Java tutorial
/* * 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 server.configureBlocking(false); // 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. selector.select(); // 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(); i.remove(); // 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) continue; // Put the client channel in non-blocking mode. client.configureBlocking(false); // 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()) continue; // Now read bytes from the client. We assume that // we get all the client's bytes in one read operation client.read(body); // 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. body.clear(); // 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]; response.append("<h2>").append(service.getName()).append("</h2><table>"); Attribute[] attrs = service.getAttributes().toArray(); for (int a = 0; a < attrs.length; a++) { Attribute attr = attrs[a]; response.append("<tr><td>").append(attr.getName()).append("</td><td>").append(attr) .append("</tr>"); } response.append("</table>"); } response.append("</body></html>\r\n"); // Encode the response into the body ByteBuffer encoder.reset(); encoder.encode(CharBuffer.wrap(response), body, true); encoder.flush(body); 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 client.write(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. } } } } }