Android媒体扫描代码分析
16lz
2021-01-25
插入u盘后，系统会发送广播android.intent.action.MEDIA_MOUNTED
位于
packages/providers/MediaProvider/src/com/android/providers/media/MediaScannerService.java
MediaScannerService可以接收开机广播和u盘插入广播，收到广播后执行scan方法，将文件或文件夹路径存储到Bundle，并启动MediaScannerService，我们看MediaScannerService中ServiceHandler的代码
private final class ServiceHandler extends Handler { @Override public void handleMessage(Message msg) { Bundle arguments = (Bundle) msg.obj; String filePath = arguments.getString("filepath");//单个文件 String path = arguments.getString("path");//文件目录 try { if (filePath != null) { IBinder binder = arguments.getIBinder("listener"); IMediaScannerListener listener = (binder == null ? null : IMediaScannerListener.Stub.asInterface(binder)); Uri uri = null; try { uri = scanFile(filePath, arguments.getString("mimetype"));//扫描单个文件 } catch (Exception e) { Log.e(TAG, "Exception scanning file", e); } if (listener != null) { listener.scanCompleted(filePath, uri); } } else { String volume = arguments.getString("volume"); String[] directories = null; if (MediaProvider.INTERNAL_VOLUME.equals(volume)) { // scan internal media storage directories = new String[] { Environment.getRootDirectory() + "/media", }; } else if (MediaProvider.EXTERNAL_VOLUME.equals(volume)) { // scan external storage volumes if (path == null) { directories = mExternalStoragePaths; } else if (path.startsWith("/mnt/usb_storage")) { directories = new String[] {path};//{"/mnt/usb_storage"}; } else { directories = new String[] {path}; } } if (directories != null) { if (true) Log.d(TAG, "start scanning volume " + volume + ": " + Arrays.toString(directories)); scan(directories, volume);//扫描文件列表 if (true) Log.d(TAG, "done scanning volume " + volume); } } } catch (Exception e) { Log.e(TAG, "Exception in handleMessage", e); } stopSelf(msg.arg1); } };可以看到代码会调用scan或者scanFile扫描
private void scan(String[] directories, String volumeName) { Uri uri = Uri.parse("file://" + directories[0]); // don't sleep while scanning mWakeLock.acquire(); try { ContentValues values = new ContentValues(); values.put(MediaStore.MEDIA_SCANNER_VOLUME, volumeName); Uri scanUri = getContentResolver().insert(MediaStore.getMediaScannerUri(), values); sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_STARTED, uri)); try { if (volumeName.equals(MediaProvider.EXTERNAL_VOLUME)) { openDatabase(volumeName); } MediaScanner scanner = createMediaScanner(); if(directories!=null){ scanner.scanDirectories(directories, volumeName); } } catch (Exception e) { Log.e(TAG, "exception in MediaScanner.scan()", e); } getContentResolver().delete(scanUri, null, null); } finally { sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_FINISHED, uri)); mWakeLock.release(); } } private Uri scanFile(String path, String mimeType) { String volumeName = MediaProvider.EXTERNAL_VOLUME; openDatabase(volumeName); MediaScanner scanner = createMediaScanner(); try { // make sure the file path is in canonical form String canonicalPath = new File(path).getCanonicalPath(); return scanner.scanSingleFile(canonicalPath, volumeName, mimeType); } catch (Exception e) { Log.e(TAG, "bad path " + path + " in scanFile()", e); return null; } }下一步进入到MediaScanner.java，文件在
frameworks/base/media/java/android/media/MediaScanner.java下面是扫描单个文件的代码
