Sending a file with Java Sockets, losing data

I'm trying to send a file from a client to a server with Sockets in Java. It works fine when I am testing on the same machine, but when I test across different machines, I lose large chunks of data, resulting in a corrupted file. If I try to send a very small file (<20 bytes), it doesn't even reach the println inside the server's while loop.

Here is my code:

Server.java

package edu.mst.cs.sensorreceiver;

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

public class Server {
    private static final int PORT = 51111;
    private static final int CHUNK_SIZE = 1024;
    private static final File _downloadDir = new File("downloads/");

    public static void main(String[] args) {
        if (!_downloadDir.exists()) {
            if (!_downloadDir.mkdirs()) {
                System.err.println("Error: Could not create download directory");
            }
        }

        Socket socket = null;
        try {
            ServerSocket server = new ServerSocket(PORT);

            while (true) {
                System.out.println("Waiting for connection...");
                socket = server.accept();

                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

                String name = in.readLine();
                File file = new File(_downloadDir, name);

                String size = in.readLine();
                int fileSize;
                try {
                    fileSize = Integer.parseInt(size);
                } catch (NumberFormatException e) {
                    System.err.println("Error: Malformed file size:" + size);
                    e.printStackTrace();
                    return;
                }

                System.out.println("Saving " + file + " from user... (" + fileSize + " bytes)");
                saveFile(file, socket.getInputStream());
                System.out.println("Finished downloading " + file + " from user.");
                if (file.length() != fileSize) {
                    System.err.println("Error: file incomplete");
                }
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (socket != null) {
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private static void saveFile(File file, InputStream inStream) {
        FileOutputStream fileOut = null;
        try {
            fileOut = new FileOutputStream(file);

            byte[] buffer = new byte[CHUNK_SIZE];
            int bytesRead;
            int pos = 0;
            while ((bytesRead = inStream.read(buffer, 0, CHUNK_SIZE)) >= 0) {
                pos += bytesRead;
                System.out.println(pos + " bytes (" + bytesRead + " bytes read)");
                fileOut.write(buffer, 0, bytesRead);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileOut != null) {
                try {
                    fileOut.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        System.out.println("Finished, filesize = " + file.length());
    }
}

Client.java

package edu.mst.cs.sensorreceiver;

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

public class Client {
    private static final String HOSTNAME = "131.151.163.153";
    private static final int PORT = 51111;
    private static final int CHUNK_SIZE = 1024;

    public static void main(String[] args) {
        sendFile(args[0]);
    }

    private static void sendFile(String path) {
        if (path == null) {
            throw new NullPointerException("Path is null");
        }

        File file = new File(path);
        Socket socket = null;
        try {
            System.out.println("Connecting to server...");
            socket = new Socket(HOSTNAME, PORT);
            System.out.println("Connected to server at " + socket.getInetAddress());

            PrintStream out = new PrintStream(socket.getOutputStream(), true);

            out.println(file.getName());
            out.println(file.length());

            System.out.println("Sending " + file.getName() + " (" + file.length() + " bytes) to server...");
            writeFile(file, socket.getOutputStream());
            System.out.println("Finished sending " + file.getName() + " to server");
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (socket != null) {
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private static void writeFile(File file, OutputStream outStream) {
        FileInputStream reader = null;
        try {
            reader = new FileInputStream(file);
            byte[] buffer = new byte[CHUNK_SIZE];
            int pos = 0;
            int bytesRead;
            while ((bytesRead = reader.read(buffer, 0, CHUNK_SIZE)) >= 0) {
                outStream.write(buffer, 0, bytesRead);
                outStream.flush();
                pos += bytesRead;
                System.out.println(pos + " bytes (" + bytesRead + " bytes read)");
            }
        } catch (IndexOutOfBoundsException e) {
            System.err.println("Error while reading file");
            e.printStackTrace();
        } catch (IOException e) {
            System.err.println("Error while writing " + file.toString() + " to output stream");
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

I've been working on this for hours and I have made almost no progress. I thought I had a pretty good understanding of how reading/writing from streams works, but clearly I'm missing something here.

Again, everything works perfectly when I am sending and receiving from the same machine. But if I try to send a file between two computers, even if the two are on the same LAN, I lose a lot of the data that was sent.

Can anybody figure out my problem? I've already tried everything I could think of.