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What is a correct MIME type for .docx, .pptx, etc.?

For older *.doc documents, this was enough: 

header("Content-Type: application/msword");

What MIME type should I use for new .docx documents? Also, for pptx and xlsx documents?

If you using linux, you can make use of this command file -bi YOUR_FILE
@ajreal that doesn't provide the MIME type. The output for a jpg with that command would look like JPEG image data, EXIF standard
@wmarbut An alternative name for the -i flag is --mime.
@wmarbut Seems to provide the mime type to me. Tried it with a jpeg and got: image/jpeg; charset=binary, where image/jpeg is the mime type.
you may have look on them here: msdn.microsoft.com/en-us/library/ms775147.aspx

G
Glorfindel

Here are the correct Microsoft Office MIME types for HTTP content streaming: 

Extension MIME Type
.doc      application/msword
.dot      application/msword

.docx     application/vnd.openxmlformats-officedocument.wordprocessingml.document
.dotx     application/vnd.openxmlformats-officedocument.wordprocessingml.template
.docm     application/vnd.ms-word.document.macroEnabled.12
.dotm     application/vnd.ms-word.template.macroEnabled.12

.xls      application/vnd.ms-excel
.xlt      application/vnd.ms-excel
.xla      application/vnd.ms-excel

.xlsx     application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
.xltx     application/vnd.openxmlformats-officedocument.spreadsheetml.template
.xlsm     application/vnd.ms-excel.sheet.macroEnabled.12
.xltm     application/vnd.ms-excel.template.macroEnabled.12
.xlam     application/vnd.ms-excel.addin.macroEnabled.12
.xlsb     application/vnd.ms-excel.sheet.binary.macroEnabled.12

.ppt      application/vnd.ms-powerpoint
.pot      application/vnd.ms-powerpoint
.pps      application/vnd.ms-powerpoint
.ppa      application/vnd.ms-powerpoint

.pptx     application/vnd.openxmlformats-officedocument.presentationml.presentation
.potx     application/vnd.openxmlformats-officedocument.presentationml.template
.ppsx     application/vnd.openxmlformats-officedocument.presentationml.slideshow
.ppam     application/vnd.ms-powerpoint.addin.macroEnabled.12
.pptm     application/vnd.ms-powerpoint.presentation.macroEnabled.12
.potm     application/vnd.ms-powerpoint.template.macroEnabled.12
.ppsm     application/vnd.ms-powerpoint.slideshow.macroEnabled.12

.mdb      application/vnd.ms-access

For further details check out this TechNet article and this blog post.

This is maybe a little old, I use application/vnd.ms-excel for .xlsx
This MSDN blog entry has both the 2007 and pre-2007 file format MIME types.
application/vnd.ms-excel is specifically for .xls files. the ability for it to work with .xlsx depends on the client software in use.
If one day there is a tutorial with example answers on how to answer, I would put this answer there.
Since no one else has said it: "application/vnd.openxmlformats-officedocument.wordprocessingml.document" - was that really necessary?!
G
General Grievance

Alternatively, if you're working in .NET v4.5 or above, try using System.Web.MimeMapping.GetMimeMapping(yourFileName) to get MIME types. It is much better than hard-coding strings.

Well, considering that most apps expect to deal with just a handful of file types, I do not think using the API is much better than hard-coding the strings. It's not like the MIMEs will change any time soon anyway. No need loading a truck of data into memory that you will never use.
There is no "right" answer - personally I just prefer to avoid hard-coding "magic strings" in my code and to be honest I'm too lazy to look them up each time when there's a simple method that wraps it up nicely for me.
Per the documentation current as of when I am writing this (27 Aug 2021), located at link the MimeMapping.GetMimeMapping only applies to .NET Framework 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8 - so if we are in Core, we might look for another way.
S
Stephan Bauer

Here is the (almost) complete file extensions's MIME in a JSON format.
Just do example: MIME["ppt"], MIME["docx"], etc 

