如何从内容类型获取文件扩展名？

您的两个关键类是MediaTypeRegistry和MimeTypes。使用这些功能，您可以执行基于 mime 类型魔术的检测，并获取有关 mime 类型及其关系的信息。

（也就是说，如果你想做一个完整的检测，可能涉及使用Tika Parsers jar中基于容器的格式的额外逻辑对文件进行一些解析，你应该使用TikaConfig.getDetector（）和/或DefaultDetector。

// Load your Tika config, find all the Tika classes etc
TikaConfig config = TikaConfig.getDefaultConfig();

// Do the detection. Use DefaultDetector / getDetector() for more advanced detection
Metadata metadata = new Metadata();    
InputStream stream = TikaInputStream.get(new File(file), metadata);
MediaType mediaType = config.getMimeRepository().detect(stream);

// Fest the most common extension for the detected type
MimeType mimeType = config.getMimeRepository().forName(mediaType.toString());
String extension = mimeType.getExtension();

这个问题的问题在于，几个扩展可以产生相同的MimeType，反之亦然很简单，你可以在许多utils类中找到它，例如：MimetypesFileTypeMap，但我发现这个有用的类MimeTypes和我做了一个小技巧添加一个扩展映射，记住这个返回MimeType的默认扩展，但可能不准确。

// Copyright (c) 2003-2009, Jodd Team (jodd.org). All Rights Reserved.

 package co.tmunited.fs.service.util;

 import java.util.HashMap;

 /**
  * Map file extensions to MIME types. Based on the Apache mime.types file.
  * http://www.iana.org/assignments/media-types/
 */
public class MimeTypes {

