Using Jersey's Dependency Injection in a Standalone application

Question

I have a interface here

interface Idemo{
  public int getDemo(int i);
}

And it's one implementation

class DemoImpl implements Idemo{
  @Override
  public int getDemo(int i){
    return i+10;
  }
}

And there is a class which has a dependency on Idemo

class Sample{
  @Inject
  Idemo demo;

  public int getSample(int i){
    return demo.getDemo(i);
  }
}

Now say I want to test Sample class

public class SampleTest extends JerseyTest {
  @Inject
  Sample s; 

  @Override
  protected Application configure() {
    AbstractBinder binder = new AbstractBinder() {
      @Override
      protected void configure() {
        bind(Demo.class).to(Idemo.class);
        bind(Sample.class).to(Sample.class); //**doesn't work**
      }
    };
    ResourceConfig config = new ResourceConfig(Sample.class);
    config.register(binder);
    return config;
  }
  @Test
  public void test_getSample() {
    assertEquals(15, s.getSample(5)); //null pointer exception
  }
}

Here the Sample instance is not getting created and s remains null.I suppose this is because by the time the execution reaches line where binding is specified this test class has already been created.But I am not sure.With Spring Autowired instead of jersey CDI the same works

Had Sample been a resource/controller class the test framework would create an instance of it with no need to inject it but is it possible to test any other non-web class using Jersey DI ?

Answer 1

The reason it works with Spring is that the test class is managed by the Spring container by using @RunWith(SpringJUnit4ClassRunner.class). The runner will inject all managed objects into the test object. JerseyTest is not managed this way.

If you want, you can create your own runner, but you need to understand a bit how HK2 (Jersey's DI framework) works. Take a look at the documentation. Everything revolves around the ServiceLocator. In a standalone, you might see something like this to bootstrap the DI container

ServiceLocatorFactory factory = ServiceLocatorFactory.getInstance();
ServiceLocator locator = factory.create(null);
ServiceLocatorUtilities.bind(locator, new MyBinder());

Then to get the service, do

Service service = locator.getService(Service.class);

In the case of the test class, we don't need to gain any access to the service object, we can simply inject the test object, using the ServiceLocator:

locator.inject(test);

Above, test is the test class instance that gets passed to us in our custom runner. Here is the example implementation of a custom runner

import java.lang.annotation.*;
import org.glassfish.hk2.api.*;
import org.glassfish.hk2.utilities.*;
import org.junit.runners.BlockJUnit4ClassRunner;
import org.junit.runners.model.*;

public class Hk2ClassRunner extends BlockJUnit4ClassRunner {

    private final ServiceLocatorFactory factory = ServiceLocatorFactory.getInstance();
    private Class<? extends Binder>[] binderClasses;

    @Target({ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    public static @interface Binders {

        public Class<? extends Binder>[] value();
    }

    public Hk2ClassRunner(Class<?> cls) throws InitializationError {
        super(cls);
        Binders bindersAnno = cls.getClass().getAnnotation(Binders.class);
        if (bindersAnno == null) {
            binderClasses = new Class[0];
        }
    }

    @Override
    public Statement methodInvoker(FrameworkMethod method, final Object test) {
        final Statement statement = super.methodInvoker(method, test);
        return new Statement() {
            @Override
            public void evaluate() throws Throwable {
                ServiceLocator locator = factory.create(null);
                for (Class<? extends Binder> c : binderClasses) {
                    try {
                        ServiceLocatorUtilities.bind(locator, c.newInstance());
                    } catch (InstantiationException | IllegalAccessException ex) {
                        throw new RuntimeException(ex);
                    }
                }
                locator.inject(test);
                statement.evaluate();
                locator.shutdown();
            }
        };
    }
}

In the runner, the methodInvoker is called for every test method, so we are creating a fresh new set of objects for each test method called.

Here is a complete test case

@Binders({ServiceBinder.class})
@RunWith(Hk2ClassRunner.class)
public class InjectTest {

    public static class Service {

        @Inject
        private Demo demo;

        public void doSomething() {
            System.out.println("Inside Service.doSomething()");
            demo.doSomething();
        }   
    }

    public static class Demo {
        public void doSomething() {
            System.out.println("Inside Demo.doSomething()");
        }
    }

    public static class ServiceBinder extends AbstractBinder {
        @Override
        protected void configure() {
            bind(Demo.class).to(Demo.class);
            bind(Service.class).to(Service.class);
        }
    }


    @Inject
    private Service service;

    @Test
    public void testInjections() {
        Assert.assertNotNull(service);
        service.doSomething();
    }
}