How do I get my Jersey 2 Endpoints to eagerly initialize on startup?

Question

I am porting some code from Jersey 1.x and my implementation of various Health Check endpoints relies on all the @Singleton endpoint resources being initialized at start up so as to be able to detect which checks to do.

In Jersey 2.0 - whatever I do I can't seem to get my resource endpoints to initialise at start up and they are only constructed+initialized when each one is accessed for the first time.

I guess I could initialise them myself in the Application class but I'd rather use the package scanning!

Does anyone have any idea if there is some config option that will tell Jersey 2 to eagerly initialise all resource endpoints that it finds during package scanning?

Or some HK2 annotation or trick?

Answer 1

"Or some HK2 annotation or trick?"

You can use HK2's Immediate Scope. Just annotate the resource class with @Immediate (which acts like @Singleton, so you can get rid of that), then enable the immediate scope on the ServiceLocator. An example:

import org.glassfish.hk2.api.ServiceLocator;
import org.glassfish.hk2.utilities.ServiceLocatorUtilities;
...

@ApplicationPath("/rest")
public class JerseyApplication extends ResourceConfig {

    @Inject
    public JerseyApplication(ServiceLocator locator) {
        ServiceLocatorUtilities.enableImmediateScope(locator);
        packages("thepackages.to.scan");
    }
}

---

UPDATE

Based on this related question, if you need to explicitly instantiate the ResourceConfig, as in the case of the linked question, you can create a Feature and register the feature, as seen in this answer

UPDATE 2

Please see related issue

UPDATE 3

Looks like Immediate scope memory leak issue previously linked to has been resolved in version 2.22.1