public static final String MIME_APPLICATION_ANDREW_INSET = "application/andrew-inset";
public static final String MIME_APPLICATION_JSON = "application/json";
public static final String MIME_APPLICATION_ZIP = "application/zip";
public static final String MIME_APPLICATION_X_GZIP = "application/x-gzip";
public static final String MIME_APPLICATION_TGZ = "application/tgz";
public static final String MIME_APPLICATION_MSWORD = "application/msword";
public static final String MIME_APPLICATION_MSWORD_2007 = "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
public static final String MIME_APPLICATION_VND_TEXT = "application/vnd.oasis.opendocument.text";
public static final String MIME_APPLICATION_POSTSCRIPT = "application/postscript";
public static final String MIME_APPLICATION_PDF = "application/pdf";
public static final String MIME_APPLICATION_JNLP = "application/jnlp";
public static final String MIME_APPLICATION_MAC_BINHEX40 = "application/mac-binhex40";
public static final String MIME_APPLICATION_MAC_COMPACTPRO = "application/mac-compactpro";
public static final String MIME_APPLICATION_MATHML_XML = "application/mathml+xml";
public static final String MIME_APPLICATION_OCTET_STREAM = "application/octet-stream";
public static final String MIME_APPLICATION_ODA = "application/oda";
public static final String MIME_APPLICATION_RDF_XML = "application/rdf+xml";
public static final String MIME_APPLICATION_JAVA_ARCHIVE = "application/java-archive";
public static final String MIME_APPLICATION_RDF_SMIL = "application/smil";
public static final String MIME_APPLICATION_SRGS = "application/srgs";
public static final String MIME_APPLICATION_SRGS_XML = "application/srgs+xml";
public static final String MIME_APPLICATION_VND_MIF = "application/vnd.mif";
public static final String MIME_APPLICATION_VND_MSEXCEL = "application/vnd.ms-excel";
public static final String MIME_APPLICATION_VND_MSEXCEL_2007 = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
public static final String MIME_APPLICATION_VND_SPREADSHEET = "application/vnd.oasis.opendocument.spreadsheet";
public static final String MIME_APPLICATION_VND_MSPOWERPOINT = "application/vnd.ms-powerpoint";
public static final String MIME_APPLICATION_VND_RNREALMEDIA = "application/vnd.rn-realmedia";
public static final String MIME_APPLICATION_X_BCPIO = "application/x-bcpio";
public static final String MIME_APPLICATION_X_CDLINK = "application/x-cdlink";
public static final String MIME_APPLICATION_X_CHESS_PGN = "application/x-chess-pgn";
public static final String MIME_APPLICATION_X_CPIO = "application/x-cpio";
public static final String MIME_APPLICATION_X_CSH = "application/x-csh";
public static final String MIME_APPLICATION_X_DIRECTOR = "application/x-director";
public static final String MIME_APPLICATION_X_DVI = "application/x-dvi";
public static final String MIME_APPLICATION_X_FUTURESPLASH = "application/x-futuresplash";
public static final String MIME_APPLICATION_X_GTAR = "application/x-gtar";
public static final String MIME_APPLICATION_X_HDF = "application/x-hdf";
public static final String MIME_APPLICATION_X_JAVASCRIPT = "application/x-javascript";
public static final String MIME_APPLICATION_X_KOAN = "application/x-koan";
public static final String MIME_APPLICATION_X_LATEX = "application/x-latex";
public static final String MIME_APPLICATION_X_NETCDF = "application/x-netcdf";
public static final String MIME_APPLICATION_X_OGG = "application/x-ogg";
public static final String MIME_APPLICATION_X_SH = "application/x-sh";
public static final String MIME_APPLICATION_X_SHAR = "application/x-shar";
public static final String MIME_APPLICATION_X_SHOCKWAVE_FLASH = "application/x-shockwave-flash";
public static final String MIME_APPLICATION_X_STUFFIT = "application/x-stuffit";
public static final String MIME_APPLICATION_X_SV4CPIO = "application/x-sv4cpio";
public static final String MIME_APPLICATION_X_SV4CRC = "application/x-sv4crc";
public static final String MIME_APPLICATION_X_TAR = "application/x-tar";
public static final String MIME_APPLICATION_X_RAR_COMPRESSED = "application/x-rar-compressed";
public static final String MIME_APPLICATION_X_TCL = "application/x-tcl";
public static final String MIME_APPLICATION_X_TEX = "application/x-tex";
