C#判断文件编码——常用字法

using system.collections.generic;
using system.io;
using system.text;

namespace yunshenbuzhichu.mimabenjiamifa
{
    /// <summary>
    /// 文字编码检测。
    /// 用于检测一篇文章使用什么编码方式进行编码。
    /// </summary>
    public class streambianmajiance
    {
        /// <summary>
        /// bigendianunicode编码高频汉字编码
        /// </summary>
        private list<byte[]> _bigendianunicodegaopinzifubianmalsit = new list<byte[]>()
        {
            new byte[2]{118,132},new byte[2]{78,0},new byte[2]{86,253},new byte[2]{87,40},new byte[2]{78,186},new byte[2]{78,134},new byte[2]{103,9},new byte[2]{78,45},
            new byte[2]{102,47},new byte[2]{94,116},new byte[2]{84,140},new byte[2]{89,39},new byte[2]{78,26},new byte[2]{78,13},new byte[2]{78,58},new byte[2]{83,209},
            new byte[2]{79,26},new byte[2]{93,229},new byte[2]{126,207},new byte[2]{78,10},new byte[2]{87,48},new byte[2]{94,2},new byte[2]{137,129},new byte[2]{78,42},
            new byte[2]{78,167},new byte[2]{143,217},new byte[2]{81,250},new byte[2]{136,76},new byte[2]{79,92},new byte[2]{117,31},new byte[2]{91,182},new byte[2]{78,229},
            new byte[2]{98,16},new byte[2]{82,48},new byte[2]{101,229},new byte[2]{108,17},new byte[2]{103,101},new byte[2]{98,17},new byte[2]{144,232},new byte[2]{91,249},
            new byte[2]{143,219},new byte[2]{89,26},new byte[2]{81,104},new byte[2]{94,250},new byte[2]{78,214},new byte[2]{81,108},new byte[2]{95,0},new byte[2]{78,236},
            new byte[2]{87,58},new byte[2]{92,85},new byte[2]{101,246},new byte[2]{116,6},new byte[2]{101,176},new byte[2]{101,185},new byte[2]{78,59},new byte[2]{79,1},
            new byte[2]{141,68},new byte[2]{91,158},new byte[2]{91,102},new byte[2]{98,165},new byte[2]{82,54},new byte[2]{101,63},new byte[2]{109,78},new byte[2]{117,40},
            new byte[2]{84,12},new byte[2]{78,142},new byte[2]{108,213},new byte[2]{154,216},new byte[2]{149,127},new byte[2]{115,176},new byte[2]{103,44},new byte[2]{103,8},
            new byte[2]{91,154},new byte[2]{83,22},new byte[2]{82,160},new byte[2]{82,168},new byte[2]{84,8},new byte[2]{84,193},new byte[2]{145,205},new byte[2]{81,115},
            new byte[2]{103,58},new byte[2]{82,6},new byte[2]{82,155},new byte[2]{129,234},new byte[2]{89,22},new byte[2]{128,5},new byte[2]{83,58},new byte[2]{128,253},
            new byte[2]{139,190},new byte[2]{84,14},new byte[2]{92,49},new byte[2]{123,73},new byte[2]{79,83},new byte[2]{78,11},new byte[2]{78,7},new byte[2]{81,67},
            new byte[2]{121,62},new byte[2]{143,199},new byte[2]{82,77},new byte[2]{151,98},new byte[2]{48,2},new byte[2]{255,12},new byte[2]{255,31},new byte[2]{255,1}
        };
        /// <summary>
        /// utf8编码高频汉字编码
        /// </summary>
        private list<byte[]> _utf8gaopinzifubianmalsit = new list<byte[]>()
        {
            new byte[3]{231,154,132},new byte[3]{228,184,128},new byte[3]{229,155,189},new byte[3]{229,156,168},new byte[3]{228,186,186},new byte[3]{228,186,134},
            new byte[3]{230,156,137},new byte[3]{228,184,173},new byte[3]{230,152,175},new byte[3]{229,185,180},new byte[3]{229,146,140},new byte[3]{229,164,167},
