closing a socket

Posted on 1998-05-28
Last Modified: 2010-03-30
I have a very basic question: how can I test a Socket to determine whether or not it is open?

I know I receive an exception if the socket is unexpectedly closed.  I also know I receive a known return code (e.g. null) if I read or write to a closed socket.  But how do I ask a Socket whether or not it is open without having to read or write?


Question by:BrindleFly
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Expert Comment

ID: 1221647
I didnt find any way to do this (as per my knowledge). The best way to handle this is

After you say
InputStream is = socket.getInputStream();
create a push back input stream
PushbackInputStream ps = new PushBackInputStream (ps);

use ps instead of is to read data from socket.

Write an utility routine to test for socket closure as below

public static boolean isSocketClosed(PushbackInputStream pInpStr) throws Exception
        int rd;
        try { rd  =; } catch (Exception e) { System.out.println("Socket closed !!"); return true; }
        System.out.println("not yet closed!!");
        return false;


Expert Comment

ID: 1221648
Do you mean to test if a socket is still valid?

// start

Socket mysocket = new Socket(hostname,portnum);

// Test if socket is valid
if(mysocket = null) {
    // socket closed, do something
} else {
    // socket open, read or write using socket

// end

Accepted Solution

evijay earned 100 total points
ID: 1221649
What i said was, once you open a socket, anyway, you will get the socket input and output streams.
Instead of using Socket input stream, i want you to pass it thru pushback input stream and then use it.
Here is an example of the code which can answer your doubts.

//server code file -
public class tserv {

      public static void main(String args[]) throws Exception
            byte b[] = new byte[1000];
            ServerSocket s = new ServerSocket(13500);
            Socket ss = s.accept();
            OutputStream os = (OutputStream) ss.getOutputStream();
            for (int i = 0; i < 100; i++) {
                  System.out.println("written ");
                  // suppose some serious error occured

// client code file -

public class tcli {
public static boolean isSocketClosed(PushbackInputStream pInpStr) throws Exception
      int rd;
      try { rd  =; } catch (Exception e) { System.out.println("Socket closed !!"); return true; }
      System.out.println("not yet closed!!");
      return false;
public static void main(String [] args) throws Exception
      Socket s  = new Socket("", 13500);
      PushbackInputStream pInpStr;
      pInpStr = new PushbackInputStream(s.getInputStream());
      byte b[] = new byte[1000];
      while (true) {
            if (isSocketClosed(pInpStr) == false)


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