Unit testing JAX-RS/Jersey servlet with Guice Injections

Question

I have an application that uses Jersey/JAX-RS for web services (annotations, etc) and Guice to inject service implementations. I don't really like the way Guice works with servlets directly, I prefer the Jersey way, so I had to do a bit of fussing to get the service injections to work since Guice wouldn't be creating my servlet classes, and I didn't want to deal with the HK2-Guice bridge. I did this by creating a listener class (called Configuration) that sets up the injectors in static fields upon application startup and then manually effecting the injections in each servlet class by creating a parent class that all my servlets extend with a constructor that contains the following:

public MasterServlet() {
    // in order for the Guice @Inject annotation to work, we have to create a constructor
    // like this and call injectMembers(this) on all our injectors in it
    Configuration.getMyServiceInjector().injectMembers(this);
    Configuration.getDriverInjector().injectMembers(this);
}

I know it's kind of hacky, but this works just fine in my servlets. I can use the Guice @Inject annotations on my services and switch between named implementations and so on. The problem comes when I go to set up my unit tests. I'm using JerseyTest to do my tests, but running a test against my servlets results in a 500 error with Guice saying the following:

com.google.inject.ConfigurationException: Guice configuration errors: 1) No implementation for com.mycompany.MyService was bound. while locating com.mycompany.MyService for field at com.mycompany.servlet.TestGetServlet.service(TestGetServlet.java:21) while locating com.mycompany.servlet.TestGetServlet

The test looks like this:

public class TestServletTest extends JerseyTest {

    @Test
    public void testServletFunctional() {
        final String response = target("/testget").request().get(String.class);
        assertEquals("get servlet functional", response);
    }

    @Before
    public void setup() {
        Configuration configuration = new Configuration();
        configuration.contextInitialized(null);
    }

    @Override
    protected Application configure() {
        return new ResourceConfig(TestGetServlet.class);
    }
}

You'll notice in the setup method I am manually creating my Configuration class since I can't rely on the test container (Grizzly) to create it (I get NullPointerExceptions without those two lines). More about this below.

And here's the servlet being tested:

@Path("/testget")
public class TestGetServlet extends MasterServlet {

    @Inject
    MyService service;

    @GET
    @Produces({"text/plain", MediaType.TEXT_PLAIN})
    public String testGet() {
        //service = Configuration.getServiceInjector().getInstance(MyService.class);
        return "get servlet functional";
    }
}

Notice the commented line in the testGet() method? If I do that instead and remove the @Inject annotation above, everything works fine, which indicates that Grizzly is not creating my servlets the way I expect.

I think what's happening is that Grizzly doesn't know about Guice. Everything seems to suggest that Grizzly isn't seeing the Configuration class, despite the fact that by putting it in my test's @Before method it seems to be at least available to the classes that use it (see: the commented line in the TestGetServlet class). I just don't know how to fix it.

Answer 1

I'm still trying to figure this out but in the meantime I switched from Guice to HK2, which took a bit of doing but I figured this might be helpful for anyone who runs into this problem in the future.

I consider this an answer because truthfully my attempt to bypass the Guice-HK2 bridge but still use Guice with Jersey might not have been the best idea.

Switching from Guice to HK2 takes a bit of doing and there's no comprehensive guide out there with all the answers. The dependencies are really fussy, for example. If you try to use Jersey 2.27 you may run into the famous

java.lang.IllegalStateException: InjectionManagerFactory not found

error. Jersey 2.27 is not backwards compatible with previous versions due to HK2 itself. I am still working on getting that all to work, but in the meantime I had to downgrade all my Jersey dependencies to 2.26-b06 to get HK2 working properly.

Jersey thankfully already implements a bunch of HK2 boilerplate, so all you need to get injection working is proper use of @Contract, @Service (see HK2 docs for those), and then two new classes that look like this:

public class MyHK2Binder extends AbstractBinder {
    @Override
    protected void configure() {
        // my service here is a singleton, yours might not be, so just omit the call to in()
        // also, the order here is switched from Guice! very subtle!
        bind(MyServiceImpl.class).to(MyService.class).in(Singleton.class);
    }
}

And this:

public class MyResourceConfig extends ResourceConfig {

    public MyResourceConfig() {
        register(new MyHK2Binder());
        packages(true, "com.mycompany");
    }
}

Simple enough, but this only works for the application itself. The test container knows nothing about it, so you have to redo the Binder and ResourceConfig yourself in your test class, like this:

public class TestServletTest extends JerseyTest {

    @Test
    public void testServletFunctional() {

        final String response = target("/testget").request().get(String.class);
        assertEquals("get servlet functional", response);
    }

    @Before
    public void setup() {
    }

    @Override
    protected Application configure() {
        return new TestServletBinder(TestGetServlet.class);
    }

    public class TestServletBinder extends ResourceConfig {
        public TestServletBinder(Class registeree) {
            super(registeree);
            register(new MyHK2Binder());
            packages(true, "com.mycompany");
        }
    }
}

Having to do this is actually fine because you can switch out the Binder for a test binder instead, in which you've bound your service to a mocked service instead or something. I haven't done that here but that's easy enough to do: replace new MyHK2Binder() in the call to register() with one that does a binding like this instead:

bind(MyTestServiceImpl.class).to(MyService.class).in(Singleton.class);

And voila. Very nice. Obviously you could achieve a similar result with Named bindings, but this works great and might even be simpler and more clear.

Hope this helps someone save the hours I spent screwing around to get this working.