使用Socket（Android）将顺序查询发送到服务器的最佳方法是什么？

Question

I have two android devices, one acting as client and other acting as server. I am trying to get n number of images from the server device. Previously, to fetch just one image I was using AsyncTask to create and open a Socket connection on the client device. And a thread was running on the server device with ServerSocket . Both were configured to use the same port.

I want to query some images. Since the connection is on the same port, I don't think I can send those queries simultaneously? Is that possible?

I was thinking of creating a Queue of AsyncTask and execute them one by one. But after reading some of the posts regarding this, it seems that AsyncTask is no the right way to do this and there's a limitation over number of AsyncTask threads.

Android Developers website suggests that IntentService is useful to perform such tasks. So I wrote a basic class.

public class ClientSyncService extends IntentService {
    private JSONObject jsonData;
    private static final int SocketServerPORT = 4000;
    private String hostAddress;
    private Bitmap queryBitmap;
    private static final String TAG = "ClientSyncService";
    private String requestString;

    public ClientSyncService(String name) {
        super(name);
    }

    @Override
    protected void onHandleIntent(Intent workIntent) {
        String jsonString = workIntent.getDataString();
        hostAddress = workIntent.getStringExtra("host-ipaddress");

        try {
            jsonData = new JSONObject(jsonString);
        } catch (JSONException e) {
            e.printStackTrace();
        }

        try {
            requestString = jsonData.getString("request");
        } catch (JSONException e1) {
            e1.printStackTrace();
        }

        Socket socket = null;
        DataInputStream dataInputStream = null;
        DataOutputStream dataOutputStream = null;

        try {
            socket = new Socket(hostAddress, SocketServerPORT);
            dataOutputStream = new DataOutputStream(
                  socket.getOutputStream());
            dataInputStream = new DataInputStream(socket.getInputStream());
            dataOutputStream.writeUTF(jsonData.toString());
            Log.i(TAG, "waiting for response from host");

            if (requestString == null) {
                socket.close();
                return;
            }

            if (requestString == "query-display-picture" || requestString == "query-album-art") {
                Log.i(TAG, "waiting for image");
                byte buf[] = new byte[4096];
                ByteArrayOutputStream bos = new ByteArrayOutputStream();
                int len;
                while((len = dataInputStream.read(buf)) != -1) {
                    bos.write(buf, 0, len);
                    bos.flush();
                }
                if (bos.size() > 0) {
                    queryBitmap = BitmapFactory.decodeByteArray(bos.toByteArray(), 0, bos.size());
                } else {
                    Log.i(TAG, "bitmap is null");
                }
                Log.i(TAG, "bitmap created");

            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // close socket and streams
        }

    }

I'll figure the rest of the part out regarding broadcasting the data to the activity. I'm unclear about how to call this IntentService . Do I prepare a queue and create new intent service for each image query or pass all the image requests to intent service and the service will have a loop and send request to the server and get data.

TL;DR : I want to get n number of images/files from client (preferably using the same port). What is the best way to do that? I have read about ThreadPoolExecutor and BlockingQueue but didn't try them out yet. I am a bit new to threading.

Answer 1

You can connect several sockets from a client to the same host:port, that will just create more sockets on the server, you'll need multiple threads accepting the connections on the server.

Or a single AsyncTask could be created with a list of images to fetch and get them all one after the other. You could also make a single request for multiple images and get them all in the same socket (eg by sending size / data / size / data / ... or by using something as Google protocol buffers (a repeated field would be just fine).

Last option could be to have a worker thread getting requests in a queue (one request per image) and processing them one by one.

Answer 2

I think best way would be to get those images sequentially only. But i think a normal java thread would be the best.

AsyncTasks should ideally be used for short operations (a few seconds at the most.) If you need to keep threads running for long periods of time, it is highly recommended you use the various APIs provided by the java.util.concurrent pacakge such as Executor, ThreadPoolExecutor and FutureTask.