Save into a file before exiting the program

Question

Hi All,
I am developing a java project. It is a console application.
Initially the program loads content of a file(customer.txt) into an ArrayList.
Then it gives 3 options:-
1. Add a Customer
2. Delete a Customer
3. Save and Exit
The changes add or delete are made in the ArrayList.
The ArrayList is saved back to the customer.txt only when we select the option 3.
It works fine.
But instead of exiting the application using option 3, if we close the eclipse window or restart the computer, the changes are not saved to the file.
So could you please suggest me how we can save the changes in such situations.?

Answer 1

- Create a class that extends Thread
- in the run() method place the code that saves your data
- in your initialization create an instance of your Thread class but do not start it - instead register the object as a shutdown hook (use Runtime.getRuntime().addShutdownHook()).
When your application terminates the VM will kick off your thread, which should save your data. You may have to experiment a little to get it working right. Remember that only a normal termination signal will allow the VM to continue running so that it can execute your shutdown thread - a kill signal will stop the VM, as will calling Runtime.halt().
(Edit: note also that this may not work in Eclipse - I've seen problems running shutdown hooks when testing an application under Eclipse.)
Edited by: PeteFord on Nov 17, 2008 1:39 PM