public static final String MIME_APPLICATION_X_TEXINFO = "application/x-texinfo";
public static final String MIME_APPLICATION_X_TROFF = "application/x-troff";
public static final String MIME_APPLICATION_X_TROFF_MAN = "application/x-troff-man";
public static final String MIME_APPLICATION_X_TROFF_ME = "application/x-troff-me";
public static final String MIME_APPLICATION_X_TROFF_MS = "application/x-troff-ms";
public static final String MIME_APPLICATION_X_USTAR = "application/x-ustar";
public static final String MIME_APPLICATION_X_WAIS_SOURCE = "application/x-wais-source";
public static final String MIME_APPLICATION_VND_MOZZILLA_XUL_XML = "application/vnd.mozilla.xul+xml";
public static final String MIME_APPLICATION_XHTML_XML = "application/xhtml+xml";
public static final String MIME_APPLICATION_XSLT_XML = "application/xslt+xml";
public static final String MIME_APPLICATION_XML = "application/xml";
public static final String MIME_APPLICATION_XML_DTD = "application/xml-dtd";
public static final String MIME_IMAGE_BMP = "image/bmp";
public static final String MIME_IMAGE_CGM = "image/cgm";
public static final String MIME_IMAGE_GIF = "image/gif";
public static final String MIME_IMAGE_IEF = "image/ief";
public static final String MIME_IMAGE_JPEG = "image/jpeg";
public static final String MIME_IMAGE_TIFF = "image/tiff";
public static final String MIME_IMAGE_PNG = "image/png";
public static final String MIME_IMAGE_SVG_XML = "image/svg+xml";
public static final String MIME_IMAGE_VND_DJVU = "image/vnd.djvu";
public static final String MIME_IMAGE_WAP_WBMP = "image/vnd.wap.wbmp";
public static final String MIME_IMAGE_X_CMU_RASTER = "image/x-cmu-raster";
public static final String MIME_IMAGE_X_ICON = "image/x-icon";
public static final String MIME_IMAGE_X_PORTABLE_ANYMAP = "image/x-portable-anymap";
public static final String MIME_IMAGE_X_PORTABLE_BITMAP = "image/x-portable-bitmap";
public static final String MIME_IMAGE_X_PORTABLE_GRAYMAP = "image/x-portable-graymap";
public static final String MIME_IMAGE_X_PORTABLE_PIXMAP = "image/x-portable-pixmap";
public static final String MIME_IMAGE_X_RGB = "image/x-rgb";
public static final String MIME_AUDIO_BASIC = "audio/basic";
public static final String MIME_AUDIO_MIDI = "audio/midi";
public static final String MIME_AUDIO_MPEG = "audio/mpeg";
public static final String MIME_AUDIO_X_AIFF = "audio/x-aiff";
public static final String MIME_AUDIO_X_MPEGURL = "audio/x-mpegurl";
public static final String MIME_AUDIO_X_PN_REALAUDIO = "audio/x-pn-realaudio";
public static final String MIME_AUDIO_X_WAV = "audio/x-wav";
public static final String MIME_CHEMICAL_X_PDB = "chemical/x-pdb";
public static final String MIME_CHEMICAL_X_XYZ = "chemical/x-xyz";
public static final String MIME_MODEL_IGES = "model/iges";
public static final String MIME_MODEL_MESH = "model/mesh";
public static final String MIME_MODEL_VRLM = "model/vrml";
public static final String MIME_TEXT_PLAIN = "text/plain";
public static final String MIME_TEXT_RICHTEXT = "text/richtext";
public static final String MIME_TEXT_RTF = "text/rtf";
public static final String MIME_TEXT_HTML = "text/html";
public static final String MIME_TEXT_CALENDAR = "text/calendar";
public static final String MIME_TEXT_CSS = "text/css";
public static final String MIME_TEXT_SGML = "text/sgml";
public static final String MIME_TEXT_TAB_SEPARATED_VALUES = "text/tab-separated-values";
public static final String MIME_TEXT_VND_WAP_XML = "text/vnd.wap.wml";
public static final String MIME_TEXT_VND_WAP_WMLSCRIPT = "text/vnd.wap.wmlscript";
public static final String MIME_TEXT_X_SETEXT = "text/x-setext";
public static final String MIME_TEXT_X_COMPONENT = "text/x-component";
public static final String MIME_VIDEO_QUICKTIME = "video/quicktime";
public static final String MIME_VIDEO_MPEG = "video/mpeg";
public static final String MIME_VIDEO_VND_MPEGURL = "video/vnd.mpegurl";
public static final String MIME_VIDEO_X_MSVIDEO = "video/x-msvideo";
public static final String MIME_VIDEO_X_MS_WMV = "video/x-ms-wmv";
public static final String MIME_VIDEO_X_SGI_MOVIE = "video/x-sgi-movie";
public static final String MIME_X_CONFERENCE_X_COOLTALK = "x-conference/x-cooltalk";

