小米开源文件管理器MiCodeFileExplorer-源码研究(6)-媒体文件MediaFile和文件类型MimeUtils

接着之前的第4篇，本篇的2个类，仍然是工具类。
MediaFile，媒体文件，定义了一大堆的常量，真正的有用的方法就几个。
isAudioFileType、isVideoFileType之类的。


MimeUtils，文件类型工具类，定义了一大堆的
   add("application/zip", "zip");
   某种扩展格式，对应的mime类型。
   
通过阅读代码观察到的2点现象，我有2点猜测：
现象
1.注释是英文的，很溜的那种~
2.好多方法没有被本项目使用。
  Ctrl+Shift+G可以查看一个想用被调用的地方。
  
猜测
1.部分代码，是从小米其它项目或者Android相关或者Java项目，copy过来的。
2.项目是经过裁剪的，毕竟这个开源项目是“社区开源版”-“The MiCode Open Source Community”。


2个类的源代码，看起来很多，我们只要理解是因为有很多文件类型，导致的就可以了~
没有必要死记,今后如果有需要，先Copy再改造~

package net.micode.fileexplorer.util;import android.mtp.MtpConstants;import java.util.HashMap;public class MediaFile {    // Audio file types    public static final int FILE_TYPE_MP3 = 1;    public static final int FILE_TYPE_M4A = 2;    public static final int FILE_TYPE_WAV = 3;    public static final int FILE_TYPE_AMR = 4;    public static final int FILE_TYPE_AWB = 5;    public static final int FILE_TYPE_WMA = 6;    public static final int FILE_TYPE_OGG = 7;    public static final int FILE_TYPE_AAC = 8;    public static final int FILE_TYPE_MKA = 9;    public static final int FILE_TYPE_FLAC = 10;    private static final int FIRST_AUDIO_FILE_TYPE = FILE_TYPE_MP3;    private static final int LAST_AUDIO_FILE_TYPE = FILE_TYPE_FLAC;    // MIDI file types    public static final int FILE_TYPE_MID = 11;    public static final int FILE_TYPE_SMF = 12;    public static final int FILE_TYPE_IMY = 13;    private static final int FIRST_MIDI_FILE_TYPE = FILE_TYPE_MID;    private static final int LAST_MIDI_FILE_TYPE = FILE_TYPE_IMY;    // Video file types    public static final int FILE_TYPE_MP4 = 21;    public static final int FILE_TYPE_M4V = 22;    public static final int FILE_TYPE_3GPP = 23;    public static final int FILE_TYPE_3GPP2 = 24;    public static final int FILE_TYPE_WMV = 25;    public static final int FILE_TYPE_ASF = 26;    public static final int FILE_TYPE_MKV = 27;    public static final int FILE_TYPE_MP2TS = 28;    public static final int FILE_TYPE_AVI = 29;    public static final int FILE_TYPE_WEBM = 30;    private static final int FIRST_VIDEO_FILE_TYPE = FILE_TYPE_MP4;    private static final int LAST_VIDEO_FILE_TYPE = FILE_TYPE_WEBM;    // Image file types    public static final int FILE_TYPE_JPEG = 31;    public static final int FILE_TYPE_GIF = 32;    public static final int FILE_TYPE_PNG = 33;    public static final int FILE_TYPE_BMP = 34;    public static final int FILE_TYPE_WBMP = 35;    public static final int FILE_TYPE_WEBP = 36;    private static final int FIRST_IMAGE_FILE_TYPE = FILE_TYPE_JPEG;    private static final int LAST_IMAGE_FILE_TYPE = FILE_TYPE_WEBP;    public static class MediaFileType {        public final int fileType;        public final String mimeType;        MediaFileType(int fileType, String mimeType) {            this.fileType = fileType;            this.mimeType = mimeType;        }    }    private static HashMap<String, MediaFileType> sFileTypeMap = new HashMap<String, MediaFileType>();    private static HashMap<String, Integer> sMimeTypeMap = new HashMap<String, Integer>();    static void addFileType(String extension, int fileType, String mimeType) {        sFileTypeMap.put(extension, new MediaFileType(fileType, mimeType));        sMimeTypeMap.put(mimeType, Integer.valueOf(fileType));    }    static void addFileType(String extension, int fileType, String mimeType, int mtpFormatCode) {        addFileType(extension, fileType, mimeType);    }    static {        addFileType("MP3", FILE_TYPE_MP3, "audio/mpeg", MtpConstants.FORMAT_MP3);        addFileType("M4A", FILE_TYPE_M4A, "audio/mp4", MtpConstants.FORMAT_MPEG);        addFileType("WAV", FILE_TYPE_WAV, "audio/x-wav", MtpConstants.FORMAT_WAV);        addFileType("AMR", FILE_TYPE_AMR, "audio/amr");        addFileType("AWB", FILE_TYPE_AWB, "audio/amr-wb");        addFileType("OGG", FILE_TYPE_OGG, "application/ogg", MtpConstants.FORMAT_OGG);        addFileType("OGA", FILE_TYPE_OGG, "application/ogg", MtpConstants.FORMAT_OGG);        addFileType("AAC", FILE_TYPE_AAC, "audio/aac", MtpConstants.FORMAT_AAC);        addFileType("AAC", FILE_TYPE_AAC, "audio/aac-adts", MtpConstants.FORMAT_AAC);        addFileType("MKA", FILE_TYPE_MKA, "audio/x-matroska");        