// this function is used to scan a single file public Uri scanSingleFile(String path, String volumeName, String mimeType) { try { initialize(volumeName); prescan(path, true); File file = new File(path); if (!file.exists()) { return null; } // lastModified is in milliseconds on Files. long lastModifiedSeconds = file.lastModified() / 1000; // always scan the file, so we can return the content://media Uri for existing files return mClient.doScanFile(path, mimeType, lastModifiedSeconds, file.length(), false, true, MediaScanner.isNoMediaPath(path)); } catch (RemoteException e) { Log.e(TAG, "RemoteException in MediaScanner.scanFile()", e); return null; } }//初始化默认的uriprivate void initialize(String volumeName) { mMediaProvider = mContext.getContentResolver().acquireProvider("media"); mAudioUri = Audio.Media.getContentUri(volumeName); mVideoUri = Video.Media.getContentUri(volumeName); mImagesUri = Images.Media.getContentUri(volumeName); mThumbsUri = Images.Thumbnails.getContentUri(volumeName); mFilesUri = Files.getContentUri(volumeName); mFilesUriNoNotify = mFilesUri.buildUpon().appendQueryParameter("nonotify", "1").build(); if (!volumeName.equals("internal")) { // we only support playlists on external media mProcessPlaylists = true; mProcessGenres = true; mPlaylistsUri = Playlists.getContentUri(volumeName); mCaseInsensitivePaths = true; } }//扫描预处理，暂时不知道做什么用private void prescan(String filePath, boolean prescanFiles) throws RemoteException { Cursor c = null; String where = null; String[] selectionArgs = null; if (mPlayLists == null) { mPlayLists = new ArrayList(); } else { mPlayLists.clear(); } if (filePath != null) { // query for only one file where = MediaStore.Files.FileColumns._ID + ">?" + " AND " + Files.FileColumns.DATA + " like '"+filePath+"%' "; selectionArgs = new String[] { "" }; } else { where = MediaStore.Files.FileColumns._ID + ">?"; selectionArgs = new String[] { "" }; } if (DEBUG_MEDIASCANNER) Log.d(TAG,"-----------enter prescan,filePath = "+filePath+"where = "+where); // Tell the provider to not delete the file. // If the file is truly gone the delete is unnecessary, and we want to avoid // accidentally deleting files that are really there (this may happen if the // filesystem is mounted and unmounted while the scanner is running). Uri.Builder builder = mFilesUri.buildUpon(); builder.appendQueryParameter(MediaStore.PARAM_DELETE_DATA, "false"); MediaBulkDeleter deleter = new MediaBulkDeleter(mMediaProvider, mPackageName, builder.build()); // Build the list of files from the content provider try { if (prescanFiles) { // First read existing files from the files table. // Because we'll be deleting entries for missing files as we go, // we need to query the database in small batches, to avoid problems // with CursorWindow positioning. long lastId = Long.MIN_VALUE; Uri limitUri = mFilesUri.buildUpon().appendQueryParameter("limit", "1000").build(); mWasEmptyPriorToScan = true; while (true) { selectionArgs[0] = "" + lastId; if (c != null) { c.close(); c = null; } c = mMediaProvider.query(mPackageName, limitUri, FILES_PRESCAN_PROJECTION, where, selectionArgs, MediaStore.Files.FileColumns._ID, null); if (c == null) { break; } int num = c.getCount(); if (num == 0) { break; } mWasEmptyPriorToScan = false; while (c.moveToNext()) { long rowId = c.getLong(FILES_PRESCAN_ID_COLUMN_INDEX); String path = c.getString(FILES_PRESCAN_PATH_COLUMN_INDEX); int format = c.getInt(FILES_PRESCAN_FORMAT_COLUMN_INDEX); long lastModified = c.getLong(FILES_PRESCAN_DATE_MODIFIED_COLUMN_INDEX); lastId = rowId; // Only consider entries with absolute path names. // This allows storing URIs in the database without the // media scanner removing them. if (path != null && path.startsWith("/")) { boolean exists = false; try { exists = Libcore.os.access(path, libcore.io.OsConstants.F_OK); } catch (ErrnoException e1) { } if (!exists && !MtpConstants.isAbstractObject(format)) { // do not delete missing playlists, since they may have been // modified by the user. // The user can delete them in the media player instead. // instead, clear the path and lastModified fields in the row MediaFile.MediaFileType mediaFileType = MediaFile.getFileType(path); int fileType = (mediaFileType == null ? 