private static HashMap<String, String> mimeTypeMapping;
private static HashMap<String, String> extMapping;

static {
    mimeTypeMapping = new HashMap<String, String>(200) {
        private void put1(String key, String value) {
            if (put(key, value) != null) {
                throw new IllegalArgumentException("Duplicated extension: " + key);
            }
        }

        {
            put1("xul", MIME_APPLICATION_VND_MOZZILLA_XUL_XML);
            put1("json", MIME_APPLICATION_JSON);
            put1("ice", MIME_X_CONFERENCE_X_COOLTALK);
            put1("movie", MIME_VIDEO_X_SGI_MOVIE);
            put1("avi", MIME_VIDEO_X_MSVIDEO);
            put1("wmv", MIME_VIDEO_X_MS_WMV);
            put1("m4u", MIME_VIDEO_VND_MPEGURL);
            put1("mxu", MIME_VIDEO_VND_MPEGURL);
            put1("htc", MIME_TEXT_X_COMPONENT);
            put1("etx", MIME_TEXT_X_SETEXT);
            put1("wmls", MIME_TEXT_VND_WAP_WMLSCRIPT);
            put1("wml", MIME_TEXT_VND_WAP_XML);
            put1("tsv", MIME_TEXT_TAB_SEPARATED_VALUES);
            put1("sgm", MIME_TEXT_SGML);
            put1("sgml", MIME_TEXT_SGML);
            put1("css", MIME_TEXT_CSS);
            put1("ifb", MIME_TEXT_CALENDAR);
            put1("ics", MIME_TEXT_CALENDAR);
            put1("wrl", MIME_MODEL_VRLM);
            put1("vrlm", MIME_MODEL_VRLM);
            put1("silo", MIME_MODEL_MESH);
            put1("mesh", MIME_MODEL_MESH);
            put1("msh", MIME_MODEL_MESH);
            put1("iges", MIME_MODEL_IGES);
            put1("igs", MIME_MODEL_IGES);
            put1("rgb", MIME_IMAGE_X_RGB);
            put1("ppm", MIME_IMAGE_X_PORTABLE_PIXMAP);
            put1("pgm", MIME_IMAGE_X_PORTABLE_GRAYMAP);
            put1("pbm", MIME_IMAGE_X_PORTABLE_BITMAP);
            put1("pnm", MIME_IMAGE_X_PORTABLE_ANYMAP);
            put1("ico", MIME_IMAGE_X_ICON);
            put1("ras", MIME_IMAGE_X_CMU_RASTER);
            put1("wbmp", MIME_IMAGE_WAP_WBMP);
            put1("djv", MIME_IMAGE_VND_DJVU);
            put1("djvu", MIME_IMAGE_VND_DJVU);
            put1("svg", MIME_IMAGE_SVG_XML);
            put1("ief", MIME_IMAGE_IEF);
            put1("cgm", MIME_IMAGE_CGM);
            put1("bmp", MIME_IMAGE_BMP);
            put1("xyz", MIME_CHEMICAL_X_XYZ);
            put1("pdb", MIME_CHEMICAL_X_PDB);
            put1("ra", MIME_AUDIO_X_PN_REALAUDIO);
            put1("ram", MIME_AUDIO_X_PN_REALAUDIO);
            put1("m3u", MIME_AUDIO_X_MPEGURL);
            put1("aifc", MIME_AUDIO_X_AIFF);
            put1("aif", MIME_AUDIO_X_AIFF);
            put1("aiff", MIME_AUDIO_X_AIFF);
            put1("mp3", MIME_AUDIO_MPEG);
            put1("mp2", MIME_AUDIO_MPEG);
            put1("mp1", MIME_AUDIO_MPEG);
            put1("mpga", MIME_AUDIO_MPEG);
            put1("kar", MIME_AUDIO_MIDI);
            put1("mid", MIME_AUDIO_MIDI);
            put1("midi", MIME_AUDIO_MIDI);
            put1("dtd", MIME_APPLICATION_XML_DTD);
            put1("xsl", MIME_APPLICATION_XML);
            put1("xml", MIME_APPLICATION_XML);
            put1("xslt", MIME_APPLICATION_XSLT_XML);
            put1("xht", MIME_APPLICATION_XHTML_XML);
            put1("xhtml", MIME_APPLICATION_XHTML_XML);
            put1("src", MIME_APPLICATION_X_WAIS_SOURCE);
            put1("ustar", MIME_APPLICATION_X_USTAR);
            put1("ms", MIME_APPLICATION_X_TROFF_MS);
            put1("me", MIME_APPLICATION_X_TROFF_ME);
            put1("man", MIME_APPLICATION_X_TROFF_MAN);
            put1("roff", MIME_APPLICATION_X_TROFF);
            put1("tr", MIME_APPLICATION_X_TROFF);
            put1("t", MIME_APPLICATION_X_TROFF);
            put1("texi", MIME_APPLICATION_X_TEXINFO);
            put1("texinfo", MIME_APPLICATION_X_TEXINFO);
            put1("tex", MIME_APPLICATION_X_TEX);
            put1("tcl", MIME_APPLICATION_X_TCL);
            put1("sv4crc", MIME_APPLICATION_X_SV4CRC);
            put1("sv4cpio", MIME_APPLICATION_X_SV4CPIO);
            put1("sit", MIME_APPLICATION_X_STUFFIT);
            put1("swf", MIME_APPLICATION_X_SHOCKWAVE_FLASH);
            put1("shar", MIME_APPLICATION_X_SHAR);
            put1("sh", MIME_APPLICATION_X_SH);
            put1("cdf", MIME_APPLICATION_X_NETCDF);
            put1("nc", MIME_APPLICATION_X_NETCDF);
            put1("latex", MIME_APPLICATION_X_LATEX);
            put1("skm", MIME_APPLICATION_X_KOAN);
            put1("skt", MIME_APPLICATION_X_KOAN);
