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Learning Netflix Governator - Part 2

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Learning Netflix Governator - Part 2

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To continue from the previous entry on some basic learnings on Netflix Governator, here I will cover one more enhancement that Netflix Governatorbrings to Google Guice - Lifecycle Management

Lifecycle Management essentially provides hooks into the different lifecycle phases that an object is taken through, to quote the wiki article on Governator: 

Allocation (via Guice)
     |
     v
Pre Configuration
     |
     v
Configuration
     |
     V
Set Resources
     |
     V
Post Construction
     |
     V
Validation and Warm Up
     |
     V
  -- application runs until termination, then... --    
     |
     V
Pre Destroy

To illustrate this, consider the following code:

package sample.gov;

import com.google.inject.Inject;
import com.netflix.governator.annotations.AutoBindSingleton;
import sample.dao.BlogDao;
import sample.model.BlogEntry;
import sample.service.BlogService;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

@AutoBindSingleton(baseClass = BlogService.class)
public class DefaultBlogService implements BlogService {
    private final BlogDao blogDao;

    @Inject
    public DefaultBlogService(BlogDao blogDao) {
        this.blogDao = blogDao;
    }

    @Override
    public BlogEntry get(long id) {
        return this.blogDao.findById(id);
    }

    @PostConstruct
    public void postConstruct() {
        System.out.println("Post-construct called!!");
    }
    @PreDestroy
    public void preDestroy() {
        System.out.println("Pre-destroy called!!");
    }
}

Here two methods have been annotated with @PostConstruct and @PreDestroy annotations to hook into these specific phases of the Governator's lifecycle for this object. The neat thing is that these annotations are not Governator specific but are JSR-250 annotations that are now baked into the JDK.

Calling the test for this class appropriately calls the annotated methods, here is a sample test:

mport com.google.inject.Injector;
import com.netflix.governator.guice.LifecycleInjector;
import com.netflix.governator.lifecycle.LifecycleManager;
import org.junit.Test;
import sample.service.BlogService;

import static org.hamcrest.MatcherAssert.*;
import static org.hamcrest.Matchers.*;

public class SampleWithGovernatorTest {

    @Test
    public void testExampleBeanInjection() throws Exception {
        Injector injector  = LifecycleInjector
                .builder()
                .withModuleClass(SampleModule.class)
                .usingBasePackages("sample.gov")
                .build()
                .createInjector();

        LifecycleManager manager = injector.getInstance(LifecycleManager.class);

        manager.start();

        BlogService blogService = injector.getInstance(BlogService.class);
        assertThat(blogService.get(1l), is(notNullValue()));
        manager.close();
    }

}
Spring Framework has supported a  similar mechanism for a long time - so the exact same JSR-250 based annotations work for Spring bean too.

If you are interested in exploring this further,  here is my github project with samples with Lifecycle management.

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