多媒体文件管理，资源的扫描MediaScanner（二）

多媒体文件的扫描MediaScanner

主要由两部分组成&＃xff0c;一是MediaScannerReceiver&＃xff0c;一是MediaScannerService&＃xff0c;扫描的执行由广播触发。MediaScannerReceiver接收4中类型的广播&＃xff1a;

AndroidManifest.xml


看下执行扫描的具体代码&＃xff1a;

Packages/providers/mediaprovider/…/MediaScannerReceiver.java
public class MediaScannerReceiver extends BroadcastReceiver {public void onReceive(Context context, Intent intent) {final String action &＃61; intent.getAction();final Uri uri &＃61; intent.getData();if (Intent.ACTION_BOOT_COMPLETED.equals(action)) {
//收到开机广播&＃xff0c;同时扫描内外存储设备。scan(context, MediaProvider.INTERNAL_VOLUME);scan(context, MediaProvider.EXTERNAL_VOLUME);
}else{if (uri.getScheme().equals("file")) {
//获取外部存储设备的路径。String path &＃61; uri.getPath();String externalStoragePath &＃61;
Environment.getExternalStorageDirectory().getPath();String legacyPath &＃61; Environment.getLegacyExternalStorageDirectory().getPath();path &＃61; new File(path).getCanonicalPath();if (path.startsWith(legacyPath)) {path &＃61; externalStoragePath &＃43; path.substring(legacyPath.length());}
}
//外部存储设备挂载的广播&＃xff0c;if (Intent.ACTION_MEDIA_MOUNTED.equals(action)) {scan(context, MediaProvider.EXTERNAL_VOLUME);
}else if(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE.equals(action) &&
path !&＃61; null && path.startsWith(externalStoragePath &＃43; "/")) {
//扫描特定的文件路径。scanFile(context, path);
}
}
}


不管是调用scan还是scanfile方法&＃xff0c;都是调用MediaScannerService来接着处理。

private void scan(Context context, String volume) {Bundle args &＃61; new Bundle();args.putString("volume", volume);context.startService(new Intent(context, MediaScannerService.class).putExtras(args));} private void scanFile(Context context, String path) {Bundle args &＃61; new Bundle();args.putString("filepath", path);context.startService(new Intent(context, MediaScannerService.class).putExtras(args));
}


接着看MediaScannerService的代码&＃xff1a;

MediaScannerService.java

public class MediaScannerService extends Service implements Runnable {
//首先创建一个唤醒锁&＃xff0c;级别是PARTIAL_WAKE_LOCK&＃xff0c;确保cpu一直在运行&＃xff0c;屏幕和键盘背光都可以被关闭&＃xff0c;在扫描开始会通过mWakeLock.acquire();获取唤醒锁&＃xff0c;这样扫描的过程中不会sleep&＃xff0c;如果用户按了power键&＃xff0c;屏幕会关掉&＃xff0c;但是cpu会保持运行&＃xff0c;知道调用mWakeLock.release();PowerManager pm &＃61; (PowerManager)getSystemService(Context.POWER_SERVICE);mWakeLock &＃61; pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, TAG);
//这里新启了一个线程&＃xff0c;因为service默认是运行在主线程的&＃xff0c;所以要在单独的线程处理扫描&＃xff0c;不然会block主线程。Thread thr &＃61; new Thread(null, this, "MediaScannerService");thr.start();
}


顺带看下他的run()方法&＃xff0c;这里展示启动一个独立线程的示例&＃xff1a;

public void run() {Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND &＃43;Process.THREAD_PRIORITY_LESS_FAVORABLE);
//prepare()这个方法是一定要调用的&＃xff0c;因为这个方法会去创建属于这个新线程的Looper&＃xff0c;同时创建属于这个线程的消息队列&＃xff0c;也即是Looper实例中的MessageQueue变量。Looper.prepare();
//获取属于这个新线程的Looper&＃xff0c;也即是上一步prepare中创建的。mServiceLooper &＃61; Looper.myLooper();mServiceHandler &＃61; new ServiceHandler();
//调用loop()方法&＃xff0c;让线程循环起来。Looper.loop();
}