            put1("skd", MIME_APPLICATION_X_KOAN);
            put1("skp", MIME_APPLICATION_X_KOAN);
            put1("js", MIME_APPLICATION_X_JAVASCRIPT);
            put1("hdf", MIME_APPLICATION_X_HDF);
            put1("gtar", MIME_APPLICATION_X_GTAR);
            put1("spl", MIME_APPLICATION_X_FUTURESPLASH);
            put1("dvi", MIME_APPLICATION_X_DVI);
            put1("dxr", MIME_APPLICATION_X_DIRECTOR);
            put1("dir", MIME_APPLICATION_X_DIRECTOR);
            put1("dcr", MIME_APPLICATION_X_DIRECTOR);
            put1("csh", MIME_APPLICATION_X_CSH);
            put1("cpio", MIME_APPLICATION_X_CPIO);
            put1("pgn", MIME_APPLICATION_X_CHESS_PGN);
            put1("vcd", MIME_APPLICATION_X_CDLINK);
            put1("bcpio", MIME_APPLICATION_X_BCPIO);
            put1("rm", MIME_APPLICATION_VND_RNREALMEDIA);
            put1("ppt", MIME_APPLICATION_VND_MSPOWERPOINT);
            put1("mif", MIME_APPLICATION_VND_MIF);
            put1("grxml", MIME_APPLICATION_SRGS_XML);
            put1("gram", MIME_APPLICATION_SRGS);
            put1("smil", MIME_APPLICATION_RDF_SMIL);
            put1("smi", MIME_APPLICATION_RDF_SMIL);
            put1("rdf", MIME_APPLICATION_RDF_XML);
            put1("ogg", MIME_APPLICATION_X_OGG);
            put1("oda", MIME_APPLICATION_ODA);
            put1("dmg", MIME_APPLICATION_OCTET_STREAM);
            put1("lzh", MIME_APPLICATION_OCTET_STREAM);
            put1("so", MIME_APPLICATION_OCTET_STREAM);
            put1("lha", MIME_APPLICATION_OCTET_STREAM);
            put1("dms", MIME_APPLICATION_OCTET_STREAM);
            put1("bin", MIME_APPLICATION_OCTET_STREAM);
            put1("mathml", MIME_APPLICATION_MATHML_XML);
            put1("cpt", MIME_APPLICATION_MAC_COMPACTPRO);
            put1("hqx", MIME_APPLICATION_MAC_BINHEX40);
            put1("jnlp", MIME_APPLICATION_JNLP);
            put1("ez", MIME_APPLICATION_ANDREW_INSET);
            put1("txt", MIME_TEXT_PLAIN);
            put1("ini", MIME_TEXT_PLAIN);
            put1("c", MIME_TEXT_PLAIN);
            put1("h", MIME_TEXT_PLAIN);
            put1("cpp", MIME_TEXT_PLAIN);
            put1("cxx", MIME_TEXT_PLAIN);
            put1("cc", MIME_TEXT_PLAIN);
            put1("chh", MIME_TEXT_PLAIN);
            put1("java", MIME_TEXT_PLAIN);
            put1("csv", MIME_TEXT_PLAIN);
            put1("bat", MIME_TEXT_PLAIN);
            put1("cmd", MIME_TEXT_PLAIN);
            put1("asc", MIME_TEXT_PLAIN);
            put1("rtf", MIME_TEXT_RTF);
            put1("rtx", MIME_TEXT_RICHTEXT);
            put1("html", MIME_TEXT_HTML);
            put1("htm", MIME_TEXT_HTML);
            put1("zip", MIME_APPLICATION_ZIP);
            put1("rar", MIME_APPLICATION_X_RAR_COMPRESSED);
            put1("gzip", MIME_APPLICATION_X_GZIP);
            put1("gz", MIME_APPLICATION_X_GZIP);
            put1("tgz", MIME_APPLICATION_TGZ);
            put1("tar", MIME_APPLICATION_X_TAR);
            put1("gif", MIME_IMAGE_GIF);
            put1("jpeg", MIME_IMAGE_JPEG);
            put1("jpg", MIME_IMAGE_JPEG);
            put1("jpe", MIME_IMAGE_JPEG);
            put1("tiff", MIME_IMAGE_TIFF);
            put1("tif", MIME_IMAGE_TIFF);
            put1("png", MIME_IMAGE_PNG);
            put1("au", MIME_AUDIO_BASIC);
            put1("snd", MIME_AUDIO_BASIC);
            put1("wav", MIME_AUDIO_X_WAV);
            put1("mov", MIME_VIDEO_QUICKTIME);
            put1("qt", MIME_VIDEO_QUICKTIME);
            put1("mpeg", MIME_VIDEO_MPEG);
            put1("mpg", MIME_VIDEO_MPEG);
            put1("mpe", MIME_VIDEO_MPEG);
            put1("abs", MIME_VIDEO_MPEG);
            put1("doc", MIME_APPLICATION_MSWORD);
            put1("docx", MIME_APPLICATION_MSWORD_2007);
            put1("odt", MIME_APPLICATION_VND_TEXT);
            put1("xls", MIME_APPLICATION_VND_MSEXCEL);
            put1("xlsx", MIME_APPLICATION_VND_MSEXCEL_2007);
            put1("ods", MIME_APPLICATION_VND_SPREADSHEET);
            put1("eps", MIME_APPLICATION_POSTSCRIPT);
            put1("ai", MIME_APPLICATION_POSTSCRIPT);
            put1("ps", MIME_APPLICATION_POSTSCRIPT);
            put1("pdf", MIME_APPLICATION_PDF);
            put1("exe", MIME_APPLICATION_OCTET_STREAM);
            put1("dll", MIME_APPLICATION_OCTET_STREAM);
            put1("class", MIME_APPLICATION_OCTET_STREAM);
            put1("jar", MIME_APPLICATION_JAVA_ARCHIVE);
        }
    };
}

