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 implem         


        

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[] binderClasses;

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

        public Class[] 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 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();
    }
}