Question

I have a program to download JSON Strings from a server. Things were working fine up until recently, when I try to call

jsonReader.execute(getUrl).get();

Where jsonReader is an AsyncTask to download JSON Strings and getUrl is the URL to execute. This method never gets executed, the weird thing is, it works on my phone.

Here is my code

Method which calls json string reader

private PointOfInterest getPointWithID(int id) {

    String getUrl;
    JSONReader jsonReader = new JSONReader();
    try {
        Log.d(TAG,"Trying to get ID: " + id);
        getUrl = url + String.valueOf(id);
        Log.d(TAG,"Trying to get json from: " + id); <-- Last Log line to get printed when run on emulator
        jsonReader.execute(getUrl).get();
    } catch (Exception e) {
        e.printStackTrace();
    }

    String jsonString = jsonReader.returnJSONString();
    Log.d(TAG,"Downloaded: " + jsonString);
    //System.out.println("JSON: " + jsonString);

    JSONResponse jsonResponse = JSONResponse.convertJSONToResponse(jsonString);
    //System.out.println("JSON RESPONSE " + jsonResponse);


    return jsonResponse.getPointofInterest();
}

jsonReader

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.params.BasicHttpParams;
import org.json.JSONException;
import org.json.JSONObject;

import android.os.AsyncTask;
import android.util.Log;

/**
 * Read JSON Strings
 * @author Tom
 *
 */
public class JSONReader extends AsyncTask <String, Void, String> {

    String result;
    DefaultHttpClient  httpclient = new DefaultHttpClient(new BasicHttpParams());
    StringBuilder sb = new StringBuilder();
    String TAG = "JSONReader";

    // constructor
    public JSONReader() {
        result = "";
    }

    @Override
    protected String doInBackground(String... url) {

        Log.d(TAG, "Executing " + url); <--Does not get printed when run on emulator 

        HttpPost httppost = new HttpPost(url[0]);
        // Depends on your web service
        httppost.setHeader("Content-type", "application/json");

        try {
            HttpResponse response = httpclient.execute(httppost);

            HttpEntity entity = response.getEntity();

            InputStream inputStream = entity.getContent();

            // json is UTF-8 by default i believe
            BufferedReader reader = null;

            reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);

            String line = null;
            while ((line = reader.readLine()) != null)
            {
                sb.append(line + "\n");
            }
        }catch(Exception e){

            e.printStackTrace();
        }
        return result = sb.toString();
    }

    public String returnJSONString(){

        return result;
    }

}

I have tried restarting adb, making new AVD’s but nothing seems to work, my only option is testing on my phone however, this is not desirable as I am developing for api 17. Thanks for your help !

Answer 1

There are a few threading rules that must be followed for this class to work properly:

The AsyncTask class must be loaded on the UI thread. This is done automatically as of JELLY_BEAN.

The task instance must be created on the UI thread.

execute(Params…) must be invoked on the UI thread.
Do not call onPreExecute(), onPostExecute(Result), doInBackground(Params…), onProgressUpdate(Progress…) manually.

The task can be executed only once (an exception will be thrown if a second execution is attempted.)