How to discover the IP address of a Tomcat server on a network?

Question

I have a Android application which consumes a webservice on a local network. There's a config screen where the user inform the server IP address, which is running Apache Tomcat.

I'm looking for a way to auto-detect the server based on the current connected wi-fi network. i.e: The smartphone's IP is 10.1.1.90 and the server IP is 10.1.1.254.

Is there a way to achieve this? I'm thinking on using ping, but I don't know if is a good ideia.

very similar: http://stackoverflow.com/questions/9446799/android-search-for-server-automatically — burna, Dec 31 '12 at 13:02
So you would have a list of IP addresses of web servers running this web service? — Will C., Dec 31 '12 at 22:23
Basically, I would have a single IP address of the server running Tomcat in my network. — fonini, Jan 02 '13 at 17:56

score 3 · Accepted Answer · answered Feb 14 '13 at 15:22

The way I understand it, you need to discover IP of your tomcat server and connect it using your client.

I am assuming , both the server and client is in your control. One simple way can be to use jGroups Cluster.

You can make your tomcat discoverable
Client can discover it using the name of the cluster you have provided .Refer the JChannel API that Jgroups uses

I simulated it making following server class

public class TomcatServer {

    JChannel channel;

    private void start() throws Exception {
        channel = new JChannel(); // use the default config, udp.xml
        channel.connect("TomcatCluster");
    }

    public static void main(String[] args) throws Exception {
        new TomcatServer().start();
    }
}

The simulated client class

public class MobileApp extends ReceiverAdapter {

    JChannel channel;

    private void start() throws Exception {
       channel = new JChannel(); // use the default config, udp.xml
        channel.setReceiver(this);
        channel.connect("TomcatCluster");
        channel.close();
    }

    public static void main(String args[]) throws Exception {
        new MobileApp().start();
    }

The client will provide you following information

GMS: address=MACHINENAME-47879, cluster=TomcatCluster, physical address=xxxxx:0:xxx:xxxx:xxxx:xxxx:xxx:xxxx:xxxx

** view: [MACHINENAME-31239|1] [MACHINENAME-31239, MACHINENAME-47879]

Where MACHINENAME-47879 is the client machine and port & MACHINENAME-31239 is the tomcat server name and port

score 2 · Answer 2 · answered Dec 31 '12 at 12:49

2

Do you want to detect "a tomcat server" or "your tomcat server" ?

I mean, do you have any way to custom your server ? If it's the case, then you could create a very simple test page on your server (say a "Hello" JSP page), which your Android application could look for.

If your Android gets a "Hello" result with a GET request on http://<tomcat_ip>/hello.jsp, then you may assume that the tomcat is online.

If you can't add this test page, then you can test any page which the server is supposed to serve. (even a 404 page which sometimes is not configured well, and shows the tomcat version...)

answered Dec 31 '12 at 12:49

Orabîg

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Before I can do that, I need to know which IP address is used by the server. – fonini Feb 14 '13 at 12:51
How can you have a tomcat server, and not knowing its IP adress ? You should explain your situation further, because it's not clear. And you didn't answer my question :"a tomcat" or "your tomcat" ? – Orabîg Feb 14 '13 at 14:17
The user needs to input the IP address of the server on the config screen. The user is stupid. I wanna a "magic button" to discover the server's IP where the web service is hosted. – fonini Feb 14 '13 at 15:23
Ok, I have 2 different possibilities, but I will answer as soon as you do answer my question... (because your answer will tell which one is better) – Orabîg Feb 14 '13 at 22:44
I want to detect my Tomcat server. – fonini Feb 15 '13 at 10:11

Audrius Meškauskas · Answer 3 · 2013-02-14T13:30:09.297

Tomcat response headers can contain the xpoweredBy field that would advertise Tomcat if enabled. However it is most often disabled due security considerations, and even disabled by default. You however could re-enable it if you need to auto-detect exactly your Tomcat servers. From the other side, indeed, if you can place a web page on your server, you can simply place a marking page with the agreed signature.

If the server IP is unknown, I would propose the following ways to detect the server on the network:

The most straightforward way is to do the breadcast ping (ping -b broadcast_address where breadcast address can be computed here, for instance). All network devices that are configured so would reply, then verify as explained above which one is the server. However pinging broadcast address requires a rooted phone. Also the router may not support.
Your DHCP service (most likely your router) can often be configured to issue always the same IP address for the same MAC address of your server network card.
If the server is a desktop computer or laptop, it could show its address as QR code on display. It is possible for a smartphone to scan the code from the screen, and this is way easier than to enter IP address through the touchscreen. QR code can also include auto-generated password for extra security.
If there is wireless router with the possible login where both server and client are connected, the internal pages of that router often contain the relevant IP addresses. You would need to implement logging into the router and doing some screen scrapping.

I need to know what is the server IP address. – fonini Feb 14 '13 at 12:52 — fonini, Feb 14 '13 at 12:52
Did as I could, maybe one of the solutions would fit. – Audrius Meškauskas Feb 14 '13 at 13:30 — Audrius Meškauskas, Feb 14 '13 at 13:30

score 2 · Answer 4 · answered Feb 14 '13 at 13:42

I made an Android app which used a local server in the WLAN. I made the terminal (the phone) broadcast it's own IP address, which the server then picked up.

I used MultiCast class on the phone, which added the ip-address of itself to the payload. The server always has a thread in multicast read class that obains the payload of the packet (which is the terminals ip-address). Set the terminal in datagram read state and send the servers ip-address to terminal.

Maybe are better ways, but a great way to get the ip-addresses of unknown terminals in the network.

score 0 · Answer 5 · edited Feb 18 '13 at 06:59

The way i had resolved this problem is with the use of enumerations.

public String getLocalIpAddress()
{

    try {
        for (Enumeration<NetworkInterface> en = NetworkInterface.getNetworkInterfaces(); en.hasMoreElements();) {
            NetworkInterface intf = en.nextElement();
            for (Enumeration<InetAddress> enumIpAddr = intf.getInetAddresses(); enumIpAddr.hasMoreElements();) {
                InetAddress inetAddress = enumIpAddr.nextElement();
                if (!inetAddress.isLoopbackAddress()) {
                    return inetAddress.getHostAddress().toString();
                }
            }
        }
    } catch (Exception ex) {
    }
    return null;
}
}

How to discover the IP address of a Tomcat server on a network?

5 Answers5