In my Android application the user has an option of using the application in offline mode. When the user opts to enter the offline mode, I download all the content from the server(which might take even upto 7 minutes) for offline usage. The usage of the application henceforth is dependent on the download of offline content.
I am using a service to download the offline content. But the service may not work in Android 8 if the app goes to the background. So what is the best approach to download the offline content for Android 8? Is it a foreground service or JobIntentService or a WorkManager?
Anything that is backed by JobScheduler — which includes JobIntentService and WorkManager — has a 10-minute limit. You indicate that your work may take up to 7 minutes, which makes me somewhat nervous.
In the short term, make your existing service be a foreground service, as that will keep your code working (other than any problems that Doze mode might impose).
If your 7-minute download work is really a series of smaller things that add up to 7 minutes, you might eventually migrate to WorkManager. Divide your work into smaller chunks and set up chained work with WorkManager, so you are certain to not go over the 10-minute limit for any of those chunks of work. Plus, WorkManager lets you establish constraints to say that your work should only be performed if you have an Internet connection. Right now (late August 2018), though, WorkManager is only 1.0.0-alpha07, so I would not ship a product based on WorkManager until it at least reaches a 1.0.0 final version.