Android Network Programming: IOExceptions and StackOverflowError

Question

Hi Everybody,

In my Android app, I try to connect to a port on a local server to get some packets. I've encased to code in some try & catch's but with the following code:

address = "192.168.175.82";
public void run() {
    try {
  smtpSocket = new Socket(address, 60001);

        os = new DataOutputStream(smtpSocket.getOutputStream());
        is = new DataInputStream(smtpSocket.getInputStream());
    } catch (UnknownHostException e) {
        System.err.println("Don't know about host: " + address);
        run();
    } catch (IOException e) {
        System.err.println("Couldn't get I/O for the connection to: " + address);
        run();
    } catch (Exception e) {
     System.out.println("retry");
     run();
    }

if ther server is not on, I obviously get the IOException a few times (e.g. a few hundred times) before I get a stack overflow error and the app crashes.

01-20 22:21:32.526: ERROR/AndroidRuntime(5678): java.lang.StackOverflowError
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.util.Hashtable.get(Hashtable.java:282)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.util.Properties.getProperty(Properties.java:177)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.lang.System.getProperty(System.java:440)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.lang.System.getProperty(System.java:412)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.lang.Boolean.getBoolean(Boolean.java:174)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at org.apache.harmony.luni.net.NetUtil$Action.run(NetUtil.java:89)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at org.apache.harmony.luni.net.NetUtil$Action.run(NetUtil.java:80)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.security.AccessController.doPrivilegedImpl(AccessController.java:264)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.security.AccessController.doPrivileged(AccessController.java:84)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at org.apache.harmony.luni.net.NetUtil.preferIPv6Addresses(NetUtil.java:51)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at org.apache.harmony.luni.net.PlainSocketImpl.bind(PlainSocketImpl.java:190)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.net.Socket.startupSocket(Socket.java:777)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.net.Socket.tryAllAddresses(Socket.java:192)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.net.Socket.<init>(Socket.java:256)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at java.net.Socket.<init>(Socket.java:220)
01-20 22:21:32.526: ERROR/AndroidRuntime(5678):     at com.example.sockets.ReadSocket.run(ReadSocket.java:83)

Could anyone please point me in the right direction of how to get this to work? Perhaps I should test the connection first somehow (if so, please say how?) Thanks

Chris

Answer 1

You can try isConnected() and isBound() on your socket to check wether you are connected or not before trying to get an inputstream.

Answer 2

For starters, drop the recursive call. This will get rid of the stack overflow. Replace it with a loop and sleep in each unsuccessful iteration

  public void run() {
     boolean connected = false;  
     while(!connected)
     {
     try {
      smtpSocket = new Socket(address, 60001);

            os = new DataOutputStream(smtpSocket.getOutputStream());
            is = new DataInputStream(smtpSocket.getInputStream());


      connected = true;
    } catch (UnknownHostException e) {
        System.err.println("Don't know about host: " + address);

    } catch (IOException e) {
        System.err.println("Couldn't get I/O for the connection to: " + address);

        } catch (Exception e) {
         System.out.println("retry");

        }
        if (!connected)
            Thread.sleep(1000)
      }
    }