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?

Answer 1

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.

Answer 2

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");      }  } }