根据文件后缀返回Http的ContentType类型的函数

protected static string GetContentType(string strFileName)
        {
            string strExtendName = strFileName.Substring(strFileName.LastIndexOf('.'));
            if (string.IsNullOrEmpty(strExtendName))
            {
                return "";
            }
            string strRet = "";
            switch (strExtendName)
            { 
                case ".*": strRet = "application/octet-stream";break;
                case ".001": strRet = "application/x-001";break; 
                case ".301": strRet = "application/x-301";break; 
                case ".323": strRet = "text/h323" ;break;
                case ".906": strRet = "application/x-906" ;break;
                case ".907": strRet = "drawing/907" ;break;
                case ".a11": strRet = "application/x-a11";break; 
                case ".acp": strRet = "audio/x-mei-aac" ;break;
                case ".ai": strRet = "application/postscript" ;break;
                case ".aif": strRet = "audio/aiff" ;break;
                case ".aifc": strRet = "audio/aiff" ;break;
                case ".aiff": strRet = "audio/aiff" ;break;
                case ".anv": strRet = "application/x-anv" ;break;
                case ".asa": strRet = "text/asa";break; 
                case ".asf": strRet = "video/x-ms-asf";break; 
                case ".asp": strRet = "text/asp";break; 
                case ".asx": strRet = "video/x-ms-asf";break; 
                case ".au": strRet = "audio/basic";break; 
                case ".avi": strRet = "video/avi";break; 
                case ".awf": strRet = "application/vnd.adobe.workflow";break; 
                case ".biz": strRet = "text/xml";break; 
                case ".bmp": strRet = "application/x-bmp";break; 
                case ".bot": strRet = "application/x-bot";break; 
                case ".c4t": strRet = "application/x-c4t";break; 
                case ".c90": strRet = "application/x-c90";break; 
                case ".cal": strRet = "application/x-cals";break; 
                case ".cat": strRet = "application/vnd.ms-pki.seccat";break; 
                case ".cdf": strRet = "application/x-netcdf";break; 
                case ".cdr": strRet = "application/x-cdr";break; 
                case ".cel": strRet = "application/x-cel";break; 
                case ".cer": strRet = "application/x-x509-ca-cert";break; 
                case ".cg4": strRet = "application/x-g4";break; 
                case ".cgm": strRet = "application/x-cgm";break; 
                case ".cit": strRet = "application/x-cit";break; 
                case ".class": strRet = "java/*";break; 
                case ".cml": strRet = "text/xml";break; 
                case ".cmp": strRet = "application/x-cmp";break; 
                case ".cmx": strRet = "application/x-cmx";break; 
                case ".cot": strRet = "application/x-cot";break; 
                case ".crl": strRet = "application/pkix-crl";break; 
                case ".crt": strRet = "application/x-x509-ca-cert";break; 
                case ".csi": strRet = "application/x-csi";break; 
                case ".css": strRet = "text/css";break; 
                case ".cut": strRet = "application/x-cut";break; 
                case ".dbf": strRet = "application/x-dbf";break; 
                case ".dbm": strRet = "application/x-dbm";break; 
                case ".dbx": strRet = "application/x-dbx";break; 
                case ".dcd": strRet = "text/xml";break; 
                case ".dcx": strRet = "application/x-dcx";break; 
                case ".der": strRet = "application/x-x509-ca-cert";break; 
                case ".dgn": strRet = "application/x-dgn";break; 
                case ".dib": strRet = "application/x-dib";break; 
                case ".dll": strRet = "application/x-msdownload";break; 
                case ".doc": strRet = "application/msword";break; 
                case ".dot": strRet = "application/msword";break; 
                case ".drw": strRet = "application/x-drw";break; 
                case ".dtd": strRet = "text/xml";break; 
                //case ".dwf": strRet = "Model/vnd.dwf";break; 
                case ".dwf": strRet = "application/x-dwf";break; 
                case ".dwg": strRet = "application/x-dwg";break; 
                case ".dxb": strRet = "application/x-dxb";break; 
                case ".dxf": strRet = "application/x-dxf";break; 
                case ".edn": strRet = "application/vnd.adobe.edn";break; 