{
    "x3d": "application/vnd.hzn-3d-crossword",
    "3gp": "video/3gpp",
    "3g2": "video/3gpp2",
    "mseq": "application/vnd.mseq",
    "pwn": "application/vnd.3m.post-it-notes",
    "plb": "application/vnd.3gpp.pic-bw-large",
    "psb": "application/vnd.3gpp.pic-bw-small",
    "pvb": "application/vnd.3gpp.pic-bw-var",
    "tcap": "application/vnd.3gpp2.tcap",
    "7z": "application/x-7z-compressed",
    "abw": "application/x-abiword",
    "ace": "application/x-ace-compressed",
    "acc": "application/vnd.americandynamics.acc",
    "acu": "application/vnd.acucobol",
    "atc": "application/vnd.acucorp",
    "adp": "audio/adpcm",
    "aab": "application/x-authorware-bin",
    "aam": "application/x-authorware-map",
    "aas": "application/x-authorware-seg",
    "air": "application/vnd.adobe.air-application-installer-package+zip",
    "swf": "application/x-shockwave-flash",
    "fxp": "application/vnd.adobe.fxp",
    "pdf": "application/pdf",
    "ppd": "application/vnd.cups-ppd",
    "dir": "application/x-director",
    "xdp": "application/vnd.adobe.xdp+xml",
    "xfdf": "application/vnd.adobe.xfdf",
    "aac": "audio/x-aac",
    "ahead": "application/vnd.ahead.space",
    "azf": "application/vnd.airzip.filesecure.azf",
    "azs": "application/vnd.airzip.filesecure.azs",
    "azw": "application/vnd.amazon.ebook",
    "ami": "application/vnd.amiga.ami",
    "N/A": "application/andrew-inset",
    "apk": "application/vnd.android.package-archive",
    "cii": "application/vnd.anser-web-certificate-issue-initiation",
    "fti": "application/vnd.anser-web-funds-transfer-initiation",
    "atx": "application/vnd.antix.game-component",
    "dmg": "application/x-apple-diskimage",
    "mpkg": "application/vnd.apple.installer+xml",
    "aw": "application/applixware",
    "mp3": "audio/mpeg",
    "les": "application/vnd.hhe.lesson-player",
    "swi": "application/vnd.aristanetworks.swi",
    "s": "text/x-asm",
    "atomcat": "application/atomcat+xml",
    "atomsvc": "application/atomsvc+xml",
    "atom, .xml": "application/atom+xml",
    "ac": "application/pkix-attr-cert",
    "aif": "audio/x-aiff",
    "avi": "video/x-msvideo",
    "aep": "application/vnd.audiograph",
    "dxf": "image/vnd.dxf",
    "dwf": "model/vnd.dwf",
    "par": "text/plain-bas",
    "bcpio": "application/x-bcpio",
    "bin": "application/octet-stream",
    "bmp": "image/bmp",
    "torrent": "application/x-bittorrent",
    "cod": "application/vnd.rim.cod",
    "mpm": "application/vnd.blueice.multipass",
    "bmi": "application/vnd.bmi",
    "sh": "application/x-sh",
    "btif": "image/prs.btif",
    "rep": "application/vnd.businessobjects",
    "bz": "application/x-bzip",
    "bz2": "application/x-bzip2",
    "csh": "application/x-csh",
    "c": "text/x-c",
    "cdxml": "application/vnd.chemdraw+xml",
    "css": "text/css",
    "cdx": "chemical/x-cdx",
    "cml": "chemical/x-cml",
    "csml": "chemical/x-csml",
    "cdbcmsg": "application/vnd.contact.cmsg",
    "cla": "application/vnd.claymore",
    "c4g": "application/vnd.clonk.c4group",
    "sub": "image/vnd.dvb.subtitle",
    "cdmia": "application/cdmi-capability",
    "cdmic": "application/cdmi-container",
    "cdmid": "application/cdmi-domain",
    "cdmio": "application/cdmi-object",
    "cdmiq": "application/cdmi-queue",
    "c11amc": "application/vnd.cluetrust.cartomobile-config",
    "c11amz": "application/vnd.cluetrust.cartomobile-config-pkg",
    "ras": "image/x-cmu-raster",
    "dae": "model/vnd.collada+xml",
    "csv": "text/csv",
    "cpt": "application/mac-compactpro",
    "wmlc": "application/vnd.wap.wmlc",
    "cgm": "image/cgm",
    "ice": "x-conference/x-cooltalk",
    "cmx": "image/x-cmx",
    "xar": "application/vnd.xara",
    "cmc": "application/vnd.cosmocaller",
    "cpio": "application/x-cpio",
    "clkx": "application/vnd.crick.clicker",
    "clkk": "application/vnd.crick.clicker.keyboard",
    "clkp": "application/vnd.crick.clicker.palette",
    "clkt": "application/vnd.crick.clicker.template",
    "clkw": "application/vnd.crick.clicker.wordbank",
    "wbs": "application/vnd.criticaltools.wbs+xml",
    "cryptonote": "application/vnd.rig.cryptonote",
    "cif": "chemical/x-cif",
    "cmdf": "chemical/x-cmdf",
    "cu": "application/cu-seeme",
    "cww": "application/prs.cww",
    "curl": "text/vnd.curl",
    "dcurl": "text/vnd.curl.dcurl",
    "mcurl": "text/vnd.curl.mcurl",
    "scurl": "text/vnd.curl.scurl",
    "car": "application/vnd.curl.car",
    "pcurl": "application/vnd.curl.pcurl",
    "cmp": "application/vnd.yellowriver-custom-menu",
    "dssc": "application/dssc+der",
    "xdssc": "application/dssc+xml",
    "deb": "application/x-debian-package",
    "uva": "audio/vnd.dece.audio",
    "uvi": "image/vnd.dece.graphic",
    "uvh": "video/vnd.dece.hd",
    "uvm": "video/vnd.dece.mobile",
    "uvu": "video/vnd.uvvu.mp4",
    "uvp": "video/vnd.dece.pd",
    "uvs": "video/vnd.dece.sd",
    "uvv": "video/vnd.dece.video",
    "dvi": "application/x-dvi",
    "seed": "application/vnd.fdsn.seed",
    "dtb": "application/x-dtbook+xml",
    "res": "application/x-dtbresource+xml",
    "ait": "application/vnd.dvb.ait",
    "svc": "application/vnd.dvb.service",
    "eol": "audio/vnd.digital-winds",
    "djvu": "image/vnd.djvu",
    "dtd": "application/xml-dtd",
    "mlp": "application/vnd.dolby.mlp",
    "wad": "application/x-doom",
    "dpg": "application/vnd.dpgraph",
    "dra": "audio/vnd.dra",
    "dfac": "application/vnd.dreamfactory",
    "dts": "audio/vnd.dts",
    "dtshd": "audio/vnd.dts.hd",
    "dwg": "image/vnd.dwg",
    "geo": "application/vnd.dynageo",
    "es": "application/ecmascript",
    "mag": "application/vnd.ecowin.chart",
    "mmr": "image/vnd.fujixerox.edmics-mmr",
    "rlc": "image/vnd.fujixerox.edmics-rlc",
    "exi": "application/exi",
    "mgz": "application/vnd.proteus.magazine",
    "epub": "application/epub+zip",
    "eml": "message/rfc822",
    "nml": "application/vnd.enliven",
    "xpr": "application/vnd.is-xpr",
    "xif": "image/vnd.xiff",
    "xfdl": "application/vnd.xfdl",
    "emma": "application/emma+xml",
    "ez2": "application/vnd.ezpix-album",
    "ez3": "application/vnd.ezpix-package",
    "fst": "image/vnd.fst",
    "fvt": "video/vnd.fvt",
    "fbs": "image/vnd.fastbidsheet",
    "fe_launch": "application/vnd.denovo.fcselayout-link",
    "f4v": "video/x-f4v",
    "flv": "video/x-flv",
    "fpx": "image/vnd.fpx",
    "npx": "image/vnd.net-fpx",
    "flx": "text/vnd.fmi.flexstor",
    "fli": "video/x-fli",
    "ftc": "application/vnd.fluxtime.clip",
    "fdf": "application/vnd.fdf",
    "f": "text/x-fortran",
    "mif": "application/vnd.mif",
    "fm": "application/vnd.framemaker",
    "fh": "image/x-freehand",
    "fsc": "application/vnd.fsc.weblaunch",
    "fnc": "application/vnd.frogans.fnc",
    "ltf": "application/vnd.frogans.ltf",
    "ddd": "application/vnd.fujixerox.ddd",
    "xdw": "application/vnd.fujixerox.docuworks",
    "xbd": "application/vnd.fujixerox.docuworks.binder",
