3 Replies Latest reply: Mar 17, 2013 4:38 AM by 996701 RSS

    Beginning Client-Server

    996701
      hi everybody, i've got a simple program, but i've encountered a problem. Can you help me,please
      --------------------------------------
      import java.io.BufferedReader;
      import java.io.IOException;
      import java.io.InputStreamReader;
      import java.io.PrintWriter;
      import java.net.Socket;


      public class Client_Server_1 {
           public static void main(String[] args){
                String hostname="localhost";
                if(args.length>0){
                     hostname=args[0];
                     
                }
                PrintWriter pw=null;
                BufferedReader br=null;
                try{
                     Socket s= new Socket(hostname,2007);
                     br=new BufferedReader(new InputStreamReader(s.getInputStream()));
                     BufferedReader user=new BufferedReader(new InputStreamReader(System.in));
                     System.out.println("Connected to Server...");
                     while(true){
                          String st=user.readLine();
                          if (st.equals("exit")){
                               break;
                          }
                          pw.println(st);
                          pw.flush();
                          System.out.println(br.readLine());
                          
                     }
                }
                catch(IOException e){
                     System.err.println(e);
                }
                
                finally{
                     try{
                          if(br!=null)br.close();
                          if(pw!=null)pw.close();
                     }
                     catch(IOException e){
                          System.err.println(e);
                          }
                     }
                     
                }
           }
      ---------------
      And Console Window:
      java.net.ConnectException: Connection refused: connect
      ------------
      I don't understand about this problem, Please explain to me. Thanh you very much!
        • 1. Re: Beginning Client-Server
          997337
          Instead of localhost give the name of Host-name which is of ur own desktop.

          You will get the Host-Name by giving the command "ipconfig/all" in cmd if ur using Microsoft OS.
          • 2. Re: Beginning Client-Server
            996701
            I've just changed the Port Number:
            ------------------
            import java.io.BufferedReader;
            import java.io.IOException;
            import java.io.InputStreamReader;
            import java.io.PrintWriter;
            import java.net.Socket;


            public class Client_Server_1 {
                 public static void main(String[] args){
                      String hostname="localhost";
                      if(args.length>0){
                           hostname=args[0];
                           
                      }
                      PrintWriter pw=null;
                      BufferedReader br=null;
                      try{
                           Socket s= new Socket(hostname,445);
                           br=new BufferedReader(new InputStreamReader(s.getInputStream()));
                           BufferedReader user=new BufferedReader(new InputStreamReader(System.in));
                           System.out.println("Connected to Server...");
                           while(true){
                                String st=user.readLine();
                                if (st.equals("exit")){
                                     break;
                                }
                                pw.println(st);
                                pw.flush();
                                System.out.println(br.readLine());
                                
                           }
                      }
                      catch(IOException e){
                           System.err.println(e);
                      }
                      
                      finally{
                           try{
                                if(br!=null)br.close();
                                if(pw!=null)pw.close();
                           }
                           catch(IOException e){
                                System.err.println(e);
                                }
                           }
                           
                      }
                 }

            ----------------------------
            And a new problem:
            Exception in thread "main" java.lang.NullPointerException
                 at Client_Server_1.main(Client_Server_1.java:27)
            -------------------
            How to fix it? (Line 27: pw.println(st);)
            Thank you for your helping!

            Edited by: 993698 on Mar 17, 2013 2:37 AM
            • 3. Re: Beginning Client-Server
              gimbal2
              993698 wrote:
              ----------------------------
              And a new problem:
              Exception in thread "main" java.lang.NullPointerException
                   at Client_Server_1.main(Client_Server_1.java:27)
              -------------------
              How to fix it? (Line 27: pw.println(st);)
              Thank you for your helping!
              You fix it by stop treating it like a problem. You do not have a problem. There is a mistake in your code on line 27 of your program, Java is preventing you from having problems by telling you that. It is also telling you that a variable that is on that line contains a null value and obviously it shouldn't have. So combine those two pieces of information and figure out what is wrong with your code, then fix it.