How can an app use files inside the JAR for read and write?

Question

I need to store data into files inside .jar file and read it again.

I know that I can use Class.getResourceAsStream() method but it returns an Inp

Answer 1

I need to store data into files inside .jar file and read it again

No you don't.

Instead store the 'default' file inside the Jar. If it is changed, store the altered file in another place. One common place is a sub-directory of user.home. When checking for the file, first check the existence of an altered file on the file system, and if it does not exist, load the default file.

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Note that it is generally better to describe the goal, rather than the strategy. 'Store changed file in Jar' is a strategy, whereas 'Save preferences between runs' might be the goal.

Related: What is the XY problem?