            new byte[3]{228,184,154},new byte[3]{228,184,141},new byte[3]{228,184,186},new byte[3]{229,143,145},new byte[3]{228,188,154},new byte[3]{229,183,165},
            new byte[3]{231,187,143},new byte[3]{228,184,138},new byte[3]{229,156,176},new byte[3]{229,184,130},new byte[3]{232,166,129},new byte[3]{228,184,170},
            new byte[3]{228,186,167},new byte[3]{232,191,153},new byte[3]{229,135,186},new byte[3]{232,161,140},new byte[3]{228,189,156},new byte[3]{231,148,159},
            new byte[3]{229,174,182},new byte[3]{228,187,165},new byte[3]{230,136,144},new byte[3]{229,136,176},new byte[3]{230,151,165},new byte[3]{230,176,145},
            new byte[3]{230,157,165},new byte[3]{230,136,145},new byte[3]{233,131,168},new byte[3]{229,175,185},new byte[3]{232,191,155},new byte[3]{229,164,154},
            new byte[3]{229,133,168},new byte[3]{229,187,186},new byte[3]{228,187,150},new byte[3]{229,133,172},new byte[3]{229,188,128},new byte[3]{228,187,172},
            new byte[3]{229,156,186},new byte[3]{229,177,149},new byte[3]{230,151,182},new byte[3]{231,144,134},new byte[3]{230,150,176},new byte[3]{230,150,185},
            new byte[3]{228,184,187},new byte[3]{228,188,129},new byte[3]{232,181,132},new byte[3]{229,174,158},new byte[3]{229,173,166},new byte[3]{230,138,165},
            new byte[3]{229,136,182},new byte[3]{230,148,191},new byte[3]{230,181,142},new byte[3]{231,148,168},new byte[3]{229,144,140},new byte[3]{228,186,142},
            new byte[3]{230,179,149},new byte[3]{233,171,152},new byte[3]{233,149,191},new byte[3]{231,142,176},new byte[3]{230,156,172},new byte[3]{230,156,136},
            new byte[3]{229,174,154},new byte[3]{229,140,150},new byte[3]{229,138,160},new byte[3]{229,138,168},new byte[3]{229,144,136},new byte[3]{229,147,129},
            new byte[3]{233,135,141},new byte[3]{229,133,179},new byte[3]{230,156,186},new byte[3]{229,136,134},new byte[3]{229,138,155},new byte[3]{232,135,170},
            new byte[3]{229,164,150},new byte[3]{232,128,133},new byte[3]{229,140,186},new byte[3]{232,131,189},new byte[3]{232,174,190},new byte[3]{229,144,142},
            new byte[3]{229,176,177},new byte[3]{231,173,137},new byte[3]{228,189,147},new byte[3]{228,184,139},new byte[3]{228,184,135},new byte[3]{229,133,131},
            new byte[3]{231,164,190},new byte[3]{232,191,135},new byte[3]{229,137,141},new byte[3]{233,157,162},new byte[3]{227,128,130},new byte[3]{239,188,140},
            new byte[3]{239,188,159},new byte[3]{239,188,129},
        };
        /// <summary>
        /// unicode编码高频汉字编码
        /// </summary>
        private list<byte[]> _unicodegaopinzifubianmalsit = new list<byte[]>()
        {
            new byte[2]{132,118},new byte[2]{0,78},new byte[2]{253,86},new byte[2]{40,87},new byte[2]{186,78},new byte[2]{134,78},new byte[2]{9,103},new byte[2]{45,78},
            new byte[2]{47,102},new byte[2]{116,94},new byte[2]{140,84},new byte[2]{39,89},new byte[2]{26,78},new byte[2]{13,78},new byte[2]{58,78},new byte[2]{209,83},
            new byte[2]{26,79},new byte[2]{229,93},new byte[2]{207,126},new byte[2]{10,78},new byte[2]{48,87},new byte[2]{2,94},new byte[2]{129,137},new byte[2]{42,78},