                case ".emf": strRet = "application/x-emf";break; 
                case ".eml": strRet = "message/rfc822";break; 
                case ".ent": strRet = "text/xml";break; 
                case ".epi": strRet = "application/x-epi";break; 
                case ".eps": strRet = "application/x-ps";break; 
                //case ".eps": strRet = "application/postscript";break; 
                case ".etd": strRet = "application/x-ebx";break; 
                case ".exe": strRet = "application/x-msdownload";break; 
                case ".fax": strRet = "image/fax";break; 
                case ".fdf": strRet = "application/vnd.fdf";break; 
                case ".fif": strRet = "application/fractals";break; 
                case ".fo": strRet = "text/xml";break; 
                case ".frm": strRet = "application/x-frm";break; 
                case ".g4": strRet = "application/x-g4";break; 
                case ".gbr": strRet = "application/x-gbr";break; 
                case ".gcd": strRet = "application/x-gcd";break; 
                case ".gif": strRet = "image/gif";break; 
                case ".gl2": strRet = "application/x-gl2";break; 
                case ".gp4": strRet = "application/x-gp4";break; 
                case ".hgl": strRet = "application/x-hgl";break; 
                case ".hmr": strRet = "application/x-hmr";break; 
                case ".hpg": strRet = "application/x-hpgl";break; 
                case ".hpl": strRet = "application/x-hpl";break; 
                case ".hqx": strRet = "application/mac-binhex40";break; 
                case ".hrf": strRet = "application/x-hrf";break; 
                case ".hta": strRet = "application/hta";break; 
                case ".htc": strRet = "text/x-component";break; 
                case ".htm": strRet = "text/html";break; 
                case ".html": strRet = "text/html";break; 
                case ".htt": strRet = "text/webviewhtml";break; 
                case ".htx": strRet = "text/html";break; 
                case ".icb": strRet = "application/x-icb";break; 
                case ".ico": strRet = "image/x-icon";break; 
                //case ".ico": strRet = "application/x-ico";break; 
                case ".iff": strRet = "application/x-iff";break; 
                case ".ig4": strRet = "application/x-g4";break; 
                case ".igs": strRet = "application/x-igs";break; 
                case ".iii": strRet = "application/x-iphone";break; 
                case ".img": strRet = "application/x-img";break; 
                case ".ins": strRet = "application/x-internet-signup";break;
                case ".isp": strRet = "application/x-internet-signup";break; 
                case ".IVF": strRet = "video/x-ivf";break; 
                case ".java": strRet = "java/*";break; 
                case ".jfif": strRet = "image/jpeg";break; 
                case ".jpe": strRet = "image/jpeg";break; 
                //case ".jpe": strRet = "application/x-jpe";break; 
                case ".jpeg": strRet = "image/jpeg";break; 
                case ".jpg": strRet = "image/jpeg";break; 
                //case ".jpg": strRet = "application/x-jpg";break; 
                case ".js": strRet = "application/x-javascript";break; 
                case ".jsp": strRet = "text/html";break; 
                case ".la1": strRet = "audio/x-liquid-file";break; 
                case ".lar": strRet = "application/x-laplayer-reg";break; 
                case ".latex": strRet = "application/x-latex";break; 
                case ".lavs": strRet = "audio/x-liquid-secure";break; 
                case ".lbm": strRet = "application/x-lbm";break; 
                case ".lmsff": strRet = "audio/x-la-lms";break; 
                case ".ls": strRet = "application/x-javascript";break; 
                case ".ltr": strRet = "application/x-ltr";break; 
                case ".m1v": strRet = "video/x-mpeg";break; 
                case ".m2v": strRet = "video/x-mpeg";break; 
                case ".m3u": strRet = "audio/mpegurl";break; 
                case ".m4e": strRet = "video/mpeg4";break; 
                case ".mac": strRet = "application/x-mac";break; 
                case ".man": strRet = "application/x-troff-man";break; 
                case ".math": strRet = "text/xml";break; 
                case ".mdb": strRet = "application/msaccess";break; 
                //case ".mdb": strRet = "application/x-mdb";break; 
