
                ms = new MemoryStream(buffer);
                ms.Seek(0, SeekOrigin.Begin);
                var byteArray = new byte[ms.Length];
                ms.Read(byteArray, 0, byteArray.Length);
                result = Encoding.UTF8.GetString(byteArray);
            }
            response.Close();
            response.Dispose();
            return result;
        }