socket not accepting data 2nd time

[Joel Bijapurkar]

I am writing a client server program in which the client accepts data from the user along with information on type of operation to be performed. It then passes this information to the server which performs the operation and returns the result to the client. I am using an array-list object to pass data to the server. It works fine the 1st time but after that the server doesn't accept the next array list object for the next operation. Please tell me what is wrong with my code. Thank you.

Here is the server code:

public class Server
{
    public static void main(String args[])
    {
        ServerSocket ss=null;
        Socket client=null;
        ObjectInputStream ois=null;
        PrintWriter pw =null;
        Operations ops =new Operations();   
        ArrayList a  = new ArrayList();
      

        
       try
        {
             ss = new ServerSocket(9999);
         
           while(true)
           {
              
               client  = ss.accept();
               ois =new ObjectInputStream(client.getInputStream());
               pw = new PrintWriter(client.getOutputStream(),true);
               
               a=(ArrayList)ois.readObject();
               
                switch(Integer.parseInt((a.get(0)).toString()))
                {
                    case 1:
                        pw.println(ops.AddDigits(Integer.parseInt(a.get(1).toString())));
                        break;
                        
                    case 2:
                        pw.println(ops.FindFactorial(Integer.parseInt(a.get(1).toString())));
                        break;
                        
                    case 3:
                        pw.println(ops.FindStringLength(a.get(1).toString()));
                        break;
                        
                    case 4:
                        pw.println(ops.StringCompare(a.get(1).toString(),a.get(2).toString()));
                        break;
                            
                    case 5:
                        pw.println(ops.StringConcatenate(a.get(1).toString(),a.get(2).toString()));
                        break;
                                
                    case 6:
                        pw.println(ops.CheckPalindrome(a.get(1).toString()));
                        break;
                                    
                    case 7:
                        pw.println(ops.FindSubstring(a.get(1).toString(),a.get(2).toString()));
                        break;
                                        
                    case 8:
                        ois.close();
                        pw.close();
                        client.close();
                        ss.close();
                        break;             
                }
            }
        }
       catch (IOException ex)
        {
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }
     catch(ClassNotFoundException ex)
        {
            ex.printStackTrace();
        }
    }
}

and here is the client code:

public class Client
{
    public static void main(String args[])
    {
        BufferedReader br =new BufferedReader(new InputStreamReader(System.in));
        int choice;

        ArrayList a =new ArrayList();
        Socket s=null;
        ObjectOutputStream oos=null;
        DataInputStream dis=null;
        try
        {
            s = new Socket("localhost", 9999);
            oos = new ObjectOutputStream(s.getOutputStream());
            dis =new DataInputStream(s.getInputStream());
        }
        catch (UnknownHostException ex)
        {
            Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex)
        {
            Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
        }
        while(true)
        {
            System.out.println("\nMenu:-");
            System.out.println("1.Add digits of a number.");
            System.out.println("2.Find factorial of a number.");
            System.out.println("3.Find length of a string.");
            System.out.println("4.Compare two strings.");
            System.out.println("5.Concatenate two strings");
            System.out.println("6.Check if a string is a palindrome");
            System.out.println("7.Find substring");
            System.out.println("8.Exit\n");
            System.out.print("Enter your choice: ");
            try
            {
                choice = Integer.parseInt(br.readLine().trim());
                System.out.println("");
                a.clear();
                a.add(choice);
                switch(choice)
                {
                    case 1:
                        System.out.print("Enter a number: ");
                        a.add( Integer.parseInt(br.readLine().trim()));
                        break;

                    case 2:
                        System.out.print("Enter a number: ");
                        a.add( Integer.parseInt(br.readLine().trim()));
                        break;

                    case 3:
                        System.out.print("Enter a string: ");
                        a.add(br.readLine().trim());
                        break;

                    case 4:
                        System.out.print("Enter first string: ");
                        a.add(br.readLine().trim());
                        System.out.print("Enter second string: ");
                        a.add(br.readLine().trim());
                        break;

                    case 5:
                        System.out.print("Enter first string: ");
                        a.add(br.readLine().trim());
                        System.out.print("Enter second string: ");
                        a.add(br.readLine().trim());
                        break;

                    case 6:
                        System.out.print("Enter a string: ");
                        a.add(br.readLine().trim());
                        break;

                    case 7:
                        System.out.print("Enter a string: ");
                        a.add(br.readLine().trim());
                        System.out.print("Enter sub-string: ");
                        a.add(br.readLine().trim());
                        break;

                    case 8:
                        oos.writeObject(a);
                        oos.close();
                        dis.close();
                        s.close();
                        System.exit(0);

                    default:
                        System.out.println("Invalid entry.");
                        choice =9;
                }
                if(choice!=9)
                {
                    oos.writeObject(a);
                    oos.flush();
                    System.out.println(dis.readLine());
                }
            }
            catch (IOException ex)
            {
                Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    }
}

[Jeff Verdegan]

Please note that ItDoesntWorkIsUseless.(⇐click) It would help if you would TellTheDetails(⇐click) about what "the server doesn't accept it" means. What exactly are you observing? In which code in particular, at least the method, preferably the specific line or two? Is there an error message? If so, copy/paste the entire thing and indicate clearly which code is causing it.

[Joel Bijapurkar]

The above code does not give me an error during run time. But when I terminate the execution of the client and server programs I get the following error messages:

1) These error messages occur in the server output window when I terminate the client first

SEVERE: null
java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:189)
at java.net.SocketInputStream.read(SocketInputStream.java:121)
at java.net.SocketInputStream.read(SocketInputStream.java:203)
at java.io.ObjectInputStream$PeekInputStream.peek(ObjectInputStream.java:2266)
at java.io.ObjectInputStream$BlockDataInputStream.peek(ObjectInputStream.java:2559)
at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2569)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1315)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
at socketprogramming.Server.main(Server.java:36)



1) These error messages occur in the client output window when I terminate the server first

in the client output window :
at java.net.SocketInputStream.read(SocketInputStream.java:189)
at java.net.SocketInputStream.read(SocketInputStream.java:121)
at java.net.SocketInputStream.read(SocketInputStream.java:203)
at java.io.DataInputStream.readLine(DataInputStream.java:513)
at socketprogramming.Client.main(Client.java:111)

[Joel Bijapurkar]

Finally found the solution.

In my server program the statement client = ss.accept() on line 21, creates a new object every time it executes . After executing once my client program is still trying to establish a connection to the old "client" object in the server program which no longer exits.

So I modified the client code and created a new instance of the socket "s" every time i want to communicate with the server. Socket "s" will then communicate with the new "client" object in the server program. I moved lines 12 -24 of the client code into the while loop beginning at line 25.

while(true)
{
        try  
        {  
            s = new Socket("localhost", 9999);  
            oos = new ObjectOutputStream(s.getOutputStream());  
            dis =new DataInputStream(s.getInputStream());  
        }  
        catch (UnknownHostException ex)  
        {  
            Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);  
        } catch (IOException ex)  
        {  
            Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);  
        }

.......  
.
.
.
}

[Jeff Verdegan]

Joel Bijapurkar wrote:The above code does not give me an error during run time. But when I terminate the execution of the client and server programs I get the following error messages:

Then it does give you an error at runtime.

Glad you figured it out though.