How do I find the DNS servers in Android from a Java program?

Question

The java.net.InetAddress.GetByName(String host) method can only return A records so to lookup other record types I need to be able to send DNS queries using the dnsjava library.

However that normally relies on being able to parse /etc/resolv.conf or similar to find the DNS server addresses and that doesn't work on Android.

The current DNS settings on Android can apparently only be obtained from within a shell by using the getprop command.

Can anyone tell me how to get those settings from Java other than by spawning a shell with Runtime.exec() and parsing the output from getprop ?

Answer 1

The DNS protocol is not that complex - can't you just do the DNS accesses using raw sockets (either TCP or UDP)? After a quick look at the dnsjava doco it seems to provide low level DNS support to assist with this.

The other possible direction is, starting with dnsjava, to remove the dependence on /etc/resolv.conf . I would think about using getprop in your launch script to set properties in the JVM, or to create a localized resolv.conf file in your app's directory from which you can read the information needed. In other words, use getprop to inject information into the JVM instead of attempting to pull it in once the JVM is going. Surely creating a file that dnsjava can use directly should be doable.

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Edit - android.net

It looks like android.net.ConnectivityManager will deliver you an array of NetworkInfo's using getAllNetworkInfo() . Then use android.net.NetworkUtils.runDhcp() to get a DhcpInfo for any given network interface - the DhcpInfo structure has the IP address for dns1 and dns2 for that interface. Surprised that the DNS's are int, therefore implying IP4 only, though.

Answer 2

I don't think it's possible for general case. For WiFi I found this:

WiFiManager wifi = (WifiManager) getSystemService(WIFI_SERVICE); 
DhcpInfo info = wifi.getDhcpInfo(); 

Answer 3

To get system properties of an android system, static methods in this class ( android.os.SystemProperties ) can be used. As it is not an open api, you can't compile it against the sdk. Work around is needed to do that, eg copy the code from AOSP to get thru the compilation. As this class is for internal use, do this at your own risk. Have fun.

Answer 4

We should be able to find dns address being irrespective to what network (wifi or ethernet) we are connected. Here is my program.

In your AndroidManifest.xml file

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

Your code:

    ConnectivityManager connectivityManager = (ConnectivityManager) getApplicationContext().getSystemService(Service.CONNECTIVITY_SERVICE);

                /* you can print your active network via using below */
                Log.i("myNetworkType: ", connectivityManager.getActiveNetworkInfo().getTypeName());
                WifiManager wifiManager= (WifiManager) getApplicationContext().getSystemService(getApplicationContext().WIFI_SERVICE);


                Log.i("routes ", connectivityManager.getLinkProperties(connectivityManager.getActiveNetwork()).getRoutes().toString());
                Log.i("domains ", connectivityManager.getLinkProperties(connectivityManager.getActiveNetwork()).getDomains().toString());
                Log.i("ip address ", connectivityManager.getLinkProperties(connectivityManager.getActiveNetwork()).getLinkAddresses().toString());
                Log.i("dns address ", connectivityManager.getLinkProperties(connectivityManager.getActiveNetwork()).getDnsServers().toString());



                if(connectivityManager.getActiveNetworkInfo().getType() == ConnectivityManager.TYPE_WIFI) {
                    Log.i("myType ", "wifi");
                    DhcpInfo d =wifiManager.getDhcpInfo();
                    Log.i("info", d.toString()+"");
                }
                else if(connectivityManager.getActiveNetworkInfo().getType() == ConnectivityManager.TYPE_ETHERNET) {
/* there is no EthernetManager class, there is only WifiManager. so, I used this below trick to get my IP range, dns, gateway address etc */

                    Log.i("myType ", "Ethernet");
                    Log.i("routes ", connectivityManager.getLinkProperties(connectivityManager.getActiveNetwork()).getRoutes().toString());
                    Log.i("domains ", connectivityManager.getLinkProperties(connectivityManager.getActiveNetwork()).getDomains().toString());
                    Log.i("ip address ", connectivityManager.getLinkProperties(connectivityManager.getActiveNetwork()).getLinkAddresses().toString());
                    Log.i("dns address ", connectivityManager.getLinkProperties(connectivityManager.getActiveNetwork()).getDnsServers().toString());

                }
                else {

                }

Output

You can't reach to know whether you are connected via wifi or network using WifiManager as WifiManager only deals with wifi. You have to use ConnectivityManager . I updated the code again where I merged WifiManager and ConnectivityManager to produce the result that you wanted.