addFileType("MPEG", FILE_TYPE_MP4, "video/mpeg", MtpConstants.FORMAT_MPEG);        addFileType("MPG", FILE_TYPE_MP4, "video/mpeg", MtpConstants.FORMAT_MPEG);        addFileType("MP4", FILE_TYPE_MP4, "video/mp4", MtpConstants.FORMAT_MPEG);        addFileType("M4V", FILE_TYPE_M4V, "video/mp4", MtpConstants.FORMAT_MPEG);        addFileType("3GP", FILE_TYPE_3GPP, "video/3gpp", MtpConstants.FORMAT_3GP_CONTAINER);        addFileType("3GPP", FILE_TYPE_3GPP, "video/3gpp", MtpConstants.FORMAT_3GP_CONTAINER);        addFileType("3G2", FILE_TYPE_3GPP2, "video/3gpp2", MtpConstants.FORMAT_3GP_CONTAINER);        addFileType("3GPP2", FILE_TYPE_3GPP2, "video/3gpp2", MtpConstants.FORMAT_3GP_CONTAINER);        addFileType("MKV", FILE_TYPE_MKV, "video/x-matroska");        addFileType("WEBM", FILE_TYPE_WEBM, "video/webm");        addFileType("TS", FILE_TYPE_MP2TS, "video/mp2ts");        addFileType("AVI", FILE_TYPE_AVI, "video/avi");        addFileType("JPG", FILE_TYPE_JPEG, "image/jpeg", MtpConstants.FORMAT_EXIF_JPEG);        addFileType("JPEG", FILE_TYPE_JPEG, "image/jpeg", MtpConstants.FORMAT_EXIF_JPEG);        addFileType("GIF", FILE_TYPE_GIF, "image/gif", MtpConstants.FORMAT_GIF);        addFileType("PNG", FILE_TYPE_PNG, "image/png", MtpConstants.FORMAT_PNG);        addFileType("BMP", FILE_TYPE_BMP, "image/x-ms-bmp", MtpConstants.FORMAT_BMP);        addFileType("WBMP", FILE_TYPE_WBMP, "image/vnd.wap.wbmp");        addFileType("WEBP", FILE_TYPE_WEBP, "image/webp");    }    public static boolean isAudioFileType(int fileType) {        return ((fileType >= FIRST_AUDIO_FILE_TYPE && fileType <= LAST_AUDIO_FILE_TYPE) || (fileType >= FIRST_MIDI_FILE_TYPE && fileType <= LAST_MIDI_FILE_TYPE));    }    public static boolean isVideoFileType(int fileType) {        return (fileType >= FIRST_VIDEO_FILE_TYPE && fileType <= LAST_VIDEO_FILE_TYPE);    }    public static boolean isImageFileType(int fileType) {        return (fileType >= FIRST_IMAGE_FILE_TYPE && fileType <= LAST_IMAGE_FILE_TYPE);    }    public static MediaFileType getFileType(String path) {        int lastDot = path.lastIndexOf(".");        if (lastDot < 0)            return null;        return sFileTypeMap.get(path.substring(lastDot + 1).toUpperCase());    }}

package net.micode.fileexplorer.util;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import java.util.HashMap;import java.util.Map;import java.util.Properties;/** * Utilities for dealing with MIME types. * Used to implement java.net.URLConnection and android.webkit.MimeTypeMap. */public final class MimeUtils {    private static final Map<String, String> mimeTypeToExtensionMap = new HashMap<String, String>();    private static final Map<String, String> extensionToMimeTypeMap = new HashMap<String, String>();    static {        // The following table is based on /etc/mime.types data minus        // chemical/* MIME types and MIME types that don't map to any        // file extensions. We also exclude top-level domain names to        // deal with cases like:        //        // mail.google.com/a/google.com        //        // and "active" MIME types (due to potential security issues).        add("application/andrew-inset", "ez");        add("application/dsptype", "tsp");        add("application/futuresplash", "spl");        add("application/hta", "hta");        add("application/mac-binhex40", "hqx");        add("application/mac-compactpro", "cpt");        add("application/mathematica", "nb");        add("application/msaccess", "mdb");        add("application/oda", "oda");        add("application/ogg", "ogg");        add("application/pdf", "pdf");        add("application/pgp-keys", "key");        add("application/pgp-signature", "pgp");        add("application/pics-rules", "prf");        add("application/rar", "rar");        add("application/rdf+xml", "rdf");        add("application/rss+xml", "rss");        add("application/zip", "zip");        add("application/vnd.android.package-archive", "apk");        add("application/vnd.cinderella", "cdy");        add("application/vnd.ms-pki.stl", "stl");        add("application/vnd.oasis.opendocument.database", "odb");        add("application/vnd.oasis.opendocument.formula", "odf");        add("application/vnd.oasis.opendocument.graphics", "odg");        