我们知道service的onCreate方法之后&＃xff0c;会调用其onStartCommand&＃xff0c;在onStartCommand方法中会通过mServiceHandler发送消息&＃xff0c;同时携带Intent中的扫描信息&＃xff0c;直接看其handleMessage方法实现&＃xff1a;

private final class ServiceHandler extends Handler {public void handleMessage(Message msg) {Bundle arguments &＃61; (Bundle) msg.obj;String filePath &＃61; arguments.getString("filepath");if (filePath !&＃61; null) {
//这里处理扫描指定文件路径的请求&＃xff0c;ACTION_MEDIA_SCANNER_SCAN_FILE。IBinder binder &＃61; arguments.getIBinder("listener");IMediaScannerListener listener &＃61;(binder &＃61;&＃61; null ? null : IMediaScannerListener.Stub.asInterface(binder));uri &＃61; scanFile(filePath, arguments.getString("mimetype"));listener.scanCompleted(filePath, uri);
}else {
//下面是扫描存储设备&＃xff0c;String volume &＃61; arguments.getString("volume");String[] directories &＃61; null;if (MediaProvider.INTERNAL_VOLUME.equals(volume)) {
//这里是扫描内部存储设备&＃xff0c;只考虑了media目录&＃xff0c;directories &＃61; new String[] {Environment.getRootDirectory() &＃43; "/media",Environment.getOemDirectory() &＃43; "/media",};} else if (MediaProvider.EXTERNAL_VOLUME.equals(volume)) {
//这里扫描外部存储设备&＃xff0c;考虑了是不是多用户。if (getSystemService(UserManager.class).isDemoUser()) {directories &＃61; ArrayUtils.appendElement(String.class,mExternalStoragePaths,Environment.getDataPreloadsMediaDirectory().getAbsolutePath());
}else{directories &＃61; mExternalStoragePaths;
}
scan(directories, volume);
}
}
}
}


接着看下他的scan()函数&＃xff1a;

private void scan(String[] directories, String volumeName) {if (volumeName.equals(MediaProvider.EXTERNAL_VOLUME)) {openDatabase(volumeName);}
//通过MediaScanner对象&＃xff0c;进一步执行扫描操作&＃xff0c;携带的参数是要扫描的目录。try (MediaScanner scanner &＃61; new MediaScanner(this, volumeName)) {scanner.scanDirectories(directories);
}
}


转到frameworks/base/media/java/…/MediaScanner.java。

private final MyMediaScannerClient mClient&＃61; new MyMediaScannerClient();

public void scanDirectories(String[] directories) &＃64; MediaScanner.java {
// mMediaInserter对象处理数据批量插入数据库的操作&＃xff0c;mMediaInserter &＃61; new MediaInserter(mMediaProvider, 500);for (int i &＃61; 0; i //这是个jni方法&＃xff0c;循环处理directories的目录。这里的mClient是MyMediaScannerClient类型的对象&＃xff0c;它是MediaScanner.java的内部类。processDirectory(directories[i], mClient);
}
//刷新剩余的插入记录。
mMediaInserter.flushAll();
mMediaInserter &＃61; null;
}


还要继续看扫描的处理&＃xff0c;转到jni层&＃xff0c;

android_media_MediaScanner_processDirectory( )
&＃64;android_media_MediaScanner.cpp{MediaScanner *mp &＃61; getNativeScanner_l(env, thiz);MyMediaScannerClient myClient(env, client);MediaScanResult result &＃61; mp->processDirectory(pathStr, myClient);
}


上面的函数中要搞清楚两个问题&＃xff0c;mp具体是什么对象&＃xff1f;myClient怎么调用的java层的client实例的方法。
先看mp具体是什么对象&＃xff1f;

//这个native_init方法&＃xff0c;是有MediaScanner.java的static block调用的。

static void android_media_MediaScanner_native_init(JNIEnv *env){//显示找到java层"android/media/MediaScanner";这个类。jclass clazz &＃61; env->FindClass(kClassMediaScanner);//然后取出java层的变量mNativeContext&＃xff0c;转成native层的变量fields.context&＃xff0c;用来存取值使用。fields.context &＃61; env->GetFieldID(clazz,
"mNativeContext", "J");}

//这个native_setup是在MediaScanner.java的构造函数中调用的。

static void android_media_MediaScanner_native_setup(JNIEnv *env, jobject thiz){
//把StagefrightMediaScanner实例存入到了fields.context中。MediaScanner *mp &＃61; new StagefrightMediaScanner;env->SetLongField(thiz, fields.context, (jlong)mp);
}


