BufferedReader.readLine（）会阻塞一段时间

Question

I am trying to get a String of http response (just a JSON object), and sometimes this piece of code waits infinite time in

line = reader.readLine()

May be, the reason of such behavior is bad Internet connection (I use 3G modem), but I need a stable solution to avoid this infinite lock. What can be done here to avoid it?

HttpResponse response = httpClient.execute(httpPost);

InputStream content = null;
JSONObject json_obj;
if (response.getStatusLine().getStatusCode() == 200) {
    HttpEntity entity = response.getEntity();

    try {
        content = entity.getContent();

        BufferedReader reader = new BufferedReader(new InputStreamReader(content, "UTF-8"), 256);
        StringBuilder sb = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            sb.append(line);
        }
    } catch (Exception e) {}
}

Answer 1

You can specify a read timeout:

HttpClient client = new DefaultHttpClient();
client.getParams().setParameter(CoreConnectionPNames.SO_TIMEOUT, 30000);

Should set a read timeout to 30 seconds. Probably, you also want to specify a connection timeout:

client.getParams().setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, 30000);

Answer 2

readLine()

Or any network/IO should be done in a background thread to prevent locking of the main thread.

If you test your code on Android 4.0+ you'll also see that networking is no longer allowed on the main thread and will throw an exception.

Take a look at AsyncTask which is a simple, painless way of running such tasks on a background thread.

Answer 3

A good solution to avoid the "infinite" lock is to do this http calls in a separate thread, and with a Handler, notice to the main thread that the info is loaded and can use it like you want.

Here an example of my own using a SaxParser too:

public void SearchFromSuperClass(String text)
{   
    mHandler = new Handler();
    Thread t = new Thread(){
        public void run() {
            try {
              String strurl="URLTOPATH";
              URL url = new  URL(strurl);
              SAXParserFactory factory = SAXParserFactory.newInstance();

              SAXParser parser = factory.newSAXParser();
              FundsHandlerRanking handler = new FundsHandlerRanking();
              parser.parse(url.openConnection().getInputStream(), handler);
              search_response = handler.getrankings();


              mHandler.post(mUpdateResults);
            } catch (Exception e) {
                search_response = null;
                mHandler.post(mUpdateResults);

            }

        }
    };

    t.start();
}
final Runnable mUpdateResults = new Runnable() {
    public void run() {
        updateResultsInUi();
    }
};

private void updateResultsInUi() {

    try
    {
        if(search_response != null)
        {
            lview.setAdapter(new SearchRankingAdapter(mycontext, search_response, false));
        }
        Pdialog.dismiss();
    }
    catch (Exception e) {
        lview.setAdapter(null);
        if (Pdialog.isShowing())
        {
            Pdialog.dismiss();
        }
    }
}

With mHandler.post(...) you put the call in the queue to be sended to the main UI thread, and there, you can modify UI objects without problem (CAN'T modify UI objects outside the Main thread).

Hope this helps