static {
    extMapping = new HashMap<String, String>(200) {
        private void put1(String key, String value) {
            if (put(key, value) != null) {
                throw new IllegalArgumentException("Duplicated Mimetype: " + key);
            }
        }

        {
            put1(MIME_APPLICATION_VND_MOZZILLA_XUL_XML, "xul");
            put1(MIME_APPLICATION_JSON, "json");
            put1(MIME_X_CONFERENCE_X_COOLTALK, "ice");
            put1(MIME_VIDEO_X_SGI_MOVIE, "movie");
            put1(MIME_VIDEO_X_MSVIDEO, "avi");
            put1(MIME_VIDEO_X_MS_WMV, "wmv");
            put1(MIME_VIDEO_VND_MPEGURL, "m4u");
            put1(MIME_TEXT_X_COMPONENT, "htc");
            put1(MIME_TEXT_X_SETEXT, "etx");
            put1(MIME_TEXT_VND_WAP_WMLSCRIPT, "wmls");
            put1(MIME_TEXT_VND_WAP_XML, "wml");
            put1(MIME_TEXT_TAB_SEPARATED_VALUES, "tsv");
            put1(MIME_TEXT_SGML, "sgml");
            put1(MIME_TEXT_CSS, "css");
            put1(MIME_TEXT_CALENDAR, "ics");
            put1(MIME_MODEL_VRLM, "vrlm");
            put1(MIME_MODEL_MESH, "mesh");
            put1(MIME_MODEL_IGES, "iges");
            put1(MIME_IMAGE_X_RGB, "rgb");
            put1(MIME_IMAGE_X_PORTABLE_PIXMAP, "ppm");
            put1(MIME_IMAGE_X_PORTABLE_GRAYMAP, "pgm");
            put1(MIME_IMAGE_X_PORTABLE_BITMAP, "pbm");
            put1(MIME_IMAGE_X_PORTABLE_ANYMAP, "pnm");
            put1(MIME_IMAGE_X_ICON, "ico");
            put1(MIME_IMAGE_X_CMU_RASTER, "ras");
            put1(MIME_IMAGE_WAP_WBMP, "wbmp");
            put1(MIME_IMAGE_VND_DJVU, "djvu");
            put1(MIME_IMAGE_SVG_XML, "svg");
            put1(MIME_IMAGE_IEF, "ief");
            put1(MIME_IMAGE_CGM, "cgm");
            put1(MIME_IMAGE_BMP, "bmp");
            put1(MIME_CHEMICAL_X_XYZ, "xyz");
            put1(MIME_CHEMICAL_X_PDB, "pdb");
            put1(MIME_AUDIO_X_PN_REALAUDIO, "ra");
            put1(MIME_AUDIO_X_MPEGURL, "m3u");
            put1(MIME_AUDIO_X_AIFF, "aiff");
            put1(MIME_AUDIO_MPEG, "mp3");
            put1(MIME_AUDIO_MIDI, "midi");
            put1(MIME_APPLICATION_XML_DTD, "dtd");
            put1(MIME_APPLICATION_XML, "xml");
            put1(MIME_APPLICATION_XSLT_XML, "xslt");
            put1(MIME_APPLICATION_XHTML_XML, "xhtml");
            put1(MIME_APPLICATION_X_WAIS_SOURCE, "src");
            put1(MIME_APPLICATION_X_USTAR, "ustar");
            put1(MIME_APPLICATION_X_TROFF_MS, "ms");
            put1(MIME_APPLICATION_X_TROFF_ME, "me");
            put1(MIME_APPLICATION_X_TROFF_MAN, "man");
            put1(MIME_APPLICATION_X_TROFF, "roff");
            put1(MIME_APPLICATION_X_TEXINFO, "texi");
            put1(MIME_APPLICATION_X_TEX, "tex");
            put1(MIME_APPLICATION_X_TCL, "tcl");
            put1(MIME_APPLICATION_X_SV4CRC, "sv4crc");
            put1(MIME_APPLICATION_X_SV4CPIO, "sv4cpio");
            put1(MIME_APPLICATION_X_STUFFIT, "sit");
