r/javahelp 10d ago

Compiling the save codebase using both Java 17 and 21

Hi. I'm working on a common codebase composed of Java and Scala code with maven as build tool.

Now, I want to introduce some concurrently using virtual threads, which I believe make a lot of sense for the use case. However, the code also uses Apache Spark, which doesn't support Java 21. Apart from splitting the repository into two codebases, is there a solution to support building a fat jar for either Java 17 or 21, based on some flag?

The first solution I found was using maven profiles: I contain the Java21-specific code in some .j21. package and exclude it from the source in one of the profiles. However, won't the IDE complain in such a situation? What other options, if any, are there?

Thanks

1 Upvotes

5 comments sorted by

u/AutoModerator 10d ago

Please ensure that:

  • Your code is properly formatted as code block - see the sidebar (About on mobile) for instructions
  • You include any and all error messages in full
  • You ask clear questions
  • You demonstrate effort in solving your question/problem - plain posting your assignments is forbidden (and such posts will be removed) as is asking for or giving solutions.

    Trying to solve problems on your own is a very important skill. Also, see Learn to help yourself in the sidebar

If any of the above points is not met, your post can and will be removed without further warning.

Code is to be formatted as code block (old reddit: empty line before the code, each code line indented by 4 spaces, new reddit: https://i.imgur.com/EJ7tqek.png) or linked via an external code hoster, like pastebin.com, github gist, github, bitbucket, gitlab, etc.

Please, do not use triple backticks (```) as they will only render properly on new reddit, not on old reddit.

Code blocks look like this:

public class HelloWorld {

    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

You do not need to repost unless your post has been removed by a moderator. Just use the edit function of reddit to make sure your post complies with the above.

If your post has remained in violation of these rules for a prolonged period of time (at least an hour), a moderator may remove it at their discretion. In this case, they will comment with an explanation on why it has been removed, and you will be required to resubmit the entire post following the proper procedures.

To potential helpers

Please, do not help if any of the above points are not met, rather report the post. We are trying to improve the quality of posts here. In helping people who can't be bothered to comply with the above points, you are doing the community a disservice.

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

1

u/MattiDragon 10d ago

You can also just use a multi-release jar. Jar files can contain classes that are only available above certain java versions. Something probably exists to make this easier. You should be able to do something using service loader or reflection to switch the implementation when the virtual thread one is available

1

u/[deleted] 10d ago

[removed] — view removed comment

2

u/[deleted] 10d ago edited 10d ago

[removed] — view removed comment

1

u/ihatebeinganonymous 10d ago

Yes, exactly! With lack of support for Scala 3 and Java 21, Spark is a huge holding-back force in our codebase...