How to put in custom scope/context (JobScoped - custom CDI scope) particular instance from request to make it injectable?

Question

Saying in a nutshell I would like to put in custom scope particular instance of Configuration class from rest request. Main problem is that custom scope (JobScoped from JBeret h

Answer 1

I think this question consists of several parts:

1. How to inject values into batch jobs?
2. How to seed context based values to batch jobs?
3. How to enter the RequestScope in a batch job?
4. How to create a custom scope?
5. How to enter a custom scope?
6. How to seed a value in a custom scope?

I will try to answer all individual questions, but keep in mind that I've only very recently started using CDI/Weld, and have no experience with JBeret.

1. How to inject values into batch jobs?

The reason I am adding this question, is because I think Configuration may not need to be a scoped entity. If Configuration has nothing specific to the scope, it could be @Singleton or @Stateless as well. Think for example from configuration files, resources, or environment variables, that will not change on runtime. Non-scoped (or Singleton-scoped) dependencies can be injected into batchlets just fine, using regular @Inject fields, without any need for a @JobScoped annotation.

2. How to seed context based values to batch jobs?

So what if the actual value depends on the context and cannot be injected in a @Singleton fashion? Based from the JBeret documentation, it is preferred to pass all configuration by Properties. These can then be read from the JobContext, or injected using the @BatchProperty annotation. This only works for a predefined list of types that are serialisable from a String.

@Named
public class MyBatchlet extends AbstractBatchlet {

    @Inject
    @BatchProperty(name = "number")
    int number;

}

3. How to enter the @RequestScope in a batch job?

I think you shouldn't. The @RequestScope is for requests solely. If you have dependencies dependent on @RequestScope that should be accessible outside of a request, consider to introduce a custom scope.

If you really need to enter the @RequestScope programatically, you can define your own context for it and enter that context (see part 4 below) or enter the context by default, as addressed in this blogpost by Dan Haywood, in his attempt to get into the @RequestScope in Java SE.

4. How to create a custom scope?

It is fairly easy to create a custom scope. A custom scope however requires an implementation for the scope context. I found this to be a little unclear in the documentation. Luckily there is the library microscoped library. For this example, you only need the microscoped-core dependency, which provides a ScopeContext implementation that is used in their custom scopes. We will use that ScopeContext for our simple scope as well.

First we have to create the Scope annotation:

@Documented
@Scope
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.FIELD, ElementType.METHOD, ElementType.TYPE})
public @interface CustomScoped {}

Secondly, we have to create an extension:

public class CustomScopedExtension implements Extension, Serializable {

    public void addScope(@Observes final BeforeBeanDiscovery event) {
        event.addScope(CustomScoped, true, false);
    }

    public void registerContext(@Observes final AfterBeanDiscovery event) {
        event.addContext(new ScopeContext<>(CustomScoped.class));
    }

}

Note that we're using the ScopeContext from microscoped here. Furthermore, you should register your extension by adding the full classname toMETA-INF/services/javax.enterprise.inject.spi.Extension`.

5. How to enter a custom scope?

Now we need to enter our scope. We can do this with a little bit of code, that you can place for example in a web Filter or method interceptor. The code uses an BeanManager instance, which can be obtained with @Inject:

ScopeContext context = (ScopeContext) beanManager.getContext(CustomScoped.class);
context.enter(key);
try {
     // continue computation
} finally {
    context.destroy(key);
}

6. How to seed a value in a custom scope?

I have been asking myself the very same question, and this is the solution I came up with. See also my question on how to properly seed from custom Weld CDI scopes: Seed value in Weld CDI custom scope . I do have a workaround for your issue though:

@Singleton
public class ConfigurationProducer {

    private final InheritableThreadLocal  threadLocalConfiguration =
    new InheritableThreadLocal<>();

    @Produces
    @ActiveDataSet
    public ConfigurationConfiguration() {
       return threadLocalConfiguration.get()
    }

    public void setConfiguration(Configuration configuration) {
         threadLocalConfiguration.set(configuration);
    }    

}

Now from your the interceptor written above, you can inject ConfigurationProducer and use ConfigurationProducer #setConfiguration(Configuration) to set the Configuration for the current thread. I am still looking for better options here.