web server sending command to a J2ME app

Question

Can a J2ME app be triggered by a message from a remote web server. I want to perform a task at the client mobile phone as soon as the J2ME app running on it receives this message. I have read of HTTP connection, however what I understand about it is a client based protocol and the server will only reply to client requests. Any idea if there is any protocol where the server can send a command to the client without client initiating any request?. How about Socket/Stream based(TCP) or UDP interfaces?.

Answer 1

If the mobile device doesnt allow you to make TCP connections, and you are limited to HTTP requests, then you're looking at implementing "long polling".

One POST a http request and the web-server will wait as long time as possible (before things time out) to answer. If something arrives while the connection is idling it can receive it directly, if something arrives between long-polling requests it is queued until a request comes in.

If you can make TCP connections, then just set up a connection and let it stay idle. I have icq and irc applications that essentially just sit there waiting for the server to send it something.

Answer 2

You should see PushRegistry feature where you can send out an SMS to a specific number have the application started when the phone receives that SMS and then make the required HTTP connection or whatever. However, the downside of it is that you might have to sign the application to have it working on devices and you also need an SMS aggregator like SMSLib or Kannel

Answer 3

You can open socket connection and implement "Hide" (or "Minimize") functionality in your app. Call this to hide:

Display.getDisplay(MyMIDlet.instance).setCurrent(null);

Listen to the server in a loop, and if you receive some message, popup the applicaion by calling this from canvas:

Display.getDisplay(MyMIDlet.instance).setCurrent(this);

But it dosen't work on all devices.

Answer 4

Socket push are supported by j2me. But it could work only if your server could deliver data to your mobile phone. Most likely that operator gateway don't allow to do this. Maybe it would be possible if your mobile has static external IP address - some operators could provide this for $$.