DownloadProvider 详细分析

Download的源码编译分为两个部分，一个是DownloadProvider.apk, 一个是DownloadProviderUi.apk.

这两个apk的源码分别位于

packages/providers/DownloadProvider/ui/src

packages/providers/DownloadProvider/src

其中，DownloadProvider的部分是下载逻辑的实现，而DownloadProviderUi是界面部分的实现。

然后DownloadProvider里面的下载虽然主要是通过DownloadService进行的操作，但是由于涉及到Notification的更新，下载进度的展示，下载的管理等。

所以还是有不少其它的类来分别进行操作。

DownloadProvider --  数据库操作的封装，继承自ContentProvider；

DownloadManager -- 大部分逻辑是进一步封装数据操作，供外部调用；
DownloadService -- 封装文件download，delete等操作，并且操纵下载的norification；继承自Service；
DownloadNotifier -- 状态栏Notification逻辑；
DownloadReceiver -- 配合DownloadNotifier进行文件的操作及其Notification；
DownloadList -- Download app主界面，文件界面交互；

下载一般是从Browser里面点击链接开始，我们先来看一下Browser中的代码

在browser的src/com/android/browser/DownloadHandler.java函数中，我们可以看到一个很完整的Download的调用，我们在写自己的app的时候，也可以对这一段进行参考：

 public static void startingDownload(Activity activity,
         String url, String userAgent, String contentDisposition,
         String mimetype, String referer, boolean privateBrowsing, long contentLength,
         String filename, String downloadPath) {
     // java.net.URI is a lot stricter than KURL so we have to encode some
     // extra characters. Fix for b 2538060 and b 1634719
     WebAddress webAddress;
     try {
         webAddress = new WebAddress(url);
         webAddress.setPath(encodePath(webAddress.getPath()));
     } catch (Exception e) {
         // This only happens for very bad urls, we want to chatch the
         // exception here
         Log.e(LOGTAG, "Exception trying to parse url:" + url);
         return;
     }

     String addressString = webAddress.toString();
     Uri uri = Uri.parse(addressString);
     final DownloadManager.Request request;
     try {
         request = new DownloadManager.Request(uri);
     } catch (IllegalArgumentException e) {
         Toast.makeText(activity, R.string.cannot_download, Toast.LENGTH_SHORT).show();
         return;
     }
     request.setMimeType(mimetype);
     // set downloaded file destination to /sdcard/Download.
     // or, should it be set to one of several Environment.DIRECTORY* dirs
     // depending on mimetype?
     try {
         setDestinationDir(downloadPath, filename, request);
     } catch (Exception e) {
         showNoEnoughMemoryDialog(activity);
         return;
     }
     // let this downloaded file be scanned by MediaScanner - so that it can
     // show up in Gallery app, for example.
     request.allowScanningByMediaScanner();
     request.setDescription(webAddress.getHost());
     // XXX: Have to use the old url since the cookies were stored using the
     // old percent-encoded url.
     String cookies = CookieManager.getInstance().getCookie(url, privateBrowsing);
     request.addRequestHeader("cookie", cookies);
     request.addRequestHeader("User-Agent", userAgent);
     request.addRequestHeader("Referer", referer);
     request.setNotificationVisibility(
             DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
     final DownloadManager manager = (DownloadManager) activity
             .getSystemService(Context.DOWNLOAD_SERVICE);
     new Thread("Browser download") {
         public void run() {
             manager.enqueue(request);
         }
     }.start();
     showStartDownloadToast(activity);
 }

在这个操作中，我们看到添加了request的各种参数，然后最后调用了DownloadManager的enqueue进行下载，并且在开始后，弹出了开始下载的这个toast。manager是一个DownloadManager的实例，DownloadManager是存在与 frameworks / base / core / java / android / app / DownloadManager.java。可以看到enqueue的实现为：

 public long enqueue(Request request) {
     ContentValues values = request.toContentValues(mPackageName);
     Uri downloadUri = mResolver.insert(Downloads.Impl.CONTENT_URI, values);
     long id = Long.parseLong(downloadUri.getLastPathSegment());
    return id;

enqueue函数主要是将Rquest实例分解组成一个ContentValues实例，并且添加到数据库中，函数返回插入的这条数据返回的ID；ContentResolver.insert函数会调用到DownloadProvider实现的ContentProvider的insert函数中去，如果我们去查看insert的code的话，我们可以看到操作是很多的。但是我们只需要关注几个关键的部分：

