我如何从Java中的服务器TCP获得答复

Question

My code just do a simple task send a text from client's console to server and receive a reply. But my code doesn't work though. I keep sending text to server and no reply sending back. I have done a several example that plus 2 number given from client. I do this the same way but i can't figure out what is the problem.

Server:

public class Server {
    public static void main(String[] args) {
        try {
            ServerSocket server = new ServerSocket(8);
            Socket client = server.accept();
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedWriter outToClient = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
            String in = inFromClient.readLine(),out;
            while(in!=null){
                out = in+" from server";
                outToClient.write(out);
                outToClient.newLine();
                outToClient.flush();
            }
            inFromClient.close();
            outToClient.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

Client:

public class Client {
    public static void main(String[] args) {
        try {
            Socket client = new Socket("localhost", 8);
            System.out.println("Connected to server");
            BufferedReader inFromServer = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedWriter outToServer = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
            Scanner input = new Scanner(System.in);
            String strClient,strServer;
            while(true){
                System.out.print("Client: ");
                strClient = input.nextLine();
                outToServer.write(strClient);
                strServer = inFromServer.readLine();
                System.out.print("Server: ");
                System.out.println(strServer);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

Answer 1

There are several problems with your code:

1. Your server is expecting to read a line and you're only writing text without a newline symbol:

Reading a line in server with: inFromClient.readLine()

Writing text without newline in client: outToServer.write(strClient); Change this to outToServer.write(strClient + "\\n");

---

2. You don't flush the writer of the client. Add a outToServer.flush(); after the line outToServer.write(...);

---

3. You only read 1 line in the server and don't read inside the loop again.

---

EDIT: To make it easier i'll post the corrected code here: (I've tried it and it works like a charm)

Client:

public class Client {
    public static void main(String[] args) {
        try (Socket client = new Socket("localhost", 8);
            BufferedReader inFromServer = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedWriter outToServer = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
            Scanner input = new Scanner(System.in)) {

            System.out.println("Connected to server");
            String strClient,strServer;

            while(true){
                System.out.print("Client: ");
                strClient = input.nextLine();
                outToServer.write(strClient);
                outToServer.newLine();
                outToServer.flush();
                strServer = inFromServer.readLine();
                System.out.println("Server: " + strServer);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Server:

public class Server {
    public static void main(String[] args) {
        try (ServerSocket server = new ServerSocket(8);
            Socket client = server.accept();
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(client.getInputStream()));
            BufferedWriter outToClient = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()))) {

            String in = inFromClient.readLine(), out;
            while(in != null){
                out = in + " from server";
                outToClient.write(out);
                outToClient.newLine();
                outToClient.flush();
                in = inFromClient.readLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Please remark that this solution uses Javas ARM (Automatic resource management) for autoclosing streams and sockets. So this will not work before java 1.7!