Determine When LoopJ has concluded all background connections

Question

Im trying to determine when LoopJ has finished all background thread http calls. So that i can then display the results of an array that is populated based on the results of my onSuccess methods.

First off, I have a String[] of file names. I'm then looping through the array and creating loopj connections like such.

 ArrayList<String> files_to_update = new ArrayList<String>(file_names.length);
 AsyncHttpClient client = new AsyncHttpClient();
    for (final String file_name : file_names) {
            client.get(BASE_URL + file_name, new AsyncHttpResponseHandler() {

            public void onStart() {
                Local_Last_Modified_Date = preferences.getString(file_name, "");
            }

            public void onSuccess(int statusCode, Header[] headers, byte[] response) {
                Server_Last_Modified_Date = headers[3].getValue();
            }

            @Override
            public void onFinish() {
                if (!Local_Last_Modified_Date.trim().equalsIgnoreCase(Server_Last_Modified_Date.trim())) {
                    files_to_update.add(file_name);
                }
            }
        });
    }

What i'm doing here is comparing 2 date strings, The first Local_Last_Modified_Date is pulled from a preference file and the 2nd is determined by the last-modified date in the header. and then compared in the OnFinish(). This determines if the file needs to be update because the server file is newer than the preference date. Now! i know this is not the best way for comparing dates, however it will work interm for what i'm trying to do.

The issue i'm having is determining that all of the background http calls from loopj have completed so that i can now display the results of array list in a list dialog or whatever ui element i choose. I've tried looping through the arraylist, but because the loopj / http connections are background threads, the loop gets executed prior to the completion of all of the connection and therefore displays an empty or not populated fully array.

Is there a if conditional that i can write to determine if loopj has not finished executing all of the connection and when it has then execute my ui code?

Answer 1

The following code should address your problem:

Class file: UploadRunner.java

public class UploadRunner extends AsyncHttpResponseHandler implements Runnable {

  private final AsyncHttpClient client;
  private final ArrayList<String> filesList;
  private final int filesCount;
  private final Handler handler;

  private String baseURI;
  private boolean isFired;
  private int filesCounter;

  // Use in case you have no AHC ready beforehand.
  public UploadRunner(ArrayList<String> filesList) {
    this(new AsyncHttpClient(), filesList);
  }

  public UploadRunner(
    AsyncHttpClient client, 
    ArrayList<String> filesList, 
    Handler handler
  ) {
    assert null != client;
    assert null != filesList;
    assert null != handler;

    this.client = client;
    this.filesList = filesList;
    this.handler = handler;

    this.baseURI = "";
    this.filesCount = filesList.size();
    this.filesCounter = 0;
  }

  public String getBaseURI() {
    return baseURI;
  }

  public void setBaseURI(String uri) {
    baseURI = uri;
  }

  @Override
  public void run() {
    // Request to download all files.
    for(final String file : filesList) {
      client.get(baseURI + file, this);
    }
  }

  @Override
  public void onSuccess(int statusCode, Header[] headers, byte[] response) {
    // This shouldn't happen really...
    if(isFired) {
      return;
    }

    // One more file downloaded.
    filesCounter++;

    // If all files downloaded, fire the callback.
    if(filesCounter >= filesCount) {
      isFired = true;
      handler.onFinish(getLastModificationDate(headers));
    }
  }

  private String getLastModificationDate(Header[] headers) {
    // Simple mechanism to get the date, but maybe a proper one
    // should be implemented.
    return headers[3].getValue();
  }

  public static interface Handler {

    public void onFinish(String lastModificationDate);

    // TODO: Add onError() maybe?
  }
}

In this case, you encapsulate the uploading mechanism in one place, plus expose just an interface for calling back a handler when all files are uploaded.

Typical use case:

// TODO: This typically should run in a different thread.
public class MyTask implements UploadRunner.Handler, Runnable {

  private final static BASE_URI = "http://www.example.com/";

  private final AsyncHttpClient client = new AsyncHttpClient();
  private final ArrayList<String> filesList = new ArrayList<>();

  @Override
  public void run() {
    filesList.add("1.png");
    filesList.add("2.png");
    filesList.add("3.png");
    filesList.add("4.png");
    filesList.add("5.png");

    // Create a new runner.
    UploadRunner ur = new UploadRunner(client, filesList, this);

    // Set base URI.
    ur.setBaseURI(BASE_URI);

    // Spring the runner to life.
    ur.run();
  }

  @Override
  public void onFinish(String lastModificationDate) {
    // All files downloaded, and last modification date is supplied to us.
  }
}