 ......
 //将相关的请求参数，配置等插入到downloads数据库；
 long rowID = db.insert(DB_TABLE, null, filteredValues);
 ......
 //将相关的请求参数，配置等插入到request_headers数据库中；
 insertRequestHeaders(db, rowID, values);
 ......
 if (values.getAsInteger(Downloads.Impl.COLUMN_DESTINATION) ==
                 Downloads.Impl.DESTINATION_NON_DOWNLOADMANAGER_DOWNLOAD) {
             // When notification is requested, kick off service to process all
             // relevant downloads.
 //启动DownloadService进行下载及其它工作
             if (Downloads.Impl.isNotificationToBeDisplayed(vis)) {
                 context.startService(new Intent(context, DownloadService.class));
             }
         } else {
             context.startService(new Intent(context, DownloadService.class));
         }
         notifyContentChanged(uri, match);
         return ContentUris.withAppendedId(Downloads.Impl.CONTENT_URI, rowID);

在这边，我们就可以看到下载的DownloadService的调用了。因为是一个startService的方法，所以我们在DownloadService里面，是要去走oncreate的方法的。

 @Override
 public void onCreate() {
     super.onCreate();
     if (Constants.LOGVV) {
         Log.v(Constants.TAG, "Service onCreate");
     }

     if (mSystemFacade == null) {
         mSystemFacade = new RealSystemFacade(this);
     }

     mAlarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
     mStorageManager = new StorageManager(this);

    mUpdateThread = new HandlerThread(TAG + "-UpdateThread");
     mUpdateThread.start();
     mUpdateHandler = new Handler(mUpdateThread.getLooper(), mUpdateCallback);
     mScanner = new DownloadScanner(this);
     mNotifier = new DownloadNotifier(this);
     mNotifier.cancelAll();

     mObserver = new DownloadManagerContentObserver();
     getContentResolver().registerContentObserver(Downloads.Impl.ALL_DOWNLOADS_CONTENT_URI,
             true, mObserver);
 }

这边的话，我们可以看到先去启动了一个handler去接收callback的处理

 mUpdateThread = new HandlerThread(TAG + "-UpdateThread");
  mUpdateThread.start();
  mUpdateHandler = new Handler(mUpdateThread.getLooper(), mUpdateCallback);

然后去

 getContentResolver().registerContentObserver(Downloads.Impl.ALL_DOWNLOADS_CONTENT_URI,
                 true, mObserver)

是去注册监听Downloads.Impl.ALL_DOWNLOADS_CONTENT_URI的Observer。

而oncreate之后，就会去调用onStartCommand方法.

 @Override
 ublic int onStartCommand(Intent intent, int flags, int startId) {
     int returnValue = super.onStartCommand(intent, flags, startId);
     if (Constants.LOGVV) {
         Log.v(Constants.TAG, "Service onStart");
     }
     mLastStartId = startId;
     enqueueUpdate();
     return returnValue;
 }

在enqueueUpdate的函数中，我们会向mUpdateHandler发送一个MSG_UPDATE Message，

 private void enqueueUpdate() {
     mUpdateHandler.removeMessages(MSG_UPDATE);
     mUpdateHandler.obtainMessage(MSG_UPDATE, mLastStartId, -1).sendToTarget();
 }

mUpdateCallback中接收到并且处理：

 private Handler.Callback mUpdateCallback = new Handler.Callback() {
         @Override
         public boolean handleMessage(Message msg) {
             Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
             final int startId = msg.arg1;
             final boolean isActive;
             synchronized (mDownloads) {
                 isActive = updateLocked();
             }
             ......
             if (isActive) {
 //如果Active，则会在Delayed 5×60000ms后发送MSG_FINAL_UPDATE Message，主要是为了“any finished operations that didn't trigger an update pass.”
                 enqueueFinalUpdate();
             } else {
 //如果没有Active的任务正在进行，就会停止Service以及其它
                 if (stopSelfResult(startId)) {
                     if (DEBUG_LIFECYCLE) Log.v(TAG, "Nothing left; stopped");
                     getContentResolver().unregisterContentObserver(mObserver);
                     mScanner.shutdown();
                     mUpdateThread.quit();
                 }
             }
             return true;
         }
     };

