socket programming multiple client to one server

Question

How do you handle multiple client to connect to one server  I have this LogServer java  import javax net ssl    import javax net    import java io    import java net     public class LogServer     private static final int PORT NUM   5000    public static void main String args          ServerSocketFactory serverSocketFactory         ServerSocketFactory getDefault        ServerSocket serverSocket   null      try         serverSocket           serverSocketFactory createServerSocket PORT NUM         catch  IOException ignored          System err println  Unable to create server          System exit -1             System out printf  LogServer running on port   s n   PORT NUM       while  true          Socket socket   null        try           socket   serverSocket accept            InputStream is   socket getInputStream            BufferedReader br   new BufferedReader            new InputStreamReader is   US-ASCII             String line   null          while   line   br readLine       null              System out println line                     catch  IOException exception               Just handle next request          finally           if  socket    null              try               socket close                catch  IOException ignored                                                and an embedded applet with part of the code like this e g  import java io    import java util logging     public class LogTest     private static Logger logger   Logger getAnonymousLogger       public static void main String argv    throws IOException         Handler handler   new SocketHandler  localhost   5000       logger addHandler handler       logger log Level SEVERE   Hello  World        logger log Level SEVERE   Welcome Home        logger log Level SEVERE   Hello  World        logger log Level SEVERE   Welcome Home            now the question is if I run  java LogServer  on the server  it will open the application and waiting for input stream and if I open my site  it will start streaming the log  But if I open one more using other computer network  the second site does not log the stream  seems like it s because the first one still bind to port 5000    How do I handle this  How does socket actually work with multiple client   one server

User · Accepted Answer

For every client you need to start separate thread. Example:

public class ThreadedEchoServer {

    static final int PORT = 1978;

    public static void main(String args[]) {
        ServerSocket serverSocket = null;
        Socket socket = null;

        try {
            serverSocket = new ServerSocket(PORT);
        } catch (IOException e) {
            e.printStackTrace();

        }
        while (true) {
            try {
                socket = serverSocket.accept();
            } catch (IOException e) {
                System.out.println("I/O error: " + e);
            }
            // new thread for a client
            new EchoThread(socket).start();
        }
    }
}

and

public class EchoThread extends Thread {
    protected Socket socket;

    public EchoThread(Socket clientSocket) {
        this.socket = clientSocket;
    }

    public void run() {
        InputStream inp = null;
        BufferedReader brinp = null;
        DataOutputStream out = null;
        try {
            inp = socket.getInputStream();
            brinp = new BufferedReader(new InputStreamReader(inp));
            out = new DataOutputStream(socket.getOutputStream());
        } catch (IOException e) {
            return;
        }
        String line;
        while (true) {
            try {
                line = brinp.readLine();
                if ((line == null) || line.equalsIgnoreCase("QUIT")) {
                    socket.close();
                    return;
                } else {
                    out.writeBytes(line + "\n\r");
                    out.flush();
                }
            } catch (IOException e) {
                e.printStackTrace();
                return;
            }
        }
    }
}

You can also go with more advanced solution, that uses NIO selectors, so you will not have to create thread for every client, but that's a bit more complicated.