                case ".mfp": strRet = "application/x-shockwave-flash";break; 
                case ".mht": strRet = "message/rfc822";break; 
                case ".mhtml": strRet = "message/rfc822";break; 
                case ".mi": strRet = "application/x-mi";break; 
                case ".mid": strRet = "audio/mid";break; 
                case ".midi": strRet = "audio/mid";break; 
                case ".mil": strRet = "application/x-mil";break; 
                case ".mml": strRet = "text/xml";break; 
                case ".mnd": strRet = "audio/x-musicnet-download";break; 
                case ".mns": strRet = "audio/x-musicnet-stream";break; 
                case ".mocha": strRet = "application/x-javascript";break; 
                case ".movie": strRet = "video/x-sgi-movie";break; 
                case ".mp1": strRet = "audio/mp1";break; 
                case ".mp2": strRet = "audio/mp2";break; 
                case ".mp2v": strRet = "video/mpeg";break; 
                case ".mp3": strRet = "audio/mp3";break; 
                case ".mp4": strRet = "video/mpeg4";break; 
                case ".mpa": strRet = "video/x-mpg";break; 
                case ".mpd": strRet = "application/vnd.ms-project";break; 
                case ".mpe": strRet = "video/x-mpeg";break; 
                case ".mpeg": strRet = "video/mpg";break; 
                case ".mpg": strRet = "video/mpg";break; 
                case ".mpga": strRet = "audio/rn-mpeg";break; 
                case ".mpp": strRet = "application/vnd.ms-project";break; 
                case ".mps": strRet = "video/x-mpeg";break; 
                case ".mpt": strRet = "application/vnd.ms-project";break; 
                case ".mpv": strRet = "video/mpg";break; 
                case ".mpv2": strRet = "video/mpeg";break; 
                case ".mpw": strRet = "application/vnd.ms-project";break; 
                case ".mpx": strRet = "application/vnd.ms-project";break; 
                case ".mtx": strRet = "text/xml";break; 
                case ".mxp": strRet = "application/x-mmxp";break; 
                case ".net": strRet = "image/pnetvue";break; 
                case ".nrf": strRet = "application/x-nrf";break; 
                case ".nws": strRet = "message/rfc822";break; 
                case ".odc": strRet = "text/x-ms-odc";break; 
                case ".out": strRet = "application/x-out";break; 
                case ".p10": strRet = "application/pkcs10";break; 
                case ".p12": strRet = "application/x-pkcs12";break; 
                case ".p7b": strRet = "application/x-pkcs7-certificates";break; 
                case ".p7c": strRet = "application/pkcs7-mime";break; 
                case ".p7m": strRet = "application/pkcs7-mime";break; 
                case ".p7r": strRet = "application/x-pkcs7-certreqresp";break; 
                case ".p7s": strRet = "application/pkcs7-signature";break; 
                case ".pc5": strRet = "application/x-pc5";break; 
                case ".pci": strRet = "application/x-pci";break; 
                case ".pcl": strRet = "application/x-pcl";break; 
                case ".pcx": strRet = "application/x-pcx";break; 
                case ".pdf": strRet = "application/pdf";break;                 
                case ".pdx": strRet = "application/vnd.adobe.pdx";break; 
                case ".pfx": strRet = "application/x-pkcs12";break; 
                case ".pgl": strRet = "application/x-pgl";break; 
                case ".pic": strRet = "application/x-pic";break; 
                case ".pko": strRet = "application/vnd.ms-pki.pko";break; 
                case ".pl": strRet = "application/x-perl";break; 
                case ".plg": strRet = "text/html";break; 
                case ".pls": strRet = "audio/scpls";break; 
                case ".plt": strRet = "application/x-plt";break; 
                case ".png": strRet = "image/png";break;                 
                case ".pot": strRet = "application/vnd.ms-powerpoint";break; 
                case ".ppa": strRet = "application/vnd.ms-powerpoint";break; 
                case ".ppm": strRet = "application/x-ppm";break; 
                case ".pps": strRet = "application/vnd.ms-powerpoint";break; 
                case ".ppt": strRet = "application/vnd.ms-powerpoint";break;                 
                case ".pr": strRet = "application/x-pr";break; 
                case ".prf": strRet = "application/pics-rules";break; 