    "oas": "application/vnd.fujitsu.oasys",
    "oa2": "application/vnd.fujitsu.oasys2",
    "oa3": "application/vnd.fujitsu.oasys3",
    "fg5": "application/vnd.fujitsu.oasysgp",
    "bh2": "application/vnd.fujitsu.oasysprs",
    "spl": "application/x-futuresplash",
    "fzs": "application/vnd.fuzzysheet",
    "g3": "image/g3fax",
    "gmx": "application/vnd.gmx",
    "gtw": "model/vnd.gtw",
    "txd": "application/vnd.genomatix.tuxedo",
    "ggb": "application/vnd.geogebra.file",
    "ggt": "application/vnd.geogebra.tool",
    "gdl": "model/vnd.gdl",
    "gex": "application/vnd.geometry-explorer",
    "gxt": "application/vnd.geonext",
    "g2w": "application/vnd.geoplan",
    "g3w": "application/vnd.geospace",
    "gsf": "application/x-font-ghostscript",
    "bdf": "application/x-font-bdf",
    "gtar": "application/x-gtar",
    "texinfo": "application/x-texinfo",
    "gnumeric": "application/x-gnumeric",
    "kml": "application/vnd.google-earth.kml+xml",
    "kmz": "application/vnd.google-earth.kmz",
    "gqf": "application/vnd.grafeq",
    "gif": "image/gif",
    "gv": "text/vnd.graphviz",
    "gac": "application/vnd.groove-account",
    "ghf": "application/vnd.groove-help",
    "gim": "application/vnd.groove-identity-message",
    "grv": "application/vnd.groove-injector",
    "gtm": "application/vnd.groove-tool-message",
    "tpl": "application/vnd.groove-tool-template",
    "vcg": "application/vnd.groove-vcard",
    "h261": "video/h261",
    "h263": "video/h263",
    "h264": "video/h264",
    "hpid": "application/vnd.hp-hpid",
    "hps": "application/vnd.hp-hps",
    "hdf": "application/x-hdf",
    "rip": "audio/vnd.rip",
    "hbci": "application/vnd.hbci",
    "jlt": "application/vnd.hp-jlyt",
    "pcl": "application/vnd.hp-pcl",
    "hpgl": "application/vnd.hp-hpgl",
    "hvs": "application/vnd.yamaha.hv-script",
    "hvd": "application/vnd.yamaha.hv-dic",
    "hvp": "application/vnd.yamaha.hv-voice",
    "sfd-hdstx": "application/vnd.hydrostatix.sof-data",
    "stk": "application/hyperstudio",
    "hal": "application/vnd.hal+xml",
    "html": "text/html",
    "irm": "application/vnd.ibm.rights-management",
    "sc": "application/vnd.ibm.secure-container",
    "ics": "text/calendar",
    "icc": "application/vnd.iccprofile",
    "ico": "image/x-icon",
    "igl": "application/vnd.igloader",
    "ief": "image/ief",
    "ivp": "application/vnd.immervision-ivp",
    "ivu": "application/vnd.immervision-ivu",
    "rif": "application/reginfo+xml",
    "3dml": "text/vnd.in3d.3dml",
    "spot": "text/vnd.in3d.spot",
    "igs": "model/iges",
    "i2g": "application/vnd.intergeo",
    "cdy": "application/vnd.cinderella",
    "xpw": "application/vnd.intercon.formnet",
    "fcs": "application/vnd.isac.fcs",
    "ipfix": "application/ipfix",
    "cer": "application/pkix-cert",
    "pki": "application/pkixcmp",
    "crl": "application/pkix-crl",
    "pkipath": "application/pkix-pkipath",
    "igm": "application/vnd.insors.igm",
    "rcprofile": "application/vnd.ipunplugged.rcprofile",
    "irp": "application/vnd.irepository.package+xml",
    "jad": "text/vnd.sun.j2me.app-descriptor",
    "jar": "application/java-archive",
    "class": "application/java-vm",
    "jnlp": "application/x-java-jnlp-file",
    "ser": "application/java-serialized-object",
    "java": "text/x-java-source,java",
    "js": "application/javascript",
    "json": "application/json",
    "joda": "application/vnd.joost.joda-archive",
    "jpm": "video/jpm",
    "jpeg, .jpg": "image/x-citrix-jpeg",
    "pjpeg": "image/pjpeg",
    "jpgv": "video/jpeg",
    "ktz": "application/vnd.kahootz",
    "mmd": "application/vnd.chipnuts.karaoke-mmd",
    "karbon": "application/vnd.kde.karbon",
    "chrt": "application/vnd.kde.kchart",
    "kfo": "application/vnd.kde.kformula",
    "flw": "application/vnd.kde.kivio",
    "kon": "application/vnd.kde.kontour",
    "kpr": "application/vnd.kde.kpresenter",
    "ksp": "application/vnd.kde.kspread",
    "kwd": "application/vnd.kde.kword",
    "htke": "application/vnd.kenameaapp",
    "kia": "application/vnd.kidspiration",
    "kne": "application/vnd.kinar",
    "sse": "application/vnd.kodak-descriptor",
    "lasxml": "application/vnd.las.las+xml",
    "latex": "application/x-latex",
    "lbd": "application/vnd.llamagraphics.life-balance.desktop",
    "lbe": "application/vnd.llamagraphics.life-balance.exchange+xml",
    "jam": "application/vnd.jam",
    "123": "application/vnd.lotus-1-2-3",
    "apr": "application/vnd.lotus-approach",
    "pre": "application/vnd.lotus-freelance",
    "nsf": "application/vnd.lotus-notes",
    "org": "application/vnd.lotus-organizer",
    "scm": "application/vnd.lotus-screencam",
    "lwp": "application/vnd.lotus-wordpro",
    "lvp": "audio/vnd.lucent.voice",
    "m3u": "audio/x-mpegurl",
    "m4v": "video/x-m4v",
    "hqx": "application/mac-binhex40",
    "portpkg": "application/vnd.macports.portpkg",
    "mgp": "application/vnd.osgeo.mapguide.package",
    "mrc": "application/marc",
    "mrcx": "application/marcxml+xml",
    "mxf": "application/mxf",
    "nbp": "application/vnd.wolfram.player",
    "ma": "application/mathematica",
    "mathml": "application/mathml+xml",
    "mbox": "application/mbox",
    "mc1": "application/vnd.medcalcdata",
    "mscml": "application/mediaservercontrol+xml",
    "cdkey": "application/vnd.mediastation.cdkey",
    "mwf": "application/vnd.mfer",
    "mfm": "application/vnd.mfmp",
    "msh": "model/mesh",
    "mads": "application/mads+xml",
    "mets": "application/mets+xml",
    "mods": "application/mods+xml",
    "meta4": "application/metalink4+xml",
    "mcd": "application/vnd.mcd",
    "flo": "application/vnd.micrografx.flo",
    "igx": "application/vnd.micrografx.igx",
    "es3": "application/vnd.eszigno3+xml",
    "mdb": "application/x-msaccess",
    "asf": "video/x-ms-asf",
    "exe": "application/x-msdownload",
    "cil": "application/vnd.ms-artgalry",
    "cab": "application/vnd.ms-cab-compressed",
    "ims": "application/vnd.ms-ims",
    "application": "application/x-ms-application",
    "clp": "application/x-msclip",
    "mdi": "image/vnd.ms-modi",
    "eot": "application/vnd.ms-fontobject",
    "xls": "application/vnd.ms-excel",
    "xlam": "application/vnd.ms-excel.addin.macroenabled.12",
    "xlsb": "application/vnd.ms-excel.sheet.binary.macroenabled.12",
    "xltm": "application/vnd.ms-excel.template.macroenabled.12",
    "xlsm": "application/vnd.ms-excel.sheet.macroenabled.12",
    "chm": "application/vnd.ms-htmlhelp",
    "crd": "application/x-mscardfile",
    "lrm": "application/vnd.ms-lrm",
    "mvb": "application/x-msmediaview",
    "mny": "application/x-msmoney",
    "pptx": "application/vnd.openxmlformats-officedocument.presentationml.presentation",
    "sldx": "application/vnd.openxmlformats-officedocument.presentationml.slide",
    "ppsx": "application/vnd.openxmlformats-officedocument.presentationml.slideshow",
    "potx": "application/vnd.openxmlformats-officedocument.presentationml.template",
