CDI Ambiguous dependency with @Produces - why?

Question

I am using code like below:

public Configuration {

    private boolean isBatmanCar = someMethod(...);

    @Produces
    public Car getCar(@New Car car) {
          


        

Answer 1

The error comes from the fact that you have 2 beans of type Car, one being the class, the other being the producer. You have 2 obvious solutions to resolve the ambiguity:

First, you put the logic behind isBatmanCar field in the original class (in a constructor or a @PostConstruct method for instance) and remove your producer. That would left only one Car bean.

Or if you really want to have 2 bean or can't avoid it you should create a qualifier for your produced bean:

 @Target({ TYPE, METHOD, PARAMETER, FIELD })
 @Retention(RUNTIME)
 @Documented
 @Qualifier
 public @interface BatmanChecked {
 }

and use it on producer,

@Produces
@BatmanChecked
public Car getCar(Car car) {...}

to be able to inject the type of car

@Inject
Car stdCar;

@Inject
@BatmanChecked
Car batCheckedCar;

Qualifier is the natural option to resolve ambiguous injection. Using @Alternative also works but it's more a trick here than a good practice.

Last remark: @New is not necessary here, since your Car bean has no scope (so is @Dependent scoped). @New is only useful when a producer inject a bean with a scope that is not @Dependent. That said, this code is not very useful if your Car class is in scope @Dependent.