How to uniquely identify a downloaded Java ME app [duplicate]

This question already has answers here: Closed 11 years ago.

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A unique identifier for cell phone other tha开发者_如何学运维n IMEI or IMSI?

I have the following problem: I want to offer a Java ME app for download, which can obviously be installed on a mobile phone (different manufacturers and models) and will afterwards - when used - communicate with a web server. During this communication I need to uniquely identify the app (i.e. the phone/user) but preferably without bothering the user to enter a username/password or something.

My first attempt was too use the phone's IMEI, but it's a pain in the a** to retrieve the IMEI from a phone using JavaME and for some phones it does not seem to be possible at all. At least I couldn't find a way to guarantee that the app will transmit a correct IMEI for every phone. Please, anyone correct me if I'm wrong.

Second idea was too encode an ID into the app before it is downloaded. Is there a standard/preferred way to do this (besides adding the ID to the .jad file)? Any hints would be appreciated.

Thanks in advance.

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How about using the System.currentTimeMillis() at the first time the user fires up the MIDlet? The chances of this being identical for two users are slim-to-none ;)