            new byte[2]{167,78},new byte[2]{217,143},new byte[2]{250,81},new byte[2]{76,136},new byte[2]{92,79},new byte[2]{31,117},new byte[2]{182,91},new byte[2]{229,78},
            new byte[2]{16,98},new byte[2]{48,82},new byte[2]{229,101},new byte[2]{17,108},new byte[2]{101,103},new byte[2]{17,98},new byte[2]{232,144},new byte[2]{249,91},
            new byte[2]{219,143},new byte[2]{26,89},new byte[2]{104,81},new byte[2]{250,94},new byte[2]{214,78},new byte[2]{108,81},new byte[2]{0,95},new byte[2]{236,78},
            new byte[2]{58,87},new byte[2]{85,92},new byte[2]{246,101},new byte[2]{6,116},new byte[2]{176,101},new byte[2]{185,101},new byte[2]{59,78},new byte[2]{1,79},
            new byte[2]{68,141},new byte[2]{158,91},new byte[2]{102,91},new byte[2]{165,98},new byte[2]{54,82},new byte[2]{63,101},new byte[2]{78,109},new byte[2]{40,117},
            new byte[2]{12,84},new byte[2]{142,78},new byte[2]{213,108},new byte[2]{216,154},new byte[2]{127,149},new byte[2]{176,115},new byte[2]{44,103},new byte[2]{8,103},
            new byte[2]{154,91},new byte[2]{22,83},new byte[2]{160,82},new byte[2]{168,82},new byte[2]{8,84},new byte[2]{193,84},new byte[2]{205,145},new byte[2]{115,81},
            new byte[2]{58,103},new byte[2]{6,82},new byte[2]{155,82},new byte[2]{234,129},new byte[2]{22,89},new byte[2]{5,128},new byte[2]{58,83},new byte[2]{253,128},
            new byte[2]{190,139},new byte[2]{14,84},new byte[2]{49,92},new byte[2]{73,123},new byte[2]{83,79},new byte[2]{11,78},new byte[2]{7,78},new byte[2]{67,81},
            new byte[2]{62,121},new byte[2]{199,143},new byte[2]{77,82},new byte[2]{98,151},new byte[2]{2,48},new byte[2]{12,255},new byte[2]{31,255},new byte[2]{1,255}
        };
        /// <summary>
        /// utf32编码高频汉字编码
        /// </summary>
        private list<byte[]> _utf32gaopinzifubianmalsit = new list<byte[]>()
        {
            new byte[4]{132,118,0,0},new byte[4]{0,78,0,0},new byte[4]{253,86,0,0},new byte[4]{40,87,0,0},new byte[4]{186,78,0,0},new byte[4]{134,78,0,0},new byte[4]{9,103,0,0},
            new byte[4]{45,78,0,0},new byte[4]{47,102,0,0},new byte[4]{116,94,0,0},new byte[4]{140,84,0,0},new byte[4]{39,89,0,0},new byte[4]{26,78,0,0},new byte[4]{13,78,0,0},
            new byte[4]{58,78,0,0},new byte[4]{209,83,0,0},new byte[4]{26,79,0,0},new byte[4]{229,93,0,0},new byte[4]{207,126,0,0},new byte[4]{10,78,0,0},new byte[4]{48,87,0,0},
            new byte[4]{2,94,0,0},new byte[4]{129,137,0,0},new byte[4]{42,78,0,0},new byte[4]{167,78,0,0},new byte[4]{217,143,0,0},new byte[4]{250,81,0,0},new byte[4]{76,136,0,0},
            new byte[4]{92,79,0,0},new byte[4]{31,117,0,0},new byte[4]{182,91,0,0},new byte[4]{229,78,0,0},new byte[4]{16,98,0,0},new byte[4]{48,82,0,0},new byte[4]{229,101,0,0},
            new byte[4]{17,108,0,0},new byte[4]{101,103,0,0},new byte[4]{17,98,0,0},new byte[4]{232,144,0,0},new byte[4]{249,91,0,0},new byte[4]{219,143,0,0},new byte[4]{26,89,0,0},
            new byte[4]{104,81,0,0},new byte[4]{250,94,0,0},new byte[4]{214,78,0,0},new byte[4]{108,81,0,0},new byte[4]{0,95,0,0},new byte[4]{236,78,0,0},new byte[4]{58,87,0,0},
            new byte[4]{85,92,0,0},new byte[4]{246,101,0,0},new byte[4]{6,116,0,0},new byte[4]{176,101,0,0},new byte[4]{185,101,0,0},new byte[4]{59,78,0,0},new byte[4]{1,79,0,0},