            put1(MIME_APPLICATION_X_SHOCKWAVE_FLASH, "swf");
            put1(MIME_APPLICATION_X_SHAR, "shar");
            put1(MIME_APPLICATION_X_SH, "sh");
            put1(MIME_APPLICATION_X_NETCDF, "cdf");
            put1(MIME_APPLICATION_X_LATEX, "latex");
            put1(MIME_APPLICATION_X_KOAN, "skm");
            put1(MIME_APPLICATION_X_JAVASCRIPT, "js");
            put1(MIME_APPLICATION_X_HDF, "hdf");
            put1(MIME_APPLICATION_X_GTAR, "gtar");
            put1(MIME_APPLICATION_X_FUTURESPLASH, "spl");
            put1(MIME_APPLICATION_X_DVI, "dvi");
            put1(MIME_APPLICATION_X_DIRECTOR, "dir");
            put1(MIME_APPLICATION_X_CSH, "csh");
            put1(MIME_APPLICATION_X_CPIO, "cpio");
            put1(MIME_APPLICATION_X_CHESS_PGN, "pgn");
            put1(MIME_APPLICATION_X_CDLINK, "vcd");
            put1(MIME_APPLICATION_X_BCPIO, "bcpio");
            put1(MIME_APPLICATION_VND_RNREALMEDIA, "rm");
            put1(MIME_APPLICATION_VND_MSPOWERPOINT, "ppt");
            put1(MIME_APPLICATION_VND_MIF, "mif");
            put1(MIME_APPLICATION_SRGS_XML, "grxml");
            put1(MIME_APPLICATION_SRGS, "gram");
            put1(MIME_APPLICATION_RDF_SMIL, "smil");
            put1(MIME_APPLICATION_RDF_XML, "rdf");
            put1(MIME_APPLICATION_X_OGG, "ogg");
            put1(MIME_APPLICATION_ODA, "oda");
            put1(MIME_APPLICATION_MATHML_XML, "mathml");
            put1(MIME_APPLICATION_MAC_COMPACTPRO, "cpt");
            put1(MIME_APPLICATION_MAC_BINHEX40, "hqx");
            put1(MIME_APPLICATION_JNLP, "jnlp");
            put1(MIME_APPLICATION_ANDREW_INSET, "ez");
            put1(MIME_TEXT_PLAIN, "txt");
            put1(MIME_TEXT_RTF, "rtf");
            put1(MIME_TEXT_RICHTEXT, "rtx");
            put1(MIME_TEXT_HTML, "html");
            put1(MIME_APPLICATION_ZIP, "zip");
            put1(MIME_APPLICATION_X_RAR_COMPRESSED, "rar");
            put1(MIME_APPLICATION_X_GZIP, "gzip");
            put1(MIME_APPLICATION_TGZ, "tgz");
            put1(MIME_APPLICATION_X_TAR, "tar");
            put1(MIME_IMAGE_GIF, "gif");
            put1(MIME_IMAGE_JPEG, "jpg");
            put1(MIME_IMAGE_TIFF, "tiff");
            put1(MIME_IMAGE_PNG, "png");
            put1(MIME_AUDIO_BASIC, "au");
            put1(MIME_AUDIO_X_WAV, "wav");
            put1(MIME_VIDEO_QUICKTIME, "mov");
            put1(MIME_VIDEO_MPEG, "mpg");
            put1(MIME_APPLICATION_MSWORD, "doc");
            put1(MIME_APPLICATION_MSWORD_2007, "docx");
            put1(MIME_APPLICATION_VND_TEXT, "odt");
            put1(MIME_APPLICATION_VND_MSEXCEL, "xls");
            put1(MIME_APPLICATION_VND_SPREADSHEET, "ods");
            put1(MIME_APPLICATION_POSTSCRIPT, "ps");
            put1(MIME_APPLICATION_PDF, "pdf");
            put1(MIME_APPLICATION_OCTET_STREAM, "exe");
            put1(MIME_APPLICATION_JAVA_ARCHIVE, "jar");
        }
    };
}

