Multi threaded HTTP server in Java that will only serve 1 single file for ANY http request

SingleFileHTTPServer.java

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.InputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.URLConnection;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.logging.Level;
import java.util.logging.Logger;

// Serve only a single specific file for ANY http request
public class SingleFileHTTPServer
{
  private static final String serverName = "SingleFileHTTPServer";
  private static final String serverVer = "1.0";
  private static final Logger logger = Logger.getLogger (serverName);
  private static final int numThreads = 2;

  private final byte[] httpHeader;
  private final int httpPort;
  private final Path filePath;

  public SingleFileHTTPServer (String fileName, int httpPort)
  {
    String mimeType = URLConnection.getFileNameMap ().getContentTypeFor (fileName);
    filePath = Paths.get (fileName);

    this.httpPort = httpPort;
    String header = "HTTP/1.0 200 OK\r\n"
        + "Server: " + serverName + " " + serverVer + "\r\n"
        + "Content-length: " + new File (fileName).length () + "\r\n"
        + "Content-type: " + mimeType + "\r\n\r\n";
    this.httpHeader = header.getBytes (Charset.forName ("US-ASCII"));
  }

  public void start ()
  {
    ExecutorService threadPool = Executors.newFixedThreadPool (numThreads);
    try (ServerSocket serverSocket = new ServerSocket (this.httpPort))
    {
      logger.info ("Accepting connections on port " + serverSocket.getLocalPort ());

      while (true)
      {
        try
        {
          Socket clientSocket = serverSocket.accept ();
          threadPool.submit (new HTTPHandler (clientSocket));
        }
        catch (IOException ex)
        {
          logger.log (Level.WARNING, "Exception accepting connection", ex);
        }
        catch (RuntimeException ex)
        {
          logger.log (Level.SEVERE, "Unexpected error", ex);
        }
      }
    }
    catch (IOException ex)
    {
      logger.log (Level.SEVERE, "Could not start server", ex);
    }
  }

  private class HTTPHandler implements Callable <Void>
  {
    private final Socket clientSocket;

    HTTPHandler (Socket clientSocket)
    {
      this.clientSocket = clientSocket;
    }

    @Override
    public Void call () throws IOException
    {
      try
      {
        OutputStream outStream = new BufferedOutputStream (clientSocket.getOutputStream ());
        InputStream inStream = new BufferedInputStream (clientSocket.getInputStream ());
        // read the first line only; that's all we need
        StringBuilder httpRequest = new StringBuilder (80);
        while (true)
        {
          int currChar = inStream.read ();
          if (currChar == '\r' || currChar == '\n' || currChar == -1) break;
          httpRequest.append ((char) currChar);
        }
        // If this is HTTP/1.0 or later send a MIME header
        if (httpRequest.toString ().indexOf ("HTTP/") != -1)
        {
          outStream.write (httpHeader);
        }
        Files.copy (filePath, outStream);
        outStream.flush ();
      }
      catch (IOException ex)
      {
        logger.log (Level.WARNING, "Error writing to client", ex);
      }
      finally
      {
        clientSocket.close ();
      }
      return null;
    }
  }

  public static void main (String[] args)
  {
    // set the port to listen on
    int port;
    try
    {
      port = Integer.parseInt (args[1]);
      if (port < 1 || port > 65535) port = 80;
    }
    catch (RuntimeException ex)
    {
      port = 80;
    }

    try
    {
      SingleFileHTTPServer server = new SingleFileHTTPServer (args[0], port);
      server.start ();
    }
    catch (ArrayIndexOutOfBoundsException ex)
    {
      System.out.println ("Usage: java SingleFileHTTPServer filename port");
    }
  }
}