所以上面的processDirectory(…)方法就转到了StagefrightMediaScanner.cpp中&＃xff0c;实质上调用的是其父类MediaScanner.cpp中的processDirectory方法。

MediaScanner.cpp

MediaScanResult MediaScanner::doProcessDirectory(char *path, int pathRemaining, MediaScannerClient &client, bool noMedia) {
//先做一些处理&＃xff0c;是不是要跳过某个目录&＃xff0c;找出所有非多媒体.nomedia&＃xff0c;打开目录&＃xff0c;跳过一些不存在的目录&＃xff0c;调用doProcessDirectoryEntry。DIR* dir &＃61; opendir(path);while ((entry &＃61; readdir(dir))) {if (doProcessDirectoryEntry(path, pathRemaining, client, noMedia, entry, fileSpot)&＃61;&＃61; MEDIA_SCAN_RESULT_ERROR){result &＃61; MEDIA_SCAN_RESULT_ERROR;break;
}
}
closedir(dir);
}
MediaScanResult MediaScanner::doProcessDirectoryEntry(char *path, int pathRemaining, MediaScannerClient &client, bool noMedia,struct dirent* entry, char* fileSpot) {const char* name &＃61; entry->d_name;
//忽略“.”和“..”if (name[0] &＃61;&＃61; &＃39;.&＃39; && (name[1] &＃61;&＃61; 0 || (name[1] &＃61;&＃61; &＃39;.&＃39; && name[2] &＃61;&＃61; 0))) {…}
//获取文件类型。int type &＃61; entry->d_type;
//接下来如果是目录&＃xff0c;继续调用doProcessDirectory&＃xff0c;类似一个递归。如果是文件&＃xff0c;调用client.scanFile方法。if (type &＃61;&＃61; DT_DIR) {MediaScanResult result &＃61; doProcessDirectory(path, pathRemaining - nameLength - 1,client, childNoMedia);
} else if (type &＃61;&＃61; DT_REG) {status_t status &＃61; client.scanFile(path, statbuf.st_mtime, statbuf.st_size,false /*isDirectory*/, noMedia);
}
}


还记得上面提到的client&＃xff0c;是android_media_MediaScanner_processDirector()&＃64;android_media_MediaScanner.cpp中传过来的&＃xff0c;实质是MyMediaScannerClient类型的对象。MyMediaScannerClient是android_media_MediaScanner.cp的子类&＃xff0c;继承自MediaScannerClient.cpp

接着看下他的scanFile()方法&＃xff1a;

class MyMediaScannerClient : public MediaScannerClient
virtual status_t scanFile(const char* path, long long lastModified,long long fileSize, bool isDirectory, bool noMedia){
//这个函数是调用java层的类MyMediaScannerClient&＃xff08;MediaScanner.java的内部类&＃xff09;中的方法scanFile方法。mEnv->CallVoidMethod(mClient, mScanFileMethodID, pathStr, lastModified,fileSize, isDirectory, noMedia);
}


以上面的代码为例&＃xff0c;插播native层如何调用java层代码的&＃xff1a;

mEnv指针变量的类型是JNIEnv&＃xff0c;而JNIEnv又是JNINativeInterface结构类型的&＃xff0c;代表了jni的本地接口&＃xff0c;里面包含了很多的函数。

jobject类型&＃xff0c;代表了调用native方法的&＃xff0c;那个java类实例&＃xff0c;当从java层调用native方法时&＃xff0c;前两个参数(JNIEnv *env, jobject thiz)都是自动带入的&＃xff0c;后面的才是函数的真正入参。

解释下mEnv->CallVoidMethod()中参数&＃xff1a;

mClient是jobject类型的对象&＃xff0c;代表了java层的类MyMediaScannerClient的类实例&＃xff0c;具体是在MyMediaScannerClient(cpp)的构造函数中的初始化列表中赋值的&＃xff1a;mClient(env->NewGlobalRef(client))。

mScanFileMethodID是jmethodID类型的变量&＃xff0c;它的赋值语句&＃xff1a;

mScanFileMethodID &＃61; env->GetMethodID(

mediaScannerClientInterface,"scanFile","(Ljava/lang/String;JJZZ)V");

