java: closing client socket resets server socket

Question

I have a very simple capitalization Java program. Client sends text read from standard input to server which converts that text into capital letters. Program works well but once client is stopped (NetBeans ide used), server is also reset. Server socket should keep listening for new connection from clients regardless of a client being stopped.

public class Client
{
public static void main(String[] args) throws IOException
{
    try(Socket s=new Socket("localhost",9090))
    {
        while(true)
        {
            PrintWriter out=new PrintWriter(s.getOutputStream(),true);
            BufferedReader rd=new BufferedReader(new InputStreamReader(s.getInputStream()));
            BufferedReader from=new BufferedReader(new InputStreamReader(System.in));

            String read=from.readLine();

            out.println(read);

            String answer;
            answer=rd.readLine();

            System.out.println(answer);
        }
    }
}
}

public class Server
{
public static void main(String[] args) throws IOException
{
    try(ServerSocket listener = new ServerSocket(9090);
            Socket socket = listener.accept();)
            {

                while (true)
                {
                    BufferedReader br=new BufferedReader(new InputStreamReader(socket.getInputStream()));
                    PrintWriter out = new PrintWriter(socket.getOutputStream(), true);

                    System.out.println("Started...");

                    String transform=br.readLine();

                    String newStr=transform.toUpperCase();

                    out.println(newStr);
                }
            }
}
}

Answer 1

What happens is a normal behaviour. You server code only includes handling of a single client. The listener.accept() function only accepts latest connection to server. You need to put the listened.accept() in loop and handle all the exceptions that are raised within. The server-side code should look like this:

public class Server
{
    public static void main(String[] args) throws IOException
    {
        try(ServerSocket listener = new ServerSocket(9090);
        while (true) {
            try {
                        Socket socket = listener.accept();)
                        …
            } catch (SocketException ex) {
                ...
            }
        }
    }
}

But keep in mind that this code will only handle single client at a time. No multi-threading in this code.

Answer 2

Your Server is closing the connection and then finishing becuase it is created outside the while loop. I believe this is what you need.

public class Server {
    public static void main (final String[] args)
            throws IOException {

        while (true) {

            try (ServerSocket listener = new ServerSocket(9090); Socket socket = listener.accept();) {

                while (true) {
                    final BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                    final PrintWriter out = new PrintWriter(socket.getOutputStream(), true);

                    System.out.println("Started...");

                    final String transform = br.readLine();
                    if (transform == null) 
                        break;

                    final String newStr = transform.toUpperCase();

                    out.println(newStr);
                }
            }
        }
    }
}