            new byte[4]{68,141,0,0},new byte[4]{158,91,0,0},new byte[4]{102,91,0,0},new byte[4]{165,98,0,0},new byte[4]{54,82,0,0},new byte[4]{63,101,0,0},new byte[4]{78,109,0,0},
            new byte[4]{40,117,0,0},new byte[4]{12,84,0,0},new byte[4]{142,78,0,0},new byte[4]{213,108,0,0},new byte[4]{216,154,0,0},new byte[4]{127,149,0,0},new byte[4]{176,115,0,0},
            new byte[4]{44,103,0,0},new byte[4]{8,103,0,0},new byte[4]{154,91,0,0},new byte[4]{22,83,0,0},new byte[4]{160,82,0,0},new byte[4]{168,82,0,0},new byte[4]{8,84,0,0},
            new byte[4]{193,84,0,0},new byte[4]{205,145,0,0},new byte[4]{115,81,0,0},new byte[4]{58,103,0,0},new byte[4]{6,82,0,0},new byte[4]{155,82,0,0},new byte[4]{234,129,0,0},
            new byte[4]{22,89,0,0},new byte[4]{5,128,0,0},new byte[4]{58,83,0,0},new byte[4]{253,128,0,0},new byte[4]{190,139,0,0},new byte[4]{14,84,0,0},new byte[4]{49,92,0,0},
            new byte[4]{73,123,0,0},new byte[4]{83,79,0,0},new byte[4]{11,78,0,0},new byte[4]{7,78,0,0},new byte[4]{67,81,0,0},new byte[4]{62,121,0,0},new byte[4]{199,143,0,0},
            new byte[4]{77,82,0,0},new byte[4]{98,151,0,0},new byte[4]{2,48,0,0},new byte[4]{12,255,0,0},new byte[4]{31,255,0,0},new byte[4]{1,255,0,0}
        };
        /// <summary>
        /// utf7编码高频汉字编码
        /// </summary>
        private list<byte[]> _utf7gaopinzifubianmalsit = new list<byte[]>()
        {
            new byte[5]{43,100,111,81,45},new byte[5]{43,84,103,65,45},new byte[5]{43,86,118,48,45},new byte[5]{43,86,121,103,45},new byte[5]{43,84,114,111,45},new byte[5]{43,84,111,89,45},
            new byte[5]{43,90,119,107,45},new byte[5]{43,84,105,48,45},new byte[5]{43,90,105,56,45},new byte[5]{43,88,110,81,45},new byte[5]{43,86,73,119,45},new byte[5]{43,87,83,99,45},
            new byte[5]{43,84,104,111,45},new byte[5]{43,84,103,48,45},new byte[5]{43,84,106,111,45},new byte[5]{43,85,57,69,45},new byte[5]{43,84,120,111,45},new byte[5]{43,88,101,85,45},
            new byte[5]{43,102,115,56,45},new byte[5]{43,84,103,111,45},new byte[5]{43,86,122,65,45},new byte[5]{43,88,103,73,45},new byte[5]{43,105,89,69,45},new byte[5]{43,84,105,111,45},
            new byte[5]{43,84,113,99,45},new byte[5]{43,106,57,107,45},new byte[5]{43,85,102,111,45},new byte[5]{43,105,69,119,45},new byte[5]{43,84,49,119,45},new byte[5]{43,100,82,56,45},
            new byte[5]{43,87,55,89,45},new byte[5]{43,84,117,85,45},new byte[5]{43,89,104,65,45},new byte[5]{43,85,106,65,45},new byte[5]{43,90,101,85,45},new byte[5]{43,98,66,69,45},
            new byte[5]{43,90,50,85,45},new byte[5]{43,89,104,69,45},new byte[5]{43,107,79,103,45},new byte[5]{43,87,47,107,45},new byte[5]{43,106,57,115,45},new byte[5]{43,87,82,111,45},
            new byte[5]{43,85,87,103,45},new byte[5]{43,88,118,111,45},new byte[5]{43,84,116,89,45},new byte[5]{43,85,87,119,45},new byte[5]{43,88,119,65,45},new byte[5]{43,84,117,119,45},
            new byte[5]{43,86,122,111,45},new byte[5]{43,88,70,85,45},new byte[5]{43,90,102,89,45},new byte[5]{43,100,65,89,45},new byte[5]{43,90,98,65,45},new byte[5]{43,90,98,107,45},
