Socket closing before server can readObject()

Question

I am trying to create a multi-threaded client server application that transmits objects. At the moment, I am having a hard time getting the sockets to coincide.
I start my server and wait for a connection:
ServerSocket ss = new ServerSocket(port_num);
Socket s = ss.accept();Then I create a new socket in the client to connect to the server:
Socket cs = new Socket("localhost", 8888);When the server class gets the connection, it creates a thread with the socket:
new DrawThread(s);The thread constructor creates an Input stream:
ois = new ObjectInputStream(sock.getInputStream());After the client creates the connection, it creates and ObjectOutputStream and writes my object:
oos = new ObjectOutputStream(cs.getOutputStream());
oos.writeObject(objects.get(0).getShape());Meanwhile in the run() method of the thread, we try to read it:
ois.readObject();However at this point I get an IOException because the client function was done and had exited so the socket was closed.
Any Idea what I can do to combat this problem? Full code for my client function, server and thread classes are below.
Client function:
   public void serverSave(){
        Date d = new Date();
        try{
        //initialize class network and IO vars
        Socket cs = new Socket("localhost", 8888);//create server
        oos = new ObjectOutputStream(cs.getOutputStream());
         //write the objects to the server
           // for(int i = 0; i< objects.size(); i++){
                 oos.writeObject(objects.get(0).getShape());
            //}//end for
       catch (UnknownHostException uhe){System.out.println("client uhe");System.out.println(uhe.getMessage());}
     catch(IOException ioe){System.out.println("client ioe");System.out.println(ioe.getMessage());}
     finally{
                //print out time to see when the function exits
          System.out.println(d.getTime());
   }Server Class:
import java.io.*;
import java.net.*;
class DrawServer{
     static int port_num = 8888;//default port number
     public void DrawServer(){}
     public static void main(String args[])throws IOException{
          //don't forget to close socket
          ServerSocket ss = new ServerSocket(port_num);
          while(true){
               System.out.println("begin listening");
               //blocking wait for a connection
               Socket s = ss.accept();
               //create new thread for the client
               new DrawThread(s);
               System.out.println("end listening");
               s.close();
          }//end while
     }//end main
}Thread Class
import java.net.*;
import java.net.Socket;
import java.io.*;
import java.util.*;
class DrawThread extends Thread{
     private Socket sock;
     private ObjectInputStream ois = null;
        private ObjectOutputStream oos = null;
        ObjectOutputStream out = null;
        //create a file input stream or buffered stream to accept filename from client???
     public DrawThread(Socket s){
          sock = s;
          try{
          ois = new ObjectInputStream(sock.getInputStream());
                oos = new ObjectOutputStream(sock.getOutputStream());
          start();
          catch( IOException ioe){}
     public void run(){
          Date d = new Date();
          System.out.println("Thread started");
          try{
          int i = 0;
          while(true){
               System.out.println("getting item " + ++i);
               ois.readObject();
          catch(FileNotFoundException fnfe){System.out.println("fnfe");}
          catch(IOException ioe){System.out.println("ioe     " + + d.getTime());System.out.println(ioe.getMessage());}
          catch(ClassNotFoundException cnfe){System.out.println("cnfe");}
          finally{
               try{out.close();}
               catch(IOException ioe2){System.out.println("ioe2");}
          System.out.println("Thread ending");
}Thanks,
Shannon

Answer 1

You have one problem with your DrawServer class:               new DrawThread(s); // this starts a thread that uses the socket
               System.out.println("end listening");
               s.close(); // this will close the socket while it is used in the DrawThread thread.Instead close the socket in the finally block of the DrawThread run() method (no need to close the ObjectOutputStream in that block).
Also since you are passing a variable number of objects between the client and the server
you should create a custom made protocol for both your ends to always be in sync with each other.
For instance the client could send first the number of objects to be sent,
then loop for this exact number and send the objects,
then upon receiving the server response close its socket.
The server could read for the number of objects to read,
then loop for the exact number and read the objects,
then send a response and close its socket.