User · Answer

This is the echo server handling multiple clients    Runs fine and good using Threads     echo server import java io BufferedReader  import java io IOException  import java io InputStreamReader  import java io PrintWriter  import java net ServerSocket  import java net Socket    public class Server X Client   public static void main String args           Socket s null      ServerSocket ss2 null      System out println  Server Listening              try          ss2   new ServerSocket 4445      can also use static final PORT NUM   when defined            catch IOException e       e printStackTrace        System out println  Server error                while true           try              s  ss2 accept                System out println  connection Established                ServerThread st new ServerThread s               st start                    catch Exception e           e printStackTrace            System out println  Connection Error                        class ServerThread extends Thread         String line null      BufferedReader  is   null      PrintWriter os null      Socket s null       public ServerThread Socket s           this s s             public void run         try          is  new BufferedReader new InputStreamReader s getInputStream              os new PrintWriter s getOutputStream           catch IOException e           System out println  IO error in server thread               try           line is readLine            while line compareTo  QUIT    0                os println line               os flush                System out println  Response to Client       line               line is readLine                       catch  IOException e             line this getName      reused String line for getting thread name         System out println  IO Error  Client   line   terminated abruptly              catch NullPointerException e           line this getName      reused String line for getting thread name         System out println  Client   line   Closed               finally          try          System out println  Connection Closing              if  is  null               is close                 System out println   Socket Input Stream Closed                       if os  null               os close                System out println  Socket Out Closed                      if  s  null           s close            System out println  Socket Closed                             catch IOException ie           System out println  Socket Close Error                 end finally           Also here is the code for the client   Just execute this code for as many times as you want to create multiple client        A simple Client Server Protocol    Client for Echo Server  import java io BufferedReader  import java io IOException  import java io InputStreamReader  import java io PrintWriter  import java net InetAddress  import java net Socket   public class NetworkClient    public static void main String args    throws IOException        InetAddress address InetAddress getLocalHost        Socket s1 null      String line null      BufferedReader br null      BufferedReader is null      PrintWriter os null       try           s1 new Socket address  4445      You can use static final constant PORT NUM         br  new BufferedReader new InputStreamReader System in            is new BufferedReader new InputStreamReader s1 getInputStream              os  new PrintWriter s1 getOutputStream               catch  IOException e           e printStackTrace            System err print  IO Exception               System out println  Client Address     address       System out println  Enter Data to echo Server   Enter QUIT to end           String response null      try          line br readLine             while line compareTo  QUIT    0                   os println line                   os flush                    response is readLine                    System out println  Server Response     response                   line br readLine                                catch IOException e           e printStackTrace        System out println  Socket read Error              finally           is close   os close   br close   s1 close                    System out println  Connection Closed

User · Answer

Here is code for Multiple Client to one Server Working Fine    Give it a try      Server java   import java io DataInputStream  import java io IOException  import java net ServerSocket  import java net Socket  import java util logging Level  import java util logging Logger   class Multi extends Thread  private Socket s null  DataInputStream infromClient  Multi   throws IOException      Multi Socket s  throws IOException      this s s      infromClient   new DataInputStream s getInputStream       public void run           String SQL new String        try           SQL   infromClient readUTF          catch  IOException ex            Logger getLogger Multi class getName    log Level SEVERE  null  ex             System out println  Query      SQL        try           System out println  Socket Closing            s close          catch  IOException ex            Logger getLogger Multi class getName    log Level SEVERE  null  ex                     public class Server    public static void main String args    throws IOException   InterruptedException          while true           ServerSocket ss new ServerSocket 11111           System out println  Server is Awaiting             Socket s ss accept            Multi t new Multi s           t start             Thread sleep 2000           ss close                               Client1 java    import java io DataOutputStream   import java io ObjectInputStream   import java net Socket    public class client1      public static void main String   arg      try         Socket socketConnection   new Socket  127 0 0 1   11111            QUERY PASSING      DataOutputStream outToServer   new DataOutputStream socketConnection getOutputStream           String SQL  I  am  client 1        outToServer writeUTF SQL         catch  Exception e   System out println e              Client2 java  import java io DataOutputStream   import java net Socket    public class client2       public static void main String   arg      try         Socket socketConnection   new Socket  127 0 0 1   11111            QUERY PASSING      DataOutputStream outToServer   new DataOutputStream socketConnection getOutputStream           String SQL  I am  Client 2        outToServer writeUTF SQL         catch  Exception e   System out println e

User · Answer

I guess the problem is that you need to start a separate thread for each connection and call serverSocket accept   in a loop to accept more than one connection   It is not a problem to have more than one connection on the same port

User · Answer

See O Reilly  Java Cookbook   Ian Darwin - recipe 17 4 Handling Multiple Clients   Pay attention that accept   is not thread safe  so the call is wrapped within synchronized   64  synchronized servSock    65      clientSocket   servSock accept    66

[java] socket programming multiple client to one server

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