    "xlsx": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
    "xltx": "application/vnd.openxmlformats-officedocument.spreadsheetml.template",
    "docx": "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
    "dotx": "application/vnd.openxmlformats-officedocument.wordprocessingml.template",
    "obd": "application/x-msbinder",
    "thmx": "application/vnd.ms-officetheme",
    "onetoc": "application/onenote",
    "pya": "audio/vnd.ms-playready.media.pya",
    "pyv": "video/vnd.ms-playready.media.pyv",
    "ppt": "application/vnd.ms-powerpoint",
    "ppam": "application/vnd.ms-powerpoint.addin.macroenabled.12",
    "sldm": "application/vnd.ms-powerpoint.slide.macroenabled.12",
    "pptm": "application/vnd.ms-powerpoint.presentation.macroenabled.12",
    "ppsm": "application/vnd.ms-powerpoint.slideshow.macroenabled.12",
    "potm": "application/vnd.ms-powerpoint.template.macroenabled.12",
    "mpp": "application/vnd.ms-project",
    "pub": "application/x-mspublisher",
    "scd": "application/x-msschedule",
    "xap": "application/x-silverlight-app",
    "stl": "application/vnd.ms-pki.stl",
    "cat": "application/vnd.ms-pki.seccat",
    "vsd": "application/vnd.visio",
    "vsdx": "application/vnd.visio2013",
    "wm": "video/x-ms-wm",
    "wma": "audio/x-ms-wma",
    "wax": "audio/x-ms-wax",
    "wmx": "video/x-ms-wmx",
    "wmd": "application/x-ms-wmd",
    "wpl": "application/vnd.ms-wpl",
    "wmz": "application/x-ms-wmz",
    "wmv": "video/x-ms-wmv",
    "wvx": "video/x-ms-wvx",
    "wmf": "application/x-msmetafile",
    "trm": "application/x-msterminal",
    "doc": "application/msword",
    "docm": "application/vnd.ms-word.document.macroenabled.12",
    "dotm": "application/vnd.ms-word.template.macroenabled.12",
    "wri": "application/x-mswrite",
    "wps": "application/vnd.ms-works",
    "xbap": "application/x-ms-xbap",
    "xps": "application/vnd.ms-xpsdocument",
    "mid": "audio/midi",
    "mpy": "application/vnd.ibm.minipay",
    "afp": "application/vnd.ibm.modcap",
    "rms": "application/vnd.jcp.javame.midlet-rms",
    "tmo": "application/vnd.tmobile-livetv",
    "prc": "application/x-mobipocket-ebook",
    "mbk": "application/vnd.mobius.mbk",
    "dis": "application/vnd.mobius.dis",
    "plc": "application/vnd.mobius.plc",
    "mqy": "application/vnd.mobius.mqy",
    "msl": "application/vnd.mobius.msl",
    "txf": "application/vnd.mobius.txf",
    "daf": "application/vnd.mobius.daf",
    "fly": "text/vnd.fly",
    "mpc": "application/vnd.mophun.certificate",
    "mpn": "application/vnd.mophun.application",
    "mj2": "video/mj2",
    "mpga": "audio/mpeg",
    "mxu": "video/vnd.mpegurl",
    "mpeg": "video/mpeg",
    "m21": "application/mp21",
    "mp4a": "audio/mp4",
    "mp4": "application/mp4",
    "m3u8": "application/vnd.apple.mpegurl",
    "mus": "application/vnd.musician",
    "msty": "application/vnd.muvee.style",
    "mxml": "application/xv+xml",
    "ngdat": "application/vnd.nokia.n-gage.data",
    "n-gage": "application/vnd.nokia.n-gage.symbian.install",
    "ncx": "application/x-dtbncx+xml",
    "nc": "application/x-netcdf",
    "nlu": "application/vnd.neurolanguage.nlu",
    "dna": "application/vnd.dna",
    "nnd": "application/vnd.noblenet-directory",
    "nns": "application/vnd.noblenet-sealer",
    "nnw": "application/vnd.noblenet-web",
    "rpst": "application/vnd.nokia.radio-preset",
    "rpss": "application/vnd.nokia.radio-presets",
    "n3": "text/n3",
    "edm": "application/vnd.novadigm.edm",
    "edx": "application/vnd.novadigm.edx",
    "ext": "application/vnd.novadigm.ext",
    "gph": "application/vnd.flographit",
    "ecelp4800": "audio/vnd.nuera.ecelp4800",
    "ecelp7470": "audio/vnd.nuera.ecelp7470",
    "ecelp9600": "audio/vnd.nuera.ecelp9600",
    "oda": "application/oda",
    "ogx": "application/ogg",
    "oga": "audio/ogg",
    "ogv": "video/ogg",
    "dd2": "application/vnd.oma.dd2+xml",
    "oth": "application/vnd.oasis.opendocument.text-web",
    "opf": "application/oebps-package+xml",
    "qbo": "application/vnd.intu.qbo",
    "oxt": "application/vnd.openofficeorg.extension",
    "osf": "application/vnd.yamaha.openscoreformat",
    "weba": "audio/webm",
    "webm": "video/webm",
    "odc": "application/vnd.oasis.opendocument.chart",
    "otc": "application/vnd.oasis.opendocument.chart-template",
    "odb": "application/vnd.oasis.opendocument.database",
    "odf": "application/vnd.oasis.opendocument.formula",
    "odft": "application/vnd.oasis.opendocument.formula-template",
    "odg": "application/vnd.oasis.opendocument.graphics",
    "otg": "application/vnd.oasis.opendocument.graphics-template",
    "odi": "application/vnd.oasis.opendocument.image",
    "oti": "application/vnd.oasis.opendocument.image-template",
    "odp": "application/vnd.oasis.opendocument.presentation",
    "otp": "application/vnd.oasis.opendocument.presentation-template",
    "ods": "application/vnd.oasis.opendocument.spreadsheet",
    "ots": "application/vnd.oasis.opendocument.spreadsheet-template",
    "odt": "application/vnd.oasis.opendocument.text",
    "odm": "application/vnd.oasis.opendocument.text-master",
    "ott": "application/vnd.oasis.opendocument.text-template",
    "ktx": "image/ktx",
    "sxc": "application/vnd.sun.xml.calc",
    "stc": "application/vnd.sun.xml.calc.template",
    "sxd": "application/vnd.sun.xml.draw",
    "std": "application/vnd.sun.xml.draw.template",
    "sxi": "application/vnd.sun.xml.impress",
    "sti": "application/vnd.sun.xml.impress.template",
    "sxm": "application/vnd.sun.xml.math",
    "sxw": "application/vnd.sun.xml.writer",
    "sxg": "application/vnd.sun.xml.writer.global",
    "stw": "application/vnd.sun.xml.writer.template",
    "otf": "application/x-font-otf",
    "osfpvg": "application/vnd.yamaha.openscoreformat.osfpvg+xml",
    "dp": "application/vnd.osgi.dp",
    "pdb": "application/vnd.palm",
    "p": "text/x-pascal",
    "paw": "application/vnd.pawaafile",
    "pclxl": "application/vnd.hp-pclxl",
    "efif": "application/vnd.picsel",
    "pcx": "image/x-pcx",
    "psd": "image/vnd.adobe.photoshop",
    "prf": "application/pics-rules",
    "pic": "image/x-pict",
    "chat": "application/x-chat",
    "p10": "application/pkcs10",
    "p12": "application/x-pkcs12",
    "p7m": "application/pkcs7-mime",
    "p7s": "application/pkcs7-signature",
    "p7r": "application/x-pkcs7-certreqresp",
    "p7b": "application/x-pkcs7-certificates",
    "p8": "application/pkcs8",
    "plf": "application/vnd.pocketlearn",
    "pnm": "image/x-portable-anymap",
    "pbm": "image/x-portable-bitmap",
    "pcf": "application/x-font-pcf",
    "pfr": "application/font-tdpfr",
    "pgn": "application/x-chess-pgn",
    "pgm": "image/x-portable-graymap",
    "png": "image/x-png",
    "ppm": "image/x-portable-pixmap",
    "pskcxml": "application/pskc+xml",
    "pml": "application/vnd.ctc-posml",
    "ai": "application/postscript",
    "pfa": "application/x-font-type1",
    "pbd": "application/vnd.powerbuilder6",