add("application/vnd.oasis.opendocument.graphics-template", "otg");        add("application/vnd.oasis.opendocument.image", "odi");        add("application/vnd.oasis.opendocument.spreadsheet", "ods");        add("application/vnd.oasis.opendocument.spreadsheet-template", "ots");        add("application/vnd.oasis.opendocument.text", "odt");        add("application/vnd.oasis.opendocument.text-master", "odm");        add("application/vnd.oasis.opendocument.text-template", "ott");        add("application/vnd.oasis.opendocument.text-web", "oth");        add("application/vnd.google-earth.kml+xml", "kml");        add("application/vnd.google-earth.kmz", "kmz");        add("application/msword", "doc");        add("application/msword", "dot");        add("application/vnd.openxmlformats-officedocument.wordprocessingml.document", "docx");        add("application/vnd.openxmlformats-officedocument.wordprocessingml.template", "dotx");        add("application/vnd.ms-excel", "xls");        add("application/vnd.ms-excel", "xlt");        add("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", "xlsx");        add("application/vnd.openxmlformats-officedocument.spreadsheetml.template", "xltx");        add("application/vnd.ms-powerpoint", "ppt");        add("application/vnd.ms-powerpoint", "pot");        add("application/vnd.ms-powerpoint", "pps");        add("application/vnd.openxmlformats-officedocument.presentationml.presentation", "pptx");        add("application/vnd.openxmlformats-officedocument.presentationml.template", "potx");        add("application/vnd.openxmlformats-officedocument.presentationml.slideshow", "ppsx");        add("application/vnd.rim.cod", "cod");        add("application/vnd.smaf", "mmf");        add("application/vnd.stardivision.calc", "sdc");        add("application/vnd.stardivision.draw", "sda");        add("application/vnd.stardivision.impress", "sdd");        add("application/vnd.stardivision.impress", "sdp");        add("application/vnd.stardivision.math", "smf");        add("application/vnd.stardivision.writer", "sdw");        add("application/vnd.stardivision.writer", "vor");        add("application/vnd.stardivision.writer-global", "sgl");        add("application/vnd.sun.xml.calc", "sxc");        add("application/vnd.sun.xml.calc.template", "stc");        add("application/vnd.sun.xml.draw", "sxd");        add("application/vnd.sun.xml.draw.template", "std");        add("application/vnd.sun.xml.impress", "sxi");        add("application/vnd.sun.xml.impress.template", "sti");        add("application/vnd.sun.xml.math", "sxm");        add("application/vnd.sun.xml.writer", "sxw");        add("application/vnd.sun.xml.writer.global", "sxg");        add("application/vnd.sun.xml.writer.template", "stw");        add("application/vnd.visio", "vsd");        add("application/x-abiword", "abw");        add("application/x-apple-diskimage", "dmg");        add("application/x-bcpio", "bcpio");        add("application/x-bittorrent", "torrent");        add("application/x-cdf", "cdf");        add("application/x-cdlink", "vcd");        add("application/x-chess-pgn", "pgn");        add("application/x-cpio", "cpio");        add("application/x-debian-package", "deb");        add("application/x-debian-package", "udeb");        add("application/x-director", "dcr");        add("application/x-director", "dir");        add("application/x-director", "dxr");        add("application/x-dms", "dms");        add("application/x-doom", "wad");        add("application/x-dvi", "dvi");        add("application/x-flac", "flac");        add("application/x-font", "pfa");        add("application/x-font", "pfb");        add("application/x-font", "gsf");        add("application/x-font", "pcf");        add("application/x-font", "pcf.Z");        add("application/x-freemind", "mm");        add("application/x-futuresplash", "spl");        add("application/x-gnumeric", "gnumeric");        add("application/x-go-sgf", "sgf");        add("application/x-graphing-calculator", "gcf");        add("application/x-gtar", "gtar");        add("application/x-gtar", "tgz");        add("application/x-gtar", "taz");        add("application/x-hdf", "hdf");        add("application/x-ica", "ica");        