/**
 * Registers MIME type for provided extension. Existing extension type will be overriden.
 */
public static void registerMimeType(String ext, String mimeType) {
    mimeTypeMapping.put(ext, mimeType);
}

/**
 * Returns the corresponding MIME type to the given extension.
 * If no MIME type was found it returns 'application/octet-stream' type.
 */
public static String getMimeType(String ext) {
    String mimeType = lookupMimeType(ext);
    if (mimeType == null) {
        mimeType = MIME_APPLICATION_OCTET_STREAM;
    }
    return mimeType;
}

/**
 * Simply returns MIME type or <code>null</code> if no type is found.
 */
public static String lookupMimeType(String ext) {
    return mimeTypeMapping.get(ext.toLowerCase());
}

/**
 * Simply returns Ext or <code>null</code> if no Mimetype is found.
 */
public static String lookupExt(String mimeType) {
    return extMapping.get(mimeType.toLowerCase());
}

/**
 * Returns the default Ext to the given MimeType.
 * If no MIME type was found it returns 'unknown' ext.
 */
public static String getDefaultExt(String mimeType) {
    String ext = lookupExt(mimeType);
    if (ext == null) {
        ext = "unknown";
    }
    return ext;
}
}

你可以像这样使用它：

@Test
public void mimetypePdf() throws Exception {

    String ext = MimeTypes.getDefaultExt(MimeTypes.MIME_APPLICATION_PDF);
    Assert.assertEquals("Not equals", "pdf", ext);
}