TCP套接字编程在台式机和Android平板电脑之间不起作用

Question

i've done an application which send datas from server to clients....the code (server & client) works perfectly in desktop application, but when i put client on android tablet and server on desktop., its not working

i'm using wifi for communication between android and desktop

permissions which i've set is as shown below

 <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
    <uses-permission android:name="android.permission.WRITE_SETTINGS" />

can anyone please tell me what's the problem behind this.....

I'm getting this exception

java.net.ConnectException: failed to connect to /192.168.1.74 (port 4545): connect failed: ECONNREFUSED (Connection refused)

Server.java

public class Server
{
  private int TAB_SERVER_PORT = 4545;
  private static PrintWriter TABout;
  private HashSet <PrintWriter> TABhs=new HashSet<PrintWriter>();
  public static void main(String args[])
  {
    new Thread(new TABServerThread()).start();
  } 

    private class TABServerThread implements Runnable {
        private ServerSocket TABserver;
        @Override
        public void run() {
            try {
                TABserver = new ServerSocket(TAB_SERVER_PORT);
                System.out.println("Server Start the server at port " + TAB_SERVER_PORT + " and waiting for clients...");
                while (true) {
                    Socket socket = TABserver.accept();
                    System.out.println("Server Accept socket connection: "+ socket.getLocalAddress());
                    new Thread(new TABClientHandler(socket)).start();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }

    private class TABClientHandler implements Runnable {
        private Socket clientSocket;
        private Scanner in;
        public TABClientHandler(Socket clietSocket) {
            this.clientSocket = clietSocket;
        }
        @Override
        public void run() {
            try {
                TABout = new PrintWriter(clientSocket.getOutputStream());
                TABhs.add(TABout);
                in = new Scanner(clientSocket.getInputStream());
                String line;
                while ((line = in.nextLine()) != null) {
                    if (line.equals("Reply")){
                        TABout.print("Server replies");
                        TABout.flush();
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }

        }

    }
}

Client.java

public class Client implements Runnable {
            private int TAB_SERVER_PORT = 4545;
            private Socket tabletclient;
            private PrintWriter tabletout;
            private Scanner in;

            @Override
            public void run() {
                    String line;
                    boolean flag=true;
                    System.out.println("Waiting for server connection....");
                    while(flag){
                    try {
                        tabletclient = new Socket("192.168.1.74", TAB_SERVER_PORT);
                        tabletout = new PrintWriter(tabletclient.getOutputStream());
                        in = new Scanner(tabletclient.getInputStream());
                        try
                        {
                            if((line = in.nextLine())!=null)
                            {
                                System.out.println("Client Server says: " + line);
                                if (line.equals("Hello client")) {
                                    tabletout.println("Reply");
                                    tabletout.flush();
                                }
                            }
                        }catch(Exception d){
                            System.out.println("Connection from server has lost.........");
                        }
                        } catch (UnknownHostException e) {
                        } catch (IOException e) {
                        }
                     }
            }

 public static void main(String[] args) {
               new Thread(new Client()).start();

            }
        }

Answer 1

It must be the firewall that blocks the connections. You can disable it and try again. Should any more issues, please use wireshark to capture some packets to check where the problem is.

You can try "netstat -n" on both Linux or Windows to see if your server socket is binding and listening there.

Answer 2

Change your android application into a Client and Desktop application into a server. This way is much easier and safe(in my opinion of course).Your mobile devices ip can change any time due to... you know it is mobile.Your clients cant't guess the ip of their mobile server.

move your Client.java to your android app and Server.java to your desktop app.

Answer 3

Try to use "ifconfig" (if you working on Linux)to check your IP address or "ipconfig" if you working on Windows system; make sure your IP address is exactly "192.168.1.74".