                case ".prn": strRet = "application/x-prn";break; 
                case ".prt": strRet = "application/x-prt";break; 
                case ".ps": strRet = "application/x-ps";break;                 
                case ".ptn": strRet = "application/x-ptn";break; 
                case ".pwz": strRet = "application/vnd.ms-powerpoint";break; 
                case ".r3t": strRet = "text/vnd.rn-realtext3d";break; 
                case ".ra": strRet = "audio/vnd.rn-realaudio";break; 
                case ".ram": strRet = "audio/x-pn-realaudio";break; 
                case ".ras": strRet = "application/x-ras";break; 
                case ".rat": strRet = "application/rat-file";break; 
                case ".rdf": strRet = "text/xml";break; 
                case ".rec": strRet = "application/vnd.rn-recording";break; 
                case ".red": strRet = "application/x-red";break; 
                case ".rgb": strRet = "application/x-rgb";break; 
                case ".rjs": strRet = "application/vnd.rn-realsystem-rjs";break; 
                case ".rjt": strRet = "application/vnd.rn-realsystem-rjt";break; 
                case ".rlc": strRet = "application/x-rlc";break; 
                case ".rle": strRet = "application/x-rle";break; 
                case ".rm": strRet = "application/vnd.rn-realmedia";break; 
                case ".rmf": strRet = "application/vnd.adobe.rmf";break; 
                case ".rmi": strRet = "audio/mid";break; 
                case ".rmj": strRet = "application/vnd.rn-realsystem-rmj";break; 
                case ".rmm": strRet = "audio/x-pn-realaudio";break; 
                case ".rmp": strRet = "application/vnd.rn-rn_music_package";break; 
                case ".rms": strRet = "application/vnd.rn-realmedia-secure";break; 
                case ".rmvb": strRet = "application/vnd.rn-realmedia-vbr";break; 
                case ".rmx": strRet = "application/vnd.rn-realsystem-rmx";break; 
                case ".rnx": strRet = "application/vnd.rn-realplayer";break; 
                case ".rp": strRet = "image/vnd.rn-realpix";break; 
                case ".rpm": strRet = "audio/x-pn-realaudio-plugin";break; 
                case ".rsml": strRet = "application/vnd.rn-rsml";break; 
                case ".rt": strRet = "text/vnd.rn-realtext";break;                 
                case ".rtf": strRet = "application/x-rtf";break; 
                case ".rv": strRet = "video/vnd.rn-realvideo";break; 
                case ".sam": strRet = "application/x-sam";break; 
                case ".sat": strRet = "application/x-sat";break; 
                case ".sdp": strRet = "application/sdp";break; 
                case ".sdw": strRet = "application/x-sdw";break; 
                case ".sit": strRet = "application/x-stuffit";break; 
                case ".slb": strRet = "application/x-slb";break; 
                case ".sld": strRet = "application/x-sld";break; 
                case ".slk": strRet = "drawing/x-slk";break; 
                case ".smi": strRet = "application/smil";break; 
                case ".smil": strRet = "application/smil";break; 
                case ".smk": strRet = "application/x-smk";break; 
                case ".snd": strRet = "audio/basic";break; 
                case ".sol": strRet = "text/plain";break; 
                case ".sor": strRet = "text/plain";break; 
                case ".spc": strRet = "application/x-pkcs7-certificates";break; 
                case ".spl": strRet = "application/futuresplash";break; 
                case ".spp": strRet = "text/xml";break; 
                case ".ssm": strRet = "application/streamingmedia";break; 
                case ".sst": strRet = "application/vnd.ms-pki.certstore";break; 
                case ".stl": strRet = "application/vnd.ms-pki.stl";break; 
                case ".stm": strRet = "text/html";break; 
                case ".sty": strRet = "application/x-sty";break; 
                case ".svg": strRet = "text/xml";break; 
                case ".swf": strRet = "application/x-shockwave-flash";break; 
                case ".tdf": strRet = "application/x-tdf";break; 
                case ".tg4": strRet = "application/x-tg4";break; 
                case ".tga": strRet = "application/x-tga";break; 
                case ".tif": strRet = "image/tiff";break;                 
                case ".tiff": strRet = "image/tiff";break; 
                case ".tld": strRet = "text/xml";break; 