    "pgp": "application/pgp-signature",
    "box": "application/vnd.previewsystems.box",
    "ptid": "application/vnd.pvi.ptid1",
    "pls": "application/pls+xml",
    "str": "application/vnd.pg.format",
    "ei6": "application/vnd.pg.osasli",
    "dsc": "text/prs.lines.tag",
    "psf": "application/x-font-linux-psf",
    "qps": "application/vnd.publishare-delta-tree",
    "wg": "application/vnd.pmi.widget",
    "qxd": "application/vnd.quark.quarkxpress",
    "esf": "application/vnd.epson.esf",
    "msf": "application/vnd.epson.msf",
    "ssf": "application/vnd.epson.ssf",
    "qam": "application/vnd.epson.quickanime",
    "qfx": "application/vnd.intu.qfx",
    "qt": "video/quicktime",
    "rar": "application/x-rar-compressed",
    "ram": "audio/x-pn-realaudio",
    "rmp": "audio/x-pn-realaudio-plugin",
    "rsd": "application/rsd+xml",
    "rm": "application/vnd.rn-realmedia",
    "bed": "application/vnd.realvnc.bed",
    "mxl": "application/vnd.recordare.musicxml",
    "musicxml": "application/vnd.recordare.musicxml+xml",
    "rnc": "application/relax-ng-compact-syntax",
    "rdz": "application/vnd.data-vision.rdz",
    "rdf": "application/rdf+xml",
    "rp9": "application/vnd.cloanto.rp9",
    "jisp": "application/vnd.jisp",
    "rtf": "application/rtf",
    "rtx": "text/richtext",
    "link66": "application/vnd.route66.link66+xml",
    "rss, .xml": "application/rss+xml",
    "shf": "application/shf+xml",
    "st": "application/vnd.sailingtracker.track",
    "svg": "image/svg+xml",
    "sus": "application/vnd.sus-calendar",
    "sru": "application/sru+xml",
    "setpay": "application/set-payment-initiation",
    "setreg": "application/set-registration-initiation",
    "sema": "application/vnd.sema",
    "semd": "application/vnd.semd",
    "semf": "application/vnd.semf",
    "see": "application/vnd.seemail",
    "snf": "application/x-font-snf",
    "spq": "application/scvp-vp-request",
    "spp": "application/scvp-vp-response",
    "scq": "application/scvp-cv-request",
    "scs": "application/scvp-cv-response",
    "sdp": "application/sdp",
    "etx": "text/x-setext",
    "movie": "video/x-sgi-movie",
    "ifm": "application/vnd.shana.informed.formdata",
    "itp": "application/vnd.shana.informed.formtemplate",
    "iif": "application/vnd.shana.informed.interchange",
    "ipk": "application/vnd.shana.informed.package",
    "tfi": "application/thraud+xml",
    "shar": "application/x-shar",
    "rgb": "image/x-rgb",
    "slt": "application/vnd.epson.salt",
    "aso": "application/vnd.accpac.simply.aso",
    "imp": "application/vnd.accpac.simply.imp",
    "twd": "application/vnd.simtech-mindmapper",
    "csp": "application/vnd.commonspace",
    "saf": "application/vnd.yamaha.smaf-audio",
    "mmf": "application/vnd.smaf",
    "spf": "application/vnd.yamaha.smaf-phrase",
    "teacher": "application/vnd.smart.teacher",
    "svd": "application/vnd.svd",
    "rq": "application/sparql-query",
    "srx": "application/sparql-results+xml",
    "gram": "application/srgs",
    "grxml": "application/srgs+xml",
    "ssml": "application/ssml+xml",
    "skp": "application/vnd.koan",
    "sgml": "text/sgml",
    "sdc": "application/vnd.stardivision.calc",
    "sda": "application/vnd.stardivision.draw",
    "sdd": "application/vnd.stardivision.impress",
    "smf": "application/vnd.stardivision.math",
    "sdw": "application/vnd.stardivision.writer",
    "sgl": "application/vnd.stardivision.writer-global",
    "sm": "application/vnd.stepmania.stepchart",
    "sit": "application/x-stuffit",
    "sitx": "application/x-stuffitx",
    "sdkm": "application/vnd.solent.sdkm+xml",
    "xo": "application/vnd.olpc-sugar",
    "au": "audio/basic",
    "wqd": "application/vnd.wqd",
    "sis": "application/vnd.symbian.install",
    "smi": "application/smil+xml",
    "xsm": "application/vnd.syncml+xml",
    "bdm": "application/vnd.syncml.dm+wbxml",
    "xdm": "application/vnd.syncml.dm+xml",
    "sv4cpio": "application/x-sv4cpio",
    "sv4crc": "application/x-sv4crc",
    "sbml": "application/sbml+xml",
    "tsv": "text/tab-separated-values",
    "tiff": "image/tiff",
    "tao": "application/vnd.tao.intent-module-archive",
    "tar": "application/x-tar",
    "tcl": "application/x-tcl",
    "tex": "application/x-tex",
    "tfm": "application/x-tex-tfm",
    "tei": "application/tei+xml",
    "txt": "text/plain",
    "dxp": "application/vnd.spotfire.dxp",
    "sfs": "application/vnd.spotfire.sfs",
    "tsd": "application/timestamped-data",
    "tpt": "application/vnd.trid.tpt",
    "mxs": "application/vnd.triscape.mxs",
    "t": "text/troff",
    "tra": "application/vnd.trueapp",
    "ttf": "application/x-font-ttf",
    "ttl": "text/turtle",
    "umj": "application/vnd.umajin",
    "uoml": "application/vnd.uoml+xml",
    "unityweb": "application/vnd.unity",
    "ufd": "application/vnd.ufdl",
    "uri": "text/uri-list",
    "utz": "application/vnd.uiq.theme",
    "ustar": "application/x-ustar",
    "uu": "text/x-uuencode",
    "vcs": "text/x-vcalendar",
    "vcf": "text/x-vcard",
    "vcd": "application/x-cdlink",
    "vsf": "application/vnd.vsf",
    "wrl": "model/vrml",
    "vcx": "application/vnd.vcx",
    "mts": "model/vnd.mts",
    "vtu": "model/vnd.vtu",
    "vis": "application/vnd.visionary",
    "viv": "video/vnd.vivo",
    "ccxml": "application/ccxml+xml,",
    "vxml": "application/voicexml+xml",
    "src": "application/x-wais-source",
    "wbxml": "application/vnd.wap.wbxml",
    "wbmp": "image/vnd.wap.wbmp",
    "wav": "audio/x-wav",
    "davmount": "application/davmount+xml",
    "woff": "application/x-font-woff",
    "wspolicy": "application/wspolicy+xml",
    "webp": "image/webp",
    "wtb": "application/vnd.webturbo",
    "wgt": "application/widget",
    "hlp": "application/winhlp",
    "wml": "text/vnd.wap.wml",
    "wmls": "text/vnd.wap.wmlscript",
    "wmlsc": "application/vnd.wap.wmlscriptc",
    "wpd": "application/vnd.wordperfect",
    "stf": "application/vnd.wt.stf",
    "wsdl": "application/wsdl+xml",
    "xbm": "image/x-xbitmap",
    "xpm": "image/x-xpixmap",
    "xwd": "image/x-xwindowdump",
    "der": "application/x-x509-ca-cert",
    "fig": "application/x-xfig",
    "xhtml": "application/xhtml+xml",
    "xml": "application/xml",
    "xdf": "application/xcap-diff+xml",
    "xenc": "application/xenc+xml",
    "xer": "application/patch-ops-error+xml",
    "rl": "application/resource-lists+xml",
    "rs": "application/rls-services+xml",
    "rld": "application/resource-lists-diff+xml",
    "xslt": "application/xslt+xml",
    "xop": "application/xop+xml",
    "xpi": "application/x-xpinstall",
    "xspf": "application/xspf+xml",
    "xul": "application/vnd.mozilla.xul+xml",
    "xyz": "chemical/x-xyz",
    "yaml": "text/yaml",
    "yang": "application/yang",
    "yin": "application/yin+xml",
    "zir": "application/vnd.zul",
    "zip": "application/zip",
    "zmm": "application/vnd.handheld-entertainment+xml",
    "zaz": "application/vnd.zzazz.deck+xml"
}
F
Faakhir

