Question

I’m starting to use Google Guice for my daily programming tasks. I needed to pass an existing object to Injector for initializing object graph, so I use method Injector#injectMembers(instance) to do it. But I wasn’t sure if it works so I wrote a unit test, but it didn’t work as I expected. Did I miss something? I use Guice 3

public class Login_Should {
    @Test
    public void testName() throws Exception {
        Login login = new Login();

        Injector injector = Guice.createInjector(new LoginModule());
        injector.injectMembers(login);

        LoginWrapper caller = injector.getInstance(LoginWrapper.class);
        assertEquals(login.getName(), caller.getName());
    }
}

public class Login {

    private int random;

    public Login() {
        this.random = new Random().nextInt();
    }

    public String getName() {
        return "Mr. A" + random;
    }
}

public class LoginWrapper {
    private Login login;

    @Inject
    public LoginWrapper(Login login) {
        this.login = login;
    }

    public String getName() {
        return login.getName();
    }
}

public class LoginModule extends AbstractModule{

    @Override
    protected void configure() {
        bind(LoginWrapper.class);
    }

}

Answer 1

injectMembers injects a none-Guice created object with its dependencies. What you want to do I think is bind(Login.class).toInstance(login); in your module.