Why does my TCP connection close after running a command? - Java

Question

I have a simple FTP server and client. For now, the client can send a file, and the server can accept it, but after i run a sendFile() command, it transfers the file, and the server and the client terminate, making it unable to run any other commands after that.

SERVER

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.ServerSocket;
import java.net.Socket;

import mmd.filetransfer.FileEvent;

public class Server {
    private ServerSocket serverSocket = null;
    private Socket socket = null;
    private ObjectInputStream inputStream = null;
    private FileEvent fileEvent;
    private File dstFile = null;
    private FileOutputStream fileOutputStream = null;

   public Server() {

    }

    /**
     * Accepts socket connection
     */
    public void doConnect() {
        try {
            serverSocket = new ServerSocket(4445);
            socket = serverSocket.accept();
            inputStream = new ObjectInputStream(socket.getInputStream());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * Reading the FileEvent object and copying the file to disk.
     */
    public void downloadFile() {
        try {
            fileEvent = (FileEvent) inputStream.readObject();
            if (fileEvent.getStatus().equalsIgnoreCase("Error")) {
                System.out.println("Error occurred ..So exiting");
                System.exit(0);
            }
            String outputFile = fileEvent.getDestinationDirectory() + fileEvent.getFilename();
            if (!new File(fileEvent.getDestinationDirectory()).exists()) {
                new File(fileEvent.getDestinationDirectory()).mkdirs();
            }
            dstFile = new File(outputFile);
            fileOutputStream = new FileOutputStream(dstFile);
            fileOutputStream.write(fileEvent.getFileData());
            fileOutputStream.flush();
            fileOutputStream.close();
            System.out.println("Output file : " + outputFile + " is successfully saved ");
            //Thread.sleep(0);
            //System.exit(0);

        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } 

    }

    public static void main(String[] args) {
        Server server = new Server();
        server.doConnect();
        server.downloadFile();
    }
}

CLIENT

package mmd.client;

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

import mmd.filetransfer.FileEvent;


public class Client {
    private Socket socket = null;
    private ObjectOutputStream outputStream = null;
    private boolean isConnected = false;
    private String sourceFilePath = "/home/jovan/Desktop/videot.mpg";
    private FileEvent fileEvent = null;
    private String destinationPath = "/home/jovan/Desktop/tp/";

    public Client() {

    }

    /**
     * Connect with server code running in local host or in any other host
     */
    public void connect() {
        while (!isConnected) {
            try {
                socket = new Socket("localHost", 4445);
                outputStream = new ObjectOutputStream(socket.getOutputStream());
                isConnected = true;

            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public void sendFile()  {
        fileEvent = new FileEvent();
        String fileName = sourceFilePath.substring(sourceFilePath.lastIndexOf("/") + 1, sourceFilePath.length());
        String path = sourceFilePath.substring(0, sourceFilePath.lastIndexOf("/") + 1);
        fileEvent.setDestinationDirectory(destinationPath);
        fileEvent.setFilename(fileName);
        fileEvent.setSourceDirectory(sourceFilePath);
        File file = new File(sourceFilePath);
        if (file.isFile()) {
            try {
                DataInputStream diStream = new DataInputStream(new FileInputStream(file));
                long len = (int) file.length();
                byte[] fileBytes = new byte[(int) len];
                int read = 0;
                int numRead = 0;
                while (read < fileBytes.length && (numRead = diStream.read(fileBytes, read,
                        fileBytes.length - read)) >= 0) {
                    read = read + numRead;
                }
                fileEvent.setFileSize(len);
                fileEvent.setFileData(fileBytes);
                fileEvent.setStatus("Success");
            } catch (Exception e) {
                e.printStackTrace();
                fileEvent.setStatus("Error");
            }
        } else {
            System.out.println("path specified is not pointing to a file");
            fileEvent.setStatus("Error");
        }
        //Now writing the FileEvent object to socket
        try {
            outputStream.writeObject(fileEvent);
            System.out.println("Done...Going to exit");
            Thread.sleep(0);
            //System.exit(0);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 

    }

    /**
     * Sending FileEvent object.
     
     * @throws IOException */


    public static void main(String[] args){
        Client client = new Client();
        client.connect();
        client.sendFile();
        client.sendFile();


    }
}

How to prevent this?

doConnect() should be in infinite loop like while(true){ // accept socket and create a thread to process IO operations }. Now your server accepts only one connection — Ravindra babu, Dec 23 '15 at 13:58
@ravindra i will try that now. What i actualy did, and it worked, is that i have a heartbeat on the server, but i dont know if it would accept more than one client. while (true) { if(heartbeat){ Thread.sleep(10000); System.out.println("heartbeat"); } } — JovanIvanoski, Dec 23 '15 at 14:01
just say while(true){ //accept the connection with out any delay} — Ravindra babu, Dec 23 '15 at 14:10
Have a look at example code: http://www.dailyfreecode.com/code/ftp-client-server-1250.aspx and one SE question: http://stackoverflow.com/questions/4687615/how-to-achieve-transfer-file-between-client-and-server-using-java-socket — Ravindra babu, Dec 23 '15 at 14:14

score 0 · Accepted Answer · answered Dec 23 '15 at 14:09

0

Calling it an FTP server is a bit confusing, as this does not implement RFC 959.

Your main() in the server code does not have any loop. It just listens, transfers one file and exits. Put it in an infinite loop as ravindra suggests.

answered Dec 23 '15 at 14:09

Árpád Magosányi

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lets say I have multiple clients on the server, and i want them to be able to download/upload files. How do i implement that? I am really inexperienced in socket programming, so any help would be very useful. – JovanIvanoski Dec 23 '15 at 14:20
There are three phases: - you create a socket, bind it , and listen on it - in a loop you accept incoming calls. this will give you a direct socket for the client - you do the heavy lifting (read/write) on the socket with the client, and close it at the end. You probably want to do it in a different thread/process, so your main loop can continue listening. – Árpád Magosányi Dec 23 '15 at 15:27

Why does my TCP connection close after running a command? - Java

1 Answers1