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MediaScanner源码分析  

2011-07-11 11:17:32|  分类: android相关 |  标签: |举报 |字号 订阅

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神马是MediaScanner呢?在Android的SDK里面是看不到这个类的,因为被google隐藏了。通过Android的源码我们可以看到MediaScanner的类注解多了一个@hide的标注。所以对于一般应用开发者,此文意义不是很大,大家可以绕道。

在 前两篇文章中,最后我们都了解了Android的媒体文件的扫描是在MediaScannerService中调用MediaScanner的scanDirectories或者scanSingleFile完成最终的扫描的。那么MediaScanner是如何工作的呢?

google对MediaScanner写了一大堆的类注释,如下:


   1: /* In summary:
   2: * Java MediaScannerService calls
   3: * Java MediaScanner scanDirectories, which calls
   4: * Java MediaScanner processDirectory (native method), which calls
   5: * native MediaScanner processDirectory, which calls
   6: * native MyMediaScannerClient scanFile, which calls
   7: * Java MyMediaScannerClient scanFile, which calls
   8: * Java MediaScannerClient doScanFile, which calls
   9: * Java MediaScanner processFile (native method), which calls
  10: * native MediaScanner processFile, which calls
  11: * native parseMP3, parseMP4, parseMidi, parseOgg or parseWMA, which calls
  12: * native MyMediaScanner handleStringTag, which calls
  13: * Java MyMediaScanner handleStringTag.
  14: * Once MediaScanner processFile returns, an entry is inserted in to the database.
  15: *
  16: * {@hide}
  17: */

下面为调用时序图,如下:

MediaScanner源码分析 - 东东 - 东东的博客

这时序图好像不是很规范!点击看大图!请见谅。吐舌笑脸 开始看代码把……

1,scanDirectories。

初始化数据并调用processDirectory处理扫描。


   1: public void scanDirectories(String[] directories, String volumeName) {
   2:         try {
   3:             long start = System.currentTimeMillis();
   4:             //初始化
   5:             initialize(volumeName);
   6:             //将数据库中的数据缓存到mFileCache
   7:             /*
   8:              * mFileCache.put(key, new FileCacheEntry(uri, rowId, path, lastModified));
   9:              */
  10:             prescan(null);
  11:             long prescan = System.currentTimeMillis();
  12:  
  13:             for (int i = 0; i < directories.length; i++) {
  14:                 //扫描处理
  15:                 processDirectory(directories[i], MediaFile.sFileExtensions, mClient);
  16:             }
  17:             long scan = System.currentTimeMillis();
  18:             //处理后续数据
  19:             postscan(directories);
  20:             long end = System.currentTimeMillis();

2,processDirectory

这是一个native方法,所以我们直接转向jni,代码如下:


   1: static void
   2: android_media_MediaScanner_processDirectory(JNIEnv *env, jobject thiz, jstring path, jstring extensions, jobject client)
   3: {   //获取MediaScanner
   4:     MediaScanner *mp = (MediaScanner *)env->GetIntField(thiz, fields.context);
   5:     //参数判断,并抛出异常
   6:     if (path == NULL) {
   7:         jniThrowException(env, "java/lang/IllegalArgumentException", NULL);
   8:         return;
   9:     }
  10:     if (extensions == NULL) {
  11:         jniThrowException(env, "java/lang/IllegalArgumentException", NULL);
  12:         return;
  13:     }
  14:     
  15:     const char *pathStr = env->GetStringUTFChars(path, NULL);
  16:     if (pathStr == NULL) {  // Out of memory
  17:         jniThrowException(env, "java/lang/RuntimeException", "Out of memory");
  18:         return;
  19:     }
  20:     const char *extensionsStr = env->GetStringUTFChars(extensions, NULL);
  21:     if (extensionsStr == NULL) {  // Out of memory
  22:         env->ReleaseStringUTFChars(path, pathStr);
  23:         jniThrowException(env, "java/lang/RuntimeException", "Out of memory");
  24:         return;
  25:     }
  26:     //初始化client实例
  27:     MyMediaScannerClient myClient(env, client);
  28:     //mp调用processDirectory
  29:     mp->processDirectory(pathStr, extensionsStr, myClient, ExceptionCheck, env);
  30:     //gc
  31:     env->ReleaseStringUTFChars(path, pathStr);
  32:     env->ReleaseStringUTFChars(extensions, extensionsStr);
  33: }

3,mp->processDirectory(pathStr, extensionsStr, myClient, ExceptionCheck, env);


