A simple HTTP server that displays information about all accessible printers on the network : Web Server « Network Protocol « Java

A simple HTTP server that displays information about all accessible printers on the network

 * Copyright (c) 2004 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 3nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose,
 * including teaching and use in open-source projects.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book, 
 * please visit http://www.davidflanagan.com/javaexamples3.
//package je3.nio;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.util.Iterator;
import java.util.Set;

import javax.print.PrintService;
import javax.print.PrintServiceLookup;
import javax.print.attribute.Attribute;

 * PrintServiceWebInterface: A simple HTTP server that displays information
 * about all accessible printers on the network.
public class PrintServiceWebInterface {
  public static void main(String[] args) throws IOException {
    // Get the character encoders and decoders we'll need
    Charset charset = Charset.forName("ISO-8859-1");
    CharsetEncoder encoder = charset.newEncoder();

    // The HTTP headers we send back to the client are fixed
    String headers = "HTTP/1.1 200 OK\r\n" + "Content-type: text/html\r\n"
        + "Connection: close\r\n" + "\r\n";

    // We'll use two buffers in our response. One holds the fixed
    // headers, and the other holds the variable body of the response.
    ByteBuffer[] buffers = new ByteBuffer[2];
    buffers[0] = encoder.encode(CharBuffer.wrap(headers));
    ByteBuffer body = ByteBuffer.allocateDirect(16 * 1024);
    buffers[1] = body;

    // Find all available PrintService objects to describe
    PrintService[] services = PrintServiceLookup.lookupPrintServices(null, null);

    // All of the channels we use in this code will be in non-blocking
    // mode. So we create a Selector object that will block while
    // monitoring all of the channels and will only stop blocking when
    // one or more of the channels is ready for I/O of some sort.
    Selector selector = Selector.open();

    // Create a new ServerSocketChannel, and bind it to port 8000.
    // Note that we have to do this using the underlying ServerSocket.
    ServerSocketChannel server = ServerSocketChannel.open();
    server.socket().bind(new java.net.InetSocketAddress(8000));

    // Put the ServerSocketChannel into non-blocking mode

    // Now register the channel with the Selector. The SelectionKey
    // represents the registration of this channel with this Selector.
    SelectionKey serverkey = server.register(selector, SelectionKey.OP_ACCEPT);

    for (;;) { // The main server loop. The server runs forever.
      // This call blocks until there is activity on one of the
      // registered channels. This is the key method in non-blocking I/O.

      // Get a java.util.Set containing the SelectionKey objects for
      // all channels that are ready for I/O.
      Set keys = selector.selectedKeys();

      // Use a java.util.Iterator to loop through the selected keys
      for (Iterator i = keys.iterator(); i.hasNext();) {
        // Get the next SelectionKey in the set, and then remove it
        // from the set. It must be removed explicitly, or it will
        // be returned again by the next call to select().
        SelectionKey key = (SelectionKey) i.next();

        // Check whether this key is the SelectionKey we got when
        // we registered the ServerSocketChannel.
        if (key == serverkey) {
          // Activity on the ServerSocketChannel means a client
          // is trying to connect to the server.
          if (key.isAcceptable()) {
            // Accept the client connection, and obtain a
            // SocketChannel to communicate with the client.
            SocketChannel client = server.accept();

            // Make sure we actually got a connection
            if (client == null)

            // Put the client channel in non-blocking mode.

            // Now register the client channel with the Selector,
            // specifying that we'd like to know when there is
            // data ready to read on the channel.
            SelectionKey clientkey = client.register(selector, SelectionKey.OP_READ);
        } else {
          // If the key we got from the Set of keys is not the
          // ServerSocketChannel key, then it must be a key
          // representing one of the client connections.
          // Get the channel from the key.
          SocketChannel client = (SocketChannel) key.channel();

          // If we got here, it should mean that there is data to
          // be read from the channel, but we double-check here.
          if (!key.isReadable())

          // Now read bytes from the client. We assume that
          // we get all the client's bytes in one read operation

          // The data we read should be some kind of HTTP GET
          // request. We don't bother checking it however since
          // there is only one page of data we know how to return.

          // Build an HTML document as our reponse.
          // The body of the document contains PrintService details
          StringBuffer response = new StringBuffer();
          response.append("<html><head><title>Printer Status</title></head>"
              + "<body><h1>Printer Status</h1>");
          for (int s = 0; s < services.length; s++) {
            PrintService service = services[s];
            Attribute[] attrs = service.getAttributes().toArray();
            for (int a = 0; a < attrs.length; a++) {
              Attribute attr = attrs[a];

          // Encode the response into the body ByteBuffer
          encoder.encode(CharBuffer.wrap(response), body, true);

          body.flip(); // Prepare the body buffer to be drained
          // While there are bytes left to write
          while (body.hasRemaining()) {
            // Write both header and body buffers
          buffers[0].flip(); // Prepare header buffer for next write
          body.clear(); // Prepare body buffer for next read

          // Once we've sent our response, we have no more interest
          // in the client channel or its SelectionKey
          client.close(); // Close the channel.
          key.cancel(); // Tell Selector to stop monitoring it.


Related examples in the same category

1.A simple, tiny, nicely embeddable HTTP 1.0 server in Java
2.A web server
3.Minimal HTTP Server by using com.sun.net.httpserver.HttpServer
4.POSTing data to an HTTP server