c#判断文档编码类别

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

namespace FileEncoding
{
	/// <summary>
	/// 获取文件的编码格式
	/// </summary>
	public class EncodingType
	{
		/// <summary>
		/// 给定文件的路径，读取文件的二进制数据，判断文件的编码类型
		/// </summary>
		/// <param name="FILE_NAME">文件路径</param>
		/// <returns>文件的编码类型</returns>
		public static System.Text.Encoding GetType(string FILE_NAME)
		{
			FileStream fs = new FileStream(FILE_NAME, FileMode.Open, FileAccess.Read);
			Encoding r = GetType(fs);
			fs.Close();
			return r;
		}

		/// <summary>
		/// 通过给定的文件流，判断文件的编码类型
		/// </summary>
		/// <param name="fs">文件流</param>
		/// <returns>文件的编码类型</returns>
		public static System.Text.Encoding GetType(FileStream fs)
		{
			byte[] Unicode = new byte[] { 0xFF, 0xFE, 0x41 };
			byte[] UnicodeBIG = new byte[] { 0xFE, 0xFF, 0x00 };
			byte[] UTF8 = new byte[] { 0xEF, 0xBB, 0xBF }; //带BOM
			Encoding reVal = Encoding.Default;

			BinaryReader r = new BinaryReader(fs, System.Text.Encoding.Default);
			int i;
			int.TryParse(fs.Length.ToString(), out i);
			byte[] ss = r.ReadBytes(i);
			if (IsUTF8Bytes(ss) || (ss[0] == 0xEF && ss[1] == 0xBB && ss[2] == 0xBF))
			{
				reVal = Encoding.UTF8;
			}
			else if (ss[0] == 0xFE && ss[1] == 0xFF && ss[2] == 0x00)
			{
				reVal = Encoding.BigEndianUnicode;
			}
			else if (ss[0] == 0xFF && ss[1] == 0xFE && ss[2] == 0x41)
			{
				reVal = Encoding.Unicode;
			}
			r.Close();
			return reVal;
		}
		/// <summary>
		/// 判断是否是不带 BOM 的 UTF8 格式
		/// </summary>
		/// <param name="data"></param>
		/// <returns></returns>
		private static bool IsUTF8Bytes(byte[] data)
		{
			int charByteCounter = 1;　 //计算当前正分析的字符应还有的字节数
			byte curByte; //当前分析的字节.
			for (int i = 0; i < data.Length; i++)
			{
				curByte = data[i];
				if (charByteCounter == 1)
				{
					if (curByte >= 0x80)
					{
						//判断当前
						while (((curByte <<= 1) & 0x80) != 0)
						{
							charByteCounter++;
						}
						//标记位首位若为非0 则至少以2个1开始 如:110XXXXX...........1111110X　
						if (charByteCounter == 1 || charByteCounter > 6)
						{
							return false;
						}
					}
				}
				else
				{
					//若是UTF-8 此时第一位必须为1
					if ((curByte & 0xC0) != 0x80)
					{
						return false;
					}
					charByteCounter--;
				}
			}
			
			if (charByteCounter > 1)
			{
				throw new Exception("非预期的byte格式");
			}
			return true;
		}
	}
}