            new byte[5]{43,84,106,115,45},new byte[5]{43,84,119,69,45},new byte[5]{43,106,85,81,45},new byte[5]{43,87,53,52,45},new byte[5]{43,87,50,89,45},new byte[5]{43,89,113,85,45},
            new byte[5]{43,85,106,89,45},new byte[5]{43,90,84,56,45},new byte[5]{43,98,85,52,45},new byte[5]{43,100,83,103,45},new byte[5]{43,86,65,119,45},new byte[5]{43,84,111,52,45},
            new byte[5]{43,98,78,85,45},new byte[5]{43,109,116,103,45},new byte[5]{43,108,88,56,45},new byte[5]{43,99,55,65,45},new byte[5]{43,90,121,119,45},new byte[5]{43,90,119,103,45},
            new byte[5]{43,87,53,111,45},new byte[5]{43,85,120,89,45},new byte[5]{43,85,113,65,45},new byte[5]{43,85,113,103,45},new byte[5]{43,86,65,103,45},new byte[5]{43,86,77,69,45},
            new byte[5]{43,107,99,48,45},new byte[5]{43,85,88,77,45},new byte[5]{43,90,122,111,45},new byte[5]{43,85,103,89,45},new byte[5]{43,85,112,115,45},new byte[5]{43,103,101,111,45},
            new byte[5]{43,87,82,89,45},new byte[5]{43,103,65,85,45},new byte[5]{43,85,122,111,45},new byte[5]{43,103,80,48,45},new byte[5]{43,105,55,52,45},new byte[5]{43,86,65,52,45},
            new byte[5]{43,88,68,69,45},new byte[5]{43,101,48,107,45},new byte[5]{43,84,49,77,45},new byte[5]{43,84,103,115,45},new byte[5]{43,84,103,99,45},new byte[5]{43,85,85,77,45},
            new byte[5]{43,101,84,52,45},new byte[5]{43,106,56,99,45},new byte[5]{43,85,107,48,45},new byte[5]{43,108,50,73,45},new byte[5]{43,77,65,73,45},new byte[5]{43,47,119,119,45},
            new byte[5]{43,47,120,56,45},new byte[5]{43,47,119,69,45}
        };
        /// <summary>
        /// gb18030编码高频汉字编码
        /// </summary>
        private list<byte[]> _gb18030gaopinzifubianmalsit = new list<byte[]>()
        {
            new byte[2]{181,196},new byte[2]{210,187},new byte[2]{185,250},new byte[2]{212,218},new byte[2]{200,203},new byte[2]{193,203},new byte[2]{211,208},new byte[2]{214,208},new byte[2]{202,199},
            new byte[2]{196,234},new byte[2]{186,205},new byte[2]{180,243},new byte[2]{210,181},new byte[2]{178,187},new byte[2]{206,170},new byte[2]{183,162},new byte[2]{187,225},new byte[2]{185,164},
            new byte[2]{190,173},new byte[2]{201,207},new byte[2]{181,216},new byte[2]{202,208},new byte[2]{210,170},new byte[2]{184,246},new byte[2]{178,250},new byte[2]{213,226},new byte[2]{179,246},
            new byte[2]{208,208},new byte[2]{215,247},new byte[2]{201,250},new byte[2]{188,210},new byte[2]{210,212},new byte[2]{179,201},new byte[2]{181,189},new byte[2]{200,213},new byte[2]{195,241},
            new byte[2]{192,180},new byte[2]{206,210},new byte[2]{178,191},new byte[2]{182,212},new byte[2]{189,248},new byte[2]{182,224},new byte[2]{200,171},new byte[2]{189,168},new byte[2]{203,251},
            new byte[2]{185,171},new byte[2]{191,170},new byte[2]{195,199},new byte[2]{179,161},new byte[2]{213,185},new byte[2]{202,177},new byte[2]{192,237},new byte[2]{208,194},new byte[2]{183,189},
            new byte[2]{214,247},new byte[2]{198,243},new byte[2]{215,202},new byte[2]{202,181},new byte[2]{209,167},new byte[2]{177,168},new byte[2]{214,198},new byte[2]{213,254},new byte[2]{188,195},
