Sometimes my app crashes with UnknownHostException

Question

In my app i have access to web server. It works fine in Some phones but while testing in Samsung Galaxy Model No - GT-S5830i Android Version - 2.3.6 it keeps on showing Unknown host exception. I have checked the url from browser its working fine.

private void submitUploadData(String url ,Map<String, String> param) throws IOException 
{  
    URL siteUrl;
    try {
        siteUrl = new URL(url); 
    HttpURLConnection conn = (HttpURLConnection) siteUrl.openConnection();
    conn.setRequestMethod("POST");
    conn.setDoOutput(true);
    conn.setDoInput(true);

    DataOutputStream out = new DataOutputStream(conn.getOutputStream());

    Set getkey = param.keySet();
    Iterator keyIter = getkey.iterator();
    String content = "";
    for(int i=0; keyIter.hasNext(); i++) {
        Object key = keyIter.next();
        if(i!=0) {
            content += "&";
        }
        content += key + "=" +  param.get(key);
    } 
    out.writeBytes(content.trim()); 
    out.flush();
    out.close();
    BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream())); 
    String line = "";
    while((line=in.readLine())!=null) {
        System.out.println(line);
    }
    in.close();  
    //Intent home = new Intent(SyncHttp.this,TimeAndExpensesSKActivity.class);
    //startActivity(home);
    db.updateTimeExported(1);
    db.updateExpensesExported(1);
    db.close();
    db.close(); 

    if(db.getLogCount()==0){ 
            db.insertSyncDateDetails(getDateandTime());}
            else{
            db.updateSyncDateDetails(1, getDateandTime());}  


    } catch (MalformedURLException e) { 
        e.printStackTrace();
    }
    this.setResult(FINISH_RESULT);
    db.close();
}

I have already added permissions

 <uses-permission android:name="android.permission.INTERNET" />
 <uses-permission android:name="android.permission.CAMERA" />
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
 <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
 <uses-permission android:name="android.permission.READ_PHONE_STATE"/>

I am really confused why this exception occurring.

Thanks for your help guys.

"Samsung Galaxy" is a generic title given to many devices. Can you be more specific about what device this error is occurring on? Also when this happens is the device connected to the internet via wifi or 3g/4g? — FoamyGuy, Jun 12 '12 at 13:11

score 1 · Answer 1 · answered Jun 12 '12 at 13:23

I have also experienced some issues using URLConnections especially HTTPS on the Samsung Galaxy TAB, but i would imagine it probably occurs on other models as well since there are a ton of devices with the same name but made for different markets and mobile providers.

So far i haven't found a way around sorry, since i tend to avoid the URLConnection class due to a ton of other issues it has.

I suggest using the Apache HTTP Client to communicate with your API's. you can google a ton of examples of using it.

Also when looking at your code i would suggest reading a bit more into the try-catch-finally block statements in java. it is really important to properly close connections at the end or in case of errors.

Other possibilities are:

There is no connection of any sort active (mobile or wifi)
You are missing the "http://www." in your url.

Thanks for your suggestion... but i could do it now because its in finishing stage... — vinothp, Jun 12 '12 at 13:32

ariefbayu · Accepted Answer · 2012-06-12T15:03:07.177

1

My app did this too. This usually caused by unstable network connection. What I did was catching this UnknownHostException and modify the code in a way that if UnknownHostException happened, I try to re-fetch the URL again, after several miliseconds sleep.

The basic algorithm is something like this:

private void submitUploadData(String url ,Map<String, String> param) throws IOException 
{  
    URL siteUrl;
    boolean isDataSubmitted = false;
    while(!isDataSubmitted){
        try {
            //do your complicated http process
            isDataSubmitted = true;
        } catch(UnknownHostException uhe){
            e.printStackTrace();
        } catch (MalformedURLException e) { 
            e.printStackTrace();
        }
    }
}

edited Jun 12 '12 at 15:03

answered Jun 12 '12 at 13:23

ariefbayu

21,849
12
71
92

Thanks for your answer.. I think this will work.. what you have done if there is not possible of internet connection for a long time... – vinothp Jun 12 '12 at 13:56
Thanks i will try it and let you know – vinothp Jun 12 '12 at 15:53

score 0 · Answer 3 · answered Jun 12 '12 at 13:24

0

I think calling close() on the DataOutputStream before you recieve your input might close the whole connection - try commenting out that line.

answered Jun 12 '12 at 13:24

Misan

1

score -1 · Answer 4 · answered Jun 12 '12 at 13:21

-1

Have you checked the URL from the phone's browser? Please log the URL you pass to the function and try it in your phone's browser. I would think of missing/incorrect protocol specifier and or URL string formation issues of which this particular phone is unforgiving.

answered Jun 12 '12 at 13:21

Alexey Vassiliev

2,349
2
17
8

Did not mention that it was the same phone. I can guess that the that particular phone might not be even connected to the network (or connected the way that URL is not accessible), so it is critical to check on the same phone. – Alexey Vassiliev Jun 12 '12 at 13:30

Sometimes my app crashes with UnknownHostException

4 Answers4