0 : mediaFileType.fileType); if (!MediaFile.isPlayListFileType(fileType)) { deleter.delete(rowId); if (path.toLowerCase(Locale.US).endsWith("/.nomedia")) { deleter.flush(); String parent = new File(path).getParent(); mMediaProvider.call(mPackageName, MediaStore.UNHIDE_CALL, parent, null); } } } } } } } } finally { if (c != null) { c.close(); } deleter.flush(); } // compute original size of images mOriginalCount = 0; c = mMediaProvider.query(mPackageName, mImagesUri, ID_PROJECTION, null, null, null, null); if (c != null) { mOriginalCount = c.getCount(); c.close(); } } 下面是真正的扫描实现
public Uri doScanFile(String path, String mimeType, long lastModified, long fileSize, boolean isDirectory, boolean scanAlways, boolean noMedia) { Uri result = null;// long t1 = System.currentTimeMillis(); try { FileEntry entry = beginFile(path, mimeType, lastModified, fileSize, isDirectory, noMedia); if (path.startsWith("/mnt/usb_storage")) mIsUsbStorage =true; else mIsUsbStorage =false; // if this file was just inserted via mtp, set the rowid to zero // (even though it already exists in the database), to trigger // the correct code path for updating its entry if (mMtpObjectHandle != 0) { entry.mRowId = 0; } // rescan for metadata if file was modified since last scan if (entry != null && (entry.mLastModifiedChanged || scanAlways)) { if (noMedia) { result = endFile(entry, false, false, false, false, false); } else { String lowpath = path.toLowerCase(Locale.ROOT); boolean ringtones = (lowpath.indexOf(RINGTONES_DIR) > 0); boolean notifications = (lowpath.indexOf(NOTIFICATIONS_DIR) > 0); boolean alarms = (lowpath.indexOf(ALARMS_DIR) > 0); boolean podcasts = (lowpath.indexOf(PODCAST_DIR) > 0); boolean music = (lowpath.indexOf(MUSIC_DIR) > 0) || (!ringtones && !notifications && !alarms && !podcasts); boolean isaudio = MediaFile.isAudioFileType(mFileType); boolean isvideo = MediaFile.isVideoFileType(mFileType); boolean isimage = MediaFile.isImageFileType(mFileType); if (isaudio || isvideo || isimage) { if (mExternalIsEmulated && path.startsWith(mExternalStoragePath)) { // try to rewrite the path to bypass the sd card fuse layer String directPath = Environment.getMediaStorageDirectory() + path.substring(mExternalStoragePath.length()); File f = new File(directPath); if (f.exists()) { path = directPath; } } } // we only extract metadata for audio and video files if (isaudio /*|| isvideo */) { //jni方法调用 processFile(path, mimeType, this); } //if (isimage) { // processImageFile(path); //} result = endFile(entry, ringtones, notifications, alarms, music, podcasts); } } } catch (RemoteException e) { Log.e(TAG, "RemoteException in MediaScanner.scanFile()", e); }// long t2 = System.currentTimeMillis();// Log.v(TAG, "scanFile: " + path + " took " + (t2-t1)); return result; }我们看一下英文说明
MediaScanner.processFile(). * - MediaScanner.processFile() calls one of several methods, depending on the type of the * file: parseMP3, parseMP4, parseMidi, parseOgg or parseWMA. * - each of these methods gets metadata key/value pairs from the file, and repeatedly * calls native MyMediaScannerClient.handleStringTag, which calls back up to its Java * counterparts in this file.大意就是，processFile会根据文件类型调用不用的方法，并由MyMediaScannerClient.handleStringTag回调