            new byte[2]{211,195},new byte[2]{205,172},new byte[2]{211,218},new byte[2]{183,168},new byte[2]{184,223},new byte[2]{179,164},new byte[2]{207,214},new byte[2]{177,190},new byte[2]{212,194},
            new byte[2]{182,168},new byte[2]{187,175},new byte[2]{188,211},new byte[2]{182,175},new byte[2]{186,207},new byte[2]{198,183},new byte[2]{214,216},new byte[2]{185,216},new byte[2]{187,250},
            new byte[2]{183,214},new byte[2]{193,166},new byte[2]{215,212},new byte[2]{205,226},new byte[2]{213,223},new byte[2]{199,248},new byte[2]{196,220},new byte[2]{201,232},new byte[2]{186,243},
            new byte[2]{190,205},new byte[2]{181,200},new byte[2]{204,229},new byte[2]{207,194},new byte[2]{205,242},new byte[2]{212,170},new byte[2]{201,231},new byte[2]{185,253},new byte[2]{199,176},
            new byte[2]{195,230},new byte[2]{161,163},new byte[2]{163,172},new byte[2]{163,191},new byte[2]{163,161}
        };
        /// <summary>
        /// 表示需要猜测编码的流。
        /// </summary>
        private stream _thisstream;
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="_canshustream">参数流</param>
        public streambianmajiance(stream _canshustream)
        {
            if (_canshustream == null || _canshustream.length < 100)
            {
                throw new system.nullreferenceexception("wenzibianmajiance构造函数参数_canshustream不能为空且长度不能小于100");
            }
            _thisstream = _canshustream;
        }
        /// <summary>
        /// 检测。
        /// </summary>
        /// <returns>流的编码</returns>
        public encoding jiance()
        {
            byte[] _streambyte = duquweizijie();
            encoding _returnencoding = encoding.utf8;
            //通过bom头来判断编码,有bom头也就没必要去猜了。
            if (genjubomcaibianma(_streambyte, out _returnencoding) == false)
            {
                _returnencoding = caijiewenzibianma(_streambyte);
            }
            return _returnencoding;
        }
        /// <summary>
        /// 读取数据为字节。
        /// </summary>
        /// <returns></returns>
        private byte[] duquweizijie()
        {
            binaryreader _binaryreader = new binaryreader(_thisstream);
            byte[] _returnbyte = new byte[_thisstream.length];
            //判断流的长度。
            if (_thisstream.length < (long)int.maxvalue)//小于整型值的情况
            {
                _binaryreader.read(_returnbyte, 0, (int)_thisstream.length);
            }
            else//大于整型值的情况
            {
                long _index = 0;
                while (_index < _returnbyte.length)
                {
                    _returnbyte.copyto(_binaryreader.readbytes(1024), _index);
                    _index = _index + 1024l;
                }
            }
            return _returnbyte;
        }
        /// <summary>
        /// 根据bom头返回编码格式。
        /// </summary>
        /// <param name="_streambyte">流的字节组。</param>
        /// <returns></returns>
        private bool genjubomcaibianma(byte[] _streambyte, out encoding _rucanencoding)
        {
            //132 49 149 51 gb-18030
            if (_streambyte[0] == 132 && _streambyte[1] == 49 && _streambyte[2] == 149 && _streambyte[3] == 51)
            {
                _rucanencoding = encoding.getencoding("gb-18030");
                return true;
            }

