outputStream.fl ush() not flushing?

[tegdim]

Hello,
I'm trying to send a string to a subprocesses' output stream in my java program. I'm writing the data to the stream and then trying to flush the stream.

This, however , isn't actually sending anything to the subprocess (a python program) and the data only actually gets sent to the outputstream when I close the stream. I'm wanting to keep sending data to the subprocess so the writing and flushing is in a loop, but because I have to close the stream for the data to be sent the loop only works on the first iteration.

I found other people having the same problem on the internet but I'm not sure if it's machine specific or down to the code. I want to be able to send data to the subprocesses' output stream without closing the stream so it can be used again in the next iteration (this is what flush is supposed to do).

Thank you
Nico

[r035198x]

Hello,
I'm trying to send a string to a subprocesses' output stream in my java program. I'm writing the data to the stream and then trying to flush the stream.

This, however , isn't actually sending anything to the subprocess (a python program) and the data only actually gets sent to the outputstream when I close the stream. I'm wanting to keep sending data to the subprocess so the writing and flushing is in a loop, but because I have to close the stream for the data to be sent the loop only works on the first iteration.

I found other people having the same problem on the internet but I'm not sure if it's machine specific or down to the code. I want to be able to send data to the subprocesses' output stream without closing the stream so it can be used again in the next iteration (this is what flush is supposed to do).

Thank you
Nico

From the docs

The flush method of OutputStream does nothing. 

Have a look at the streams and pick the one which provides an implementation of flush in its contract

[tegdim]

From the docs

The flush method of OutputStream does nothing. 

Have a look at the streams and pick the one which provides an implementation of flush in its contract

Thanks, I gave it a try with a BufferedOutputS tream which should implement the abstract flush() method and it still didn't work. I'll fiddle around with some other ones though and see if they help.
Thanks

[r035198x]

Thanks, I gave it a try with a BufferedOutputS tream which should implement the abstract flush() method and it still didn't work. I'll fiddle around with some other ones though and see if they help.
Thanks

Yuck. According to the contracts, anything extending FilterOutputStr eam should work, if BufferedOutputS tream wouldn't do it, then I suppose the problem is elsewhere.

[tegdim]

Yuck. According to the contracts, anything extending FilterOutputStr eam should work, if BufferedOutputS tream wouldn't do it, then I suppose the problem is elsewhere.

Thanks for the fast replies, I'm still new to IO coding so no doubt it'll be some little mistake in my code. It's just annoying that it works for the first iteration if i just close the stream after writing to it. Thanks again :)

[horace1]

I tend to use sockets (TCP virtual circuit or UDP datagrams) or RMI to pass information between process (and they don't have to be on the same machine), see
http://java.sun.com/docs/books/tutorial/networking/sockets/index.html
http://java.sun.com/javase/technologies/core/basic/rmi/index.jsp

[horace1]

Example using UDP datagrams to send data from a Java program to a Python program

this Python program binds to UDP socket 999, it then wait for datagrams and displays the contents

from socket import *
 
receiverSocket=socket(AF_INET, SOCK_DGRAM)
receiverSocket.bind(('',999))
 
while True :                   # from_physical
   data, address = receiverSocket.recvfrom(1024)
   if not data : break
   print data                   # to_network
receiverSocket.close()
 
 

this Java program reads a string from the keyboard, creates a datagram and sends it to UDP socket 999 on the same machine, i.e. IP address 127.0.0.1

// simple client sending a string in a datagram to a server
 
import java.io.*;
import java.util.*;
import java.net.*;
 
public class UDPclient
{
 
private final static BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
public static void main(String args[])
{
   String remoteIPaddress="127.0.0.1";
   int remotePort = 999;   
   System.out.println("enter text to transmit");
   while(true)
       try
          {
           String s = in.readLine();
           byte[] data = s.getBytes();                            // get array with data
           DatagramSocket theSocket = new DatagramSocket();       // create datagram socket
           // build the datagram packet
           DatagramPacket   theOutput = new DatagramPacket(data, data.length, InetAddress.getByName(remoteIPaddress), remotePort);
           System.out.println("sendFrame: sent " + s + " to host " + remoteIPaddress + " socket " + remotePort);
           theSocket.send(theOutput);                             // and send the datagram
          }  // end try
       catch (IOException e) {System.err.println("error " +  e); }
}
}