在这条赋值语句中mediaScannerClientInterface是jclass 类型的java层类&＃xff08;MediaScannerClient.java&＃xff09;实例&＃xff08;注意不是对象实例&＃xff09;&＃xff1a;

static const char* constkClassMediaScannerClient &＃61;"android/media/MediaScannerClient";

jclass mediaScannerClientInterface &＃61; env->FindClass(kClassMediaScannerClient);

"scanFile"是java层类MediaScannerClient.java中方法名。

"(Ljava/lang/String;JJZZ)V"是scanFile这个方法的类型签名&＃xff0c;括号中是参数&＃xff0c;最后是返回值。

JNI对所有的数据类型做了类型定义&＃xff1a;

JNI基础类型对照表

JNI引用数据类型对照表

JNI中类型签名&＃xff0c;注意boolean&＃xff0c;long

接着前面扫描流程分析&＃xff1a;

scanFile又直接调用了doScanFile方法&＃xff1a;

MediaScanner.java

public Uri doScanFile(String path, String mimeType, long lastModified, long fileSize,boolean isDirectory, boolean scanAlways, boolean noMedia)&＃64; MyMediaScannerClient {
//获取文件类型&＃xff0c;生成FileEntry对象。FileEntry entry &＃61; beginFile(path, mimeType, lastModified,fileSize, isDirectory, noMedia);
//接下来区分多媒体文件&＃xff0c;非多媒体文件。if (noMedia) {
//非多媒体文件&＃xff0c;直接调用endFile。result &＃61; endFile(entry, false, false, false, false, false);
}else{
//根据beginFile中获取的文件类型mFileType&＃xff0c;判断是音频&＃xff0c;视频&＃xff0c;图片。boolean isaudio &＃61; MediaFile.isAudioFileType(mFileType);boolean isvideo &＃61; MediaFile.isVideoFileType(mFileType);boolean isimage &＃61; MediaFile.isImageFileType(mFileType);
//做路径转化&＃xff0c;这里的模拟外部存储设备&＃xff0c;应该是指手机内存中除PRIVATE外的部分&＃xff1f;if (isaudio || isvideo || isimage) {path &＃61; Environment.maybeTranslateEmulatedPathToInternal(new File(path)).getAbsolutePath();
}
//如果是音视频文件&＃xff0c;只提取元数据&＃xff0c;ID3信息&＃xff0c;比如&＃xff1a;宽高&＃xff0c;日期&＃xff0c;专辑名&＃xff0c;艺术家等。
if (isaudio || isvideo) {processFile(path, mimeType, this);
}
//如果是图片&＃xff0c;执行解码。
if (isimage) {processImageFile(path);
}
// endFile&＃xff0c;做的一个主要工作就是往数据库插入数据。
result &＃61; endFile(entry, ringtones, notifications, alarms, music, podcasts);
}
}

private Uri endFile(FileEntry entry, boolean ringtones, boolean notifications,boolean alarms, boolean music, boolean podcasts){
//生成一个存入数据库的数据对象ContentValues values &＃61; toValues();
//对jpg的对象&＃xff0c;处理下其ExifInterface信息&＃xff0c;主要角度调整。if((mFileType &＃61;&＃61; MediaFile.FILE_TYPE_JPEG|| MediaFile.isRawImageFileType(mFileType)) && !mNoMedia){ExifInterface exif &＃61; new ExifInterface(entry.mPath);int orientation &＃61; exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, -1);if (orientation !&＃61; -1) {int degree;switch(orientation) {case ExifInterface.ORIENTATION_ROTATE_90:degree &＃61; 90;
}
values.put(Images.Media.ORIENTATION, degree);
}
}
//处理数据插入的对象&＃xff0c;
MediaInserter inserter &＃61; mMediaInserter;
//根据不同的类型&＃xff0c;设置相应的uri&＃xff0c;这些uri来自MediaStore.java。
if (MediaFile.isVideoFileType(mFileType)) {tableUri &＃61; mVideoUri;
} else if (MediaFile.isImageFileType(mFileType)) {tableUri &＃61; mImagesUri;
}
//有了uri&＃xff0c;有了要插入的数据values&＃xff0c;调用MediaInserter插入数据库。一个新的文件插入时&＃xff0c;要先插入其目录&＃xff0c;然后在插入文件&＃xff0c;记得调用flushAll&＃xff0c;或者flush清空缓冲区。
inserter.insert(tableUri, values);
}