add("application/x-internet-signup", "ins");        add("application/x-internet-signup", "isp");        add("application/x-iphone", "iii");        add("application/x-iso9660-image", "iso");        add("application/x-jmol", "jmz");        add("application/x-kchart", "chrt");        add("application/x-killustrator", "kil");        add("application/x-koan", "skp");        add("application/x-koan", "skd");        add("application/x-koan", "skt");        add("application/x-koan", "skm");        add("application/x-kpresenter", "kpr");        add("application/x-kpresenter", "kpt");        add("application/x-kspread", "ksp");        add("application/x-kword", "kwd");        add("application/x-kword", "kwt");        add("application/x-latex", "latex");        add("application/x-lha", "lha");        add("application/x-lzh", "lzh");        add("application/x-lzx", "lzx");        add("application/x-maker", "frm");        add("application/x-maker", "maker");        add("application/x-maker", "frame");        add("application/x-maker", "fb");        add("application/x-maker", "book");        add("application/x-maker", "fbdoc");        add("application/x-mif", "mif");        add("application/x-ms-wmd", "wmd");        add("application/x-ms-wmz", "wmz");        add("application/x-msi", "msi");        add("application/x-ns-proxy-autoconfig", "pac");        add("application/x-nwc", "nwc");        add("application/x-object", "o");        add("application/x-oz-application", "oza");        add("application/x-pkcs12", "p12");        add("application/x-pkcs7-certreqresp", "p7r");        add("application/x-pkcs7-crl", "crl");        add("application/x-quicktimeplayer", "qtl");        add("application/x-shar", "shar");        add("application/x-shockwave-flash", "swf");        add("application/x-stuffit", "sit");        add("application/x-sv4cpio", "sv4cpio");        add("application/x-sv4crc", "sv4crc");        add("application/x-tar", "tar");        add("application/x-texinfo", "texinfo");        add("application/x-texinfo", "texi");        add("application/x-troff", "t");        add("application/x-troff", "roff");        add("application/x-troff-man", "man");        add("application/x-ustar", "ustar");        add("application/x-wais-source", "src");        add("application/x-wingz", "wz");        add("application/x-webarchive", "webarchive");        add("application/x-webarchive-xml", "webarchivexml");        add("application/x-x509-ca-cert", "crt");        add("application/x-x509-user-cert", "crt");        add("application/x-xcf", "xcf");        add("application/x-xfig", "fig");        add("application/xhtml+xml", "xhtml");        add("audio/3gpp", "3gpp");        add("audio/amr", "amr");        add("audio/basic", "snd");        add("audio/midi", "mid");        add("audio/midi", "midi");        add("audio/midi", "kar");        add("audio/midi", "xmf");        add("audio/mobile-xmf", "mxmf");        add("audio/mpeg", "mpga");        add("audio/mpeg", "mpega");        add("audio/mpeg", "mp2");        add("audio/mpeg", "mp3");        add("audio/mpeg", "m4a");        add("audio/mpegurl", "m3u");        add("audio/prs.sid", "sid");        add("audio/x-aiff", "aif");        add("audio/x-aiff", "aiff");        add("audio/x-aiff", "aifc");        add("audio/x-gsm", "gsm");        add("audio/x-mpegurl", "m3u");        add("audio/x-ms-wma", "wma");        add("audio/x-ms-wax", "wax");        add("audio/x-pn-realaudio", "ra");        add("audio/x-pn-realaudio", "rm");        add("audio/x-pn-realaudio", "ram");        add("audio/x-realaudio", "ra");        add("audio/x-scpls", "pls");        add("audio/x-sd2", "sd2");        add("audio/x-wav", "wav");        add("image/bmp", "bmp");        add("audio/x-qcp", "qcp");        add("image/gif", "gif");        add("image/ico", "cur");        add("image/ico", "ico");        add("image/ief", "ief");        add("image/jpeg", "jpeg");        add("image/jpeg", "jpg");        add("image/jpeg", "jpe");        add("image/pcx", "pcx");        add("image/png", "png");        add("image/svg+xml", "svg");        add("image/svg+xml", "svgz");        add("image/tiff", "tiff");        add("image/tiff", "tif");        add("image/vnd.djvu", "djvu");        