   1: status_t MediaScanner::processDirectory(const char *path, const char* extensions,
   2:         MediaScannerClient& client, ExceptionCheck exceptionCheck, void* exceptionEnv)
   3: {//这方法不知道干吗的,估计跟线程有关
   4:     InitializeForThread();
   5:  
   6:     int pathLength = strlen(path);
   7:     if (pathLength >= PATH_MAX) {
   8:         return PVMFFailure;
   9:     }
  10:     char* pathBuffer = (char *)malloc(PATH_MAX + 1);
  11:     if (!pathBuffer) {
  12:         return PVMFFailure;
  13:     }
  14:  
  15:     int pathRemaining = PATH_MAX - pathLength;
  16:     strcpy(pathBuffer, path);
  17:     if (pathBuffer[pathLength - 1] != '/') {
  18:         pathBuffer[pathLength] = '/';
  19:         pathBuffer[pathLength + 1] = 0;
  20:         --pathRemaining;
  21:     }
  22:  
  23:     client.setLocale(mLocale);
  24:     //有是一个关键点
  25:     status_t result = doProcessDirectory(pathBuffer, pathRemaining, extensions, client, exceptionCheck, exceptionEnv);
  26:     //释放内存
  27:     free(pathBuffer);
  28:     return result;
  29: }

4,doProcessDirectory


   1: status_t MediaScanner::doProcessDirectory(char *path, int pathRemaining, const char* extensions,
   2:         MediaScannerClient& client, ExceptionCheck exceptionCheck, void* exceptionEnv)
   3: {
   4:     ……
   5:      ……
   6:         if (type == DT_REG || type == DT_DIR) {
   7:             int nameLength = strlen(name);
   8:             bool isDirectory = (type == DT_DIR);
   9:  
  10:             if (nameLength > pathRemaining || (isDirectory && nameLength + 1 > pathRemaining)) {
  11:                 // path too long!
  12:                 continue;
  13:             }
  14:  
  15:             strcpy(fileSpot, name);
  16:             if (isDirectory) {
  17:                 // ignore directories with a name that starts with '.'
  18:                 // for example, the Mac ".Trashes" directory
  19:                 if (name[0] == '.') continue;
  20:  
  21:                 strcat(fileSpot, "/");
  22:                 //文件夹,递归调用
  23:                 int err = doProcessDirectory(path, pathRemaining - nameLength - 1, extensions, client, exceptionCheck, exceptionEnv);
  24:                 if (err) {
  25:                     // pass exceptions up - ignore other errors
  26:                     if (exceptionCheck && exceptionCheck(exceptionEnv)) goto failure;
  27:                     LOGE("Error processing '%s' - skipping\n", path);
  28:                     continue;
  29:                 }
  30:             } else if (fileMatchesExtension(path, extensions)) {
  31:                 //文件,扩展名符合
  32:                 struct stat statbuf;
  33:                 stat(path, &statbuf);
  34:                 if (statbuf.st_size > 0) {
  35:                     //调用client的scanFile方法
  36:                     client.scanFile(path, statbuf.st_mtime, statbuf.st_size);
  37:                 }
  38:                 if (exceptionCheck && exceptionCheck(exceptionEnv)) goto failure;
  39:             }
  40:         }
  41: ……
  42: ……

5,client.scanFile
   1: // returns true if it succeeded, false if an exception occured in the Java code
   2:  virtual bool scanFile(const char* path, long long lastModified, long long fileSize)
   3:  {
   4:      jstring pathStr;
   5:      if ((pathStr = mEnv->NewStringUTF(path)) == NULL) return false;
   6:      //有点反射的感觉,调用java里面mClient中的scanFile方法
   7:      mEnv->CallVoidMethod(mClient, mScanFileMethodID, pathStr, lastModified, fileSize);
   8:  
   9:      mEnv->DeleteLocalRef(pathStr);
  10:      return (!mEnv->ExceptionCheck());
  11:  }

6,mEnv->CallVoidMethod(mClient, mScanFileMethodID, pathStr, lastModified, fileSize); 让我们回到Java大笑

在android.media.MediaScanner.MyMediaScannerClient中的scanFile方法是直接调用doScanFile的,来看看doScanFile


