读写服务器

Question

Objective: send data to server and have server return something back and to print what the server sends back

Problem: If I close the out stream then it will send the data to the server but my input stream won't work and I can't receive what the server tries to give me. If I use flush() to send data to server the server never receives the data. I have been stuck on this for literally 3 hours. How do you do read and Write at the same time.

Client.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

class Client {
    public static void main(String args[]) {
        String data = "head";
        try {
            Socket skt = new Socket("server", 5050);
            PrintWriter out = new PrintWriter(skt.getOutputStream(), true);
            BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));
            out.print(data);
            out.close();

            System.out.println("Sent data");
            while (!in.ready()) {
            }

            String input = in.readLine();
            System.out.println(input);

            out.close();
            in.close();
            skt.close();
        } catch (Exception e) {
            System.out.print("Whoops! It didn't work!\n" +e.toString());
        }
    }
}

Server.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;
import java.io.PrintWriter;

class Server {
    public static void main(String args[]) {
        String data;
        String input;
        try {
            ServerSocket srvr = new ServerSocket(5050);
            Socket skt = srvr.accept();
            BufferedReader in = new BufferedReader(new InputStreamReader(
                    skt.getInputStream()));
            PrintWriter out = new PrintWriter(skt.getOutputStream(), true);

            // /////Waits for message from client/////////
            while (!in.ready()) {
            }
            // ///////////////////////////////////////////

            input = in.readLine(); // Read the message
            System.out.println("Received String input: " + input);
            // Send output to client
            System.out.println("After output");
            if (input.equals("head"))
                data = "haha";
            else
                data = "Wtf did you send me";
            Thread.sleep(2000);
            out.print(data);
            // ///////////////////

            System.out.println("Sent data: " + data);
            in.close();
            out.close();
            skt.close();
            srvr.close();
        } catch (Exception e) {
            System.out.print("Whoops! It didn't work!\n");
        }

    }
}

Answer 1

In your client you have:

out.print(data);
out.close();

and in your server you have:

input = in.readLine();

Client send message without new line character - that's why in.ready() is true . What's more - it closes PrintWriter instead of flushing (you are also closing stream at the end of program). If you change that lines to:

out.println(data); // sends message with new line character
out.flush();       // unnecessary

Client sends a message. The same thing is when Server sends message - you use print instead of println but Client reads using readLine that reads until new line character, or to be more precise ( BufferedReader|readLine() ):

Reads a line of text. A line is considered to be terminated by any one of a line feed ('\\n'), a carriage return ('\\r'), or a carriage return followed immediately by a linefeed.

One more thing - you are connecting to the server using "server" hostname. For my tests I changed it to "localhost" . Maybe there is other mistake?