Optionally inject ContainerRequestContext

Question

In my Jersey application, I'd like to have a ContainerRequestContext instance injected into various objects. In the case that the object in being created outside of the context of a request, I would like null to be injected.

I noticed HK2 has an @Optional annotation that you can annotate dependencies with, and I was hoping that would do the job for, unfortunately it doesn't change the behaviour at all.

public class MyObject {

    private final ContainerRequestContext containerRequestContext;

    @Inject
    public MyObject(@Optional ContainerRequestContext containerRequestContext) {
        this.containerRequestContext = containerRequestContext;
    }

}

If this object is instantiated outside of a request scope (in my case, a Job run by a Quartz scheduler), then an exception like this gets thrown:

java.lang.IllegalStateException: Not inside a request scope.

It would massively simplify my code if Jersey would just inject null when outside of a request scope, any ideas how to do this?

Answer 1

I've figured out a way of doing it, but it's basically a hack. Instead of having ContainerRequestContext injected, you can instead try to explicitly get a ContainerRequestContext instance from the ServiceLocator, and handle the exception when the context is outside of a request scope.

public class MyObject {

    private final Optional<ContainerRequestContext> containerRequestContext;

    @Inject
    public MyObject(ServiceLocator serviceLocator) {
        this.containerRequestContext = getContainerRequestContext(serviceLocator);
    }

    private Optional<ContainerRequestContext> getContainerRequestContext(ServiceLocator serviceLocator) {
        try {
            return Optional.of(serviceLocator.getService(ContainerRequestContext.class));
        } catch (MultiException e) {
            if (e.getCause() instanceof IllegalStateException) {
                return Optional.empty();
            } else {
                throw new ExceptionInInitializerError(e);
            }
        }
    }
}

It's then possible to go one step further and create your own OptionalContainerRequestContext type.

public class OptionalContainerRequestContext {

    private final Optional<ContainerRequestContext> containerRequestContext;

    @Inject
    public OptionalContainerRequestContext(ServiceLocator serviceLocator) {
        this.containerRequestContext = getContainerRequestContext(serviceLocator);
    }

    public ContainerRequestContext get() {
        return containerRequestContext.get();
    }

    public boolean isPresent() {
        return containerRequestContext.isPresent();
    }

    private Optional<ContainerRequestContext> getContainerRequestContext(ServiceLocator serviceLocator) {
        try {
            return Optional.of(serviceLocator.getService(ContainerRequestContext.class));
        } catch (MultiException e) {
            if (e.getCause() instanceof IllegalStateException) {
                return Optional.empty();
            } else {
                throw new ExceptionInInitializerError(e);
            }
        }
    }
}

You can then bind it:

bind(OptionalContainerRequestContext.class).to(OptionalContainerRequestContext.class);

And then inject it wherever you need:

public class MyObject {

    private final OptionalContainerRequestContext optionalContainerRequestContext;

    @Inject
    public MyObject(OptionalContainerRequestContext optionalContainerRequestContext) {
        this.optionalContainerRequestContext = optionalContainerRequestContext;
    }

}

Answer 2

The simple way to deal with optional injection is to @Inject into javax.enterprise.inject.Instance<T>, and then to call instance.isUnsatisfied() before instance.get().