这段native方法可以在下面的文件目录找到
frameworks/base/media/jni/android_media_MediaScanner.cppstatic voidandroid_media_MediaScanner_processFile( JNIEnv *env, jobject thiz, jstring path, jstring mimeType, jobject client){ ALOGV("processFile"); // Lock already hold by processDirectory MediaScanner *mp = getNativeScanner_l(env, thiz); if (mp == NULL) { jniThrowException(env, kRunTimeException, "No scanner available"); return; } if (path == NULL) { jniThrowException(env, kIllegalArgumentException, NULL); return; } const char *pathStr = env->GetStringUTFChars(path, NULL); if (pathStr == NULL) { // Out of memory return; } const char *mimeTypeStr = (mimeType ? env->GetStringUTFChars(mimeType, NULL) : NULL); if (mimeType && mimeTypeStr == NULL) { // Out of memory // ReleaseStringUTFChars can be called with an exception pending. env->ReleaseStringUTFChars(path, pathStr); return; } MyMediaScannerClient myClient(env, client); MediaScanResult result = mp->processFile(pathStr, mimeTypeStr, myClient); if (result == MEDIA_SCAN_RESULT_ERROR) { ALOGE("An error occurred while scanning file '%s'.", pathStr); } env->ReleaseStringUTFChars(path, pathStr); if (mimeType) { env->ReleaseStringUTFChars(mimeType, mimeTypeStr); }}mp->processFile在路径
通过grep搜索发现，方法定义在文件frameworks/av/media/libmedia/MediaScanner.h可以看到这是一个虚函数
virtual MediaScanResult processFile( const char *path, const char *mimeType, MediaScannerClient &client) = 0;虚函数定义如下：如果父类的函数（方法）根本没有必要或者无法实现，完全要依赖子类去实现的话，可以把此函数（方法）设为virtual 函数名=0 我们把这样的函数（方法）称为纯虚函数如果一个类包含了纯虚函数，称此类为抽象类。
我们接着往下跟，找到真正实现的地方
回到前一个jni
frameworks/base/media/jni/android_media_MediaScanner.cpp这里面有实例化mediascanner的地方
static voidandroid_media_MediaScanner_native_setup(JNIEnv *env, jobject thiz){ ALOGV("native_setup"); MediaScanner *mp = new StagefrightMediaScanner; if (mp == NULL) { jniThrowException(env, kRunTimeException, "Out of memory"); return; } env->SetIntField(thiz, fields.context, (int)mp);}马上就能找到实例化的地方了，打开
frameworks\av\media\libstagefright\StagefrightMediaScanner.cppMediaScanResult StagefrightMediaScanner::processFile( const char *path, const char *mimeType, MediaScannerClient &client) { ALOGV("processFile '%s'.", path); client.setLocale(locale()); client.beginFile(); MediaScanResult result = processFileInternal(path, mimeType, client); client.endFile(); return result;}MediaScanResult StagefrightMediaScanner::processFileInternal( const char *path, const char *mimeType, MediaScannerClient &client) { const char *extension = strrchr(path, '.'); if (!extension) { return MEDIA_SCAN_RESULT_SKIPPED; } //过滤类型 if (!FileHasAcceptableExtension(extension)) { return MEDIA_SCAN_RESULT_SKIPPED; } //根据扩展名调用不同的解析方法 if (!strcasecmp(extension, ".mid") || !strcasecmp(extension, ".smf") || !strcasecmp(extension, ".imy") || !strcasecmp(extension, ".midi") || !strcasecmp(extension, ".xmf") || !strcasecmp(extension, ".rtttl") || !strcasecmp(extension, ".rtx") || !strcasecmp(extension, ".ota") || !strcasecmp(extension, ".mxmf")) { return HandleMIDI(path, &client); } //parse ape audio file if (!strcasecmp(extension, ".ape")) { return parseAPE(path, client); } sp mRetriever(new MediaMetadataRetriever); int fd = open(path, O_RDONLY | O_LARGEFILE); status_t status; if (fd < 0) { // couldn't open it locally, maybe the media server can? status = mRetriever->setDataSource(path); } else { status = mRetriever->setDataSource(fd, 0, 0x7ffffffffffffffL); close(fd); } if (status) { return MEDIA_SCAN_RESULT_ERROR; } const char *value; if ((value = mRetriever->extractMetadata( METADATA_KEY_MIMETYPE)) != NULL) { status = client.setMimeType(value); if (status) { return MEDIA_SCAN_RESULT_ERROR; } } client.endFile()这个方法的实现在