                case ".top": strRet = "drawing/x-top";break; 
                case ".torrent": strRet = "application/x-bittorrent";break; 
                case ".tsd": strRet = "text/xml";break; 
                case ".txt": strRet = "text/plain";break; 
                case ".uin": strRet = "application/x-icq";break; 
                case ".uls": strRet = "text/iuls";break; 
                case ".vcf": strRet = "text/x-vcard";break; 
                case ".vda": strRet = "application/x-vda";break; 
                case ".vdx": strRet = "application/vnd.visio";break; 
                case ".vml": strRet = "text/xml";break; 
                case ".vpg": strRet = "application/x-vpeg005";break; 
                case ".vsd": strRet = "application/vnd.visio";break;                 
                case ".vss": strRet = "application/vnd.visio";break; 
                case ".vst": strRet = "application/vnd.visio";break;
                case ".vsw": strRet = "application/vnd.visio";break; 
                case ".vsx": strRet = "application/vnd.visio";break; 
                case ".vtx": strRet = "application/vnd.visio";break; 
                case ".vxml": strRet = "text/xml";break; 
                case ".wav": strRet = "audio/wav";break; 
                case ".wax": strRet = "audio/x-ms-wax";break; 
                case ".wb1": strRet = "application/x-wb1";break; 
                case ".wb2": strRet = "application/x-wb2";break; 
                case ".wb3": strRet = "application/x-wb3";break; 
                case ".wbmp": strRet = "image/vnd.wap.wbmp";break; 
                case ".wiz": strRet = "application/msword";break; 
                case ".wk3": strRet = "application/x-wk3";break; 
                case ".wk4": strRet = "application/x-wk4";break; 
                case ".wkq": strRet = "application/x-wkq";break; 
                case ".wks": strRet = "application/x-wks";break; 
                case ".wm": strRet = "video/x-ms-wm";break; 
                case ".wma": strRet = "audio/x-ms-wma";break; 
                case ".wmd": strRet = "application/x-ms-wmd";break; 
                case ".wmf": strRet = "application/x-wmf";break; 
                case ".wml": strRet = "text/vnd.wap.wml";break; 
                case ".wmv": strRet = "video/x-ms-wmv";break; 
                case ".wmx": strRet = "video/x-ms-wmx";break; 
                case ".wmz": strRet = "application/x-ms-wmz";break; 
                case ".wp6": strRet = "application/x-wp6";break; 
                case ".wpd": strRet = "application/x-wpd";break; 
                case ".wpg": strRet = "application/x-wpg";break; 
                case ".wpl": strRet = "application/vnd.ms-wpl";break; 
                case ".wq1": strRet = "application/x-wq1";break; 
                case ".wr1": strRet = "application/x-wr1";break; 
                case ".wri": strRet = "application/x-wri";break; 
                case ".wrk": strRet = "application/x-wrk";break; 
                case ".ws": strRet = "application/x-ws";break; 
                case ".ws2": strRet = "application/x-ws";break; 
                case ".wsc": strRet = "text/scriptlet";break; 
                case ".wsdl": strRet = "text/xml";break; 
                case ".wvx": strRet = "video/x-ms-wvx";break; 
                case ".xdp": strRet = "application/vnd.adobe.xdp";break; 
                case ".xdr": strRet = "text/xml";break; 
                case ".xfd": strRet = "application/vnd.adobe.xfd";break; 
                case ".xfdf": strRet = "application/vnd.adobe.xfdf";break; 
                case ".xhtml": strRet = "text/html";break; 
                case ".xls": strRet = "application/vnd.ms-excel";break;                 
                case ".xlw": strRet = "application/x-xlw";break; 
                case ".xml": strRet = "text/xml";break; 
                case ".xpl": strRet = "audio/scpls";break; 
                case ".xq": strRet = "text/xml";break; 
                case ".xql": strRet = "text/xml";break; 
                case ".xquery": strRet = "text/xml";break; 
                case ".xsd": strRet = "text/xml";break; 
                case ".xsl": strRet = "text/xml";break; 
                case ".xslt": strRet = "text/xml";break; 
                case ".xwd": strRet = "application/x-xwd";break; 
                case ".x_b": strRet = "application/x-x_b";break;
                case ".x_t": strRet = "application/x-x_t"; break;
            }
            return strRet;
        }