Can I use spring injection, for injecting into an enum?

Question

I am trying to use spring injection to inject into an enum. Like this:

public enum Car {
HONDA("Honda", "hondas") {
    @Inject
    Carparts carparts;

    @Override
    public List<Carpart> getCarparts() {
        return carparts.getCarpartsListings();
    }
};
//more logic here
}

My Carparts bean is defined as follows in the configuration class:

@Bean
@Singleton
public Carparts geCarparts() {
    return new Carparts();
}

But no matter what I get a null value for carparts injection. Any help will be greatly appreciated.

I'm not sure if this works at all but *if* that works, then you'll have to make this enum at least a component s.t. it gets picked up by spring. This is not particularly a qualified answer but you need at least something like a [`@Component` annotation](https://stackoverflow.com/a/6897038/826983) on a class that you want to inject into. — Stefan Falk, May 23 '18 at 23:43
@StefanFalk isn't annotating a class with "Component" another way of making that class a bean? I did not know that a class needs to be annotated with "Component" even for injection. — ASR4, May 23 '18 at 23:47
`@Component` tells Spring that this class should be managed by Spring. [See this answer](https://stackoverflow.com/questions/6827752/whats-the-difference-between-component-repository-service-annotations-in/6897038#6897038) for more details but the essence is that Spring won't inject anything if you don't tell Spring to take care about a class. — Stefan Falk, May 23 '18 at 23:49
Also [take a look at this](https://stackoverflow.com/a/10604537/826983). — Stefan Falk, May 23 '18 at 23:52
Still null, but when I have Carparts carparts = new Carparts(); it works fine. — ASR4, May 23 '18 at 23:53
Have you tried `@Autowired` instead of `@Inject`? Shouldn't make a difference but you can try. To be honest I have no idea if this will actually work on `enum` types at all. You'll have to wait for somebody who can answer that in more detail I'm afraid. — Stefan Falk, May 23 '18 at 23:55
I think it's not possible and [this thread](http://forum.spring.io/forum/spring-projects/container/85134-inject-a-dependency-into-an-enum) seems to confirm that. You'll have to consider a workaround I guess. — Stefan Falk, May 23 '18 at 23:56
What do you want to achieve? Tell your ultimate goal and we might help by provide a workaround. You cannot inject into an enum because enum's static final, and the inject process is happens after enum loaded — Mạnh Quyết Nguyễn, May 23 '18 at 23:58
@MạnhQuyếtNguyễn I have a junit which uses powermock, because of which the code coverage is not showing up. So I was trying to create a wrapper around the class with static methods. Now I am trying to inject this wrapper in the enum, instead of the original class with static methods. — ASR4, May 24 '18 at 00:09
Your `Enum` should not contain logic. If it contains logic, then your design is wrong. Refactoring the logic part out. You test your util class which has static methods is enough. — Mạnh Quyết Nguyễn, May 24 '18 at 00:12
a `Car` is not a finite designation that is known ahead of time, so an Enum is not an appropriate way to model it in any case. a _Honda_ is an _AutoMaker_, not a _Car_, and you would have to re-build your application when Koenigsegg entered the market. Use a `Class`. — Stephen P, May 24 '18 at 00:19
@StephenP I used car and honda as examples they are not the names I have actually used, I appreciate your suggestion thanks :) — ASR4, May 24 '18 at 00:27
Why has this been marked as duplicate? It is not similar to any of the question feeling unwelcome has marked here. He definitely is very unwelcoming. — ASR4, May 24 '18 at 06:13
I disagree with the statement that an `enum` should contain no logic. Check Joshua Bloch's usage of Enums in Effective Java, there are some helpful patterns. — Hein Blöd, May 15 '20 at 11:55

J-Alex · Accepted Answer · 2018-05-24T00:07:32.447

You need to create a workaround with an inner static class that will be a Spring component, inject it and set carparts for entire Car EnumSet.

public enum Car {
    private Carparts carparts;

    @Component
    public static class CarPartsInjector {
        @Inject
        private Carparts carparts;

        @PostConstruct
        public void construct() {
            for (Car car: EnumSet.allOf(Car.class))
               car.setCarparts(carparts);
        }

        private void setCarparts(Carparts carparts) {
            this.carparts = carparts;
        }
    //...

}

In general, I think this is not a proper solution.

The problem here is Data Model.

The Car shouldn't be an enum. It thould be a class with list of Carparts, enum as type like CarType or ManufacturerType.

Can I use spring injection, for injecting into an enum?

1 Answers1