   1:  
   2:         public Uri doScanFile(String path, String mimeType, long lastModified, long fileSize,
   3:                 boolean scanAlways) {
   4:             Uri result = null;
   5:             // long t1 = System.currentTimeMillis();
   6:             try {
   7:                 FileCacheEntry entry = beginFile(path, mimeType, lastModified, fileSize);
   8:                 // rescan for metadata if file was modified since last scan
   9:                 if (entry != null && (entry.mLastModifiedChanged || scanAlways)) {
  10:                     String lowpath = path.toLowerCase();
  11:                     boolean ringtones = (lowpath.indexOf(RINGTONES_DIR) > 0);
  12:                     boolean notifications = (lowpath.indexOf(NOTIFICATIONS_DIR) > 0);
  13:                     boolean alarms = (lowpath.indexOf(ALARMS_DIR) > 0);
  14:                     boolean podcasts = (lowpath.indexOf(PODCAST_DIR) > 0);
  15:                     boolean music = (lowpath.indexOf(MUSIC_DIR) > 0)
  16:                             || (!ringtones && !notifications && !alarms && !podcasts);
  17:  
  18:                     if (isMetadataSupported(mFileType)) {
  19:                         // 调用jni方法
  20:                         processFile(path, mimeType, this);
  21:                     } else if (MediaFile.isImageFileType(mFileType)) {
  22:                         // we used to compute the width and height but it's not
  23:                         // worth it
  24:                     }
  25:  
  26:                     result = endFile(entry, ringtones, notifications, alarms, music, podcasts);
  27:                 }
  28:             } catch (RemoteException e) {
  29:                 Log.e(TAG, "RemoteException in MediaScanner.scanFile()", e);
  30:             }
  31:             // long t2 = System.currentTimeMillis();
  32:             // Log.v(TAG, "scanFile: " + path + " took " + (t2-t1));
  33:             return result;
  34:         }

补充:result = endFile(entry, ringtones, notifications, alarms, music, podcasts);就是在这里将媒体数据信息存放到数据库的

7,接着是native的 processFile


   1: static void
   2: android_media_MediaScanner_processFile(JNIEnv *env, jobject thiz, jstring path, jstring mimeType, jobject client)
   3: {
   4:     MediaScanner *mp = (MediaScanner *)env->GetIntField(thiz, fields.context);
   5:  
   6:     if (path == NULL) {
   7:         jniThrowException(env, "java/lang/IllegalArgumentException", NULL);
   8:         return;
   9:     }
  10:     
  11:     const char *pathStr = env->GetStringUTFChars(path, NULL);
  12:     if (pathStr == NULL) {  // Out of memory
  13:         jniThrowException(env, "java/lang/RuntimeException", "Out of memory");
  14:         return;
  15:     }
  16:     const char *mimeTypeStr = (mimeType ? env->GetStringUTFChars(mimeType, NULL) : NULL);
  17:     if (mimeType && mimeTypeStr == NULL) {  // Out of memory
  18:         env->ReleaseStringUTFChars(path, pathStr);
  19:         jniThrowException(env, "java/lang/RuntimeException", "Out of memory");
  20:         return;
  21:     }
  22:  
  23:     MyMediaScannerClient myClient(env, client);
  24:     //调用MediaScanner的processFile
  25:     mp->processFile(pathStr, mimeTypeStr, myClient);
  26:     env->ReleaseStringUTFChars(path, pathStr);
  27:     if (mimeType) {
  28:         env->ReleaseStringUTFChars(mimeType, mimeTypeStr);
  29:     }
  30: }

8,mp->processFile(pathStr, mimeTypeStr, myClient);
在此方法中根据不同的文件扩展名调用更加底层的解析方法,我想主要是ID3信息解析
   1: status_t MediaScanner::processFile(const char *path, const char* mimeType, MediaScannerClient& client)
   2: {
   3:     status_t result;
   4:     InitializeForThread();
   5:     //初始化client
   6:     client.setLocale(mLocale);
   7:     client.beginFile();
   8:     
   9:     //LOGD("processFile %s mimeType: %s\n", path, mimeType);
  10:     const char* extension = strrchr(path, '.');
  11:     //根据扩展名调用不同的解析方法
  12:     if (extension && strcasecmp(extension, ".mp3") == 0) {
  13:         result = parseMP3(path, client);
  14:     } else if (extension &&
  15:         (strcasecmp(extension, ".mp4") == 0 || strcasecmp(extension, ".m4a") == 0 ||
  16:          strcasecmp(extension, ".3gp") == 0 || strcasecmp(extension, ".3gpp") == 0 ||
  17:          strcasecmp(extension, ".3g2") == 0 || strcasecmp(extension, ".3gpp2") == 0)) {
  18:         result = parseMP4(path, client);
  19:     } else if (extension && strcasecmp(extension, ".ogg") == 0) {
  20:         result = parseOgg(path, client);
  21:     } else if (extension &&
  22:         ( strcasecmp(extension, ".mid") == 0 || strcasecmp(extension, ".smf") == 0
  23:         || strcasecmp(extension, ".imy") == 0)) {
  24:         result = parseMidi(path, client);
  25:     } else if (extension &&
  26:        (strcasecmp(extension, ".wma") == 0 || strcasecmp(extension, ".aac") == 0)) {
  27:         //TODO: parseWMA needs to be renamed to reflect what it is really doing,
  28:         //ie. using OpenCORE frame metadata utility(FMU) to retrieve metadata.
  29:         result = parseWMA(path, client);
  30:     } else {
  31:         result = PVMFFailure;
  32:     }
  33:     //调用client
  34:     client.endFile();
  35:  
  36:     return result;
  37: }