            //239 187 191 utf-8
            if (_streambyte[0] == 239 && _streambyte[1] == 187 && _streambyte[2] == 191)
            {
                _rucanencoding = encoding.utf8;
                return true;
            }

            //254 255 unicode
            if (_streambyte[0] == 254 && _streambyte[1] == 255)
            {
                _rucanencoding = encoding.unicode;
                return true;
            }

            if (_streambyte[0] == 255 && _streambyte[1] == 254)
            {
                //255 254 0 0 utf-32
                if (_streambyte[2] == 0 && _streambyte[3] == 0)
                {
                    _rucanencoding = encoding.utf32;
                }

                //255 254 bigendianunicode
                _rucanencoding = encoding.bigendianunicode;
                return true;
            }

            //43 47 118 utf-7
            if (_streambyte[0] == 43 && _streambyte[1] == 47 && _streambyte[2] == 118)
            {
                //[ 56 | 57 | 43 | 47 ]
                if (_streambyte[3] == 56 || _streambyte[3] == 57 || _streambyte[3] == 43 || _streambyte[3] == 47)
                {
                    _rucanencoding = encoding.utf7;
                    return true;
                }
            }

            _rucanencoding = null;
            return false;
        }
        /// <summary>
        /// 猜解文字编码，适用于没有bom头的情况。
        /// </summary>
        /// <param name="_streambyte">流的字节组。</param>
        /// <returns></returns>
        private encoding caijiewenzibianma(byte[] _streambyte)
        {
            //按照中文世界编码使用概率确定猜解顺序。         
            //utf8
            if (gaopinzijianceuft8(_streambyte) == true)
            {
                return encoding.utf8;
            }
            //gb18030
            if (gaopinzijiancegb18030(_streambyte) == true)
            {
                return encoding.getencoding("gb18030");
            }
            //utf7
            if (gaopinzijianceutf7(_streambyte) == true)
            {
                return encoding.utf7;
            }
            //utf-32任何字符都以四个字节编码，必然可以被四整除
            if (_streambyte.length % 4 == 0)
            {
                if (gaopinzijianceutf32(_streambyte) == true)//utf32
                {
                    return encoding.utf32;
                }

            }
            //bigendianunicode和unicode任何字符都以二个字节编码，必然可以被二整除
            if (_streambyte.length % 2 == 0)
            {
                //unicode
                if (gaopinzijianceunicode(_streambyte) == true)
                {
                    return encoding.unicode;
                }
                //bigendianunicod
                if (gaopinzijiancebigendianunicode(_streambyte) == true)
                {
                    return encoding.bigendianunicode;
                }
            }
            //如果上述猜解都失败了，则返回utf-8。
            return encoding.utf8;
        }
        /// <summary>
        /// 高频字检查法，uft8编码方法
        /// </summary>
        /// <param name="_streambyte">流字节组</param>
        /// <returns></returns>
        private bool gaopinzijianceuft8(byte[] _streambyte)
        {
            //命中次数。
            int _mingzhongcishu = 0;

            foreach (byte[] bshuzu in _utf8gaopinzifubianmalsit)
            {
                for (int i = 0; i < _streambyte.length; i++)
                {
                    //判断首编码是否相等
                    if (bshuzu[0] == _streambyte[i])
                    {
                        //如果首字节相等，则检查后面二个字节是否也相等
                        if ((i + 1 < _streambyte.length && _streambyte[i + 1] == bshuzu[1])
                            && (i + 2 < _streambyte.length && _streambyte[i + 2] == bshuzu[2]))
                        {
                            _mingzhongcishu++;
                        }
                    }
                }

                //utf-8有一定几率与其他编码冲突，故而增加命中次数，减少误差。
                if (_mingzhongcishu > 2)
                {
                    return true;
                }
            }

