A simple, one-file HTTP file server(HFS) writen in Java without any external dependencies. I use this to stream videos from computer to other devices on the network.

FileServer.java

import java.io.*;
import java.net.*;
import java.nio.file.Files;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
public class FileServer {
    public static String BASE_DIR = "/";
    public static final int PORT = 8080;
    static ServerSocket server;
    public static void main(String[] args) {
        try {
            Collections.list(NetworkInterface.getNetworkInterfaces()).stream()
                    .flatMap(a -> Collections.list(a.getInetAddresses()).stream())
                    .filter(InetAddress::isSiteLocalAddress)
                    .filter(a -> !a.isLoopbackAddress())
                    .forEach(a -> System.out.println(a.getHostAddress()));
            server = new ServerSocket(PORT);
            System.out.println("Listening on port: " + PORT);
            while (server.isBound()) {
                (new Thread(new ConnectionHandler(server.accept()))).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class ConnectionHandler implements Runnable {
    Socket client;
    InputStream in;
    OutputStream out;
    public ConnectionHandler(Socket client) throws IOException {
        this.client = client;
        in = client.getInputStream();
        out = client.getOutputStream();
    }
    @Override
    public void run() {
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        try {
            String line = reader.readLine();
            if (line != null && line.startsWith("GET")) {
                System.out.println(client.getInetAddress() + " : " + line);
                String req = URLDecoder.decode(FileServer.BASE_DIR + line.substring(4, line.indexOf(' ', 4)).replaceAll("/../", "/./"));
                System.out.println(req);
                HashMap<String, String> headers = new HashMap<>();
                while (!(line = reader.readLine()).isEmpty()) {
                    int div = line.indexOf(':');
                    headers.put(line.substring(0, div), line.substring(div+1));
                }
                BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(out));
                File request = new File(req);
                if (!request.canRead()) {
                    System.out.println(request);
                    writer.write("HTTP/1.1 404 Not Found\r\n\r\n");
                    writer.write("404 The requested URL was not found on this server.\r\n\r\n");
                    writer.flush();
                } else {
                    if (request.isDirectory()) writeDirectory(request, writer);
                    else writeFile(request, out, writer, headers.get("Range"));
                    writer.close();
                }
            }
            else {
                BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(out));
                writer.write("HTTP/1.1 501 Not Implemented\r\n\r\n");
                writer.write("501 Not Implemented\r\n\r\n");
                writer.flush();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            client.close();
            in.close();
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    static void writeFile(File file, OutputStream out, BufferedWriter writer, String range) throws IOException {
        long from = 0, to = 0;
        if (range != null) {
            range = range.trim();
            System.out.println(range);
            if (!range.startsWith("bytes")) range = null;
            else if (range.contains(",")) range = null;
            else {
                try {
                    String[] ranges = range.substring("bytes=".length()).split("-");
                    if (range.charAt("bytes=".length()-1) == '-') {
                        ranges = new String[]{"0", ranges[0]}; //TODO this is not how it works, fixme
                    }
                    from = Long.parseLong(ranges[0]);
                    to = ranges.length > 2 && ranges[1].isEmpty() ? Long.parseLong(ranges[1]) : Files.size(file.toPath());
                    assert from < to;
                    assert to <= Files.size(file.toPath());
                } catch (Exception e) {
                    range = null;
                }
                if (range != null) {
                    writer.write("HTTP/1.1 206 Partial Content\r\n");
                    writer.write("Content-Type: " + Files.probeContentType(file.toPath()) + "\r\n");
                    writer.write("Content-Length: " + (to - from) + "\r\n");
                    writer.write("Content-Range: bytes " + to  + "-" + from + "/" + Files.size(file.toPath()) + "\r\n");
                    writer.write("Accept-Ranges: bytes\r\n");
                    writer.write("Connection: close\r\n");
                    writer.write("\r\n");
                }
            }
        }
        if (range == null) {
            // we do not support this. We can send a 200 OK according to https://tools.ietf.org/html/rfc2616#section-3.12
            writer.write("HTTP/1.1 200 OK\r\n");
            writer.write("Content-Type: " + Files.probeContentType(file.toPath()) + "\r\n");
            writer.write("Content-Length: " + (to = Files.size(file.toPath())) + "\r\n");
            writer.write("Accept-Ranges: bytes\r\n");
            writer.write("Connection: close\r\n");
            writer.write("\r\n");
        }
        writer.flush();
        FileInputStream in = new FileInputStream(file);
        long skipped = from;
        while (skipped > 0) skipped -= in.skip(skipped);
        long toTransfer = to-from;
        int read;
        byte[] buffer;
        for(buffer = new byte[8192]; (read = in.read(buffer, 0, (int) Math.min(8192, toTransfer))) >= 0; toTransfer -= (long)read) {
            out.write(buffer, 0, read);
        }
        out.flush();
    }

    static void writeDirectory(File dir, BufferedWriter writer) throws IOException {
        File[] listOfFiles = dir.listFiles();
        writer.write("HTTP/1.1 200 OK\r\n");
        writer.write("Content-Type: text/html; charset=UTF-8\r\n");
        writer.write("\r\n");
        writer.write("<!DOCTYPE html>\n" +
                "<html>\n" +
                "<head>\n" +
                "\t<title>Index of " + dir.getAbsolutePath() + "</title>\n" +
                "</head>\n" +
                "<body>\n");
        if (listOfFiles == null || listOfFiles.length == 0) {
            writer.write("No files found.\n");
        } else {
            Arrays.sort(listOfFiles);
            for (File f : listOfFiles) {
                if (f.isFile()) {
                    writer.write("<a href=\"" + f.getPath().substring(FileServer.BASE_DIR.length()) + "\">" + f.getName() + "</a>");
                    writer.write("<br>");
                } else if (f.isDirectory()) {
                    writer.write("<a href=\"" + f.getPath().substring(FileServer.BASE_DIR.length()) + "\">" + f.getName() + '/' + "</a>");
                    writer.write("<br>");
                }
            }
        }
        writer.write("<hr>");
        writer.write("</body>\n" +
                "</html>\n");
        writer.write("\r\n\r\n");
        writer.flush();
    }
}