服务器未通过套接字通信接收

Question

I'm trying to make a Java program in which the server generates a random number and, after establishing a connection with a client, lets it guess the number. However, they both don't seem able to receive each others' messages.
Server side:

package numberguessserv;

import java.net.*;
import java.io.*;
import java.util.Random;
import java.util.Scanner;

public class NumberGuessServ {

    public static void main(String[] args) {
        Scanner inpkb = new Scanner(System.in);
        Random randomGenerator = new Random();
        int randomNum = randomGenerator.nextInt(10);
        String number = Integer.toString(randomNum);
        int port;
        boolean isGuessed = false;
        String msgReceived;
        Socket connect = new Socket();
        System.out.print("port: ");
        port = inpkb.nextInt();
        try {
            ServerSocket clSock = new ServerSocket(port);
            System.out.println("Waiting...");
            connect = clSock.accept();
            System.out.println("Connection established with"+connect.getInetAddress());
            InputStreamReader isr = new InputStreamReader(connect.getInputStream());
            BufferedReader isrBuff = new BufferedReader(isr);
            OutputStreamWriter osw = new OutputStreamWriter(connect.getOutputStream());
            BufferedWriter oswBuff = new BufferedWriter(osw);
            while (!isGuessed) {
                msgReceived = isrBuff.readLine();
                System.out.println("Number received: "+msgReceived);
                if (msgReceived.equals(number)) {
                    isGuessed = true;
                    oswBuff.write("Right!");
                    oswBuff.flush();
                }
                else {
                    oswBuff.write("Wrong!");
                    oswBuff.flush();
                }
                if (isGuessed)
                    System.out.println("Number was guessed right.");
                else
                    System.out.println("Number was guessed wrong.");
                }
            }
            catch (Exception ex) {
                System.out.println("An exception has occurred: "+ex);
            }
            finally {
                try {
                    connect.close();
                }
                catch (Exception ex) {
                    System.out.println("An exception has occurred: "+ex);
                }
           }
      }
 }

Client side:

package numberguessclient;

import java.io.*;
import java.util.Scanner;
import java.net.*;

public class NumberGuessClient {

    public static void main(String[] args) {
        Scanner inpkb = new Scanner(System.in);
        int port;
        String IP;
        boolean isGuessed = false;
        String number, msg;
        Socket serv = new Socket();
        System.out.print("IP: ");
        IP = inpkb.next();
        System.out.print("port: ");
        port = inpkb.nextInt();
        try {
            serv = new Socket(IP,port);
            System.out.println("Connetion established with"+serv.getInetAddress());
            InputStreamReader isr = new InputStreamReader(serv.getInputStream());
            BufferedReader isrBuff = new BufferedReader(isr);
            OutputStreamWriter osw = new OutputStreamWriter(serv.getOutputStream());
            BufferedWriter oswBuff = new BufferedWriter(osw);
            while (!isGuessed) {
                System.out.print("number: ");
                number = inpkb.next();
                oswBuff.write(number);
                oswBuff.flush();
                System.out.println("Number sent.");
                msg = isrBuff.readLine();
                System.out.println("The reply was received: "+msg);
                if (msg.equals("Right!")) {
                    isGuessed = true;
                    System.out.println(msg);
                }
                else {
                    System.out.println(msg+"\nTry again...");
                }
            }
        }
        catch (Exception ex) {
            System.out.print("An exception has occurred: "+ex);
        }
        finally {
            try {
                serv.close();
            }
            catch (Exception ex) {
                System.out.print("An exception has occurred: "+ex);
            }
        }
    }
}

Answer 1

That's expected. Both ends read using

isrBuff.readLine();

So, they both expect the other end to send a line. But none of them sends a line. They both do

oswBuff.write(number);
oswBuff.flush();

That sends some characters, but doesn send any newline character. The receiving end doesn't have any way to know that the end of line has been reached, and it thus continues blocking until it receives the EOL.

Answer 2

The readLine () waits for the end of line. Unless and until it gets a new line character, it will wait up there reading.

So, you need to give a new line characer '\\n' every time you give an input to the output stream so that the readLine() reads a new line character and does not wait.

Currently in your code, you need to give a new line character everytime you are giving input by doing the following:

oswBuff.write("any message");
oswBuff.write('\n');      //add this statement everywhere you are writing to the output stream
oswBuff.flush();

This complies well for both the server as well as client.