MediaScanner.java 研究笔记（一）
1、/frameworks/base/media/java/android/media/MediaScanner.java
一来就是一大段调用来调用去的话，直接给你把思路理顺了~~剩下的就是咱们自个去找内幕喽！
/**
* Internal service helper that no-one should use directly.*
* The way the scan currently works is:
* - The Java MediaScannerService creates a MediaScanner (this class), and calls
* MediaScanner.scanDirectories on it.
* - scanDirectories() calls the native processDirectory() for each of the specified directories.
* - the processDirectory() JNI method wraps the provided mediascanner client in a native
* 'MyMediaScannerClient' class, then calls processDirectory() on the native MediaScanner
* object (which got created when the Java MediaScanner was created).
* - native MediaScanner.processDirectory() (currently part of opencore) calls
* doProcessDirectory(), which recurses over the folder, and calls
* native MyMediaScannerClient.scanFile() for every file whose extension matches.
* - native MyMediaScannerClient.scanFile() calls back on Java MediaScannerClient.scanFile,
* which calls doScanFile, which after some setup calls back down to native code, calling
* 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.
* - Java handleStringTag() gathers the key/value pairs that it's interested in.
* - once processFile returns and we're back in Java code in doScanFile(), it calls
* Java MyMediaScannerClient.endFile(), which takes all the data that's been
* gathered and inserts an entry in to the database.
*
* In summary:
* Java MediaScannerService calls
* Java MediaScanner scanDirectories, which calls
* Java MediaScanner processDirectory (native method), which calls
* native MediaScanner processDirectory, which calls
* native MyMediaScannerClient scanFile, which calls
* Java MyMediaScannerClient scanFile, which calls
* Java MediaScannerClient doScanFile, which calls
* Java MediaScanner processFile (native method), which calls
* native MediaScanner processFile, which calls
* native parseMP3, parseMP4, parseMidi, parseOgg or parseWMA, which calls
* native MyMediaScanner handleStringTag, which calls
* Java MyMediaScanner handleStringTag.
* Once MediaScanner processFile returns, an entry is inserted in to the database.
*
* The MediaScanner class is not thread-safe, so it should only be used in a single threaded manner.
*
* {@hide}
*/
2、 public void scanDirectories(String[] directories, String volumeName) {
try {
long start = System.currentTimeMillis();
initialize(volumeName);
prescan(null, true);
long prescan = System.currentTimeMillis();
if (ENABLE_BULK_INSERTS) {
// create MediaInserter for bulk inserts
mMediaInserter = new MediaInserter(mMediaProvider, 500);
}
for (int i = 0; i < directories.length; i++) {
processDirectory(directories[i], mClient);
}
3、 private native void processDirectory(String path, MediaScannerClient client);
/frameworks/base/media/jni/android_media_MediaScanner.cpp
static void
android_media_MediaScanner_processDirectory(
JNIEnv *env, jobject thiz, jstring path, jobject client)
{
LOGV("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;
}
MyMediaScannerClient myClient(env, client); // MyMediaScannerClient实例话
MediaScanResult result = mp->processDirectory(pathStr, myClient);
if (result == MEDIA_SCAN_RESULT_ERROR) {
LOGE("An error occurred while scanning directory '%s'.", pathStr);
}
env->ReleaseStringUTFChars(path, pathStr);
}
4、从* native MyMediaScannerClient scanFile, which calls
* Java MyMediaScannerClient scanFile ，JNI调用JAVA方法，通过env->GetMethodID完成。
class MyMediaScannerClient : public MediaScannerClient
{
public:
MyMediaScannerClient(JNIEnv *env, jobject client)
: mEnv(env),
mClient(env->NewGlobalRef(client)),
mScanFileMethodID(0),
mHandleStringTagMethodID(0),
mSetMimeTypeMethodID(0)
{
LOGV("MyMediaScannerClient constructor");
jclass mediaScannerClientInterface =
env->FindClass(kClassMediaScannerClient);
if (mediaScannerClientInterface == NULL) {
LOGE("Class %s not found", kClassMediaScannerClient);
} else {
mScanFileMethodID = env->GetMethodID(
mediaScannerClientInterface,
"scanFile",
"(Ljava/lang/String;JJZZ)V");
mHandleStringTagMethodID = env->GetMethodID(
mediaScannerClientInterface,
"handleStringTag",
"(Ljava/lang/String;Ljava/lang/String;)V");
mSetMimeTypeMethodID = env->GetMethodID(
mediaScannerClientInterface,
"setMimeType",
"(Ljava/lang/String;)V");
}
}
。。。
在MediaScanner中，MyMediaScannerClient implements MediaScannerClient{
......
public void scanFile(String path, long lastModified, long fileSize,
boolean isDirectory, boolean noMedia) {
// This is the callback funtion from native codes.
