// 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.
}
}
}
