cometd bayeux can't send message to a specific client - cometd

Question

//StockPriceEmitter is a "dead loop" thread which generate data, and invoke StockPriceService.onUpdates() to send data.
#Service
public class StockPriceService implements StockPriceEmitter.Listener
{
#Inject
private BayeuxServer bayeuxServer;
#Session
private LocalSession sender;
public void onUpdates(List<StockPriceEmitter.Update> updates)
{
for (StockPriceEmitter.Update update : updates)
{
// Create the channel name using the stock symbol
String channelName = "/stock/" + update.getSymbol().toLowerCase(Locale.ENGLISH);
// Initialize the channel, making it persistent and lazy
bayeuxServer.createIfAbsent(channelName, new ConfigurableServerChannel.Initializer()
{
public void configureChannel(ConfigurableServerChannel channel)
{
channel.setPersistent(true);
channel.setLazy(true);
}
});
// Convert the Update business object to a CometD-friendly format
Map<String, Object> data = new HashMap<String, Object>(4);
data.put("symbol", update.getSymbol());
data.put("oldValue", update.getOldValue());
data.put("newValue", update.getNewValue());
// Publish to all subscribers
ServerChannel channel = bayeuxServer.getChannel(channelName);
channel.publish(sender, data, null); // this code works fine
//this.sender.getServerSession().deliver(sender, channel.getId(), data, null); // this code does not work
}
}
}
this line channel.publish(sender, data, null); // this code works fine works fine, now I don't want channel to publish message to all clients subscirbed with it, I want to send to a specific client, so I write this this.sender.getServerSession().deliver(sender, channel.getId(), data, null);, but it does not work, browser can't get message.
thx in advance.

Answer 1

I strongly recommend that you spend some time reading the CometD concepts page, in particular the section about sessions.
Your code does not work because you are sending the message to the sender, not to the recipient.
You need to pick which remote ServerSession you want to send the message to among the many that may be connected to your server, and call serverSession.deliver(...) on that remote ServerSession.
How to pick the remote ServerSession depends on your application.
For example:
for (ServerSession session : bayeuxServer.getSessions())
{
if (isAdminUser(session))
session.deliver(sender, channel.getId(), data, null);
}
You have to provide an implementation of isAdmin(ServerSession) with your logic, of course.
Note that you don't need to iterate over the sessions: if you happen to know the session id to deliver to, you can do:
bayeuxServer.getSession(sessionId).deliver(sender, channel.getId(), data, null);
Also refer to the CometD chat demo shipped with the CometD distribution, that contain a full fledged example of how to send a message to particular session.