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  4. Learning Netflix Governator - Part 2

Learning Netflix Governator - Part 2

Biju Kunjummen user avatar by
Biju Kunjummen
·
Feb. 03, 15 · Interview
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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.
Spring Framework

Published at DZone with permission of Biju Kunjummen, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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