A working method in android to populates the mapping list mime types. 

private static void fileMimeTypeMapping() {
     MIMETYPE_MAPPING.put("3gp", Collections.list("video/3gpp"));
     MIMETYPE_MAPPING.put("7z", Collections.list("application/x-7z-compressed"));
     MIMETYPE_MAPPING.put("accdb", Collections.list("application/msaccess"));
     MIMETYPE_MAPPING.put("ai", Collections.list("application/illustrator"));
     MIMETYPE_MAPPING.put("apk", Collections.list("application/vnd.android.package-archive"));
     MIMETYPE_MAPPING.put("arw", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("avi", Collections.list("video/x-msvideo"));
     MIMETYPE_MAPPING.put("bash", Collections.list("text/x-shellscript"));
     MIMETYPE_MAPPING.put("bat", Collections.list("application/x-msdos-program"));
     MIMETYPE_MAPPING.put("blend", Collections.list("application/x-blender"));
     MIMETYPE_MAPPING.put("bin", Collections.list("application/x-bin"));
     MIMETYPE_MAPPING.put("bmp", Collections.list("image/bmp"));
     MIMETYPE_MAPPING.put("bpg", Collections.list("image/bpg"));
     MIMETYPE_MAPPING.put("bz2", Collections.list("application/x-bzip2"));
     MIMETYPE_MAPPING.put("cb7", Collections.list("application/x-cbr"));
     MIMETYPE_MAPPING.put("cba", Collections.list("application/x-cbr"));
     MIMETYPE_MAPPING.put("cbr", Collections.list("application/x-cbr"));
     MIMETYPE_MAPPING.put("cbt", Collections.list("application/x-cbr"));
     MIMETYPE_MAPPING.put("cbtc", Collections.list("application/x-cbr"));
     MIMETYPE_MAPPING.put("cbz", Collections.list("application/x-cbr"));
     MIMETYPE_MAPPING.put("cc", Collections.list("text/x-c"));
     MIMETYPE_MAPPING.put("cdr", Collections.list("application/coreldraw"));
     MIMETYPE_MAPPING.put("class", Collections.list("application/java"));
     MIMETYPE_MAPPING.put("cnf", Collections.list("text/plain"));
     MIMETYPE_MAPPING.put("conf", Collections.list("text/plain"));
     MIMETYPE_MAPPING.put("cpp", Collections.list("text/x-c++src"));
     MIMETYPE_MAPPING.put("cr2", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("css", Collections.list("text/css"));
     MIMETYPE_MAPPING.put("csv", Collections.list("text/csv"));
     MIMETYPE_MAPPING.put("cvbdl", Collections.list("application/x-cbr"));
     MIMETYPE_MAPPING.put("c", Collections.list("text/x-c"));
     MIMETYPE_MAPPING.put("c++", Collections.list("text/x-c++src"));
     MIMETYPE_MAPPING.put("dcr", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("deb", Collections.list("application/x-deb"));
     MIMETYPE_MAPPING.put("dng", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("doc", Collections.list("application/msword"));
     MIMETYPE_MAPPING.put("docm", Collections.list("application/vnd.ms-word.document.macroEnabled.12"));
     MIMETYPE_MAPPING.put("docx", Collections.list("application/vnd.openxmlformats-officedocument.wordprocessingml.document"));
     MIMETYPE_MAPPING.put("dot", Collections.list("application/msword"));
     MIMETYPE_MAPPING.put("dotx", Collections.list("application/vnd.openxmlformats-officedocument.wordprocessingml.template"));
     MIMETYPE_MAPPING.put("dv", Collections.list("video/dv"));
     MIMETYPE_MAPPING.put("eot", Collections.list("application/vnd.ms-fontobject"));
     MIMETYPE_MAPPING.put("epub", Collections.list("application/epub+zip"));
     MIMETYPE_MAPPING.put("eps", Collections.list("application/postscript"));
     MIMETYPE_MAPPING.put("erf", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("exe", Collections.list("application/x-ms-dos-executable"));
     MIMETYPE_MAPPING.put("flac", Collections.list("audio/flac"));
     MIMETYPE_MAPPING.put("flv", Collections.list("video/x-flv"));
     MIMETYPE_MAPPING.put("gif", Collections.list("image/gif"));
     MIMETYPE_MAPPING.put("gpx", Collections.list("application/gpx+xml"));
     MIMETYPE_MAPPING.put("gz", Collections.list("application/gzip"));
     MIMETYPE_MAPPING.put("gzip", Collections.list("application/gzip"));
     MIMETYPE_MAPPING.put("h", Collections.list("text/x-h"));
     MIMETYPE_MAPPING.put("heic", Collections.list("image/heic"));
     MIMETYPE_MAPPING.put("heif", Collections.list("image/heif"));
     MIMETYPE_MAPPING.put("hh", Collections.list("text/x-h"));
     MIMETYPE_MAPPING.put("hpp", Collections.list("text/x-h"));
     MIMETYPE_MAPPING.put("htaccess", Collections.list("text/plain"));
     MIMETYPE_MAPPING.put("ical", Collections.list("text/calendar"));
     MIMETYPE_MAPPING.put("ics", Collections.list("text/calendar"));
     MIMETYPE_MAPPING.put("iiq", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("impress", Collections.list("text/impress"));
     MIMETYPE_MAPPING.put("java", Collections.list("text/x-java-source"));
     MIMETYPE_MAPPING.put("jp2", Collections.list("image/jp2"));
     MIMETYPE_MAPPING.put("jpeg", Collections.list("image/jpeg"));
     MIMETYPE_MAPPING.put("jpg", Collections.list("image/jpeg"));
     MIMETYPE_MAPPING.put("jps", Collections.list("image/jpeg"));
     MIMETYPE_MAPPING.put("k25", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("kdc", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("key", Collections.list("application/x-iwork-keynote-sffkey"));
     MIMETYPE_MAPPING.put("keynote", Collections.list("application/x-iwork-keynote-sffkey"));
     MIMETYPE_MAPPING.put("kml", Collections.list("application/vnd.google-earth.kml+xml"));
     MIMETYPE_MAPPING.put("kmz", Collections.list("application/vnd.google-earth.kmz"));
     MIMETYPE_MAPPING.put("kra", Collections.list("application/x-krita"));
     MIMETYPE_MAPPING.put("ldif", Collections.list("text/x-ldif"));
     MIMETYPE_MAPPING.put("love", Collections.list("application/x-love-game"));
     MIMETYPE_MAPPING.put("lwp", Collections.list("application/vnd.lotus-wordpro"));
     MIMETYPE_MAPPING.put("m2t", Collections.list("video/mp2t"));
     MIMETYPE_MAPPING.put("m3u", Collections.list("audio/mpegurl"));
     MIMETYPE_MAPPING.put("m3u8", Collections.list("audio/mpegurl"));
     MIMETYPE_MAPPING.put("m4a", Collections.list("audio/mp4"));
     MIMETYPE_MAPPING.put("m4b", Collections.list("audio/m4b"));
     MIMETYPE_MAPPING.put("m4v", Collections.list("video/mp4"));
     MIMETYPE_MAPPING.put("markdown", Collections.list(MIMETYPE_TEXT_MARKDOWN));
     MIMETYPE_MAPPING.put("mdown", Collections.list(MIMETYPE_TEXT_MARKDOWN));
     MIMETYPE_MAPPING.put("md", Collections.list(MIMETYPE_TEXT_MARKDOWN));
     MIMETYPE_MAPPING.put("mdb", Collections.list("application/msaccess"));
     MIMETYPE_MAPPING.put("mdwn", Collections.list(MIMETYPE_TEXT_MARKDOWN));
     MIMETYPE_MAPPING.put("mkd", Collections.list(MIMETYPE_TEXT_MARKDOWN));
     MIMETYPE_MAPPING.put("mef", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("mkv", Collections.list("video/x-matroska"));
     MIMETYPE_MAPPING.put("mobi", Collections.list("application/x-mobipocket-ebook"));
     MIMETYPE_MAPPING.put("mov", Collections.list("video/quicktime"));
     MIMETYPE_MAPPING.put("mp3", Collections.list("audio/mpeg"));
     MIMETYPE_MAPPING.put("mp4", Collections.list("video/mp4"));
     MIMETYPE_MAPPING.put("mpeg", Collections.list("video/mpeg"));
     MIMETYPE_MAPPING.put("mpg", Collections.list("video/mpeg"));
     MIMETYPE_MAPPING.put("mpo", Collections.list("image/jpeg"));
     MIMETYPE_MAPPING.put("msi", Collections.list("application/x-msi"));
     MIMETYPE_MAPPING.put("mts", Collections.list("video/MP2T"));
     MIMETYPE_MAPPING.put("mt2s", Collections.list("video/MP2T"));
     MIMETYPE_MAPPING.put("nef", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("numbers", Collections.list("application/x-iwork-numbers-sffnumbers"));
     MIMETYPE_MAPPING.put("odf", Collections.list("application/vnd.oasis.opendocument.formula"));
     MIMETYPE_MAPPING.put("odg", Collections.list("application/vnd.oasis.opendocument.graphics"));
