从URL下载android 2.2中的5-40 MB数据文件。 开发使用哪些类？

Question

I am developing an application in which i need to download a file(.zip / .txt / .jpg etc) size- 5 to 50 MB.. Application based on Android 2.2.

The user provides the URL and triggers the download but then the downloading process runs in background until complete.

streaming should be used for downloading file.
I want to know how can this be done using HTTP connections .
what classes can be used for this?
Does android 2.2 provides an API for this?

Any kind of help is appreciated....

Answer 1

Android did include an API called DownloadManager for just this purpose...but it was release in 2.3; so while it won't be useful in your application targeting 2.2, it might still be a good resource for you to research the implementation.

A simple implementation I would recommend is something like this:

• Use an HttpURLConnection to connect and download the data. This will require the INTERNET permission to be declared in your manifest
• Determine where you want the file to be. If you want it on the device's SD card, you will also need the WRITE_EXTERNAL_STORAGE permission.
• Wrap this operation in the doInBackground() method of an AsyncTask . This is a long-running operation, so you need to put it into a background thread, which AsyncTask manages for you.
• Implement this in a Service so the operation can run protected without the user keeping the an Activity in the foreground.
• Use NotificationManager to notify the user when the download is complete, which will post a message to their status bar.

To simplify things further, if you use IntentService , it will handle the threading for you (everything in onHandleIntent gets called on a background thread) and you can queue up multiple downloads for it to handle one at a time by simply sending multiple Intents to it. Here's a skeleton example of what I'm saying:

public class DownloadService extends IntentService {

public static final String EXTRA_URL = "extra_url";
public static final int NOTE_ID = 100;

public DownloadService() {
    super("DownloadService");
}

@Override
protected void onHandleIntent(Intent intent) {
    if(!intent.hasExtra(EXTRA_URL)) {
        //This Intent doesn't have anything for us
        return;
    }
    String url = intent.getStringExtra(EXTRA_URL);
    boolean result = false;
    try {
        URL url = new URL(params[0]);
        HttpURLConnection connection = (HttpURLConnection)url.openConnection();
        //Input stream from the connection
        InputStream in = new BufferedInputStream(connection.getInputStream());
        //Output stream to a file in your application's private space
        FileOutputStream out = openFileOutput("filename", Activity.MODE_PRIVATE);

        //Read and write the stream data here

        result = true;
    } catch (Exception e) {
        e.printStackTrace();
    }

    //Post a notification once complete
    NotificationManager manager = (NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);
    Notification note;
    if(result) {
        note = new Notification(0, "Download Complete", System.currentTimeMillis());
    } else {
        note = new Notification(0, "Download Failed", System.currentTimeMillis());
    }
    manager.notify(NOTE_ID, note);

}
}

Then you can call this service with the URL you want to download anywhere in an Activity like this:

Intent intent = new Intent(this, DownloadService.class);
intent.putExtra(DownloadService.EXTRA_URL,"http://your.url.here");
startService(intent);

Hope that is helpful!

EDIT: I'm fixing this example to remove the unnecessary double-threading for anyone who comes upon this later.