Replacing finalize() in Java
Object.finalize() is deprecated in Java 9, and I think I understand the reasons why, but I'm having trouble seeing how to replace it.
I have a utility class called Configuration which essentially has a single instance that owns everything in the application and lasts for the duration of the application. One of the services it provides is logging: on first request to log a message, a logger is created (for various legacy reasons it's my own Logger rather than a standard one), with a reference held in a field of the Configuration object, and on application termination, whether normal or abnormal, I want to release any resources held by the logger (which is a black box since users of my library can supply their own implementation).
Currently this is achieved with a Configuration.finalize() method that calls logger.close().
What should I be doing instead?
Answer
Java 9 introduces the Cleaner and Cleanable utility classes which take care of wiring up phantom references to a queue and a cleaning thread draining that queue.
While this lets you separate out the witness that will perform a post-mortem cleanup after the owning object has died, all the caveats about GC-triggered resource management still apply, i.e. it is still preferable to rely on AutoClosable and try-with-resources blocks to manage the lifecycle of resources, not on the garbage collector.