            return false;
        }
        /// <summary>
        /// 高频字检查法，unicode编码方法
        /// </summary>
        /// <param name="_streambyte">流字节组</param>
        /// <returns></returns>
        private bool gaopinzijianceunicode(byte[] _streambyte)
        {
            foreach (byte[] bshuzu in _unicodegaopinzifubianmalsit)
            {
                for (int i = 0; i < _streambyte.length; i++)
                {
                    //判断首编码是否相等
                    if (bshuzu[0] == _streambyte[i]
                        && (i + 1 < _streambyte.length && _streambyte[i + 1] == bshuzu[1]))
                    {
                        //如果首字节相等，则检查后面二个字节是否也相等
                        return true;
                    }
                }
            }
            return false;
        }
        /// <summary>
        /// 高频字检查法，utf32编码方法
        /// </summary>
        /// <param name="_streambyte">流字节组</param>
        /// <returns></returns>
        private bool gaopinzijianceutf32(byte[] _streambyte)
        {
            foreach (byte[] bshuzu in _utf32gaopinzifubianmalsit)
            {
                for (int i = 0; i < _streambyte.length; i++)
                {
                    //判断首编码是否相等
                    if (bshuzu[0] == _streambyte[i])
                    {
                        //如果首字节相等，则检查后面二个字节是否也相等
                        if ((i + 1 < _streambyte.length && _streambyte[i + 1] == bshuzu[1])
                            && (i + 2 < _streambyte.length && _streambyte[i + 2] == bshuzu[2])
                            && (i + 3 < _streambyte.length && _streambyte[i + 3] == bshuzu[3]))
                        {
                            return true;
                        }
                    }
                }
            }
            return false;
        }
        /// <summary>
        /// 高频字检查法，utf7编码方法
        /// </summary>
        /// <param name="_streambyte">流字节组</param>
        /// <returns></returns>
        private bool gaopinzijianceutf7(byte[] _streambyte)
        {
            foreach (byte[] bshuzu in _utf7gaopinzifubianmalsit)
            {
                for (int i = 0; i < _streambyte.length; i++)
                {
                    //判断首编码是否相等
                    if (bshuzu[0] == _streambyte[i])
                    {
                        //如果首字节相等，则检查后面二个字节是否也相等
                        if ((i + 1 < _streambyte.length && _streambyte[i + 1] == bshuzu[1])
                            && (i + 2 < _streambyte.length && _streambyte[i + 2] == bshuzu[2])
                            && (i + 3 < _streambyte.length && _streambyte[i + 3] == bshuzu[3])
                            && (i + 4 < _streambyte.length && _streambyte[i + 4] == bshuzu[4]))
                        {
                            return true;
                        }
                    }
                }
            }
            return false;
        }
        /// <summary>
        /// 高频字检查法，gb18030编码方法
        /// </summary>
        /// <param name="_streambyte">流字节组</param>
        /// <returns></returns>
        private bool gaopinzijiancegb18030(byte[] _streambyte)
        {
            foreach (byte[] bshuzu in _gb18030gaopinzifubianmalsit)
            {
                for (int i = 0; i < _streambyte.length; i++)
                {
                    //判断首编码是否相等
                    if (bshuzu[0] == _streambyte[i])
                    {
                        //如果首字节相等，则检查后面二个字节是否也相等
                        if ((i + 1 < _streambyte.length && _streambyte[i + 1] == bshuzu[0]))
                        {
                            return true;
                        }
                    }
                }
            }
            return false;
        }
        /// <summary>
        /// 高频字检查法，unicode编码方法
        /// </summary>
        /// <param name="_streambyte">流字节组</param>
        /// <returns></returns>
        private bool gaopinzijiancebigendianunicode(byte[] _streambyte)
        {
            foreach (byte[] bshuzu in _bigendianunicodegaopinzifubianmalsit)
            {
                for (int i = 0; i < _streambyte.length; i++)
                {

                    //判断首编码是否相等
                    if (bshuzu[0] == _streambyte[i])
                    {
                        //如果首字节相等，则检查后面二个字节是否也相等
                        if ((i + 1 < _streambyte.length && _streambyte[i + 1] == bshuzu[1]))
                        {
                            return true;
                        }
                    }
                }
            }
            return false;
        }
    }
}

//使用示例
//爬虫判断网页编码
webrequest _webrequest = webrequest.create(@"https://www.cnblogs.com/j20171203/");
webresponse _webresponse = _webrequest.getresponse();
stream _stream = _webresponse.getresponsestream();

memorystream _memorystream = new memorystream();
const int bufferlength = 1024;
byte[] buffer = new byte[bufferlength];
int actual = 1;
while (true)
{
   actual = _stream.read(buffer, 0, bufferlength);
   _memorystream.write(buffer, 0, actual);

   if (actual == 0)
   {
      break;
   }
}
_memorystream.position = 0;

streambianmajiance _streambianmajiance = new streambianmajiance(_memorystream);
encoding _jieguoencoding = _streambianmajiance.jiance();

_stream.close();
_stream.dispose();
_webresponse.close();