9,client.endFile()


   1: void MediaScannerClient::endFile()
   2: {
   3:     if (mLocaleEncoding != kEncodingNone) {
   4:         int size = mNames->size();
   5:         uint32_t encoding = kEncodingAll;
   6:         
   7:         // compute a bit mask containing all possible encodings
   8:         for (int i = 0; i < mNames->size(); i++)
   9:             encoding &= possibleEncodings(mValues->getEntry(i));
  10:         
  11:         // if the locale encoding matches, then assume we have a native encoding.
  12:         if (encoding & mLocaleEncoding)
  13:             convertValues(mLocaleEncoding);
  14:         
  15:         // finally, push all name/value pairs to the client
  16:         for (int i = 0; i < mNames->size(); i++) {
  17:             //在handleStringTag中是通过类反射的方法调用java中的handleStringTag
  18:             if (!handleStringTag(mNames->getEntry(i), mValues->getEntry(i)))
  19:                 break;
  20:         }
  21:     }
  22:     // else addStringTag() has done all the work so we have nothing to do
  23:     
  24:     delete mNames;
  25:     delete mValues;
  26:     mNames = NULL;
  27:     mValues = NULL;
  28: }

10,java中的handleStringTag,这个方法主要处理那些在底层解析后的数据返回到java层


   1: public void handleStringTag(String name, String value) {
   2:      if (name.equalsIgnoreCase("title") || name.startsWith("title;")) {
   3:          // Don't trim() here, to preserve the special \001 character
   4:          // used to force sorting. The media provider will trim() before
   5:          // inserting the title in to the database.
   6:          mTitle = value;
   7:      } else if (name.equalsIgnoreCase("artist") || name.startsWith("artist;")) {
   8:          mArtist = value.trim();
   9:      } else if (name.equalsIgnoreCase("albumartist") || name.startsWith("albumartist;")) {
  10:          mAlbumArtist = value.trim();
  11:      } else if (name.equalsIgnoreCase("album") || name.startsWith("album;")) {
  12:          mAlbum = value.trim();
  13:      } else if (name.equalsIgnoreCase("composer") || name.startsWith("composer;")) {
  14:          mComposer = value.trim();
  15:      } else if (name.equalsIgnoreCase("genre") || name.startsWith("genre;")) {
  16:          // handle numeric genres, which PV sometimes encodes like "(20)"
  17:          if (value.length() > 0) {
  18:              int genreCode = -1;
  19:              char ch = value.charAt(0);
  20:              if (ch == '(') {
  21:                  genreCode = parseSubstring(value, 1, -1);
  22:              } else if (ch >= '0' && ch <= '9') {
  23:                  genreCode = parseSubstring(value, 0, -1);
  24:              }
  25:              if (genreCode >= 0 && genreCode < ID3_GENRES.length) {
  26:                  value = ID3_GENRES[genreCode];
  27:              }
  28:          }
  29:          mGenre = value;
  30:      } else if (name.equalsIgnoreCase("year") || name.startsWith("year;")) {
  31:          mYear = parseSubstring(value, 0, 0);
  32:      } else if (name.equalsIgnoreCase("tracknumber") || name.startsWith("tracknumber;")) {
  33:          // track number might be of the form "2/12"
  34:          // we just read the number before the slash
  35:          int num = parseSubstring(value, 0, 0);
  36:          mTrack = (mTrack / 1000) * 1000 + num;
  37:      } else if (name.equalsIgnoreCase("discnumber") ||
  38:              name.equals("set") || name.startsWith("set;")) {
  39:          // set number might be of the form "1/3"
  40:          // we just read the number before the slash
  41:          int num = parseSubstring(value, 0, 0);
  42:          mTrack = (num * 1000) + (mTrack % 1000);
  43:      } else if (name.equalsIgnoreCase("duration")) {
  44:          mDuration = parseSubstring(value, 0, 0);
  45:      } else if (name.equalsIgnoreCase("writer") || name.startsWith("writer;")) {
  46:          mWriter = value.trim();
  47:      }
  48:  }

此致,此文结束,累。忍者

三篇有关MediaScanner的文章,希望对大家有所帮助。

对C/C++不是很熟悉,如发现分析有误,请告知。

--------END-------

 

转自:http://www.cnblogs.com/tanlon/archive/2011/03/11/1981804.html

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