这边的 重点是updateLocked()函数

     private boolean updateLocked() {
         final long now = mSystemFacade.currentTimeMillis();

         boolean isActive = false;
         long nextActionMillis = Long.MAX_VALUE;
 //mDownloads初始化是一个空的Map<Long, DownloadInfo>
         final Set<Long> staleIds = Sets.newHashSet(mDownloads.keySet());

         final ContentResolver resolver = getContentResolver();
 //获取所有的DOWNLOADS任务
         final Cursor cursor = resolver.query(Downloads.Impl.ALL_DOWNLOADS_CONTENT_URI,
                 null, null, null, null);
         try {
             final DownloadInfo.Reader reader = new DownloadInfo.Reader(resolver, cursor);
             final int idColumn = cursor.getColumnIndexOrThrow(Downloads.Impl._ID);
 //迭代Download Cusor
             while (cursor.moveToNext()) {
                 final long id = cursor.getLong(idColumn);
                 staleIds.remove(id);

                 DownloadInfo info = mDownloads.get(id);
 //开始时，mDownloads是没有任何内容的，info==null
                 if (info != null) {
 //从数据库更新最新的Download info信息，来监听数据库的改变并且反应到界面上
                     updateDownload(reader, info, now);
                 } else {
 //添加新下载的Dwonload info到mDownloads，并且从数据库读取新的Dwonload info
                     info = insertDownloadLocked(reader, now);
                 }
 //这里的mDeleted参数表示的是当我删除了正在或者已经下载的内容时，首先数据库会update这个info.mDeleted为true，而不是直接删除文件
                 if (info.mDeleted) {
 //不详细解释delete函数，主要是删除数据库内容和现在文件内容
                     if (!TextUtils.isEmpty(info.mMediaProviderUri)) {
                 resolver.delete(Uri.parse(info.mMediaProviderUri), null, null);
                     }
                     deleteFileIfExists(info.mFileName);
                     resolver.delete(info.getAllDownloadsUri(), null, null);

                 } else {
                     // 开始下载文件
                     final boolean activeDownload = info.startDownloadIfReady(mExecutor);

                     // 开始media scanner
                     final boolean activeScan = info.startScanIfReady(mScanner);
                     isActive |= activeDownload;
                     isActive |= activeScan;
                 }

                 // Keep track of nearest next action
                 nextActionMillis = Math.min(info.nextActionMillis(now), nextActionMillis);
             }
         } finally {
             cursor.close();
         }
         // Clean up stale downloads that disappeared
         for (Long id : staleIds) {
             deleteDownloadLocked(id);
         }
         // Update notifications visible to user
         mNotifier.updateWith(mDownloads.values());
         if (nextActionMillis > 0 && nextActionMillis < Long.MAX_VALUE) {
             final Intent intent = new Intent(Constants.ACTION_RETRY);
             intent.setClass(this, DownloadReceiver.class);
             mAlarmManager.set(AlarmManager.RTC_WAKEUP, now + nextActionMillis,
                     PendingIntent.getBroadcast(this, 0, intent, PendingIntent.FLAG_ONE_SHOT));
         }
         return isActive;
     }

重点来看看文件的下载，startDownloadIfReady函数:

  public boolean startDownloadIfReady(ExecutorService executor) {
         synchronized (this) {
             final boolean isReady = isReadyToDownload();
             final boolean isActive = mSubmittedTask != null && !mSubmittedTask.isDone();
             if (isReady && !isActive) {
 //更新数据库的任务状态为STATUS_RUNNING
                 if (mStatus != Impl.STATUS_RUNNING) {
                     mStatus = Impl.STATUS_RUNNING;
                     ContentValues values = new ContentValues();
                     values.put(Impl.COLUMN_STATUS, mStatus);
                     mContext.getContentResolver().update(getAllDownloadsUri(), values, null, null);
                 }
 //开始下载任务
                 mTask = new DownloadThread(
                         mContext, mSystemFacade, this, mStorageManager, mNotifier);
                 mSubmittedTask = executor.submit(mTask);
             }
             return isReady;
         }
     }

在DownloadThread的处理中，如果HTTP的状态是ok的话，会去进行transferDate的处理。

   
   
   
   
private void transferData(State state, HttpURLConnection conn) throws StopRequestException {
......
in = conn.getInputStream();
......
//获取InputStream和OutPutStream
if (DownloadDrmHelper.isDrmConvertNeeded(state.mMimeType)) {
                    drmClient = new DrmManagerClient(mContext);
                    final RandomAccessFile file = new RandomAccessFile(
                            new File(state.mFilename), "rw");
                    out = new DrmOutputStream(drmClient, file, state.mMimeType);
                    outFd = file.getFD();
                } else {
                    out = new FileOutputStream(state.mFilename, true);
                    outFd = ((FileOutputStream) out).getFD();
                }
......
// Start streaming data, periodically watch for pause/cancel
            // commands and checking disk space as needed.
            transferData(state, in, out);
......
}
------

