How do I access the ApplicationContext from a service within the micronaut framework?

Question

Every attempt I have made to access the ApplicationContext in my service has failed with the ApplicationContext being returned as null. In Spring I was able to use ApplicationContextAware which according to (https://micronaut-projects.github.io/micronaut-spring/latest/guide/index.html) should be replaced with @Autowired in micronaut. I have attempted

@Autowired ApplicationContext context

with no luck however. It is always null. Any help would be appreciated!

Answer 1

The project at https://github.com/jeffbrown/injectcontext shows 2 ways to inject the ApplicationContext.

https://github.com/jeffbrown/injectcontext/blob/1f319a3bb3db8eff05f159dd8dc642b227662307/src/main/java/injectcontext/FirstService.java

package injectcontext;

import io.micronaut.context.ApplicationContext;

import javax.inject.Singleton;

@Singleton
public class FirstService {

    private final ApplicationContext applicationContext;

    public FirstService(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    public boolean isContextNull() {
        return applicationContext == null;
    }
}

https://github.com/jeffbrown/injectcontext/blob/1f319a3bb3db8eff05f159dd8dc642b227662307/src/main/java/injectcontext/SecondService.java

package injectcontext;

import io.micronaut.context.ApplicationContext;

import javax.inject.Inject;
import javax.inject.Singleton;

@Singleton
public class SecondService {

    @Inject
    ApplicationContext applicationContext;

    public boolean isContextNull() {
        return applicationContext == null;
    }
}

https://github.com/jeffbrown/injectcontext/blob/1f319a3bb3db8eff05f159dd8dc642b227662307/src/main/java/injectcontext/DemoController.java

package injectcontext;

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;

@Controller("/")
public class DemoController {

    FirstService firstService;

    SecondService secondService;

    public DemoController(FirstService firstService, SecondService secondService) {
        this.firstService = firstService;
        this.secondService = secondService;
    }

    @Get("/first")
    public String first() {
        boolean isNull = firstService.isContextNull();

        return "firstService.isContextNull() == " + isNull;
    }

    @Get("/second")
    public String second() {
        boolean isNull = secondService.isContextNull();

        return "secondService.isContextNull() == " + isNull;
    }
}

That all works:

 $ curl http://localhost:8080/first
firstService.isContextNull() == false
 $ 
 $ curl http://localhost:8080/second
secondService.isContextNull() == false

EDIT

If what you really want is to just retrieve the service ids, you can do something like this:

package injectcontext;

import io.micronaut.discovery.DiscoveryClient;
import org.reactivestreams.Publisher;

import javax.inject.Singleton;
import java.util.List;

@Singleton
public class DiscoveryHelper {

    private final DiscoveryClient consulClient;

    public DiscoveryHelper(DiscoveryClient consulClient) {
        this.consulClient = consulClient;
    }

    public Publisher<List<String>> getIds() {
        // do whatever you want with the ids...
        return consulClient.getServiceIds();
    }
}

That will work if you have that in a service that has consul enabled.

consul:
  client:
    registration:
      enabled: false # set to true if you want this service to register itself
    defaultZone: "${CONSUL_HOST:localhost}:${CONSUL_PORT:8500}"