CODEWITHSUNDEEP
javafilememory-managementsoftware-design
Syed Zubair Bokhari
Syed Zubair Bokhari

Reputation: 23

How to Save the system state in Java and resume the system when I recompile the project?

I have a system in Java where different classes stores different information. There is a main class where the user will input the information of these classes and make them interact with each other. After the user is done, he will exit the system. The Next time the user recompile the project, all the previously entered data should be there. The user can use that same data or add more information.

So Simply, How to pause/save the system on close and resume it when I execute it again? PS. I can't use Database in this. It must be something else.

Upvotes: 1

Views: 416

Answers (1)

rzwitserloot
rzwitserloot

Reputation: 102872

The Next time the user recompile the project

Users dont recompile projects. They just run your app.

You keep saying 'not DB', so, then, the answer is trivially: impossible.

A database, by definition, persists some data, hence the name: It's a base of data. If that's off the table, you're out of luck and what you want is not possible.

Perhaps you are careless in your wording there as well and all you mean is perhaps:

I do not want to bother with forcing the user to install a database

Okay, then, don't. Use an in-process database, such as h2. The user doesn't know an SQL-based database system is involved, all they see is a file appear. No extra processes are launched.

I hate SQL

Okay, then, don't. There are tools out there that turn an entire object structure into a bag o bytes which you can then save to a file, for example Jackson which can turn one object (which can contain all the relevant user data if you want) into JSON data, which you can then save to a file, and restore later. Of course, if someone trips over a powercable halfway through writing it, the file is corrupted. There are ways to fix that (save to .tmp, then move it into place, as that's usually atomic), but you're sort of committed to re-inventing the wheel here, due to your insistence you don't want databases.

I just want to save the entire system state

You can't. Not how java works.

Can't I do it with zero dependencies?

There's java's built in serialization system, which sucks, has a list of caveats as long as my leg on how to use it, and is more or less disliked by the maintainers of the java platform itself. This is not the way to go. It also still won't 'save the entire system state', it just saves one object, and does a much worse job at this than e.g. jackson.

Upvotes: 2

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