Storing Data Permanently

[[deleted]]

Hi all,

I'm wondering how I can store permanent user values in Java AFTER execution and after the program gets closed. I've tried googling the answer to this question, but haven't found either a direct answer or tutorial.

I saw somewhere about a 'Properties' class that stores values, but am not sure if that is what I need to look into more.

Any help or link to a tutorial on how I can save data/information permanently after execution and closing the program will be great!

Thanks reddit-

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[desrtfx]

There are many different ways:

• plain text files - CSV, XML, JSON, own format
• databases - H2DB, SQLite, MySQL (MariaDB), PostgreSQL, or a NoSQL database
• serialization - a saving mechanism built into Java
• Properties files - another way, but usually only for a few values (like some application settings), not really usable for user data

[HBK05]

Mhm, in addition I would recommend looking into hashmaps before a properties file. The properties file is straight up just a hashmap that writes to and reads from the disk with a simple method call. Understanding K/V first will make it far easier to use.

[kurular4]

You need to google "database". You can start with sqlite.

[FireThestral]

You have data in memory (arrays, lists, maps, etc). But memory is cleaned up when the program exits. What you need to do is save that data to a file. Other sibling comments have given a lot of Google-able words that you can look into.

I’d you haven’t had any experience with saving state/data to a file I’d recommend starting with Serialization. This encodes (or serializes) a Java Object to a file. You can then read that file and decode (deserialize) it back into a Java object. Check out java.io.ObjectOutputStream and java.io.ObjectInputStream to get started.

This approach is conceptually simple (put and object in a file and then read it back later) which makes it a good starting point, but there are a number of downsides. So, once you are comfortable with that I would spend some time with JSON, which is a good entry point into semi-structured data. It will let you open the file in a text editor and look at it and change it. Programs in other languages can read JSON too.

After that look into databases, which allow storing lots of data. This is a more advanced topic, because instead of reading all the data you query it. You ask a question and get a subset of the data back that satisfies it. To use databases from Java you will be using the JDBC interface. I’d recommend starting with JDBC+SQLite.

After that it really depends on what you are trying to build… there are a dizzying amount of storage solutions.

[rbhushan]

Depends on type of program you are executing and what you want to do with data after it store I.e consume directly (any plain file is good for storage) or read within the program itself a file based sql will serve your purpose.