How to Inject EJBs into JAX-RS Services?

Injecting EJBs into JAX-RS Services

Problem Description

Attempting to inject a Stateless EJB into a JAX-RS webservice through annotations results in a null EJB reference, leading to a NullPointerException upon usage.

Solution

While annotating the JAX-RS web service as @Stateless may seem like a direct solution, it is not feasible with JAX-RS alone. Consider the following alternative approaches:

Option 1: Injection Provider SPI

Implement an injection provider that performs the lookup and injection of the EJB. Register the provider accordingly.

Option 2: Embed BookResource as an EJB

Annotate the BookResource class as @Stateless and manage its lifecycle within an EJB. However, this approach makes unit testing more challenging.

Option 3: Utilize CDI

Employ CDI for dependency injection, as shown in the provided example. This approach offers simplicity and flexibility, particularly in testing environments.

Working Example (Option 1)

@Path("book")
public class BookResource {

    @Inject
    private BookEJB bookEJB;

    //...
}

// EJBProvider.java

@Provider
public class EJBProvider implements InjectableProvider<EJB, Type> {
    // ... (Implementation as provided in the answer)
}

Conclusion

By implementing an injection provider or adopting CDI, it becomes possible to inject EJBs into JAX-RS services, expanding the integration options between the two frameworks.

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