check if network is working.txt

answer url
https://stackoverflow.com/a/27312494/9243764


isConnectedOrConnecting() (used in most answers) checks for any network connection
To know whether any of those networks have internet access, use one of the following
A) Ping a Server (easy)
// ICMP 
public boolean isOnline() {
    Runtime runtime = Runtime.getRuntime();
    try {
        Process ipProcess = runtime.exec("/system/bin/ping -c 1 8.8.8.8");
        int     exitValue = ipProcess.waitFor();
        return (exitValue == 0);
    }
    catch (IOException e)          { e.printStackTrace(); }
    catch (InterruptedException e) { e.printStackTrace(); }

    return false;
}
+ could run on main thread

- does not work on some old devices (Galays S3, etc.), it blocks a while if no internet is available

B) Connect to a Socket on the Internet (advanced)
// TCP/HTTP/DNS (depending on the port, 53=DNS, 80=HTTP, etc.)
public boolean isOnline() {
    try {
        int timeoutMs = 1500;
        Socket sock = new Socket();
        SocketAddress sockaddr = new InetSocketAddress("8.8.8.8", 53);

        sock.connect(sockaddr, timeoutMs);
        sock.close();

        return true;
    } catch (IOException e) { return false; }
}
+ very fast (either way), works on all devices, very reliable

~ can't run on the ui task

- none

This works very reliably, on every device, and is very fast. It needs to run in a separate task though (e.g. ScheduledExecutorService or AsyncTask).

Possible Questions
Is it really fast enough?

Yes, very fast ;-)

Is there no reliable way to check internet, other than testing something on the internet?

Not as far as I know, but let me know, and I will edit my answer.

What if the DNS is down?

Google DNS (e.g. 8.8.8.8) is the largest public DNS in the world.
 As of 2013 it served 130 billion requests a day. Let 's just say, your app would probably not be the talk of the day.

Which permissions are required?

<uses-permission android:name="android.permission.INTERNET" />
Just internet access - surprise ^^ (Btw have you ever thought about, 
how some of the methods suggested here could even have a remote glue about internet access, without this permission?)

 

Extra: One-shot AsyncTask Example
class InternetCheck extends AsyncTask<Void,Void,Boolean> {

    private Consumer mConsumer;
    public  interface Consumer { void accept(Boolean internet); }

    public  InternetCheck(Consumer consumer) { mConsumer = consumer; execute(); }

    @Override protected Boolean doInBackground(Void... voids) { try {
        Socket sock = new Socket();
        sock.connect(new InetSocketAddress("8.8.8.8", 53), 1500);
        sock.close();
        return true;
    } catch (IOException e) { return false; } }

    @Override protected void onPostExecute(Boolean internet) { mConsumer.accept(internet); }
}

///////////////////////////////////////////////////////////////////////////////////
// Usage

    new InternetCheck(internet -> { /* do something with boolean response */ });