Question

I have problem with Android using the class HttpUrlConnection my method is this:

public InputStream test() {
        URL url = null;
        try {
            url = new URL("http://www.android.com/");
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
       HttpURLConnection urlConnection = null;
    try {
        urlConnection = (HttpURLConnection) url.openConnection();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    InputStream in= null;

       try {
         in = new BufferedInputStream(urlConnection.getInputStream());
       }catch(IOException e){
           e.printStackTrace();
       }
        finally {
         urlConnection.disconnect();
       }
return in;
}

When i execute this method android generates this exception:

05-03 15:15:19.116: W/System.err(1085): android.os.NetworkOnMainThreadException
05-03 15:15:19.116: W/System.err(1085): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099)
05-03 15:15:19.116: W/System.err(1085): at java.net.InetAddress.lookupHostByName(InetAddress.java:391)
05-03 15:15:19.116: W/System.err(1085): at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
05-03 15:15:19.116: W/System.err(1085): at java.net.InetAddress.getAllByName(InetAddress.java:220)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpConnection.(HttpConnection.java:71)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpConnection.(HttpConnection.java:50)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:351)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:86)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:308)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpEngine.connect(HttpEngine.java:303)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232)
05-03 15:15:19.126: W/System.err(1085): at libcore.net.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:273)
05-03 15:15:19.136: W/System.err(1085): at libcore.net.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:168)
05-03 15:15:19.136: W/System.err(1085): at com.BertacchiMazzoni.HTTPClient.HttpClientTutorial.test(HttpClientTutorial.java:35)
05-03 15:15:19.136: W/System.err(1085): at com.BertacchiMazzoni.HTTPClient.HTTPClientActivity.onCreate(HTTPClientActivity.java:18)
05-03 15:15:19.136: W/System.err(1085): at android.app.Activity.performCreate(Activity.java:4465)
05-03 15:15:19.136: W/System.err(1085): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
05-03 15:15:19.136: W/System.err(1085): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
05-03 15:15:19.136: W/System.err(1085): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
05-03 15:15:19.136: W/System.err(1085): at android.app.ActivityThread.access$600(ActivityThread.java:123)
05-03 15:15:19.136: W/System.err(1085): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
05-03 15:15:19.146: W/System.err(1085): at android.os.Handler.dispatchMessage(Handler.java:99)
05-03 15:15:19.146: W/System.err(1085): at android.os.Looper.loop(Looper.java:137)
05-03 15:15:19.146: W/System.err(1085): at android.app.ActivityThread.main(ActivityThread.java:4424)
05-03 15:15:19.146: W/System.err(1085): at java.lang.reflect.Method.invokeNative(Native Method)
05-03 15:15:19.146: W/System.err(1085): at java.lang.reflect.Method.invoke(Method.java:511)
05-03 15:15:19.146: W/System.err(1085): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-03 15:15:19.146: W/System.err(1085): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-03 15:15:19.146: W/System.err(1085): at dalvik.system.NativeStart.main(Native Method)

Can i resolve this problem? Where is the error?

Thanks a lot!
Regards!

Answer 1

A quick google for the exception leads you here: http://developer.android.com/reference/android/os/NetworkOnMainThreadException.html

Which states:

The exception that is thrown when an application attempts to perform a
networking operation on its main thread.

This is only thrown for applications targeting the Honeycomb SDK or
higher. Applications targeting earlier SDK versions are allowed to do
networking on their main event loop threads, but it’s heavily
discouraged. See the document Designing for Responsiveness.

So basically I’m guessing you’re performing your network operation on the main application thread; and for Honeycomb and up it looks like you can’t do this. It’s a bad idea anyway, as it’s likely to make your application hang and appear unresponsive. You’d need to use another thread or handler or asynctask or Loader to perform the operation.