Java Community | Help. Code. Learn.•5d ago

Guice with empty Module

I'm learning Guice and I have working code, but my Module (extending AbstractModule) is empty (because I'm injecting a class not an interface). I can see that there's no overload of Guice.createInjector() which takes no params. Is there some way of not needing a module in my scenario? Not sure if: 1) it's not a big deal; you might add bindings to it later 2) using Guice with an empty module is an anti-pattern - always use interfaces (but I don't think that's correct) 3) I'm missing something.

18 Replies

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dan1st•5d ago

What do you mean with the module being empty? How do you see that?

Dave12345OP•5d ago

There's no bindings defined in it.

dan1st•5d ago

Can you show a minimal reproducer or similar? Can you show the class you are injecting and its implementation? Can you show the module? Can you show whatever shows you the (empty) bindings?

Dave12345OP•5d ago

Below is the relevant code. To be clear, this is a "best practice" type question. Like I said up front, this works. There's nothing that shows me "empty bindings". I simply have a (what looks to me at least) pointless empty module and I'm wondering if there's a way to do away with it.

public class HibernateModule extends AbstractModule {
    
}


public class Library {
    public static void main(String[] args) {
        Injector injector = Guice.createInjector(new HibernateModule());
        HibernateSandbox hs = injector.getInstance(HibernateSandbox.class);
        hs.test();
    }
}

public class HibernateSandbox {
    @Inject
    EntityManagerProvider emp;
    
    public void test() {
        EntityManager em = emp.get();
        if (em == null) {
            System.out.println("Couldn't get entitymanager");
            return;
        }
Etc etc

public class HibernateModule extends AbstractModule {
    
}


public class Library {
    public static void main(String[] args) {
        Injector injector = Guice.createInjector(new HibernateModule());
        HibernateSandbox hs = injector.getInstance(HibernateSandbox.class);
        hs.test();
    }
}

public class HibernateSandbox {
    @Inject
    EntityManagerProvider emp;
    
    public void test() {
        EntityManager em = emp.get();
        if (em == null) {
            System.out.println("Couldn't get entitymanager");
            return;
        }
Etc etc

dan1st•5d ago

so the code/body is the thing that's empty

Dave12345OP•5d ago

Yes. "my Module (extending AbstractModule) is empty". I'm probably phrasing it wrongly?

dan1st•5d ago

I think this should be perfectly fine but you might be able to use an anonymous class

Dave12345OP•5d ago

Usually it's not empty as you need to bind an implementation to an interface

dan1st•5d ago

Guice.createInjector(new AbstractModule(){ });

Guice.createInjector(new AbstractModule(){ });

Dave12345OP•5d ago

ok, i'll give that a go - thanks!

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dan1st•5d ago

yeah I understand what you mean with that However, I would personally prefer an empty module class

Dave12345OP•5d ago

that's my instinctual preference too. I'm using java at lot at work and it's a huge project with every technology in the world in it. I'm spending a little time at home using some of the tech but in a much smaller test project and trying to learn how to do stuff very cleanly and properly. At work there's some crazy injector class which is populated from multiple modules and service loaders and god knows where else so you can inject anything anywhere so you never need to know which module is used etc. So I've never had to actually create a module or write a .createInjector etc - it's already done somewhere!

dan1st•5d ago

yeah if your application is sufficiently big, you'd probably have something you need to declare mappings for anyway

Dave12345OP•5d ago

ok thanks for your help!

JavaBot•5d ago

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