     MIMETYPE_MAPPING.put("odp", Collections.list("application/vnd.oasis.opendocument.presentation"));
     MIMETYPE_MAPPING.put("ods", Collections.list("application/vnd.oasis.opendocument.spreadsheet"));
     MIMETYPE_MAPPING.put("odt", Collections.list("application/vnd.oasis.opendocument.text"));
     MIMETYPE_MAPPING.put("oga", Collections.list("audio/ogg"));
     MIMETYPE_MAPPING.put("ogg", Collections.list("audio/ogg"));
     MIMETYPE_MAPPING.put("ogv", Collections.list("video/ogg"));
     MIMETYPE_MAPPING.put("one", Collections.list("application/msonenote"));
     MIMETYPE_MAPPING.put("opus", Collections.list("audio/ogg"));
     MIMETYPE_MAPPING.put("orf", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("otf", Collections.list("application/font-sfnt"));
     MIMETYPE_MAPPING.put("pages", Collections.list("application/x-iwork-pages-sffpages"));
     MIMETYPE_MAPPING.put("pdf", Collections.list("application/pdf"));
     MIMETYPE_MAPPING.put("pfb", Collections.list("application/x-font"));
     MIMETYPE_MAPPING.put("pef", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("php", Collections.list("application/x-php"));
     MIMETYPE_MAPPING.put("pl", Collections.list("application/x-perl"));
     MIMETYPE_MAPPING.put("pls", Collections.list("audio/x-scpls"));
     MIMETYPE_MAPPING.put("png", Collections.list("image/png"));
     MIMETYPE_MAPPING.put("pot", Collections.list("application/vnd.ms-powerpoint"));
     MIMETYPE_MAPPING.put("potm", Collections.list("application/vnd.ms-powerpoint.template.macroEnabled.12"));
     MIMETYPE_MAPPING.put("potx", Collections.list("application/vnd.openxmlformats-officedocument.presentationml.template"));
     MIMETYPE_MAPPING.put("ppa", Collections.list("application/vnd.ms-powerpoint"));
     MIMETYPE_MAPPING.put("ppam", Collections.list("application/vnd.ms-powerpoint.addin.macroEnabled.12"));
     MIMETYPE_MAPPING.put("pps", Collections.list("application/vnd.ms-powerpoint"));
     MIMETYPE_MAPPING.put("ppsm", Collections.list("application/vnd.ms-powerpoint.slideshow.macroEnabled.12"));
     MIMETYPE_MAPPING.put("ppsx", Collections.list("application/vnd.openxmlformats-officedocument.presentationml.slideshow"));
     MIMETYPE_MAPPING.put("ppt", Collections.list("application/vnd.ms-powerpoint"));
     MIMETYPE_MAPPING.put("pptm", Collections.list("application/vnd.ms-powerpoint.presentation.macroEnabled.12"));
     MIMETYPE_MAPPING.put("pptx", Collections.list("application/vnd.openxmlformats-officedocument.presentationml.presentation"));
     MIMETYPE_MAPPING.put("ps", Collections.list("application/postscript"));
     MIMETYPE_MAPPING.put("psd", Collections.list("application/x-photoshop"));
     MIMETYPE_MAPPING.put("py", Collections.list("text/x-python"));
     MIMETYPE_MAPPING.put("raf", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("rar", Collections.list("application/x-rar-compressed"));
     MIMETYPE_MAPPING.put("reveal", Collections.list("text/reveal"));
     MIMETYPE_MAPPING.put("rss", Collections.list("application/rss+xml"));
     MIMETYPE_MAPPING.put("rtf", Collections.list("application/rtf"));
     MIMETYPE_MAPPING.put("rw2", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("schema", Collections.list("text/plain"));
     MIMETYPE_MAPPING.put("sgf", Collections.list("application/sgf"));
     MIMETYPE_MAPPING.put("sh-lib", Collections.list("text/x-shellscript"));
     MIMETYPE_MAPPING.put("sh", Collections.list("text/x-shellscript"));
     MIMETYPE_MAPPING.put("srf", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("sr2", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("tar", Collections.list("application/x-tar"));
     MIMETYPE_MAPPING.put("tar.bz2", Collections.list("application/x-bzip2"));
     MIMETYPE_MAPPING.put("tar.gz", Collections.list("application/x-compressed"));
     MIMETYPE_MAPPING.put("tbz2", Collections.list("application/x-bzip2"));
     MIMETYPE_MAPPING.put("tcx", Collections.list("application/vnd.garmin.tcx+xml"));
     MIMETYPE_MAPPING.put("tex", Collections.list("application/x-tex"));
     MIMETYPE_MAPPING.put("tgz", Collections.list("application/x-compressed"));
     MIMETYPE_MAPPING.put("tiff", Collections.list("image/tiff"));
     MIMETYPE_MAPPING.put("tif", Collections.list("image/tiff"));
     MIMETYPE_MAPPING.put("ttf", Collections.list("application/font-sfnt"));
     MIMETYPE_MAPPING.put("txt", Collections.list("text/plain"));
     MIMETYPE_MAPPING.put("vcard", Collections.list("text/vcard"));
     MIMETYPE_MAPPING.put("vcf", Collections.list("text/vcard"));
     MIMETYPE_MAPPING.put("vob", Collections.list("video/dvd"));
     MIMETYPE_MAPPING.put("vsd", Collections.list("application/vnd.visio"));
     MIMETYPE_MAPPING.put("vsdm", Collections.list("application/vnd.ms-visio.drawing.macroEnabled.12"));
     MIMETYPE_MAPPING.put("vsdx", Collections.list("application/vnd.ms-visio.drawing"));
     MIMETYPE_MAPPING.put("vssm", Collections.list("application/vnd.ms-visio.stencil.macroEnabled.12"));
     MIMETYPE_MAPPING.put("vssx", Collections.list("application/vnd.ms-visio.stencil"));
     MIMETYPE_MAPPING.put("vstm", Collections.list("application/vnd.ms-visio.template.macroEnabled.12"));
     MIMETYPE_MAPPING.put("vstx", Collections.list("application/vnd.ms-visio.template"));
     MIMETYPE_MAPPING.put("wav", Collections.list("audio/wav"));
     MIMETYPE_MAPPING.put("webm", Collections.list("video/webm"));
     MIMETYPE_MAPPING.put("woff", Collections.list("application/font-woff"));
     MIMETYPE_MAPPING.put("wpd", Collections.list("application/vnd.wordperfect"));
     MIMETYPE_MAPPING.put("wmv", Collections.list("video/x-ms-wmv"));
     MIMETYPE_MAPPING.put("xcf", Collections.list("application/x-gimp"));
     MIMETYPE_MAPPING.put("xla", Collections.list("application/vnd.ms-excel"));
     MIMETYPE_MAPPING.put("xlam", Collections.list("application/vnd.ms-excel.addin.macroEnabled.12"));
     MIMETYPE_MAPPING.put("xls", Collections.list("application/vnd.ms-excel"));
     MIMETYPE_MAPPING.put("xlsb", Collections.list("application/vnd.ms-excel.sheet.binary.macroEnabled.12"));
     MIMETYPE_MAPPING.put("xlsm", Collections.list("application/vnd.ms-excel.sheet.macroEnabled.12"));
     MIMETYPE_MAPPING.put("xlsx", Collections.list("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"));
     MIMETYPE_MAPPING.put("xlt", Collections.list("application/vnd.ms-excel"));
     MIMETYPE_MAPPING.put("xltm", Collections.list("application/vnd.ms-excel.template.macroEnabled.12"));
     MIMETYPE_MAPPING.put("xltx", Collections.list("application/vnd.openxmlformats-officedocument.spreadsheetml.template"));
     MIMETYPE_MAPPING.put("xrf", Collections.list("image/x-dcraw"));
     MIMETYPE_MAPPING.put("yaml", Arrays.asList("application/yaml", "text/plain"));
     MIMETYPE_MAPPING.put("yml", Arrays.asList("application/yaml", "text/plain"));
     MIMETYPE_MAPPING.put("zip", Collections.list("application/zip"));
     MIMETYPE_MAPPING.put("url", Collections.list("application/internet-shortcut"));
     MIMETYPE_MAPPING.put("webloc", Collections.list("application/internet-shortcut"));
     MIMETYPE_MAPPING.put("js", Arrays.asList("application/javascript", "text/plain"));
     MIMETYPE_MAPPING.put("json", Arrays.asList("application/json", "text/plain"));
     MIMETYPE_MAPPING.put("fb2", Arrays.asList("application/x-fictionbook+xml", "text/plain"));
     MIMETYPE_MAPPING.put("html", Arrays.asList("text/html", "text/plain"));
     MIMETYPE_MAPPING.put("htm", Arrays.asList("text/html", "text/plain"));
     MIMETYPE_MAPPING.put("m", Arrays.asList("text/x-matlab", "text/plain"));
     MIMETYPE_MAPPING.put("svg", Arrays.asList("image/svg+xml", "text/plain"));
     MIMETYPE_MAPPING.put("swf", Arrays.asList("application/x-shockwave-flash", "application/octet-stream"));
     MIMETYPE_MAPPING.put("xml", Arrays.asList("application/xml", "text/plain"));