add("image/vnd.djvu", "djv");        add("image/vnd.wap.wbmp", "wbmp");        add("image/x-cmu-raster", "ras");        add("image/x-coreldraw", "cdr");        add("image/x-coreldrawpattern", "pat");        add("image/x-coreldrawtemplate", "cdt");        add("image/x-corelphotopaint", "cpt");        add("image/x-icon", "ico");        add("image/x-jg", "art");        add("image/x-jng", "jng");        add("image/x-ms-bmp", "bmp");        add("image/x-photoshop", "psd");        add("image/x-portable-anymap", "pnm");        add("image/x-portable-bitmap", "pbm");        add("image/x-portable-graymap", "pgm");        add("image/x-portable-pixmap", "ppm");        add("image/x-rgb", "rgb");        add("image/x-xbitmap", "xbm");        add("image/x-xpixmap", "xpm");        add("image/x-xwindowdump", "xwd");        add("model/iges", "igs");        add("model/iges", "iges");        add("model/mesh", "msh");        add("model/mesh", "mesh");        add("model/mesh", "silo");        add("text/calendar", "ics");        add("text/calendar", "icz");        add("text/comma-separated-values", "csv");        add("text/css", "css");        add("text/html", "htm");        add("text/html", "html");        add("text/h323", "323");        add("text/iuls", "uls");        add("text/mathml", "mml");        // add ".txt" first so it will be the default for ExtensionFromMimeType        add("text/plain", "txt");        add("text/plain", "asc");        add("text/plain", "text");        add("text/plain", "diff");        add("text/plain", "po");     // reserve "pot" for vnd.ms-powerpoint        add("text/richtext", "rtx");        add("text/rtf", "rtf");        add("text/texmacs", "ts");        add("text/text", "phps");        add("text/tab-separated-values", "tsv");        add("text/xml", "xml");        add("text/x-bibtex", "bib");        add("text/x-boo", "boo");        add("text/x-c++hdr", "h++");        add("text/x-c++hdr", "hpp");        add("text/x-c++hdr", "hxx");        add("text/x-c++hdr", "hh");        add("text/x-c++src", "c++");        add("text/x-c++src", "cpp");        add("text/x-c++src", "cxx");        add("text/x-chdr", "h");        add("text/x-component", "htc");        add("text/x-csh", "csh");        add("text/x-csrc", "c");        add("text/x-dsrc", "d");        add("text/x-haskell", "hs");        add("text/x-java", "java");        add("text/x-literate-haskell", "lhs");        add("text/x-moc", "moc");        add("text/x-pascal", "p");        add("text/x-pascal", "pas");        add("text/x-pcs-gcd", "gcd");        add("text/x-setext", "etx");        add("text/x-tcl", "tcl");        add("text/x-tex", "tex");        add("text/x-tex", "ltx");        add("text/x-tex", "sty");        add("text/x-tex", "cls");        add("text/x-vcalendar", "vcs");        add("text/x-vcard", "vcf");        add("video/3gpp", "3gpp");        add("video/3gpp", "3gp");        add("video/3gpp", "3g2");        add("video/dl", "dl");        add("video/dv", "dif");        add("video/dv", "dv");        add("video/fli", "fli");        add("video/m4v", "m4v");        add("video/mpeg", "mpeg");        add("video/mpeg", "mpg");        add("video/mpeg", "mpe");        add("video/mp4", "mp4");        add("video/mpeg", "VOB");        add("video/quicktime", "qt");        add("video/quicktime", "mov");        add("video/vnd.mpegurl", "mxu");        add("video/webm", "webm");        add("video/x-la-asf", "lsf");        add("video/x-la-asf", "lsx");        add("video/x-mng", "mng");        add("video/x-ms-asf", "asf");        add("video/x-ms-asf", "asx");        add("video/x-ms-wm", "wm");        add("video/x-ms-wmv", "wmv");        add("video/x-ms-wmx", "wmx");        add("video/x-ms-wvx", "wvx");        add("video/x-msvideo", "avi");        add("video/x-sgi-movie", "movie");        add("x-conference/x-cooltalk", "ice");        add("x-epoc/x-sisx-app", "sisx");        applyOverrides();    }    private static void add(String mimeType, String extension) {        //        // if we have an existing x --> y mapping, we do not want to        // override it with another mapping x --> ?        // this is mostly because of the way the mime-type map below        // is constructed (if a mime type maps to several extensions        // the first extension is considered the most popular and is        // added first; we do not want to overwrite it later).        //        if (!mimeTypeToExtensionMap.containsKey(mimeType)) {            mimeTypeToExtensionMap.put(mimeType, extension);        }        extensionToMimeTypeMap.put(extension, mimeType);    }    private static InputStream getContentTypesPropertiesStream() {        // User override?        String userTable = System.getProperty("content.types.user.table");        if (userTable != null) {            File f = new File(userTable);            if (f.exists()) {                try {                    return new FileInputStream(f);                } catch (IOException ignored) {                }            }        }        // Standard location?        File f = new File(System.getProperty("java.home"), "lib" + File.separator + "content-types.properties");        if (f.exists()) {            try {                return new FileInputStream(f);            } catch (IOException ignored) {            }        }        return null;    }    /**     * This isn't what the RI does. The RI doesn't have hard-coded defaults, so supplying your     * own "content.types.user.table" means you don't get any of the built-ins, and the built-ins     * come from "$JAVA_HOME/lib/content-types.properties".     */    private static void applyOverrides() {        // Get the appropriate InputStream to read overrides from, if any.        InputStream stream = getContentTypesPropertiesStream();        if (stream == null) {            return;        }        try {            try {                // Read the properties file...                Properties overrides = new Properties();                overrides.load(stream);                // And translate its mapping to ours...                for (Map.Entry<Object, Object> entry : overrides.entrySet()) {                    String extension = (String) entry.getKey();                    String mimeType = (String) entry.getValue();                    add(mimeType, extension);                }            } finally {                stream.close();            }        } catch (IOException ignored) {        }    }    private MimeUtils() {    }       /**     * Returns the MIME type for the given extension.     * @param extension A file extension without the leading '.'     * @return The MIME type for the given extension or null iff there is none.     */    public static String guessMimeTypeFromExtension(String extension) {        if (extension == null || extension.isEmpty()) {            return null;        }        return extensionToMimeTypeMap.get(extension);    }    //下面3个方法根本没有被调用过，因此，我猜测这个类很可能是从其它项目copy过来的。    //也有可能是因为本项目是经过裁剪的，毕竟是开源社区版    /**     * Returns true if the given extension has a registered MIME type.     * @param extension A file extension without the leading '.'     * @return True iff there is an extension entry in the map.     */    public static boolean hasExtension(String extension) {        if (extension == null || extension.isEmpty()) {            return false;        }        return extensionToMimeTypeMap.containsKey(extension);    }    /**     * Returns the registered extension for the given MIME type. Note that some     * MIME types map to multiple extensions. This call will return the most     * common extension for the given MIME type.     * @param mimeType A MIME type (i.e. text/plain)     * @return The extension for the given MIME type or null iff there is none.     */    public static String guessExtensionFromMimeType(String mimeType) {        if (mimeType == null || mimeType.isEmpty()) {            return null;        }        return mimeTypeToExtensionMap.get(mimeType);    }        /**     * Returns true if the given MIME type has an entry in the map.     * @param mimeType A MIME type (i.e. text/plain)     * @return True iff there is a mimeType entry in the map.     */    public static boolean hasMimeType(String mimeType) {        if (mimeType == null || mimeType.isEmpty()) {            return false;        }        return mimeTypeToExtensionMap.containsKey(mimeType);    }}

代码比自己码的文字还多，感觉自己纯粹是在贴代码哦~
代码整体比较简单，确实没啥好解释的~


再说了，晚上相对要累一些，写点轻松的也好啊~
接下来，再介绍相对难一点的~


等把基础介绍完了，再回头看界面、Activity、事件，才会容易一些~