Assuming your Java application restarts are related to dyno restarts or deploys:
you might want to look into the preboot feature on Heroku.
From their documentation:
Preboot changes the standard dyno start behavior for web dynos. Instead of stopping the existing set of web dynos before starting the new ones, preboot ensures that the new web dynos are started (and receive traffic) before the existing ones are terminated. This can contribute to zero downtime deployments.
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