}
j
jainashish

This post will explore various approaches of fetching MIME Type across various programming languages with their CONS in one-line description as header. So, use them accordingly and the one which works for you.

For eg. the code below is especially helpful when user may supply either of .xls, .xlsx or .xlsm and you don't want to write code testing extension and supplying MIME-type for each of them. Let the system do this job.

Python 3

Using python-magic 

>>> pip install python-magic
>>> import magic
>>> magic.from_file("Employee.pdf", mime=True)
'application/pdf'

Using built-in mimeypes module - Map filenames to MimeTypes modules 

>>> import mimetypes
>>> mimetypes.init()
>>> mimetypes.knownfiles
['/etc/mime.types', '/etc/httpd/mime.types', ... ]
>>> mimetypes.suffix_map['.tgz']
'.tar.gz'
>>> mimetypes.encodings_map['.gz']
'gzip'
>>> mimetypes.types_map['.tgz']
'application/x-tar-gz'

JAVA 7

Source: Baeldung's blog on File MIME Types in Java

Operating System dependent 

@Test
public void get_JAVA7_mimetype() {
    Path path = new File("Employee.xlsx").toPath();
    String mimeType = Files.probeContentType(path);

    assertEquals(mimeType, "application/vnd.ms-excel");
}

It will use FileTypeDetector implementations to probe the MIME type and invokes the probeContentType of each implementation to resolve the type. Hence, if the file is known to the implementations then the content type is returned. However, if that doesn’t happen, a system-default file type detector is invoked.

Resolve using first few characters of the input stream 

@Test
public void getMIMEType_from_Extension(){
    File file = new File("Employee.xlsx");
    String mimeType = URLConnection.guessContentTypeFromName(file.getName());

    assertEquals(mimeType, "application/vnd.ms-excel");
}

Using built-in table of MIME types 

@Test
public void getMIMEType_UsingGetFileNameMap(){
    File file = new File("Employee.xlsx");
    FileNameMap fileNameMap = URLConnection.getFileNameMap();
    String mimeType = fileNameMap.getContentTypeFor(file.getName());

    assertEquals(mimeType, "image/png");
}

It returns the matrix of MIME types used by all instances of URLConnection which then is used to resolve the input file type. However, this matrix of MIME types is very limited when it comes to URLConnection.

By default, the class uses content-types.properties file in JRE_HOME/lib. We can, however, extend it, by specifying a user-specific table using the content.types.user.table property: 

System.setProperty("content.types.user.table","<path-to-file>");

JavaScript

Source: FileReader API & Medium's article on using Magic Numbers in JavaScript to get Mime Types

Interpret the Magic Number fetched using FileReader API

Final result looks something like this when one use javaScript to fetch the MimeType based on filestream. Open the embedded jsFiddle to see and understand this approach.

Bonus: It's accessible for most of the MIME Types and also you can add custom Mime Types in the getMimetype function. Also, it has FULL SUPPORT for MS Office Files Mime Types.

https://i.stack.imgur.com/7Aoxu.png

The steps to calculate mime type for a file in this example would be:

The user selects a file. Take the first 4 bytes of the file using the slice method. Create a new FileReader instance Use the FileReader to read the 4 bytes you sliced out as an array buffer. Since the array buffer is just a generic way to represent a binary buffer we need to create a TypedArray, in this case an Uint8Array. With a TypedArray at our hands we can retrieve every byte and transform it to hexadecimal (by using toString(16)). We now have a way to get the magic numbers from a file by reading the first four bytes. The final step is to map it to a real mime type.

https://i.stack.imgur.com/WwIKx.png

https://i.stack.imgur.com/Vo49A.png

const uploads = [] const fileSelector = document.getElementById('file-selector') fileSelector.addEventListener('change', (event) => { console.time('FileOpen') const file = event.target.files[0] const filereader = new FileReader() filereader.onloadend = function(evt) { if (evt.target.readyState === FileReader.DONE) { const uint = new Uint8Array(evt.target.result) let bytes = [] uint.forEach((byte) => { bytes.push(byte.toString(16)) }) const hex = bytes.join('').toUpperCase() uploads.push({ filename: file.name, filetype: file.type ? file.type : 'Unknown/Extension missing', binaryFileType: getMimetype(hex), hex: hex }) render() } console.timeEnd('FileOpen') } const blob = file.slice(0, 4); filereader.readAsArrayBuffer(blob); }) const render = () => { const container = document.getElementById('files') const uploadedFiles = uploads.map((file) => { return `

Filename: ${file.filename}
File Object (Mime Type): ${file.filetype}
Binary (Mime Type): ${file.binaryFileType}
Hex Code (Magic Number): ${file.hex}
` }) container.innerHTML = uploadedFiles.join('') } const getMimetype = (signature) => { switch (signature) { case '89504E47': return 'image/png' case '47494638': return 'image/gif' case '25504446': return 'application/pdf' case 'FFD8FFDB': case 'FFD8FFE0': case 'FFD8FFE1': return 'image/jpeg' case '504B0304': return 'application/zip' case '504B34': return 'application/vnd.ms-excel.sheet.macroEnabled.12' default: return 'Unknown filetype' } } .result { font-family: Palatino, "Palatino Linotype", "Palatino LT STD", "Book Antiqua", Georgia, serif; line-height: 20px; font-size: 14px; margin: 10px 0; } .filename { color: #333; font-size: 16px; } .fileObject { color: #a53; } .binaryObject { color: #63f; } .HexCode { color: #262; } em { padding: 2px 4px; background-color: #efefef; font-style: normal; } input[type=file] { background-color: #4CAF50; border: none; color: white; padding: 8px 16px; text-decoration: none; margin: 4px 2px; cursor: pointer; }

T
TRiG

In case anyone wants the answer of Dirk Vollmar in a C# switch statement: 

case "doc": return "application/msword";
case "dot": return "application/msword";
case "docx": return "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
case "dotx": return "application/vnd.openxmlformats-officedocument.wordprocessingml.template";
case "docm": return "application/vnd.ms-word.document.macroEnabled.12";
case "dotm": return "application/vnd.ms-word.template.macroEnabled.12";
case "xls": return "application/vnd.ms-excel";
case "xlt": return "application/vnd.ms-excel";
case "xla": return "application/vnd.ms-excel";
case "xlsx": return "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
case "xltx": return "application/vnd.openxmlformats-officedocument.spreadsheetml.template";
case "xlsm": return "application/vnd.ms-excel.sheet.macroEnabled.12";
case "xltm": return "application/vnd.ms-excel.template.macroEnabled.12";
case "xlam": return "application/vnd.ms-excel.addin.macroEnabled.12";
case "xlsb": return "application/vnd.ms-excel.sheet.binary.macroEnabled.12";
case "ppt": return "application/vnd.ms-powerpoint";
case "pot": return "application/vnd.ms-powerpoint";
case "pps": return "application/vnd.ms-powerpoint";
case "ppa": return "application/vnd.ms-powerpoint";
case "pptx": return "application/vnd.openxmlformats-officedocument.presentationml.presentation";
case "potx": return "application/vnd.openxmlformats-officedocument.presentationml.template";
case "ppsx": return "application/vnd.openxmlformats-officedocument.presentationml.slideshow";
case "ppam": return "application/vnd.ms-powerpoint.addin.macroEnabled.12";
case "pptm": return "application/vnd.ms-powerpoint.presentation.macroEnabled.12";
case "potm": return "application/vnd.ms-powerpoint.template.macroEnabled.12";
case "ppsm": return "application/vnd.ms-powerpoint.slideshow.macroEnabled.12";
case "mdb": return "application/vnd.ms-access";
C
Community

Swift4 

 func mimeTypeForPath(path: String) -> String {
        let url = NSURL(fileURLWithPath: path)
        let pathExtension = url.pathExtension

        if let uti = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, pathExtension! as NSString, nil)?.takeRetainedValue() {
            if let mimetype = UTTypeCopyPreferredTagWithClass(uti, kUTTagClassMIMEType)?.takeRetainedValue() {
                return mimetype as String
            }
        }
        return "application/octet-stream"
    }
Don't forget to import MobileCoreServices
P
Peter Mortensen

To load a .docx file: 

    if let htmlFile = Bundle.main.path(forResource: "fileName", ofType: "docx") {
        let url = URL(fileURLWithPath: htmlFile)
        do{
            let data = try Data(contentsOf: url)
            self.webView.load(data, mimeType: "application/vnd.openxmlformats-officedocument.wordprocessingml.document", textEncodingName: "UTF-8", baseURL: url)
        }catch{
            print("errrr")
        }
    }
F
Fendi

WPS spreadsheet : 

application/wps-office.xlsx
Please add further details to expand on your answer, such as working code or documentation citations.
I substituted application/wps-office.xlsx by application/wps-office.xltx and it works fine, especially on Firefox . It saves me. I recommand the answer. What I can deduce is that we can substitute .xlsx with any office extension, and it stills work fine

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