frameworks\av\media\libmedia\MediaScannerClient.cppvoid MediaScannerClient::endFile(){ if (mLocaleEncoding != kEncodingNone) { int size = mNames->size(); uint32_t encoding = kEncodingAll; // compute a bit mask containing all possible encodings char* isUtf8 = new char[size]; memset(isUtf8,0,size); for (int i = 0; i < mNames->size(); i++) { // ALOGE("I=%d ,names=%s , values=%s,mLocaleEncoding =0x%x \n",i,mNames->getEntry(i),mValues->getEntry(i),mLocaleEncoding); uint32_t tmpEncoding = kEncodingAll; const char * name = mNames->getEntry(i); //when the system languge is russian ,the title/album/artist/must think it is win1251 . if((mLocaleEncoding == kEncodingWin1251 || mLocaleEncoding == kEncodingWin1252) && (!strncmp(name, "tit", 3)||!strncmp(name, "alb", 3)||!strncmp(name, "art", 3))) tmpEncoding = kEncodingNone; else tmpEncoding = possibleEncodings(mValues->getEntry(i)); if(tmpEncoding == kEncodingNone) { ALOGI("%s value can't discern,the value is %s",mNames->getEntry(i),mValues->getEntry(i)); if( mLocaleEncoding == kEncodingWin1251 || mLocaleEncoding == kEncodingWin1252 ) { //revert the string value the original string int8_t ch1, ch2; int8_t *src = (int8_t *)mValues->getEntry(i); int8_t *dst = src; while ((ch1 = *src++)) { if (ch1 & 0x80) { ch2 = *src++; ch1 = ((ch1 << 6) & 0xC0) | (ch2 & 0x3F); } *dst++ = ch1; } *dst = '\0'; unsigned char value[1024]; memset(value,0,1024); if( mLocaleEncoding == kEncodingWin1251) Win1251ToUtf8((unsigned char *)mValues->getEntry(i),strlen(mValues->getEntry(i)),value,1024); else Win1252ToUtf8((unsigned char *)mValues->getEntry(i),strlen(mValues->getEntry(i)),value,1024); //ALOGI("%s value do change encode type,the value is %s",mNames->getEntry(i),value); handleStringTag(name, (const char *)value); } else { //if the id3 value can't discern the encoding,we can think it is a utf8 handleStringTag(name, mValues->getEntry(i)); } isUtf8[i] = 0xff; continue; } //LOGI("%s value is %x coding,the value is %s",mNames->getEntry(i),tmpEncoding,mValues->getEntry(i)); encoding &= tmpEncoding; } if(encoding != kEncodingAll) { if(encoding == kEncodingNone) encoding = mLocaleEncoding; // if the locale encoding matches, then assume we have a native encoding. if (encoding & mLocaleEncoding) convertValues(mLocaleEncoding); else if(encoding & kEncodingEUCKR) convertValues(kEncodingEUCKR); else if(encoding & kEncodingGBK) convertValues(kEncodingGBK); else if(encoding & kEncodingBig5) convertValues(kEncodingBig5); else if(encoding & kEncodingShiftJIS) convertValues(kEncodingShiftJIS); } // finally, push all name/value pairs to the client for (int i = 0; i < mNames->size(); i++) { if(isUtf8[i] == 0xff) continue; status_t status = handleStringTag(mNames->getEntry(i), mValues->getEntry(i)); if (status) { break; } } } // else addStringTag() has done all the work so we have nothing to do delete mNames; delete mValues; mNames = NULL; mValues = NULL;}这个方法会处理底层解析后的数据，返回给java层调用，第一次自己边跟代码边写CSDN，谢谢各位
PS:今天在测试媒体扫描时候发现，如果在开发者模式下，禁用后台进程，则媒体扫描会被系统kill，原因是媒体扫描是后台进程，发现相册图片更新问题的朋友注意了，可能跟这个有关
更多相关文章
- 一款常用的 Squid 日志分析工具
- GitHub 标星 8K+！一款开源替代 ls 的工具你值得拥有！
- RHEL 6 下 DHCP+TFTP+FTP+PXE+Kickstart 实现无人值守安装
- Linux 环境下实战 Rsync 备份工具及配置 rsync+inotify 实时同步
- android调用matlab中的函数方法
- Mac下 android 模拟器 host修改
- 用Preferences,通过xml文件跳转到另一个Activity
- Android中banner的使用步骤
- Android(安卓)Mediascanner实现机制