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I created a working Google Channel AP and now I would like to send a message to all clients.

I have two servlets. The first creates the channel and tells the clients the userid and token. The second one is called by an http post and should send the message.

To send a message to a client, I use:

channelService.sendMessage(new ChannelMessage(channelUserId, "This is a server message!"));

This sends the message just to one client. How could I send this to all?

Have I to store every Id which I use to create a channel and send the message for every id? How could I pass the Ids to the second servlet?

Andre Hofmeister
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2 Answers2

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Using Channel API it is not possible to create one channel and then having many subscribers to it. The server creates a unique channel for individual JavaScript clients, so if you have the same Client ID the messages will be received only by one.

If you want to send the same message to multiple clients, in short, you will have to keep a track of active clients and send the same message to all of them.

If that approach sounds scary and messy, consider using PubNub for your push notification messages, where you can easily create one channel and have many subscribers. To make it run on Google App Engine is not that hard, since they support almost any platform or device.

Lipis
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I know this is an old question, but I just finished an open source project that uses the Channel API to implement a publish/subscribe model, i.e. you can have multiple users subscribe to a single topic, and then all those subscribers will be notified when anyone publishes a message to the topic. It also has some nice features like automatic message persistence if desired, and "return receipts", where a subscriber can be notified whenever OTHER subscribers receive that message. See https://github.com/adevine/gaewebpubsub#gae-web-pubsub. Licensed under Apache 2.0 license.

adevine
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