Constructor Injection with CDI + Weld

Question

I want to use Constructor Injection, as it makes my unit tests safer and easier to write: I can't forget to set the fields to be injected. CDI supports that, and the javadoc of the @Inject annotation says: "@Inject is optional for public, no-argument constructors when no other constructors are present. This enables injectors to invoke default constructors."

I understand that other standards require a no-arg constructor (e.g. JAX-RS; see this question), which is a bummer. But even for a simple class like:

public class Bar {
    private final Foo foo;

    public Bar(Foo foo) {
        this.foo = foo;
    }
}

Weld fails, saying: DeploymentException: WELD-001408: Unsatisfied dependencies for type Bar. When I add the @Inject annotation, it works.

I really don't expect any bugs in Weld any more, as it's well established for years; I probably got something wrong. But maybe it slipped attention, just because the Jakarta EE community simply doesn't do any constructor injection.

Answer 1

This is not a Weld bug. As the specification indicates, you need @javax.inject.Inject on your constructor. The only time you don't need it is when you have a zero-argument constructor and you do not wish for any other constructor to be called by the container.