Sockets

    //file: DateAtHost.java
    import java.net.Socket;
    import java.io.*;
      
    public class DateAtHost extends java.util.Date {
        static int timePort = 37;
        // seconds from start of 20th century to Jan 1, 1970 00:00 GMT
        static final long offset = 2208988800L;

        public DateAtHost( String host ) throws IOException {
            this( host, timePort );
        }
      
        public DateAtHost( String host, int port ) throws IOException {
            Socket server = new Socket( host, port );
            DataInputStream din =
              new DataInputStream( server.getInputStream() );
            int time = din.readInt();
            server.close();

            setTime( (((1L << 32) + time) - offset) * 1000 );
        }
    }

That’s all there is to it. It’s not very long, even with a few frills. We have supplied two possible constructors for DateAtHost. Normally we’d expect to use the first, which simply takes the name of the remote host as an argument. The second constructor specifies the hostname and the port number of the remote time service. (If the time service were running on a nonstandard port, we would use the second constructor to specify the alternate port number.) This second constructor does the work of making the connection and setting the time. The first constructor simply invokes the second (using the this() construct) with the default port as an argument. Supplying simplified constructors that invoke their siblings with default arguments is a common and useful pattern in Java; that is the main reason we’ve shown it here.

    try {
        Date d = new DateAtHost( "someserver.net" );
        System.out.println( "The time over there is: " + d );
    }
    catch ( IOException e ) { ... }

    GET /path/filename [ optional stuff ]

Your web browser sends one or more of these requests for each document it retrieves from a web server. Upon reading a request, our server attempts to open the specified file and send its contents. If that document contains references to images or other items to be displayed inline, the browser follows up with additional GET requests. For best performance, TinyHttpd services each request in its own thread. Therefore, TinyHttpd can service several requests concurrently.

    //file: TinyHttpd.java
    import java.net.*;
    import java.io.*;
    import java.util.regex.*;
    import java.util.concurrent.*;
     
    public class TinyHttpd {
      public static void main( String argv[] ) throws IOException {
        Executor executor = Executors.newFixedThreadPool(3);
        ServerSocket ss = new ServerSocket( Integer.parseInt(argv[0]) );
        while ( true )
          executor.execute( new TinyHttpdConnection( ss.accept() ) );
      }
    }

    class TinyHttpdConnection implements Runnable {
      Socket client;
      TinyHttpdConnection ( Socket client ) throws SocketException {
        this.client = client;
      }
      public void run() {
        try {
          BufferedReader in = new BufferedReader(
            new InputStreamReader(client.getInputStream(), "8859_1" ) );
          OutputStream out = client.getOutputStream();
          PrintWriter pout = new PrintWriter(
            new OutputStreamWriter(out, "8859_1"), true );
          String request = in.readLine();
          System.out.println( "Request: "+request);

          Matcher get = Pattern.compile("GET /?(\\S*).*").matcher( request );
          if ( get.matches() ) {
            request = get.group(1);
            if ( request.endsWith("/") || request.equals("") )
              request = request + "index.html";
            try {
              FileInputStream fis = new FileInputStream ( request );
              byte [] data = new byte [ 64*1024 ];
              for(int read; (read = fis.read( data )) > -1; )
                  out.write( data, 0, read );
              out.flush();
            } catch ( FileNotFoundException e ) {
              pout.println( "404 Object Not Found" ); }
          } else
            pout.println( "400 Bad Request" );
          client.close();
        } catch ( IOException e ) {
          System.out.println( "I/O error " + e ); }
       }
    }

    % java TinyHttpd 1234

You should now be able to use your web browser to retrieve files from your host. You’ll have to specify the port number you chose in the URL. For example, if your hostname is foo.bar.com, and you started the server as shown, you could reference a file as in:

    http://foo.bar.com:1234/welcome.html

Or, more likely, if you’re running both the server and your web browser on the same machine, you could reference a file as in:

    http://localhost:1234/welcome.html

TinyHttpd looks for files relative to its current directory, so the pathnames you provide should be relative to that location. (Retrieved some files? Did you notice that when you retrieved an HTML file, your web browser automatically generated more requests for items like images that were contained within it?) Let’s take a closer look.

    % java -Dhttp.proxyServer=foo.bar.com -Dhttp.proxyPort=1234 MyProgram