CODEWITHSUNDEEP
java
Arslan Anwar
Arslan Anwar

Reputation: 18746

How to restrict a java program to execute only N times

I want to make a java program that must run for a specific number of times only. e.g 2,5,10 etc. after that it must throw an Exception.

It is not allowed to use any FILE or Database for this. Someone gave me a hint of REGISTRY! But i don't know how to use it for this. Please help me is this regard...

Upvotes: 2

Views: 543

Answers (4)

Stephen C
Stephen C

Reputation: 718788

Whether this problem is solvable depends on what is meant by "any FILE or Database".

  • Depending on your point of view, the Windows Registry is a kind of file / database. Certainly, the only reason that values stay in the registry over a reboot is because registry changes are written to disc.

  • You can move state (such as a count of the number of times an application has been run) to some other service on the local machine. But once again, unless the service saves that state to disc (or some other stable storage medium) it will be lost is the local machine reboots.

  • You can move state to a service on a remote machine, but once again it may be lost if not saved to disc, etc. Moreover, you may not be able contact that remote service at the time you need the state; e.g. when starting the application.

  • You can copy the state to lots of remote services without discs, but a network failure (or the user unplugging from the network) will stop you accessing the state.

So to summarize, if you cannot write to disc (or nvram, tape, etc) locally, you cannot guarantee that the counter won't get reset, and that it will be available when needed. Therefore you cannot guarantee that the application won't be run more times than is allowed.

I imagine that you are trying to come up with some limited use scheme that users cannot subvert; e.g. by deleting stuff from the file / database / whatever that counter. Unfortunately, unless you physically control BOTH the hardware AND the operating system on which the application runs, you cannot prevent someone from subverting any counter stored on the machine itself. Anyone with "root" or full administrator rights, or with physical access, can ultimately change any data on the machine itself.

The best you can do is establish a secure connection to a remote server and use that to hold the usage counter. But even that is futile, because a motivated person can reverse engineer the critical part of your application and disable the code that checks the counter.

Upvotes: 4

Gary
Gary

Reputation: 7257

Even though this sounds like an attempt at copy protection, you may want to consider self-modifying code. There is an interesting discussion on this subject in Java here: Self modifying code in Java

Upvotes: 0

Andrew Thompson
Andrew Thompson

Reputation: 168825

If the app. has a GUI, it can be launched using Java Web Start and use the PersistenceService. Here is a small demo. of the PersistenceService. The code is available for download.

Edit: And the PersistenceService should work on any machine that has a JRE, as opposed to just Windows.

Upvotes: 0

Alois Cochard
Alois Cochard

Reputation: 9862

You can use java preferences (registry on windows) :

You can find some sample usage here:

Upvotes: 4

Related Questions