Question

Why does this program not work properly? Client reads SOME_MESSAGE and after that nothing happens. It seems that println method from server in some way have influence on transferring long type numbers.

SERVER

import java.net.*;
import java.io.*;

public class Server {

  public static void main(String[] args) throws Exception {
    ServerSocket socket = new ServerSocket(9999);
    while (true) {
      Socket sock = socket.accept();
      PrintWriter out = new PrintWriter(new BufferedWriter(
          new OutputStreamWriter(sock.getOutputStream())), true);
      DataOutputStream outByte = new DataOutputStream(sock.getOutputStream());
      out.println("SOME_MESSAGE");
      outByte.writeLong(948L);
    }
  }
}

CLIENT

import java.net.*;
import java.io.*;

public class Client {

  public static void main(String[] args) throws Exception {
    Socket sock = new Socket("127.0.0.1", 9999);
    DataInputStream inByte = new DataInputStream(sock.getInputStream());
    BufferedReader in = new BufferedReader(new InputStreamReader(
        sock.getInputStream()));

    System.out.println(in.readLine());
    long number = inByte.readLong();
    System.out.println(number);
  }
}

Answer 1

Your problem is that the BufferedReader is buffering bytes from the socket’s input stream, so the long 948 value isn’t in the DataInputStream because the BufferedReader has it read and is buffering it. In general you don’t want to be using 2 different wrappers around the same underlying stream, especially if one is buffered. Same with your Server class, but that seems to at least be working.

Your Client needs to use only one wrapper for the socket’s input stream. You should just stick with the DataInputStream and along with the Server code, use DataInputStream.readUTF() on the Client while using DataOutputStream.writeUTF() on the Server, getting rid of both the BufferedReader and the PrintWriter.

So on the Server:

while(true) {
    Socket sock = socket.accept();
    DataOutputStream outByte = new DataOutputStream(sock.getOutputStream());
    outByte.writeUTF("SOME_MESSAGE");
    outByte.writeLong(948L);
    outByte.flush();

}

and on the Client:

public static void main(String[]args)throws Exception
{
    Socket sock = new Socket("127.0.0.1",9999);
    DataInputStream inByte = new DataInputStream(sock.getInputStream());

    System.out.println(inByte.readUTF());
    long number  = inByte.readLong();
    System.out.println(number);
}