   
   
   
   
private void transferData(State state, InputStream in, OutputStream out)
            throws StopRequestException {
        final byte data[] = new byte[Constants.BUFFER_SIZE];
        for (;;) {
//从InputStream中读取内容信息，“in.read(data)”，并且对数据库中文件下载大小进行更新
            int bytesRead = readFromResponse(state, data, in);
            if (bytesRead == -1) { // success, end of stream already reached
                handleEndOfStream(state);
                return;
            }
            state.mGotData = true;
//利用OutPutStream写入读取的InputStream，"out.write(data, 0, bytesRead)"
            writeDataToDestination(state, data, bytesRead, out);
            state.mCurrentBytes += bytesRead;
            reportProgress(state);
            }
            checkPausedOrCanceled(state);
        }
    }
至此，下载文件的流程就说完了，继续回到DownloadService的updateLocked()函数中来；重点来分析DownloadNotifier的updateWith()函数，这个方法用来更新Notification

   
   
   
   
//这段代码是根据不同的状态设置不同的Notification的icon
 if (type == TYPE_ACTIVE) {
                builder.setSmallIcon(android.R.drawable.stat_sys_download);
            } else if (type == TYPE_WAITING) {
                builder.setSmallIcon(android.R.drawable.stat_sys_warning);
            } else if (type == TYPE_COMPLETE) {
                builder.setSmallIcon(android.R.drawable.stat_sys_download_done);
            }
   
   
   
   
//这段代码是根据不同的状态来设置不同的notification Intent
// Build action intents
            if (type == TYPE_ACTIVE || type == TYPE_WAITING) {
                // build a synthetic uri for intent identification purposes
                final Uri uri = new Uri.Builder().scheme("active-dl").appendPath(tag).build();
                final Intent intent = new Intent(Constants.ACTION_LIST,
                        uri, mContext, DownloadReceiver.class);
                intent.putExtra(DownloadManager.EXTRA_NOTIFICATION_CLICK_DOWNLOAD_IDS,
                        getDownloadIds(cluster));
                builder.setContentIntent(PendingIntent.getBroadcast(mContext,
                        0, intent, PendingIntent.FLAG_UPDATE_CURRENT));
                builder.setOngoing(true);

            } else if (type == TYPE_COMPLETE) {
                final DownloadInfo info = cluster.iterator().next();
                final Uri uri = ContentUris.withAppendedId(
                        Downloads.Impl.ALL_DOWNLOADS_CONTENT_URI, info.mId);
                builder.setAutoCancel(true);

                final String action;
                if (Downloads.Impl.isStatusError(info.mStatus)) {
                    action = Constants.ACTION_LIST;
                } else {
                    if (info.mDestination != Downloads.Impl.DESTINATION_SYSTEMCACHE_PARTITION) {
                        action = Constants.ACTION_OPEN;
                    } else {
                        action = Constants.ACTION_LIST;
                    }
                }

                final Intent intent = new Intent(action, uri, mContext, DownloadReceiver.class);
                intent.putExtra(DownloadManager.EXTRA_NOTIFICATION_CLICK_DOWNLOAD_IDS,
                        getDownloadIds(cluster));
                builder.setContentIntent(PendingIntent.getBroadcast(mContext,
                        0, intent, PendingIntent.FLAG_UPDATE_CURRENT));

                final Intent hideIntent = new Intent(Constants.ACTION_HIDE,
                        uri, mContext, DownloadReceiver.class);
                builder.setDeleteIntent(PendingIntent.getBroadcast(mContext, 0, hideIntent, 0));
            }

   
   
   
   
//这段代码是更新下载的Progress
if (total > 0) {
                    final int percent = (int) ((current * 100) / total);
                    percentText = res.getString(R.string.download_percent, percent);

                    if (speed > 0) {
                        final long remainingMillis = ((total - current) * 1000) / speed;
                        remainingText = res.getString(R.string.download_remaining,
                                DateUtils.formatDuration(remainingMillis));
                    }

                    builder.setProgress(100, percent, false);
                } else {
                    builder.setProgress(100, 0, true);
                }
最后调用mNotifManager.notify(tag, 0, notif);根据不同的状态来设置不同的Notification的title和description