// Log.v(TAG, "scanFile: "+path);
doScanFile(path, null, lastModified, fileSize, isDirectory, false, noMedia);
}
......
}
5、Java MediaScannerClient doScanFile, which calls
* Java MediaScanner processFile (native method), which calls
在MediaScanner中，MyMediaScannerClient implements MediaScannerClient{
......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 {
FileCacheEntry entry = beginFile(path, mimeType, lastModified,
fileSize, isDirectory, noMedia);
// 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();
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);
// we only extract metadata for audio and video files
if (MediaFile.isAudioFileType(mFileType)
|| MediaFile.isVideoFileType(mFileType)) {
processFile(path, mimeType, this);
}
if (MediaFile.isImageFileType(mFileType)) {
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;
}
6、private native void processFile(String path, String mimeType, MediaScannerClient client);
static void
android_media_MediaScanner_processFile(
JNIEnv *env, jobject thiz, jstring path,
jstring mimeType, jobject client)
{
LOGV("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) {
LOGE("An error occurred while scanning file '%s'.", pathStr);
}
env->ReleaseStringUTFChars(path, pathStr);
if (mimeType) {
env->ReleaseStringUTFChars(mimeType, mimeTypeStr);
}
}
7、class MyMediaScannerClient : public MediaScannerClient
{
public:
MyMediaScannerClient(JNIEnv *env, jobject client)
: mEnv(env),
mClient(env->NewGlobalRef(client)),
mScanFileMethodID(0),
mHandleStringTagMethodID(0),
mSetMimeTypeMethodID(0)
{
LOGV("MyMediaScannerClient constructor");
jclass mediaScannerClientInterface =
env->FindClass(kClassMediaScannerClient);
if (mediaScannerClientInterface == NULL) {
LOGE("Class %s not found", kClassMediaScannerClient);
} else {
mScanFileMethodID = env->GetMethodID(
mediaScannerClientInterface,
"scanFile",
"(Ljava/lang/String;JJZZ)V");
mHandleStringTagMethodID = env->GetMethodID(
mediaScannerClientInterface,
"handleStringTag",
"(Ljava/lang/String;Ljava/lang/String;)V");
mSetMimeTypeMethodID = env->GetMethodID(
mediaScannerClientInterface,
"setMimeType",
"(Ljava/lang/String;)V");
}
}
8、public void handleStringTag(String name, String value) {
if (name.equalsIgnoreCase("title") || name.startsWith("title;")) {
// Don't trim() here, to preserve the special \001 character
// used to force sorting. The media provider will trim() before
// inserting the title in to the database.
mTitle = value;
} else if (name.equalsIgnoreCase("artist") || name.startsWith("artist;")) {
mArtist = value.trim();
} else if (name.equalsIgnoreCase("albumartist") || name.startsWith("albumartist;")
|| name.equalsIgnoreCase("band") || name.startsWith("band;")) {
mAlbumArtist = value.trim();
} else if (name.equalsIgnoreCase("album") || name.startsWith("album;")) {
mAlbum = value.trim();
} else if (name.equalsIgnoreCase("composer") || name.startsWith("composer;")) {
mComposer = value.trim();
} else if (mProcessGenres &&
(name.equalsIgnoreCase("genre") || name.startsWith("genre;"))) {
mGenre = getGenreName(value);
} else if (name.equalsIgnoreCase("year") || name.startsWith("year;")) {
mYear = parseSubstring(value, 0, 0);
} else if (name.equalsIgnoreCase("tracknumber") || name.startsWith("tracknumber;")) {
// track number might be of the form "2/12"
// the second part is the total number of tracks
int num = parseSubstring(value, 0, 0);
mTrack = (mTrack / 1000) * 1000 + num;
// if (SystemProperties.BLUETI_ENHANCEMENT) {
// int index = value.indexOf('/');
// mNumberOfTracks = parseSubstring(value, index + 1, 0);
// }
} else if (name.equalsIgnoreCase("discnumber") ||
name.equals("set") || name.startsWith("set;")) {
// set number might be of the form "1/3"
// we just read the number before the slash
int num = parseSubstring(value, 0, 0);
mTrack = (num * 1000) + (mTrack % 1000);
} else if (name.equalsIgnoreCase("duration")) {
mDuration = parseSubstring(value, 0, 0);
} else if (name.equalsIgnoreCase("writer") || name.startsWith("writer;")) {
mWriter = value.trim();
} else if (name.equalsIgnoreCase("compilation")) {
mCompilation = parseSubstring(value, 0, 0);
} else if (name.equalsIgnoreCase("isdrm")) {
mIsDrm = (parseSubstring(value, 0, 0) == 1);
}
}